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1
Tsutsumi, Hiroyuki, and Robert S. Yeats. "Tectonic setting of the 1971 Sylmar and 1994 Northridge earthquakes in the San Fernando Valley, California." Bulletin of the Seismological Society of America 89, no. 5 (October 1, 1999): 1232–49. http://dx.doi.org/10.1785/bssa0890051232.
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Abstract The San Fernando Valley lies above the north-dipping 1971 Sylmar and south-dipping 1994 Northridge earthquake faults. To understand the tectonic setting of these two earthquakes, we mapped subsurface geology of the San Fernando Valley down to a depth of ∼3 km, using industry oil-well and seismic data. The 1994 Northridge earthquake did not rupture the surface, and the south-dipping aftershock zone terminated against the north-dipping 1971 aftershock zone at a depth of 5-8 km. However, the blind Northridge fault has a near surface geologic expression; fault-propagation folding related to the Northridge fault has preserved a thick forelimb sequence of Plio-Pleistocene Saugus Formation in the Sylmar basin and Merrick syncline, which are located on the hanging wall side of north-dipping reverse faults. The north-dipping Mission Hills, Verdugo, and Northridge Hills reverse faults are interpreted to be potential seismic sources because fault-propagation folds above these faults have tectonic geomorphic expression. These north-dipping reverse faults were initiated during the deposition of the Saugus Formation between 2.3 and 0.5 Ma. and have minimum dip-slip rates of 0.35 to 1.1 mm/yr based on the oldest possible age of the initiation of faulting. The Northridge Hills and Mission Hills faults are interpreted to merge at depth and are located at the updip extension of the 1971 aftershock zone, even though these faults did not rupture during the 1971 earthquake. Surface breaks appeared north of these faults mostly along north-dipping bedding planes and are interpreted as secondary features related to flexural-slip folding rather than a direct extension of the 1971 seismogenic fault. Surface and subsurface geology, together with seismological data of the 1971 and 1994 earthquakes, suggests that the north- and south-dipping deformation zones in the San Fernando Valley are divided into multiple segments separated by northeast-trending structural discontinuities.
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Smith, Stewart, Olesya Zimina, Surender Manral, and Michael Nickel. "Machine-learning assisted interpretation: Integrated fault prediction and extraction case study from the Groningen gas field, Netherlands." Interpretation 10, no. 2 (February 22, 2022): SC17—SC30. http://dx.doi.org/10.1190/int-2021-0137.1.
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Seismic fault detection using machine-learning techniques, in particular the convolution neural network (CNN), is becoming a widely accepted practice in the field of seismic interpretation. Machine-learning algorithms are trained to mimic the capabilities of an experienced interpreter by recognizing patterns within seismic data and classifying them. Regardless of the method of seismic fault detection, interpretation or extraction of 3D fault representations from edge evidence or fault probability volumes is routine. Extracted fault representations are important to the understanding of the subsurface geology and are a critical input to upstream workflows including structural framework definition, static reservoir and petroleum system modeling, and well planning and derisking activities. Efforts to automate the detection and extraction of geologic features from seismic data have evolved in line with advances in computer algorithms, hardware, and machine-learning techniques. We have developed an assisted fault interpretation workflow for seismic fault detection and extraction, demonstrated through a case study from the Groningen gas field of the Upper Permian, Dutch Rotliegend; a heavily faulted, subsalt gas field located onshore, northeast Netherlands. Supervised using interpreter-led labeling, we apply a 2D multi-CNN to detect faults within a 3D prestack depth migrated seismic data set. After prediction, we apply a geometric evaluation of predicted faults, using a principal component analysis to produce geometric attribute representations (strike azimuth and planarity) of the fault prediction. Strike azimuth and planarity attributes are used to validate and automatically extract consistent 3D fault geometries, providing geologic context to the interpreter and input to dependent workflows more efficiently.
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Milsom, J., and P. F. Rawson. "The Peak Trough – a major control on the geology of the North Yorkshire coast." Geological Magazine 126, no. 6 (November 1989): 699–705. http://dx.doi.org/10.1017/s0016756800007007.
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AbstractAlthough the Mesozoic sediments of the Cleveland Basin (North Yorkshire) have generally not been strongly faulted, several approximately N–S trending faults have been identified along the coast. New seismic data from adjacent coastal waters has allowed the offshore extension to the fault system to be examined for the first time. The coastal faults from Peak (Ravenscar) to Red Cliff (Cayton Bay) are shown to form part of a linked system defining a narrow graben only some 5 km wide, the Peak Trough. Faulting has been complex, with decollement levels apparently developed in weak layers at various horizons in the Triassic and Permian strata: fault geometries and regional considerations suggest that extension has been dominant. Movement occurred intermittently from Triassic to latest Cretaceous or early Tertiary times.
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Reitherman, Robert. "The Effectiveness of Fault Zone Regulations in California." Earthquake Spectra 8, no. 1 (February 1992): 57–77. http://dx.doi.org/10.1193/1.1585670.
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In 1990 a study was completed for the California Division of Mines and Geology on the effectiveness of California's fault zone regulations (the Alquist-Priolo Special Studies Zones Act and associated policies and activities). The Act, passed in 1972, instituted the following elements of a statewide mandatory approach to dealing with the hazard of surface fault rupture: state mapping of fault zones (Special Study Zones) where active faults are suspected; local government imposition of the requirement of a geologic study on new building projects within these Zones (with some single family dwellings and low-occupancy structures exempt); review procedures for the studies submitted by an applicant's geologist; prohibition of the siting of projects on active faults; notification of real estate purchasers that a property is located within a Zone. This paper presents the results of that evaluation and comments more broadly on applying the Alquist-Priolo model to other regions and to other geologic hazards.
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Ren, Huan Song, Shuang Fang Lu, and Dian Shi Xiao. "Interpretation Methods and Application of Small Faults." Advanced Materials Research 962-965 (June 2014): 132–37. http://dx.doi.org/10.4028/www.scientific.net/amr.962-965.132.
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It is difficult to distinguish off from <5m fault in sections, because lateral variation of the amplitude and changes arising from differential compaction sand. Seismic coherence cube is to highlight those irrelevant seismic data. Draw three-dimensional seismic coherence with Partial wave analysis in the longitudinal and transverse. Ant agents: the ant, which found in the seismic data volume to meet the pre-fracture conditions, will release of a “signal”. It can call other regions ant for focusing on the breaks in its tracks, until the completion of the fault tracking and identification. Structural heterogeneity imaging can generate several geological attribute bodies, when compound with different geological attribute volume to different geology research target. It can extrude geologic feature we needed. Identifying a series of small faults which development between the main faults using a variety of small faults interpretation. Discovering and implementation of a number of block trap.
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Le, Anh Ngoc. "Characterization and Distribution of Cenozoic Polygonal Fault: Case Studies in West Africa and Vietnam Continental Margins." Iraqi Geological Journal 54, no. 1E (May 31, 2021): 19–28. http://dx.doi.org/10.46717/igj.54.1e.2ms-2021-05-23.
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The Cenozoic sequence of offshore Cameroon and Vietnam has been analysed based on newly 1500 km2 3D seismic data (Kribi-Campo basin) and 75 km 2D seismic data (Hoang Sa basin). Polygonal faults are widely developed in both passive margins and have relatively similar characteristics. These highly faulted intervals are up to c. 1000 m, characterized by normal faults with a throw of 10-20 ms TWT and 100 m - 1000 m spacing, displaying a polygonal pattern in the map view. Polygonal faults in the Kribi-Campo basin developed almost in the entire Cenozoic sequence mainly in two sets, one in deep section and one in shallow section whereas the Hoang Sa basin developed the polygonal fault only in the shallow section up to the seafloor corresponding to the Pliocene- Pleistocene sequence. In the Kribi-Campo basin, polygonal faults are developed extensively in the high gradient slope (3.4o) which is relatively rare in the low gradient slope (0.7o). Hoang Sa basin shows the widespread polygonal fault except for the area of canyon occurrence. The occurrence of thick and widespread polygonal fault formations associated with the low amplitude reflections suggests the interpretation of fine-grained sediments, thus possibly great seal potential for the study areas.
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Atallah, Mohammad, Raw’a Harahsheh, and Masdouq Al-Taj. "Tectonic Analysis of the Tall Al Qarn Pressure Ridge, Dead Sea Transform Fault, Jordan." Iraqi Geological Journal 56, no. 2D (October 31, 2023): 346–55. http://dx.doi.org/10.46717/igj.56.2d.25ms-2023-10-31.
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Jordan's Dead Sea Transform is made up of three morphotectonic elements: Wadi Araba, Dead Sea Basin, and Jordan Valley. A few pressure ridges and depressions exist in the Jordan Valley Fault. Among these, the Tall Al Qarn pressure ridge is one of the active Dead Sea Transform's morphotectonic features. Stratigraphically, the Waqqas (Miocene), Ghor Al Katar (Early Pleistocene), and Lisan (Late Pleistocene) Formations constitute the rock outcrops in the study area. The ridge was created when the sinistral strike-slip fault of the Jordan Valley bent rightward. The major structures include the Waqqas and Ghor Al Katar inclined beds, the NW-SE oriented normal and NE-SW reverse faults and the ESE-WNW oriented dextral strike-slip faults. Faults and folds indicate a local NW-SE compressional stress caused by the sinistral Jordan Valley Fault's right bending. The steeply dipping Ghor Al Katar strata, which are overlain by the horizontal Lisan beds, display a prominent angular unconformity. Many horizontal Lisan beds exhibit abundant synsedimentary deformational features, indicating the energetic seismic activity at that time.
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Cooke, Michele L., Kevin Toeneboehn, and Jennifer L. Hatch. "Onset of slip partitioning under oblique convergence within scaled physical experiments." Geosphere 16, no. 3 (March 10, 2020): 875–89. http://dx.doi.org/10.1130/ges02179.1.
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Abstract Oblique convergent margins host slip-partitioned faults with simultaneously active strike-slip and reverse faults. Such systems defy energetic considerations that a single oblique-slip fault accommodates deformation more efficiently than multiple faults. To investigate the development of slip partitioning, we record deformation throughout scaled experiments of wet kaolin over a low-convergence (<30°), obliquely slipping basal dislocation. The presence of a precut vertical weakness in the wet kaolin impacts the morphology of faults but is not required for slip partitioning. The experiments reveal three styles of slip partitioning development delineated by the order of faulting and the extent of slip partitioning. Low-convergence angle experiments (5°) produce strike-slip faults prior to reverse faults. In moderate-convergence experiments (10°–25°), the reverse fault forms prior to the strike-slip fault. Strike-slip faults develop either along existing weaknesses (precut or previous reverse-slip faults) or through the coalescence of new echelon cracks. The third style of local slip partitioning along two simultaneously active dipping faults is transient while global slip partitioning persists. The development of two active fault surfaces arises from changes in off-fault strain pattern after development of the first fault. With early strike-slip faults, off-fault contraction accumulates to produce a new reverse fault. Systems with early lobate reverse faults accommodate limited strike-slip and produce extension in the hanging wall, thereby promoting strike-slip faulting. The observation of persistent slip partitioning under a wide range of experimental conditions demonstrates why such systems are frequently observed in oblique convergence crustal margins around the world.
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Bader, Jeffrey. "Structural analysis of the Casper Mountain fault zone and area, Wyoming surrounding area, Wyoming: Implications for Laramide kinematics and structural inheritance across the Wyoming Province." Mountain Geologist 58, no. 4 (October 27, 2021): 433–52. http://dx.doi.org/10.31582/rmag.mg.58.4.433.
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Casper Mountain is an E–W trending anticlinal structure that is bound on the north by the oblique-slip Casper Mountain fault. The fault is postulated to reflect preexisting Precambrian structure/fabrics that were reactivated and/or guided deformation during the Laramide orogeny. A structural analysis of the fault zone and surrounding area was conducted to confirm this hypothesis, and to garner insight into both Precambrian origins and Laramide kinematics. Surface and subsurface data for structural analysis was collected and synthesized from numerous published sources along the proposed deformation corridor that roughly coincides with the Oregon Trail structural belt of central Wyoming. The Casper Mountain fault zone is characterized by an E–W rectilinear zone of en échelon, steeply inclined faults. The Casper Mountain fault strikes E–W with smaller faults in the zone striking N65°E. Folds trend to the WNW and are left-stepping. Foliations in Precambrian rocks of Casper Mountain are oriented subparallel to the Casper Mountain fault. The North Granite Mountains fault zone is located due west of Casper Mountain and is similarly oriented E–W with associated faults striking NE, NW/SE, and ENE/WSW, off the dominant master fault. Curvilinear, left-stepping, en échelon folds trend to the northwest and are truncated on the south by the North Granite Mountains fault. Faults in basement rocks of the Popo Agie Primitive Area of the central Wind River Mountains are characterized by moderate to high-angle faults striking E–W, NNW, and NE that coincide with mapped surface lineaments and fabric data. Fabric data suggest that Laramide deformation along the Casper Mountain fault was guided by Precambrian anisotropies. Surface and subsurface mapping of the fault zone and the deformation corridor to the west indicate that the Casper Mountain and North Granite Mountains faults are part of a basement-rooted system (wrench fault) that likely extends westward into the Popo Agie Primitive Area. Here, the steeply inclined (75–90°) proposed master fault is exposed within a WNW-striking corridor of faults that sinistrally offset steeply dipping, NE-striking Proterozoic diabase dikes. The dikes likely intruded older faults that are antithetic to the WNW-striking faults. Other faults strike to the NNW and have shallower dips of 45–65°. These three directions of anisotropy (WNW, NE, and NNW) are proposed to have formed from SW–NE-directed subduction along a long-lived, Neoarchean, active continental margin.
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Bellot, Jean-Philippe, Jean-Yves Roig, and Antonin Genna. "The Hospital coal basin (Massif Central, France): relay on the left-lateral strike-slip Argentat fault in relation to the Variscan postorogenic extension." Bulletin de la Société Géologique de France 176, no. 2 (March 1, 2005): 151–59. http://dx.doi.org/10.2113/176.2.151.
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Abstract Structural and microstructural analyses of the Argentat fault, combined with sedimentological and structural analyses of the associated Hospital basin allow us to discuss the tectonic control of coal basins by crustal-scale faults during the late Palaeozoic evolution of the Variscan lithosphere in the French Massif Central. The brittle Argentat fault zone consists of first- and second-order strike-slip faults, with dominant NNW-sinistral faults, NNE-dextral or sinistral faults and secondary ENE-dextral faults. Several experimental and theoretical models explain the observed fault patterns, like en echelon faults, A-type secondary faults, conjugate faults and Riedel shears. Strike-slip faulting is responsible for folding of the metamorphic formations characterized by N-S to NE-SW-trending axis. The regional-scale geometry of brittle faults and associated folds corresponds to a positive flower structure centered on the brittle Argentat fault, combined to a negative flower structure centered on the coal basin. Using tectonic inversion software, we show that these structures result from a left-lateral movement of the brittle Argentat fault in relation to a tectonic regime intermediate between extension and strike-slip, with a horizontal NE-SW to NNE-SSW-trending maximum stretching axis. Detailed map and cross-sections, and sedimentological interpretations of the late Stephanian Hospital basin show the occurrence of intra-basin syn-sedimentary strike-slip faults and progressive overlaying, indicating that sedimentation occurs during left-lateral strike-slip faulting and folding of basement along the Argentat fault. These data are consistent with a model of N-S to NE-SW-trending postorogenic extension proposed to account for the late Carboniferous evolution of the Variscan lithosphere. They also point out the complexity and the variety of structures developed along a regional brittle strike-slip fault zone and the necessity to take into account all the structures and the resulting geometry of the basement in order to better constrain the tectonic setting of intra-continental deposits.
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Omale, Abah P., Juan M. Lorenzo, Ali AlDhamen, Peter D. Clift, and A. Alexander G. Webb. "Fault kinematics: A record of tectono-climatically controlled sedimentation along passive margins, an example from the U.S. Gulf of Mexico." GSA Bulletin 133, no. 9-10 (February 9, 2021): 2226–40. http://dx.doi.org/10.1130/b35623.1.
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Abstract Faults offsetting sedimentary strata can record changes in sedimentation driven by tectonic and climatic forcing. Fault kinematic analysis is effective at evaluating changes in sediment volumes at salt/shale-bearing passive margins where sediment loading drives faulting. We explore these processes along the northern Gulf of Mexico. Incremental throw along 146 buried faults studied across onshore Louisiana revealed continual Cenozoic fault reactivation punctuated by inactive periods along a few faults. Fault scarp heights measured from light detection and ranging (LiDAR) data are interpreted to show that Cenozoic fault reactivation continued through the Pleistocene. The areas of highest fault throw and maximum sediment deposition shifted from southwest Louisiana in the early Miocene to southeast Louisiana in the middle–late Miocene. These changes in the locus of maximum fault reactivation and sediment deposition were controlled by changing tectonics and climate in the source areas. Early Miocene fault throw estimates indicate a depocenter farther east than previously mapped and support the idea that early Miocene Appalachian Mountain uplift and erosion routed sediment to southeast Louisiana. By correlating changes in fault throw with changes in sediment deposition, we suggest that (1) fault kinematic analysis can be used to evaluate missing sediment volumes because fault offsets can be preserved despite partial erosion, (2) fault throw estimates can be used to infer changes in past tectonic and climate-related processes driving sedimentation, and (3) these observations are applicable to other passive margins with mobile substrates and faulted strata within overfilled sedimentary basins.
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BURBERRY, C. M., and J. M. PALU. "The influence of the Great Falls Tectonic Zone on the thrust sheet geometry of the southern Sawtooth Range, Montana, USA." Geological Magazine 153, no. 5-6 (June 3, 2016): 845–65. http://dx.doi.org/10.1017/s0016756816000431.
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AbstractThe reactivation potential of pre-existing deep-seated structures influences deformation structures produced in subsequent compression. This contribution investigates thrust geometries produced in surface thrust sheets of the Sawtooth Range, Montana, USA, deforming over a previously faulted sedimentary section. Surface thrust fault patterns were picked using existing maps and remote sensing. Thrust location and regional transport direction was also verified in the field. These observations were used to design a series of analogue models, involving deformation of a brittle cover sequence over a lower section with varying numbers of vertical faults. A final model tested the effect of decoupling the upper cover and lower section with a ductile detachment, in a scenario closer to that of the Sawtooth Range. Results demonstrate that complexity in surface thrust sheets can be related to heterogeneity within the lower sedimentary section, even when there is a detachment between this section and the rest of the cover. This complexity is best observed in the map view, as the models do not show the deep-seated faults propagating into the cover. These results were then used to predict specific locations of discrete basement fault strands in the study area, associated with what is generally mapped as the Scapegoat-Bannatyne Trend. The deep-seated faults are more likely to be reactivated as strike-slip features in nature, given the small obliquity between the ENE-directed compression direction and the NE-oriented basement faults. More generally, these results can be used to govern evaluation of thrust belts deforming over faulted basement, and to predict the locations of specific fault strands in a region where this information is unknown.
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Cao, Anye, Yaoqi Liu, Siqi Jiang, Qi Hao, Yujie Peng, Xianxi Bai, and Xu Yang. "Numerical Investigation on Influence of Two Combined Faults and Its Structure Features on Rock Burst Mechanism." Minerals 11, no. 12 (December 19, 2021): 1438. http://dx.doi.org/10.3390/min11121438.
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With the increase in coal mining depth, engineering geological conditions and the stress environment become more complex. Many rock bursts triggered by two combined faults have been observed in China, but the mechanism is not understood clearly. The focus of this research aims at investigating the influence of two combined faults on rock burst mechanisms. The six types of two combined faults were first introduced, and two cases were utilized to show the effects of two combined faults types on coal mining. The mechanical response of the numerical model with or without combined faults was compared, and a conceptual model was set up to explain the rock burst mechanism triggered by two combined faults. The influence of fault throw, dip, fault pillar width, and mining height on rock burst potential was analyzed. The main control factors of rock burst in six models that combined two faults were identified by an orthogonal experiment. Results show that six combinations of two faults can be identified, including stair-stepping fault, imbricate fault, graben fault, horst fault, back thrust fault, and ramp fault. The particular roof structure near the two combined faults mining preventing longwall face lateral abutment pressure from transferring to deep rock mass leads to stress concentration near the fault areas. Otherwise, a special roof structure causing the lower system stiffness of mining gives rise to the easier gathering of elastic energy in the coal pillars, which makes it easier to trigger a rock burst. There is a nonlinear relationship between fault parameters and static or dynamic load for graben faults mining. The longwall face has the highest rock burst risk when the fault throw is between 6 and 8 m, the fault dip is larger than 65°, the mining height is greater than 6 m, and the coal pillar width is less than 50 m. The stair-stepping, imbricate, horst, and ramp fault compared to the other fault types will produce higher dynamic load stress during longwall retreat. Fault pillar width is the most significant factor for different two combined faults, leading to the rise of static load stress and dynamic proneness.
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Rodriguez Padilla, Alba M., Michael E. Oskin, Thomas K. Rockwell, Irina Delusina, and Drake M. Singleton. "Joint earthquake ruptures of the San Andreas and San Jacinto faults, California, USA." Geology 50, no. 4 (December 7, 2021): 387–91. http://dx.doi.org/10.1130/g49415.1.
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Abstract Large, multi-fault earthquakes increase the threat of strong ground shaking and reshape the probability of future events across a system of faults. Fault junctions act as conditional barriers, or earthquake gates, that stop most earthquakes but permit junction-spanning events when stress conditions are favorable. Constraining the physical conditions that favor multi-fault earthquakes requires information on the frequency of isolated events versus events that activate faults through the junction. Measuring this frequency is challenging because dating uncertainties limit correlation of paleoseismic events at different faults, requiring a direct approach to measuring rupture through an earthquake gate. We show through documentation and finite-element modeling of secondary fault slip that co-rupture of the San Andreas and San Jacinto faults (California, USA) through the Cajon Pass earthquake gate occurred at least three times in the past 2000 yr, most recently in the historic 1812 CE earthquake. Our models show that gate-breaching events taper steeply and halt abruptly as they transfer slip between faults. Comparison to independent chronologies shows that 20%–23% of earthquakes on the San Andreas and the San Jacinto faults are co-ruptures through Cajon Pass.
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Osmond, Johnathon L., and Timothy A. Meckel. "Enhancing trap and fault seal analyses by integrating observations from HR3D seismic data with well logs and conventional 3D seismic data, Texas inner shelf." Geological Society, London, Special Publications 496, no. 1 (August 7, 2019): 253–79. http://dx.doi.org/10.1144/sp496-2018-142.
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AbstractAn understanding of trap and fault seal quality is critical for assessing hydrocarbon prospectivity. To achieve this, modern analytical techniques leverage well data and conventional industry-standard 3D seismic data to evaluate the trap, and any faults displacing the reservoir and top seal intervals. Above all, geological interpretation provides the framework of trap and fault seal analyses, but can be hindered by the data resolution, quality and acquisition style of the conventional seismic data. Furthermore, limiting the analysis to only the petroleum system at depth may lead to erroneous perceptions because interpreting overburden features, such as shallow faults or gas chimneys, can provide valuable observations with respect to container performance, and can to help validate trap and fault seal predictions. A supplement to conventional 3D data are high-resolution 3D seismic (HR3D) data, which provide detailed images of the overburden geology. This study utilizes an HR3D seismic volume in the San Luis Pass area of the Texas inner shelf, where shallow fault tips and a sizeable gas chimney are interpreted over an unsuccessful hydrocarbon prospect. Static post-drill fault seal and trap analyses suggest that the primary fault displacing the structural closure could have withheld columns of gas c. 100 m high, but disagree with our HR3D seismic interpretations and dry-well analyses. From our results, we hypothesize that tertiary gas migration through fault conduits reduced the hydrocarbon column in the prospective Early Miocene reservoir, and may have resulted from continued movement along the intersecting faults. Overall, this study reinforces the importance of understanding the overburden geology and geohistory of faulted prospects, and demonstrates the utility of pre-drill HR3D acquisition when conducting trap and fault seal analyses.
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Homberg, Catherine, Johann Schnyder, and Mohamed Benzaggagh. "Late Jurassic-Early Cretaceous faulting in the Southeastern French basin: does it reflect a tectonic reorganization?" Bulletin de la Société Géologique de France 184, no. 4-5 (July 1, 2013): 501–14. http://dx.doi.org/10.2113/gssgfbull.184.4-5.501.
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AbstractWe present new data constraining the Late Jurassic to Early Cretaceous evolution of the Southeastern French basin (SFB). Meso-scale faults with displacement of several decimeters to 1–2 meters were sampled for geometric and kinematic data analysis and the faulted and un-faulted sedimentary units were examined for sedimentologic and bio-stratigraphic purposes. Small-scale faults were also extensively collected to determine the local stress states during this period. Meso-scale normal faults formed during sediment deposition or before its complete lithification attest of a recurrent activity in the Late Jurassic to Early Cretaceous period in an overall extensional context. The fault network cutting the Oxfordian to Aptian sequences included normal faults of various trends, ranging between WSW-ENE and NNW-SSE. We show that the deformation mechanism in the SFB drastically changed in the Jurassic-Cretaceous transition (latermost Tithonian?), with the direction of extension rotating from a WNW-ESE to a NNE-SSW direction. Lateral thickness variation of the sequences, redistribution of sediments, faulting at various scales concur that the Early Cretaceous period marks a tectono-stratigraphic reorganization of the basin. We suggest that it traduces the rifting and later opening of the North Atlantic (main branch and bay of Biscay branch).
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King, James J., and Joe A. Cartwright. "Ultra-slow throw rates of polygonal fault systems." Geology 48, no. 5 (February 27, 2020): 473–77. http://dx.doi.org/10.1130/g47221.1.
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Abstract Polygonal fault systems (PFSs) are an enigmatic class of small nontectonic extensional faults. PFSs are predominantly hosted in fine-grained sedimentary tiers and are prevalent along many continental margin basins. The genesis of PFSs is widely debated, and little is known about the time frame for polygonal fault growth. We present the first measurements of throw rates for polygonal faults by measuring the vertical offset of seven age-calibrated horizons mapped using three-dimensional seismic reflection data from the Norwegian Sea. Individual polygonal faults exhibit a range of throw rate profiles through time, ranging from near linear to singly or multiply stepped. The stepped profiles have short-term throw rates ranging from 0 to 18 m/m.y. Time-averaged throw rates of 180 polygonal faults over the entire 2.61–0 Ma interval are normally distributed and range between 1.4 and 10.9 m/m.y. We convert our PFS throw rates to displacement rates and compare these to published displacement rates for gravity-driven and tectonic normal faults. We find that the displacement rates of polygonal faults mark the lower limit of a continuous spectrum of extensional fault displacement rates; they are as much as two orders of magnitude slower than those of gravity-driven faults, and as much as three orders of magnitude slower than those of the fastest-growing tectonic faults. We attribute the ultra-slow kinematic behavior to the nontectonic nature of polygonal faults, where throw accumulates primarily through dewatering of the largely fine-grained sediments composing the host layers for the PFSs, and through differential volumetric strain between the fault footwalls and hanging walls.
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Reichenbacher, Renee, Roy Van Arsdale, Randel Cox, and Chris Cramer. "Geomorphology, Three-Dimensional Geology, and Seismologic Hazards of the New Madrid Seismic Zone in Dyer County, Tennessee." Environmental & Engineering Geoscience 28, no. 2 (April 22, 2022): 147–71. http://dx.doi.org/10.2113/eeg-d-21-00005.
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ABSTRACT Geomorphic and three-dimensional geologic mapping reveals two major fault systems of the seismically active Reelfoot rift pass beneath Dyer County in northwestern Tennessee, the Reelfoot South fault, and the east-bounding faults of the Reelfoot rift. The Dyer County mapping also indicates that the two principal Reelfoot South fault hanging wall structures, the Lake County uplift and Tiptonville dome, pass beneath the county. Quaternary displacement was identified on southeastern Reelfoot rift margin faults in Dyer County, thus indicating that this rift margin has been active during the Quaternary from adjacent Obion County through Dyer County to Lauderdale County, Tennessee, for a distance of at least 60 km. The three-dimensional geologic mapping also provides stratigraphic thicknesses of surface sediment and underlying Paleogene and Cretaceous strata that significantly contribute to the estimation of ground motion in the event of a future large New Madrid seismic zone earthquake. The new ground motion maps using the three-dimensional geology of Dyer County are compared to the current U.S. Geological Survey earthquake hazard maps. This comparison reveals generally lower acceleration for buildings less than four stories high and greater acceleration for buildings greater than 10 stories high in the event of a large New Madrid seismic zone earthquake.
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Soliva, Roger, Antonio Benedicto, Pierre Vergély, and Thierry Rives. "Mechanical control of a lithological alternation on normal fault morphology, growth and reactivation." Bulletin de la Société Géologique de France 176, no. 4 (July 1, 2005): 329–42. http://dx.doi.org/10.2113/176.4.329.
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Abstract This paper presents an analysis of the control of lithological variation on normal fault morphology, growth and reactivation. We study a normal fault population contained within an inter-bedded sequence of marly-limestones and clay rich layers. The analysis of cross sectional and bedding plane exposure of faults reveals that the plastic clay layers act as barriers to vertical fault propagation. Only the long vertically restricted normal faults (i.e. confined between two clay layers) are later reactivated and show extensional-shear mode of deformation. The likelihood of reactivation of the faults was probably favoured by the small plastic strength of the clay rich layers. We discuss the extensional-shear mode in terms of structural context, reactivation and rock rigidity. Displacement profile analysis of only isolated non-reactivated faults allows us to distinguish the faults mechanically influenced by the rheological discontinuities from those that are contained within the same lithological unit. Using both cross-sectional observations and displacement-length data of the fault population we estimate the average aspect ratio (length/height ~ 2) of the faults contained within the same lithological unit. A 3-D displacement-length scaling law that integrates post yield fracture mechanics (PYFM) and the principal fault dimensions (length and height) reveals the importance of the low rigidity of the marly-limestone on the displacement of the faults contained into a same lithological unit. A comparison of our displacement-length data with those compiled from the literature suggests that the displacement-length variability is strongly related to the rock mechanical properties and contrasts in layered rocks. The bulk of our analysis, based on field observations and theory, shows that: (i) fault shape, (ii) fault ability to be reactivated, (iii) shear mode, and (iv) displacement-length values are strongly sensitive to the lithological contrasts, and are therefore dependent on the fault dimension relative to the thicknesses of the sedimentary bodies. Therefore, regardless the variety of fault initiation processes, our analysis confirms that both fault morphology and fault growth are not self similar in heterogeneous layered rocks from centimetre to kilometre scale.
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Durling, P., K. Howells, and P. Harvey. "The near-surface geology of St. Georges Bay, Nova Scotia: implications for the Hollow Fault." Canadian Journal of Earth Sciences 32, no. 5 (May 1, 1995): 603–13. http://dx.doi.org/10.1139/e95-051.
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A formline contour map, which depicts the near-surface, structural configuation of the strata underlying St. Georges Bay, northeastern Nova Scotia, was made from bedding attitude data compiled in the coastal areas; apparent dips measured from single-channel seismic reflection data; and true strikes and dips calculated at survey track intersections. The geology interpreted from the formline map is characterized by northeast-striking faults and fold axes. The folds in the bay comprise broad, open synclines and narrow, tightly folded or faulted anticlines. Gravity and deep seismic reflection data suggest that the faulted anticlines are intruded by salt. Correlations from offshore to onshore suggest that the structures mapped offshore in the bay extend onshore. The onshore extensions of the faulted anticlines are mapped as faults, and their antiformal nature is subdued. They are locally associated onshore with Carboniferous Windsor Group outcrop. The offshore extension of the Hollow Fault, which is interpreted as a major northeast-striking, Carboniferous strike-slip fault, was mapped as a 1500–2500 m wide deformation zone, using deep seismic reflection data. Gravity lows coincident with the deformation zone are interpreted as being caused by salt intrusions. The trend of the Hollow Fault Zone suggests that this fault complex (and its associated strike-slip movement) continues on land near Mabou, Cape Breton Island. However, it does not appear to continue offshore along the northwest coast of Cape Breton Island, as previously suggested.
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Deng, Hongdan, and Ken McClay. "Three-dimensional geometry and growth of a basement-involved fault network developed during multiphase extension, Enderby Terrace, North West Shelf of Australia." GSA Bulletin 133, no. 9-10 (January 28, 2021): 2051–78. http://dx.doi.org/10.1130/b35779.1.
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Abstract Basement fault reactivation, and the growth, interaction, and linkage with new fault segments are fundamentally three-dimensional and critical for understanding the evolution of fault network development in sedimentary basins. This paper analyzes the evolution of a complex, basement-involved extensional fault network on the Enderby Terrace on the eastern margin of the Dampier sub-basin, North West Shelf of Australia. A high-resolution, depth-converted, 3-D seismic reflection data volume is used to show that multiphase, oblique extensional reactivation of basement-involved faults controlled the development of the fault network in the overlying strata. Reactivation of the pre-existing faults initially led to the formation of overlying, en échelon Late Triassic–Middle Jurassic fault segments that, as WNW-directed rifting progressed on the margin, linked by breaching of relay zones to form two intersecting fault systems (F1 and F2–F4). Further reactivation in the latest Jurassic–Early Cretaceous (NNW-SSE extension) produced an additional set of en échelon fault arrays in the cover strata. The final fault network consists of main or principal faults and subordinate or splay faults, together with branch lines that link the various components. Our study shows that breaching of relay ramps and/or vertical linkages produces vertical and horizontal branch lines giving complex final fault geometries. We find that repeated activity of the basement-involved faults tends to form continuous and planar fault architectures that favor displacement transfer between the main constituent segments along strike and with depth.
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Tamura, Yoshihiko, Futoshi Tsuneyama, Hitoshi Okamura, and Keiichi Furuya. "Fault characterization by seismic attributes and geomechanics in a Thamama oil field, United Arab Emirates." GeoArabia 9, no. 2 (April 1, 2004): 63–76. http://dx.doi.org/10.2113/geoarabia090263.
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ABSTRACT Faults and fractures were interpreted using attributes that were extracted from a 3-D seismic data set recorded over a Lower Cretaceous Thamama oil field in offshore Abu Dhabi, United Arab Emirates. The Thamama reservoir has good matrix porosity (frequently exceeding 20%), but poor permeability (averaging 15 mD). Because of the low permeability, faults and fractures play an important role in fluid movement in the reservoir. The combination of the similarity and dip attributes gave clear images of small-displacement fault geometry, and the orientation of subseismic faults and fractures. The study better defined faults and fractures and improved geomechanical interpretations, thus reducing the uncertainty in the preferred fluid-flow direction. Two fault systems were recognized: (1) the main NW-trending fault system with mapped fault-length often exceeding 5 km; and (2) a secondary NNE-trending system with shorter faults. The secondary system is parallel to the long axis of the elliptical domal structure of the field. Some of the main faults appear to be composed of en-echelon segments with displacement transfer between the overlapping normal faults (relay faults with relay ramps). The fault systems recognized from the seismic attributes were correlated with well data and core observations. About 13 percent of the fractures seen in cores are non-mineralized. The development of the fault systems was studied by means of clay modeling, computer simulation, and a regional tectonics review. The existing fluid-flow characteristics of individual faults and fractures in the field can be modeled using the present-day stress regime, with the maximum horizontal stress oriented north-northeast. Slip-tendency and dilation-tendency analyses simulating present-day regional stress conditions are indicators of fault and fracture transmissibility. The NNE-striking secondary fault system is parallel to the present-day maximum horizontal stress and could act as a flow conduit in the reservoir.
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Ehteshami-Moinabadi, Mohsen. "Fossil fault zones: significance and applications." Geologica Balcanica 47, no. 1 (May 2018): 61–71. http://dx.doi.org/10.52321/geolbalc.47.1.61.
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Fossil faults are permanently inactive fault zones, preserved and recognized in the geological record of an area by major brittle, semi-brittle, or mylonitic fault rocks, showing significant width and displacement. Applications and purposes of fossil fault researches include, but are not limited to, investigation on seismic faulting, analog model of active faults, metal ore deposits, paleo-path and fluid migration, deformation mechanism and fault migration along-strike and down-dip. These categories involve subsidiary subjects, some of which are relatively new and seem to attract more attention. Fossil faults are a major source of information about past geological processes that were active at some depth in Earth’s lithosphere, and also provide an opportunity for assuming and predicting the future in structural geology. This paper reviews the researches done on fossil faults and their applications since the early 1970s, albeit not always listed as “fossil faults”.
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Chatellier, Jean-Yves. "Fault locking and alternate fault activity revealed by simple tools and approaches — Examples from the Western Canadian Sedimentary Basin with implications for hydrocarbon exploration and production." Leading Edge 43, no. 3 (March 2024): 145–54. http://dx.doi.org/10.1190/tle43030145.1.
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The geology toolkit that is used to reveal faults and fractures is much wider than before. This is due to 3D and 4D views in exploratory statistics programs and to the availability of user-friendly GIS software. These tools allow us to visualize a multitude of parameters that will be briefly explored here. A review of many geologic and nongeologic parameters led to evidence of fault locking and alternate fault activity. It also resulted in new structural models for the Western Canadian Sedimentary Basin (WCSB). The presented data sets include earthquakes, drilling, production, well data, aeromagnetic data, and more. Various integrated approaches reveal well-defined fault patterns that are typical of a strike-slip regime and the existence of previously unrecognized detachments that are important for hydrocarbon exploration. Some of the new geometries and associated mechanisms are illustrated here with outcrop analogues and present-day cross sections, maps, and 3D views. Only the most recent of the two identified strike-slip regimes is covered in this paper. Some emphasis is given to the recognition of detachments at various scales. Among these is the importance of megadetachments displacing the sedimentary cover by up to 16 km with respect to the aeromag. Hence, there is a need for reconstruction before making conclusions. The WCSB has a lot more to offer to explorers who understand faults, fractures, and migration paths. Integrating many types of information in map or 3D views offers new tools to identify and characterize faults.
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Song, Jing, T. M. Alves, K. O. Omosanya, T. C. Hales, and Tao Ze. "Tectonic evolution of strike-slip zones on continental margins and their impact on the development of submarine landslides (Storegga Slide, northeast Atlantic)." GSA Bulletin 132, no. 11-12 (April 6, 2020): 2397–414. http://dx.doi.org/10.1130/b35421.1.
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Abstract Submarine landslides have affected the mid-Norwegian margin since the Last Glacial Maximum. However, the role of tectonic movements, and most especially fault reactivation, in generating landslides offshore Norway is largely unconstrained. This study uses high-quality three-dimensional seismic and borehole data to understand how landslide development is controlled by faults propagating within the uplifted south Modgunn arch. Variance and structural maps above the south Modgunn arch show that: (1) local scarps of recurrent landslides were formed close to the largest faults, and mainly above strike-slip faults; (2) distinct periods of fault generation were associated with tectonic events, such as the breakup of the northeast Atlantic Ocean, and those events forming the south Modgunn arch; and (3) important fluid-flow features coincide with faults and sill intrusions. In total, 177 faults were analyzed to demonstrate that fault throw values vary from 10 ms to 115 ms two-way traveltime (8 m to 92 m). We propose that the long-term activity of faults in the study area has contributed to fluid migration, weakened post-breakup strata, and controlled the development of submarine slope instability. In particular, strike-slip faults coincide with the locations of several Quaternary landslide scars near the modern seafloor. Similar processes to those documented in Norway may explain the onset of large-scale landslides on other continental margins.
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Mora, Jose P., Heather Bedle, and Kurt J. Marfurt. "Fault enhancement using probabilistic neural networks and Laplacian of a Gaussian filter: A case study in the Great South Basin, New Zealand." Interpretation 10, no. 2 (February 22, 2022): SC1—SC15. http://dx.doi.org/10.1190/int-2021-0127.1.
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Fault identification is critical in defining the structural framework for exploration and reservoir characterization studies. Interpreters routinely use edge-sensitive attributes to accelerate the manual picking process, in which the actual choice of a particular edge-sensitive attribute varies with the seismic data quality and with the reflectivity response of the faulted geologic formations. The cyan-magenta-yellow (CMY) color blending provides an effective way to combine the information content of two or three edge-sensitive attributes when more than one attribute is sensitive to faults. We have evaluated whether combining the information content of more than three attributes using probabilistic neural networks (PNNs) provides any additional uplift. We use training data consisting of manually picked faults on a coarse grid of 3D seismic lines, and then, we use an exhaustive search PNN to identify the optimal set of attributes to create a fault probability volume for a 3D survey acquired over the Great South Basin, New Zealand. We construct a suite of candidate attributes using our understanding of the attribute response to faults seen in the data and examples extracted from the published literature to use the list as the analyzed attributes. Using a subset of picked faults as training data, we evaluate which suite of attributes and hyperparameters exhibits the highest validation on the remaining training data. When used together, we find that volume aberrancy magnitude, gray-level cooccurrence matrix (GLCM) homogeneity, GLCM entropy, Sobel filter similarity, and envelope best predict the faults for this data set. The PNN supervised classification creates a seismic image volume that exhibits fault probabilities providing a simple combination of multiple seismic attributes. We also find that applying a directional Laplacian of a Gaussian and skeletonization filters to the PNN fault volumes provides a superior result to simple CMY blending techniques.
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Davis, Thomas L. "Seismic Evidence of Tectonic Influence on Development of Cretaceous Listric Normal Faults, Boulder-Wattenberg-Greeley Area, Denver Basin, Colorado." Mountain Geologist 22, no. 2 (April 1, 1985): 47–54. http://dx.doi.org/10.31582/rmag.mg.22.2.47.
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Reflection seismic studies in the Denver basin near Greeley, Colorado, illustrate an association between listric normal faults (which sole out in detachment or decollement zones) and basement-controlled faults. Recurrent movement on basement-controlled faults triggered development of listric normal faults in tectonically sensitive stratigraphic intervals of the Cretaceous. Stratigraphic intervals exhibiting listric normal faults include the Cretaceous Laramie-Fox Hills-Upper Pierre, Middle Pierre Hygiene zone, and the Niobrara-Carlile Greenhorn. Listric normal faults are prevalent on the flank of a fault-bounded basement-controlled paleostructural block termed the Wattenberg block by Weimer and Sonnenberg (1982). Listric normal faults influence Cretaceous reservoir systems in the Hambert field area on the north flank of the Wattenberg-Greeley Lineament Zone.
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Fittall, A. M., and R. G. Cowley. "THE HV11 3-D SEISMIC SURVEY: SKUA – SWIFT AREA GEOLOGY REVEALED?" APPEA Journal 32, no. 1 (1992): 159. http://dx.doi.org/10.1071/aj91013.
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The 4630 km of HV11 3-D seismic survey data, shot over the Skua and Swift fault blocks in Timor Sea licence AC/L4, reveals details of Tithonian faulting not evident previously. The HV11 survey provided 10 times the data density of previous coverage and significantly improved data quality through the recording of lower frequencies and use of accurate navigation systems and high resolution processing parameters.Tithonian faulting is revealed as a series of northeast-trending en echelon faults overprinting a deeper, north-northeastern, possibly latest Triassic, trend which defines the major fault block boundaries. Transfer of fault throw between en echelon segments appears to be by strike ramps with no evidence for cross-cutting transfer faults. Skua Field fault geometries preclude Upper Jurassic, right lateral strike-slip tectonics. Semi-regional fault trends also have an en echelon style with transfer of fault throw by strike ramps. Escarpments developed along the Tithonian faults are also evident on the HV11 data.The direction of Tithonian extension is interpreted to be oblique to the deeper fault trend, giving rise to the en echelon Tithonian fault style. Each en echelon segment appears to control an hydrocarbon accumulation, which may be due to fault-independent drape over palaeotopographic relief.En echelon Miocene faulting, incisement and depositional mounding in the Puffin Formation are also detailed by the HV11 seismic data. The HV11 survey demonstrates the value of acquisition of 3-D seismic data as an exploration tool in an area of complex and subtle structural geology.
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Shi, Pengcheng, Meng (Matt) Wei, and Robert A. Pockalny. "The ubiquitous creeping segments on oceanic transform faults." Geology 50, no. 2 (November 2, 2021): 199–204. http://dx.doi.org/10.1130/g49562.1.
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ABSTRACT Oceanic transform faults are a significant component of the global plate boundary system and are well known for generating fewer and smaller earthquakes than expected. Detailed studies at a handful of sites support the hypothesis that an abundance of creeping segments is responsible for most of the observed deficiency of earthquakes on those faults. We test this hypothesis on a global scale. We relocate Mw ≥5 earthquakes on 138 oceanic transform faults around the world and identify creeping segments on these faults. We demonstrate that creeping segments occur on almost all oceanic transform faults, which could explain their deficiency of earthquakes. We also find that most of the creeping segments are not associated with any large-scale geological structure such as a fault step-over, indicating that along-strike variation of fault zone properties may be the main reason for their existence.
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Seminsky, К. Zh, A. S. Cheremnykh, O. M. Khlystov, and G. G. Akhmanov. "Fault Zones and Stress Fields in the Sedimentary Fill of Lake Baikal: Tectonophysical Approach for Seismic and Hydroacoustic Data Interpretation." Russian Geology and Geophysics 63, no. 7 (July 1, 2022): 840–55. http://dx.doi.org/10.2113/rgg20204293.
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Abstract —This paper presents a schematic summary of comprehensive analysis of seismic, reflection profiling, and hydroacoustic data on faults which caused sediment deformation in the central segment of the Central Baikal basin. According to the tectonophysical analysis results, the fault pattern within sediment fill has been recognized as zone-block, i.e., it represents a network of high-density fracture zones limiting weakly deformed blocks. The structure of large NE-trending fault zones (Olkhon, Beregovoy, Gydratny, and Svyatoy Nos) is controlled by main fault planes (or their segments) bounded by subsidiary faults. Geomorphic expression of NW cross faults in the sedimentary cover as broad zones of smaller-scale fractures accounts for early stages of the evolution of basement faults. In a longitudinal direction, they divide the basin into large fragments. The zone–block structure of the sedimentary strata was developed in different stress regimes: strike-slip and extension at the early and late orogenic rifting stages, respectively. At the modern stage of tectogenesis, the established network of fault zones controls the gaseous (including hydrate formation) and seismic activity expression in the subsurface. Hydrate-bearing mud volcanoes and seeps are confined to major faults, while earthquake epicenters are confined to fault zones and form clusters at junctions of large NE-trending faults with NW-oriented extension zones and E–W left-lateral strike-slip faults.
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Guzmán-Speziale, Marco. "The triple junction of the North America, Cocos, and Caribbean plates. What we know, what we don’t." Revista Mexicana de Ciencias Geológicas 39, no. 2 (July 26, 2022): 190–205. http://dx.doi.org/10.22201/cgeo.20072902e.2022.2.1666.
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We present a summary of the tectonic elements of the North America-Caribbean-Cocos triple junction area. In the vicinity of the triple junction, displacement related to the North America-Caribbean plate boundary takes place along the left-lateral Motagua-Polochic fault system, and convergence between the Cocos and the other two plates occurs along the Middle America trench.
The trace of the Motagua-Polochic system is lost at its westernmost end and does not reach the convergent boundary. Deformation of the plate boundary in this location is then distributed along a system of reverse faults (the Reverse-faults tectonic province), a system of left-lateral faults (Strike-slip faults province), two or more large NW-SE oriented left-lateral faults (Angostura and Concordia faults), and a left-lateral fault (Tonalá) that might be construed as the continuation of the Polochic fault along the southern border of the Chiapas Massif.
Somewhere within this deformation zone, transition in overriding plate between North America and Caribbean takes place, but it is not clear exactly where. It is probably at about longitude 96° W because both the dip and the shape of the subducted Cocos slab change significantly at this longitude.
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Nkodia, H. M. D.-V., T. Miyouna, D. Delvaux, and F. Boudzoumou. "Flower structures in sandstones of the Paleozoic Inkisi Group (Brazzaville, Republic of Congo): evidence for two major strike-slip fault systems and geodynamic implications." South African Journal of Geology 123, no. 4 (November 16, 2020): 531–50. http://dx.doi.org/10.25131/sajg.123.0038.
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Abstract Few studies have reported field descriptions of flower structures associated with strike-slip faults. This study describes and illustrates flower structures near Brazzaville (Republic of Congo) and explains their implication for the tectonic history of the Paleozoic Inkisi Group. Field observations show that the Inkisi Group is affected by two major strike-slip fault systems. The oldest system is dominated by north-northwest–south-southeast striking sinistral strike-slip faults and minor east–west striking dextral strike-slip faults. The youngest system consists of dominant northeast–southwest striking dextral strike-slip faults and minor northwest–southeast striking sinistral strike-slip faults. Flower structures within these major strike slip faults show four types of arrangements that likely depend on fault growth, propagation and damage zones: (i) flower structures associated with wall damage zones; (ii) flower structures associated with linking damage zones; (iii) flower structures associated with tip damage zones; and (iv) “hourglass” flower structures. Paleostress analysis reveals that both major fault systems originated from two differently oriented pure strike-slip regime stress stages. The first stage, which engendered the first major fault system, developed under northwest–southeast compression (i.e, σ1 = 322°). This phase probably coincided with north–south collision in the southern part of Gondwana in the Permo-Triassic and the Late Cretaceous compression times. The second stress stage, creating the second major fault system, developed under east–west (i.e, σ1 = 078°) compression. This phase is correlated with compression from the east–west opening of the Atlantic Ocean in the Miocene times.
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Xu, Shunshan, Angel Francisco Nieto-Samaniego, Huilong Xu, Wei Li, and Ricardo Nieto-Fuentes. "Quantitative determination of fault slip magnitude: a review." Revista Mexicana de Ciencias Geológicas 40, no. 1 (April 1, 2023): 85–95. http://dx.doi.org/10.22201/cgeo.20072902e.2023.1.1728.
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In geology, a fault is a rock fracture with perceptible relative displacement of the opposite sides of the fracture. Quantitatively obtaining the activity history of faults depends mainly on the estimation of fault slip and the study of markers, which can be used to understand and analyze the tectonic evolution of the faulted regions. Fault slip is calculated by restoring points that were originally adjacent before the deformation, those points are named piercing points. In this paper, we review some published methods to determine fault slip, using: (1) the offset of contours on structural contour maps; (2) offset on seismic reflection sections; (3) a known slip vector (fault striae) and one marker; (4) two known markers. Cases (3) and (4) are commonly applied to field work and geological maps.
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Filbrandt, Jacek B., Pascal D. Richard, and Raymond Franssen. "Fault growth and coalescence: insights from numerical modelling and sandbox experiments." GeoArabia 12, no. 1 (January 1, 2007): 17–32. http://dx.doi.org/10.2113/geoarabia120117.
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ABSTRACT Displacement of strata varies along the strike of faults. This has important implications for the hydrocarbon industry, since for example this affects the occurrence and distribution of fractures along faults in a reservoir and can influence the sealing capacity of faults. As faults grow, neighbouring faults will interact with each other and eventually connect or coalesce. Geometrical fault growth models for coalescence are used to explain a large part of the observed spread of one order of magnitude in Length and Maximum Throw in natural examples of fault populations. Numerical modelling indicates that coalesced (merged) faults tend to return to their steady state growth evolution by accumulating displacement more rapidly than increasing in length, if no further coalescence occurs. Therefore, repetitive coalescence leaves faults “under-displaced” and results in a considerable spread in Length and Maximum Throw. To confirm and support these observations, a series of sandbox experiments was performed, which help improve our understanding of fault growth processes. The fault geometries observed in these models reflect geometries in natural examples, for example in the Natih Formation of Al Jabal al Akhdar in Oman. With increasing strain, repetitive coalescence takes place at all scales. After linkage, a new, coalesced fault behaves as a single, linked segment and accumulates more displacement than increasing length during an increment of strain. The slope of the best fit line of Length vs. Maximum Throw data for the fault population, in double logarithmic space, steepens with increasing strain and stabilises at about one.
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Robinson, Laura N., and Bruce E. Barnum. "Southeastern Extension of the Lake Basin Fault Zone in South-Central Montana: Implications for Coal and Hydrocarbon Exploration." Mountain Geologist 23, no. 2 (April 1, 1986): 37–44. http://dx.doi.org/10.31582/rmag.mg.23.2.37.
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The Lake Basin fault zone, which is the eastern extension of the Lewis and Clark line, is a structural lineament extending west-northwest across central Montana and consists mainly of en echelon northeast-striking normal faults that have been interpreted to be surface expressions of left-lateral movement along a basement wrench fault. Information gathered from recent field mapping of coal beds and from shallow, closely-spaced drill holes resulted in detailed coal bed correlations, which revealed another linear zone of en echelon faulting directly on the extended trend of the Lake Basin fault zone. This faulted area, referred to as the Sarpy Creek area, is located 30 mi (48 km) east of Hardin, Montana. It is about 10 mi (16 km) long, 8 mi (13 km) wide, and contains 21 en echelon normal faults that have an average strike of N 63° E. We therefore extend the Lake Basin fault zone 20 mi (32 km) farther southeast than previously mapped to include the Sarpy Creek area. The Ash Creek oil field, Wyoming, 60 mi (97 km) due south of the Sarpy Creek area, produces from faulted anticlinal structures that have been interpreted to be genetically related to the primary wrench-fault system known as the Nye-Bowler fault zone. The structural similarities between the Sarpy Creek area and the Ash Creek area indicate that the Sarpy Creek area is a possible site for hydrocarbon accumulation.
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El-Hussaini, A., M. Youssef, and H. Ibrahim. "An application of the second derivative as a tool in tectonic analysis in the Qattara Depression area, Egypt." Geological Magazine 123, no. 3 (May 1986): 307–13. http://dx.doi.org/10.1017/s0016756800034786.
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AbstractThe second derivative of gravity anomalies of the Qattara area was analysed and statistically studied for determining the tectonic elements. Zones of zero second derivative were considered as the locations of possible faults. The analysis of a constructed tectonic map portrays the predominance of N45°W, N85°E and N45°E fault trends in addition to less pronounced N15°E and N–S faults. The NW–SE faults are very old and inherited from the basement structures. They acted as first order right-lateral wrench faults during the Alpine tectonism. Second and higher orders of faults, developed as a consequence of these movements, are represented by the N85°E and other less abundant trends. Vertical movements along the existing fault system, in addition to the horizontal displacement, is supported by the analysis of the pronounced anomalies of the second derivative map. The subsurface structural picture of the area is composed of uplifted and downfaulted adjoining blocks.
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Bramham, Emma K., Tim J. Wright, Douglas A. Paton, and David M. Hodgson. "A new model for the growth of normal faults developed above pre-existing structures." Geology 49, no. 5 (January 26, 2021): 587–91. http://dx.doi.org/10.1130/g48290.1.
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Abstract Constraining the mechanisms of normal fault growth is essential for understanding extensional tectonics. Fault growth kinematics remain debated, mainly because the very earliest phase of deformation through recent syn-kinematic deposits is rarely documented. To understand how underlying structures influence surface faulting, we examined fault growth in a 10 ka magmatically resurfaced region of the Krafla fissure swarm, Iceland. We used a high-resolution (0.5 m) digital elevation model derived from airborne lidar to measure 775 fault profiles with lengths ranging from 0.015 to 2 km. For each fault, we measured the ratio of maximum vertical displacement to length (Dmax/L) and any nondisplaced portions of the fault. We observe that many shorter faults (<200 m) retain fissure-like features, with no vertical displacement for substantial parts of their displacement profiles. Typically, longer faults (>200 m) are vertically displaced along most of their surface length and have Dmax/L at the upper end of the global population for comparable lengths. We hypothesize that faults initiate at the surface as fissure-like fractures in resurfaced material as a result of flexural stresses caused by displacements on underlying faults. Faults then accrue vertical displacement following a constant-length model, and grow by dip and strike linkage or lengthening when they reach a bell-shaped displacement-length profile. This hybrid growth mechanism is repeated with deposition of each subsequent syn-kinematic layer, resulting in a remarkably wide distribution of Dmax/L. Our results capture a specific early period in the fault slip-deposition cycle in a volcanic setting that may be applicable to fault growth in sedimentary basins.
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Bracken, Kyle. "Mechanical stratigraphy and layer-bound normal faulting in the Upper Cretaceous Niobrara Formation, Wattenberg Field, Colorado." Mountain Geologist 57, no. 2 (April 1, 2020): 67–93. http://dx.doi.org/10.31582/rmag.mg.57.2.67.
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Layer-bound normal faults are pervasive within the very fine-grained rocks of the Upper Cretaceous Niobrara and Carlile formations in the Denver Basin. 3-D seismic and well log interpretation reveal a complex, segmented fault system that is divided into two discrete tiers: an upper tier located in the Pierre Shale, and a lower tier located in the Niobrara Formation. 3-D fault throw analysis shows maximum throw near the top of the Niobrara Formation with steep, asymmetrical throw gradient down section in the lower Niobrara and Carlile formations. Faults are laterally well-connected in the upper Niobrara Formation and commonly form linear arrays of linked graben systems. In contrast, faults deeper in the stratigraphic section that offset the Carlile and Greenhorn formations are more segmented and commonly form half grabens (as opposed to full, fault-bound grabens). In cross-section, fault planes measured from seismic have a general dip of 45°. However, close inspection reveals that faults consistently change dip angle as they pass through the lower Niobrara Formation, refracting from ~55° to ~35° through the Niobrara C Marl, then back up to ~50° in the Carlile and Greenhorn formations. The fault dip refraction produces a contractional step or bend in the fault plane associated with the lower dip segments. This geometry is investigated further with horizontal image logs and other borehole data to reveal a kinematic relationship between fault dip angle and mechanical stratigraphy. Field examples of normal faults that cut mechanically layered rock help better understand these complex fault geometries and provide reasonable inferences to their development and propagation history. In summary, it is argued that the mechanically layered nature of the Niobrara and Carlile formations is responsible for many of the fault characteristics described and provides valuable insight into understanding the fault system
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Fletcher, John M., Orlando J. Teran, Thomas K. Rockwell, Michael E. Oskin, Kenneth W. Hudnut, Ronald M. Spelz, Pierre Lacan, et al. "An analysis of the factors that control fault zone architecture and the importance of fault orientation relative to regional stress." GSA Bulletin 132, no. 9-10 (March 6, 2020): 2084–104. http://dx.doi.org/10.1130/b35308.1.
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Abstract The moment magnitude 7.2 El Mayor–Cucapah (EMC) earthquake of 2010 in northern Baja California, Mexico produced a cascading rupture that propagated through a geometrically diverse network of intersecting faults. These faults have been exhumed from depths of 6–10 km since the late Miocene based on low-temperature thermochronology, synkinematic alteration, and deformational fabrics. Coseismic slip of 1–6 m of the EMC event was accommodated by fault zones that displayed the full spectrum of architectural styles, from simple narrow fault zones (< 100 m in width) that have a single high-strain core, to complex wide fault zones (> 100 m in width) that have multiple anastomosing high-strain cores. As fault zone complexity and width increase the full spectrum of observed widths (20–200 m), coseismic slip becomes more broadly distributed on a greater number of scarps that form wider arrays. Thus, the infinitesimal slip of the surface rupture of a single earthquake strongly replicates many of the fabric elements that were developed during the long-term history of slip on the faults at deeper levels of the seismogenic crust. We find that factors such as protolith, normal stress, and displacement, which control gouge production in laboratory experiments, also affect the architectural complexity of natural faults. Fault zones developed in phyllosilicate-rich metasedimentary gneiss are generally wider and more complex than those developed in quartzo-feldspathic granitoid rocks. We hypothesize that the overall weakness and low strength contrast of faults developed in phyllosilicate rich host rocks leads to strain hardening and formation of broad, multi-stranded fault zones. Fault orientation also strongly affects fault zone complexity, which we find to increase with decreasing fault dip. We attribute this to the higher resolved normal stresses on gently dipping faults assuming a uniform stress field compatible with this extensional tectonic setting. The conditions that permit slip on misoriented surfaces with high normal stress should also produce failure of more optimally oriented slip systems in the fault zone, promoting complex branching and development of multiple high-strain cores. Overall, we find that fault zone architecture need not be strongly affected by differences in the amount of cumulative slip and instead is more strongly controlled by protolith and relative normal stress.
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Michie, Emma A. H., Behzad Alaei, and Alvar Braathen. "Assessing the accuracy of fault interpretation using machine-learning techniques when risking faults for CO2 storage site assessment." Interpretation 10, no. 1 (November 19, 2021): T73—T93. http://dx.doi.org/10.1190/int-2021-0077.1.
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Generating an accurate model of the subsurface for the purpose of assessing the feasibility of a CO2 storage site is crucial. In particular, how faults are interpreted is likely to influence the predicted capacity and integrity of the reservoir; whether this is through identifying high-risk areas along the fault, where fluid is likely to flow across the fault, or by assessing the reactivation potential of the fault with increased pressure, causing fluid to flow up the fault. New technologies allow users to interpret faults effortlessly, and in much quicker time, using methods such as deep learning (DL). These DL techniques use knowledge from neural networks to allow end users to compute areas where faults are likely to occur. Although these new technologies may be attractive due to reduced interpretation time, it is important to understand the inherent uncertainties in their ability to predict accurate fault geometries. Here, we compare DL fault interpretation versus manual fault interpretation, and we can see distinct differences to those faults where significant ambiguity exists due to poor seismic resolution at the fault; we observe an increased irregularity when DL methods are used over conventional manual interpretation. This can result in significant differences between the resulting analyses, such as fault reactivation potential. Conversely, we observe that well-imaged faults indicate a close similarity between the resulting fault surfaces when DL and manual fault interpretation methods are used; hence, we also observe a close similarity between any attributes and fault analyses made.
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Currie, Lisel D., Tom A. Brent, and Elizabeth C. Turner. "Offshore bedrock geology of Eclipse Sound and Pond Inlet: connecting the structure and stratigraphy of Bylot and northern Baffin islands." Canadian Journal of Earth Sciences 57, no. 10 (October 2020): 1254–67. http://dx.doi.org/10.1139/cjes-2019-0159.
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Understanding the Mesoproterozoic and younger structural history of the Eclipse Sound/Pond Inlet area is essential for the interpretation of its Archean to Paleoproterozoic geological history and could have important implications for mineral and petroleum exploration models in the northern Baffin Bay area. The identification of potentially active faults is critical for understanding possible earthquake-related hazards in the area. The integrated interpretation of 1970s-vintage marine seismic data with hill-shaded bathymetry, aeromagnetic data, and onshore geology maps has facilitated the identification of probable Mesoproterozoic (Bylot Supergroup) to Holocene strata on and below the sea floor and a suite of episodically reactivated northwest-striking horst- and graben-bounding normal faults and fault zones. Fault displacement likely occurred during the development of the Mesoproterozoic Borden basin and the Cretaceous–Paleogene opening of Baffin Bay, and in some cases may continue today. Some faults become more west-trending toward the south, which requires parts of these faults to have intermittently accommodated transtensional and (or) transpressional motion, possibly explaining local folds and out-of-graben thrusting. Numerous previously unrecognised faults have been documented, with faults beneath Eclipse Sound (Eclipse Trough) spaced at 5 to 7 km intervals, and at least one fault zone (Cape Hay Fault Zone) that appears to be at least 250 km in length, suggesting faults of similar spacing and scale may be present under Baffin Bay. This study uses a multi-thematic office-based methodology that inexpensively, and with little environmental impact, facilitates the mapping of structures that intersect the sea floor in areas where glaciers have exposed bedrock.
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Baechler, Fred. "Geology and Hydrogeology of Faults on Cape Breton Island, Nova Scotia, Canada: an overview." Atlantic Geology 51, no. 1 (July 30, 2015): 242. http://dx.doi.org/10.4138/atlgeol.2015.010.
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Cape Breton Island provides a hydrogeological view into the roots of an ancient mountain range, now exhumed, glaciated, and tectonically inactive. It exhibits deep crustal faults and magma chambers associated with formation of the Appalachian mountain belt and the Maritimes Basin during the Paleozoic, as well as Mesozoic rifting relating to the opening of the Atlantic Ocean. Cenozoic exhumation brought these features near surface and into the active groundwater flow field where they were impacted by glaciation and fluctuating sea level. The faults have been important from a societal viewpoint in development of municipal groundwater supplies, controlling inflows to excavations, hydrocarbon exploration, quarry development, and geotechnical investigations. Conceptual models presented here outline fault control on groundwater flow based on seven case studies. Future research should focus on basin-bounding faults in support of managing their role in aquifer development and protection, mountain-front recharge, controlling large-magnitude springs, groundwater–stream interaction, and channel morphology. The hydrogeological importance of these faults has historically been underappreciated.
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El Ghali, Abdessalem, Claude Bobier, and Noureddine Ben Ayed. "Significance of the E-W fault system in the geodynamic evolution of the Tunisian Alpine Chain foreland. Example of the Sbiba-Cherichira fault system in Central Tunisia." Bulletin de la Société Géologique de France 174, no. 4 (July 1, 2003): 373–81. http://dx.doi.org/10.2113/174.4.373.
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Abstract The recent sedimentary basins in Central Tunisia correspond to a set of depocenters with complex geometry which are bounded by E-W, N070 and N-S brittle structures. These bordering faults, active during Eocene and Cretaceous times, have been rejuvenated at the end of the Neogene and during Quaternary in a relay pattern system associated with compressive and extensive deformations according to the alternance of extension and compression phases (Tortonian Atlasic Phase of compression, post tectonic top Miocene-early Pleistocene extension associated to the rifting of the Tyrrhenian Basin, and Pleistocene Phase of compression). These tectonic regime changes involve subsidence inversions. Moreover, the neotectonic study carried out along the strike-slip faults corridories and their associated structures enable us : – to precise the timing of the tectonic deformations ; – to establish tectono-sedimentary relationships of Mio-Plio-Quaternary age. Introduction : geodynamical context and objectives of the study. – In Central Tunisia as in the whole Maghreb [Piqué et al., 1998 ; Piqué et al., 2002], the Mesozoic and Cenozoic evolution of sedimentary basins is largely controlled by tectonic heredity due to rejuvenation of basement discontinuities. In fact, previous studies have shown that the normal kinematics activity of The Sbiba-Cherichira fault has governed the opening and the distribution of the Cretaceous and the Eocene basins evolving in a globally extensive tectonic regime [Boltenhagen, 1981 ; El Ghali, 1993]. These old tectonics is proven, also, by the interpretation of NNE-SSW seismic profiles through this collapsed zone [Ben Ayed, 1986, fig. 3] and who reveal that subsidence had been active during the Lower Cretaceous and continued up to the Albian. In the late Miocene and early Quaternary, following the Langhian collision of Sardinia against the Northern Platform of Tunisia [Cohen et al., 1980], the Atlasic and Villafranchian Phases of compression are the most important. They were responsible for the formation of important N040° to N070°E Atlasic folds , N040° to N090°E thrusts , the opening of N120° to N150° E basins parallel to the shortening axis and E-W strike slip fault [Burollet, 1956 ; Ben Ayed, 1986]. In this paper, we present and discuss results of research carried out in the Sbiba-Cherichira area. This research combines interpretation of sedimentological observations and microtectonic or structural field studies [El Ghali et Batik, 1992] carried out along and near the Sbiba-Cherichira faults system, which corresponds to two separated master faults (fig. 2): – the « Southern Sbiba Fault » developed to the west with a direction N090°E which acted as is the southern boundary of the “Sbiba Trough” subsident area as early as the Albian (fig. 3) ; – the “Cherichira Fault” developed to the north-east with a direction N070°E. These faults are connected by the N040°E Labaied-Trozza Fault. Tortonian tectonic activity. – During Tortonian compression (orientation of the shortening axis N120°to N140°E) [Burollet, 1956 ; Ben Ayed, 1986 ; Philip et al., 1986 ; Martinez et al., 1990], many transformations were induced in the studied area (fig. 4a). In fact, the E-W faults of Sbiba and the N070 to N90°E faults of Cherichira, disposed in left relay, were reactivated as dextral strike-slip faults inducing simultaneous distensive deformations (normal faults, grabens, half-grabens…) and compressive ones (folds, reverse faults, overlappings….) localised at fracturing extremity [El Ghali, 1993]. Compressive structures. – The brittle structures are associated with ductile deformations of two types : *The first one corresponds to en echelon folds including : – to the south of the E-W Sbiba Fault, in J. Tiouacha and J. Labaied, Eocene and Neogene strata which are involved in hectometric folds with a N040° to N060°E axial direction (fig. 4a) and an axial westward dip changing from 05° to 60°E ; – to the west of the J. Rebeiba fault, Lutetian and Oligocene to Lower Miocene Strata which are affected by hectometric folds with a N070° to N090°E direction (fig. 4a) and an axial westward dip, changing from 05°to 20°E [El Ghali, 1993]. All these folds are abruptly cut up by the master faults and they can be interpreted as en echelon fault propagation folds. * The second includes plurikilometric folds parallel to the strike slip faults : – the E-W anticline of J. Labaied due to the transpression responsible for reactivation of the southern Sbiba Fault with a dextral strike slip component (fig. 4a); – the N040°E anticline of J. Trozza and the N070°E anticline of J. Cherichira respectively associated with the Trozza-Labaied fault and the Cherichira fault. Because of their orientation approximatively normal to the shortening axis, these faults are reactivated reversed faults giving fault-bend folds [Suppe, 1983] thrusted to the SE with a decollement level in Triassic evaporites extruded along the fault between J. M’Rhila and J. Cherichira (fig. 4a). Distensive structures : syntectonic depocenters associated to dextral strike-slip faults. – The dextral strike-slip faults extremities develop as normal faults N140 to N160°E in the dampening zone (fig. 4a). The east and west endings of Sbiba strike slip fault are two distensive extremities the opening mecanism of which is compatible with that of a megasplit basin at a strike-slip extremity [Harding, 1973 ; Odonne, 1981 ; Granier, 1985 ; Faugère et al., 1986…]. Top Miocene to early Pleistocene tectonic activity. – During upper top Miocene and early Pleistocene times, the Sbiba Trough was characterized by a subsidence more important than in any other place in Tunisia and was filled by continental deposits of the Segui Formation (conglomerates, sands, black clays and lacustrine limestones, fig. 5). Subsidence (500m near Haffouz, 3000m in Sbiba Trough, fig. 4b) was controlled by the activity of synsedimentary normal and strike-slip faults, forming small grabens, monoclinal grabens N090° to N130°E trending often cut by the Sbiba Fault (figs. 4b and 7). This extension can be considered as a post-tectonic extension relative to the Atlasic phase of compression, the orientation of the tensile axis being the same. Pleistocene tectonic activity. – In Central Tunisia, a NNW-SSE compressive phase, intervening in early Quaternary, has been demonstrated out [Burollet, 1956 ; Ben Ayed, 1986 ; Philip et al., 1986]. This “Villafranchian phase” follows distensive strike-slip tectonics of top Miocene Lowermost Pleistocene [El Ghali, 1993] and involves subsidence inversion. This phase is manifested by reverse dextral strike-slip faults on E-W segments (Sbiba and Ain Grab faults, fig. 4c) and by SE vergence overlappings on the NE-SW segments of J. Trozza (fig. 6) and N070°E ones of Cherichira (fig. 8). In other places the top Miocene-early Pleistocene deposits of the Segui Formation are folded, producing in the Sbiba basin N070° to N090°E en echelon folds (fig. 4c) with westward or eastward axial dipping between 05° and 15°. In Jebel Ain Grab area, the folds are overturned and locally thrusted northwards producing a morphostructural dam. This latter limits to the south a sag filled with fluviatile and lacustrine deposits (fig. 9). Comparison with neighbouring regions and conclusions. – The Sbiba-Cherichira faults system correspond to an en-echelon strike slip fault inherited from a basement discontinuity. It recorded most of the main tectonic processes which affected the southern margin of the Tethys. In Central Tunisia, this faults system constitutes an evolution model of one of the major scars which affects the sedimentary cover and controls basins distribution and evolution since the Cretaceous to the Quaternary. * The Tortonian compressional episode corresponding to the Compression Atlasic Phase described from the Rif in Morocco to northern Tunisia [Viguier et al., 1980 ; Philip, 1983 ; Ben Ayed, 1986 ; Morel, 1989 ; Aite, 1995 ; Piqué et al., 2002]. The N120° to N130°E orientation of the shortening axis induced the most important transpression which has triggered the rejuvenation of the Sbiba-Cherichira system as a very active fault driving halokinesis of Triassic evaporites and large development of brittle and folded structures associated to wrench faulting activity as in the eastern platform of Tunisia (fig. 10) [Ellouz, 1984]. * During the top Miocene-early Pleistocene postectonic extension, the rejuvenation of older faults generated a multidirectional extension near the Sbiba-Cherichira faults system as in northern Tunisian platform [Tricart et al., 1994] or in the north-eastern platform and in the strait of Sicily [Bobier et Martin, 1976 ; Ellouz, 1984]. In the Sbiba and Haffouz basins, the multidirectional extension is responsible for the development, along the N070°E dextral strike slip faults and N120°E left lateral strike slip faults, of depocenters for the Segui Formation which is superimposed to Middle Cretaceous subident areas [El Ghali, 1993]. * The Upper-Pleistocene episode which corresponds to the Villafranchian Phase with a N170° to N180°E shortening axis in agreement with the convergence of the European and African Plate and very well documented from the southern margin of Grande Kabilie [Aite, 1995] to northern Tunisia [Ben Ayed, 1986]. Near Sbiba it induced formation of folds, thrusts or reversed faults forming morphostructural dams in which fluvio-lacustrine deposits are accumulated.
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Bogolub, Kyren R., Jackson P. Bell, Enrique R. Chon, Robert M. Kirkham, and Anne F. Sheehan. "Earthquake swarm near Great Sand Dunes, Colorado, investigated with temporary seismic network and machine learning sesmic phase analysis." Mountain Geologist 60, no. 3 (August 1, 2023): 81–101. http://dx.doi.org/10.31582/rmag.mg.60.3.81.
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In November of 2018, residents living in the Zapata Subdivision south of Great Sand Dunes National Park and Preserve reported hearing and feeling multiple small earthquakes. Reports of additional earthquakes continued, escalating in late February of 2019, when the USGS recorded over 27 magnitude 0.9 and larger earthquakes over a two-day period. Subdivision residents became concerned that these could be foreshocks to a future, larger earthquake. To further study these earthquakes, we installed a temporary network of seismometers in the area during 2019 and used a convolution neural network seismic phase picker along with the GLASS3 associator to detect over 700 earthquakes in a 3.5-month period during the earthquake swarm. The earthquakes were located using a regional velocity model and a double-difference algorithm. The Northern Sangre de Cristo Fault (NSCF) cuts through the subdivision at the base of the Sangre de Cristo Mountains. Based on geologic evidence, it is one of the most active faults in Colorado but has been nearly aseismic historically. Initially, minor movement on the NSCF was suspected of being the geologic source of the earthquakes. However, nearly all recorded epicenters lie east of the trace of west-dipping fault and are not located on it. Instead, the earthquake epicenters define a narrow, linear, east-west-trending zone that projects eastward across the entire Northern Sangre de Cristo Range and into the headwaters of the Huerfano River Valley. We propose several possible geologic sources for the earthquakes including several mapped, but unnamed faults. Available evidence for any particular source in this geologically complex area is not conclusive. Additional geologic and geophysical investigations are needed to better understand the geology of the earthquake swarm and its implications for seismic hazards.
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Wang, Yang, Yuejun Wang, Peizhen Zhang, Lindsay M. Schoenbohm, Bo Zhang, Jinjiang Zhang, Renjie Zhou, et al. "Intracontinental deformation within the India-Eurasia oblique convergence zone: Case studies on the Nantinghe and Dayingjiang faults." GSA Bulletin 132, no. 3-4 (August 29, 2019): 850–62. http://dx.doi.org/10.1130/b35338.1.
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Abstract The most striking structural features in the interior of the Shan Plateau, southeast of the eastern Himalayan syntaxis, are a series of NE-trending faults that exhibit sinistral movement and an arcuate geometry. Their origin and tectonic evolution remain poorly understood. Furthermore, a switch in slip sense is recorded along many of these faults, but the timing of kinematic reversal is still unclear, hindering an understanding of the causal geodynamic mechanisms. We conducted an integrative study of apatite and zircon (U-Th)/He thermochronology, 40Ar/39Ar geochronology, and structural and geomorphic analysis to decipher the evolution of two major NE-trending faults: the Nantinghe and Dayingjiang faults. At least three deformation stages are identified within the Nantinghe fault zone, including top-to-the-SE/ESE thrusting, dextral ductile strike-slip shearing, and sinistral movement. Zircon and apatite (U-Th)/He data, collected from the northeastern terminus of the Nantinghe fault, reveal rapid cooling in the early Miocene. Combined with the 40Ar/39Ar data from sinistrally sheared mylonite, left-lateral movement on the Nantinghe fault is inferred to have initiated as early as ca. 20 Ma. The Dayingjiang fault reactivated as a sinistral brittle fault along the dextral Yingjiang shear zone. A two-stage thermal history is identified along the shear zone, with prominent cooling during dextral ductile shearing in the early- to mid-Miocene followed by a lower-magnitude cooling episode at ca. 11 Ma caused by sinistral transtension along the Dayingjiang fault. The evolution of the Nantinghe and Dayingjiang faults suggests that the NE-trending fault system in the Shan Plateau may have developed along preexisting structures and underwent diachronous slip-sense inversion in the late Cenozoic. The northward advance of the eastern Himalayan syntaxis caused a major change in both the regional stress field and fault geometries in the eastern India-Eurasia oblique convergence zone, contributing to the inversion of fault kinematics.
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Sayed, M. G. Salah Abou, and Mohamed A. Mersal. "Surface Geology of Jebel Rawdah, Oman Mountains." GeoArabia 3, no. 3 (July 1, 1998): 401–14. http://dx.doi.org/10.2113/geoarabia0303401.
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ABSTRACT Jebel Rawdah is a west-northwest to east-southeast trending, post-obduction fold located at the western edge of the Hatta Zone of the Northern Oman Mountains. The main syncline plunges about 5 kilometers to the northwest and it is flanked to the west by a minor anticline. The outcrops in the area consist of: (1) allochthonous Semail Ophiolite, consisting of slices of oceanic crust and upper mantle, together with the Haybi Complex of volcanic rocks and associated metamorphics; (2) the parautochthonous Sumeini Group consisting of shelf edge and slope carbonates and clastics; and (3) the post-obduction neoautochthonous clastics and carbonates of the Qahlah, Simsima and Muthaymimah formations (Maastrichtian to Early Tertiary). Two stages of folding were detected in the Jebel Rawdah area. The older folds affect the allochthonous rocks and result from shearing deformation along the westward extension of the Hatta Zone. The younger deformation is manifested in drape folds in the neoautochthonous rocks which was caused by differential vertical movements of fault blocks in the underlying allochthonous rocks. Three sets of faults were observed: (1) northwest-southeast trending vertical to steeply-dipping scissor faults; (b) reverse faults which form flower structures; and (c) northeast-southwest trending normal faults. Field observations, biostratigraphic studies and petrographic examination suggest three stages in the development of the stratigraphic units in Jebel Rawdah. The first stage occurred during the Early Maastrichtian when the Oman Mountains emerged and were subsequently exposed to subaerial erosion. In the second stage a transgression occurred during the gradual subsidence of the area which led to the deposition of the Qahlah Formation in a fluviatile to shallow-marine environment, and the overlying Simsima in a shallow shelf setting. In the final Tertiary stage the Muthaymimah Formation was deposited in a subsiding basin and slope setting.
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Cheng, Feng, Andrew V. Zuza, Peter J. Haproff, Chen Wu, Christina Neudorf, Hong Chang, Xiangzhong Li, and Bing Li. "Accommodation of India–Asia convergence via strike-slip faulting and block rotation in the Qilian Shan fold–thrust belt, northern margin of the Tibetan Plateau." Journal of the Geological Society 178, no. 3 (January 29, 2021): jgs2020–207. http://dx.doi.org/10.1144/jgs2020-207.
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Existing models of intracontinental deformation have focused on plate-like rigid body motion v. viscous-flow-like distributed deformation. To elucidate how plate convergence is accommodated by intracontinental strike-slip faulting and block rotation within a fold–thrust belt, we examine the Cenozoic structural framework of the central Qilian Shan of northeastern Tibet, where the NW-striking, right-slip Elashan and Riyueshan faults terminate at the WNW-striking, left-slip Haiyuan and Kunlun faults. Field- and satellite-based observations of discrete right-slip fault segments, releasing bends, horsetail termination splays and off-fault normal faulting suggest that the right-slip faults accommodate block rotation and distributed west–east crustal stretching between the Haiyuan and Kunlun faults. Luminescence dating of offset terrace risers along the Riyueshan fault yields a Quaternary slip rate of c. 1.1 mm a−1, which is similar to previous estimates. By integrating our results with regional deformation constraints, we propose that the pattern of Cenozoic deformation in northeastern Tibet is compatible with west–east crustal stretching/lateral displacement, non-rigid off-fault deformation and broad clockwise rotation and bookshelf faulting, which together accommodate NE–SW India–Asia convergence. In this model, the faults represent strain localization that approximates continuum deformation during regional clockwise lithospheric flow against the rigid Eurasian continent.Supplementary material: Luminescence dating procedures and protocols is available at https://doi.org/10.17605/OSF.IO/CR9MNThematic collection: This article is part of the Fold-and-thrust belts and associated basins collection available at: https://www.lyellcollection.org/cc/fold-and-thrust-belts
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Dichiarante, A. M., R. E. Holdsworth, E. D. Dempsey, K. J. W. McCaffrey, and T. A. G. Utley. "Outcrop-scale manifestations of reactivation during multiple superimposed rifting and basin inversion events: the Devonian Orcadian Basin, northern Scotland." Journal of the Geological Society 178, no. 1 (September 15, 2020): jgs2020–089. http://dx.doi.org/10.1144/jgs2020-089.
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The Devonian Orcadian Basin in Scotland hosts extensional fault systems assumed to be related to the initial formation of the basin, with only limited post-Devonian inversion and reactivation. However, a recent detailed structural study across Caithness, underpinned by published Re–Os geochronology, shows that three phases of deformation are present. North–south- and NW–SE-trending Group 1 faults are related to Devonian ENE–WSW transtension associated with sinistral shear along the Great Glen Fault during the formation of the Orcadian Basin. Metre- to kilometre-scale north–south-trending Group 2 folds and thrusts are developed close to earlier sub-basin-bounding faults and reflect late Carboniferous–early Permian east–west inversion associated with dextral reactivation of the Great Glen Fault. The dominant Group 3 structures are dextral oblique NE–SW-trending and sinistral east–west-trending faults with widespread syndeformational carbonate mineralization (± pyrite and bitumen) and are dated using Re–Os geochronology as Permian (c. 267 Ma). Regional Permian NW–SE extension related to the development of the offshore West Orkney Basin was superimposed over pre-existing fault networks, leading to local oblique reactivation of Group 1 faults in complex localized zones of transtensional folding, faulting and inversion. The structural complexity in surface outcrops onshore therefore reflects both the local reactivation of pre-existing faults and the superimposition of obliquely oriented rifting episodes during basin development in the adjacent offshore areas.Supplementary material: Stereographic projections of compiled structural data from individual fieldwork localities are available at https://doi.org/10.6084/m9.figshare.c.5115228
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Levy, Y., T. K. Rockwell, J. H. Shaw, A. Plesch, N. W. Driscoll, and H. Perea. "Structural modeling of the Western Transverse Ranges: An imbricated thrust ramp architecture." Lithosphere 11, no. 6 (November 4, 2019): 868–83. http://dx.doi.org/10.1130/l1124.1.
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Abstract Active fold-and-thrust belts can potentially accommodate large-magnitude earthquakes, so understanding the structure in such regions has both societal and scientific importance. Recent studies have provided evidence for large earthquakes in the Western Transverse Ranges of California, USA. However, the diverse set of conflicting structural models for this region highlights the lack of understanding of the subsurface geometry of faults. A more robust structural model is required to assess the seismic hazard of the Western Transverse Ranges. Toward this goal, we developed a forward structural model using Trishear in MOVE® to match the first-order structure of the Western Transverse Ranges, as inferred from surface geology, subsurface well control, and seismic stratigraphy. We incorporated the full range of geologic observations, including vertical motions from uplifted fluvial and marine terraces, as constraints on our kinematic forward modeling. Using fault-related folding methods, we predicted the geometry and sense of slip of the major faults at depth, and we used these structures to model the evolution of the Western Transverse Ranges since the late Pliocene. The model predictions are in good agreement with the observed geology. Our results suggest that the Western Transverse Ranges comprises a southward-verging imbricate thrust system, with the dominant faults dipping as a ramp to the north and steepening as they shoal from ∼16°–30° at depth to ∼45°–60° near the surface. We estimate ∼21 km of total shortening since the Pliocene in the eastern part of the region, and a decrease of total shortening west of Santa Barbara down to 7 km near Point Conception. The potential surface area of the inferred deep thrust ramp is up to 6000 km2, which is of sufficient size to host the large earthquakes inferred from paleoseismic studies in this region.
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Lee, Jeffrey, Andrew K. R. Hoxey, Andrew Calvert, and Peter Dubyoski. "Plate boundary trench retreat and dextral shear drive intracontinental fault-slip histories: Neogene dextral faulting across the Gabbs Valley and Gillis Ranges, Central Walker Lane, Nevada." Geosphere 16, no. 5 (July 31, 2020): 1249–75. http://dx.doi.org/10.1130/ges02240.1.
Full textAbstract:
Abstract The spatial-temporal evolution of intracontinental faults and the forces that drive their style, orientation, and timing are central to understanding tectonic processes. Intracontinental NW-striking dextral faults in the Gabbs Valley–Gillis Ranges (hereafter referred to as the GVGR), Nevada, define a structural domain known as the eastern Central Walker Lane located east of the western margin of the North American plate. To consider how changes in boundary type along the western margin of the North American plate influenced both the initiation and continued dextral fault slip to the present day in the GVGR, we combine our new detailed geologic mapping, structural studies, and 40Ar/39Ar geochronology with published geologic maps to calculate early to middle Miocene dextral fault-slip rates. In the GVGR, Mesozoic basement is nonconformably overlain by a late Oligocene to Miocene sequence dominated by tuffs, lavas, and sedimentary rocks. These rocks are cut and offset by four primary NW-striking dextral faults, from east to west the Petrified Spring, Benton Spring, Gumdrop Hills, and Agai Pah Hills–Indian Head faults. A range of geologic markers, including tuff- and lava-filled paleovalleys, the southern extent of lava flows, and a normal fault, show average dextral offset magnitudes of 9.6 ± 1.1 km, 7.0 ± 1.7 km, 9.7 ± 1.0 km, and 4.9 ± 1.1 km across the four faults, respectively. Cumulative dextral offset across the GVGR is 31.2 ± 2.3 km. Initiation of slip along the Petrified Spring fault is tightly bracketed between 15.99 ± 0.05 Ma and 15.71 ± 0.03 Ma, whereas slip along the other faults initiated after 24.30 ± 0.05 Ma to 20.14 ± 0.26 Ma. Assuming that slip along all four faults initiated at the same time as the Petrified Spring fault yields calculated dextral fault-slip rates of 0.4 ± 0.1–0.6 ± 0.1 mm/yr, 0.4 ± 0.1–0.5 ± 0.1 mm/yr, 0.6 ± 0.1 mm/yr, and 0.3 ± 0.1 mm/yr on the four faults, respectively. Middle Miocene initiation of dextral fault slip across the GVGR overlaps with the onset of normal slip along range-bounding faults in the western Basin and Range to the north and the northern Eastern California shear zone to the south. Based on this spatial-temporal relationship, we propose that dextral fault slip across the GVGR defines a kinematic link or accommodation zone between the two regions of extension. At the time of initiation of dextral slip across the GVGR, the plate-boundary setting to the west was characterized by subduction of the Farallon plate beneath the North American plate. To account for the middle Miocene onset of extension across the Basin and Range and dextral slip in the GVGR, we hypothesize that middle Miocene trench retreat drove westward motion of the Sierra Nevada and behind it, crustal extension across the Basin and Range and NW-dextral shear within the GVGR. During the Pliocene, the plate boundary to the west changed to NW-dextral shear between the Pacific and North American plates, which drove continued dextral slip along the same faults within the GVGR because they were fortuitously aligned subparallel to plate boundary motion.