Journal articles: 'Stepover faults'

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Wang, Hui, Mian Liu, Benchun Duan, and Jianling Cao. "Rupture Propagation along Stepovers of Strike-Slip Faults: Effects of Initial Stress and Fault Geometry." Bulletin of the Seismological Society of America 110, no. 3 (April 7, 2020): 1011–24. http://dx.doi.org/10.1785/0120190233.

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ABSTRACT Large earthquakes on strike-slip faults often rupture multiple fault segments by jumping over stepovers. Previous studies, based on field observations or numerical modeling with a homogeneous initial stress field, have suggested that stepovers more than ∼5 km wide would stop the propagation of rupture, but many exceptions have been observed in recent years. Here, we integrate a dynamic rupture model with a long-term fault stress model to explore the effects of background stress perturbation on rupture propagation across stepovers along strike-slip faults. Our long-term fault models simulate steady-state stress perturbation around stepovers. Considering such stress perturbation in dynamic rupture models leads to prediction of larger distance a dynamic rupture can jump over stepovers: over 15 km for a releasing stepover or 7 km for a restraining stepover, comparing with the 5 km limit in models with the same fault geometry and frictional property but assuming a homogeneous initial stress. The effect of steady-state stress perturbations is stronger in an overlapping stepover than in an underlapping stepover. The maximum jumping distance can reach 20 km in an overlapping releasing stepover with low-static frictional coefficients. These results are useful for estimating the maximum length of potential fault ruptures and assessing seismic hazard.

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Konon, Andrzej, Szymon Ostrowski, Barbara Rybak-Ostrowska, Mirosław Ludwiniak, Michał Śmigielski, Michał Wyglądała, Joanna Uroda, Sebastian Kowalczyk, Radosław Mieszkowski, and Agnieszka Kłopotowska. "Mnin restraining stepover – evidence of significant Cretaceous–Cenozoic dextral strike-slip faulting along the Teisseyre-Tornquist Zone?" Acta Geologica Polonica 66, no. 3 (September 1, 2016): 435–55. http://dx.doi.org/10.1515/agp-2016-0019.

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Abstract A newly recognized Mnin restraining stepover is identified in the Permo-Mesozoic cover of the western part of the Late Palaeozoic Holy Cross Mountains Fold Belt (Poland), within a fault pattern consisting of dextral strike-slip faults. The formation of a large contractional structure at the Late Cretaceous – Cenozoic transition displays the significant role of strike-slip faulting along the western border of the Teisseyre-Tornquist Zone, in the foreland of the Polish part of the Carpathian Orogen. Theoretical relationships between the maximum fault offsets/ mean step length, as well as between the maximum fault offsets/mean step width allowed the estimation of the values of possible offsets along the Snochowice and Mieczyn faults forming the Mnin stepover. The estimated values suggest displacements of as much as several tens of kilometres. The observed offset along the Tokarnia Fault and theoretical calculations suggest that the strike-slip faults west of the Late Palaeozoic Holy Cross Mountains Fold Belt belong to a large strike-slip fault system. We postulate that the observed significant refraction of the faults forming the anastomosing fault pattern is related also to the interaction of the NW-SE-striking faults formed along the western border of the Teisseyre- Tornquist Zone and the reactivated WNW-ESE-striking faults belonging to the fault systems of the northern margin of the Tethys Ocean.

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DeLano, Kevin, Jeffrey Lee, Rachelle Roper, and Andrew Calvert. "Dextral, normal, and sinistral faulting across the eastern California shear zone–Mina deflection transition, California-Nevada, USA." Geosphere 15, no. 4 (June 24, 2019): 1206–39. http://dx.doi.org/10.1130/ges01636.1.

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Abstract Strike-slip faults commonly include extensional and contractional bends and stepovers, whereas rotational stepovers are less common. The Volcanic Tableland, Black Mountain, and River Spring areas (California and Nevada, USA) (hereafter referred to as the VBR region) straddle the transition from the dominantly NW-striking dextral faults that define the northwestern part of the eastern California shear zone into a rotational stepover characterized by dominantly NE-striking sinistral faults that define the southwestern Mina deflection. New detailed geologic mapping, structural studies, and 40Ar/39Ar geochronology across the VBR region allow us to calculate Pliocene to Pleistocene fault slip rates and test predictions for the kinematics of fault slip transfer into this rotational stepover. In the VBR, Mesozoic basement is nonconformably overlain by a Miocene sequence of rhyolite, dacite, and andesite volcanic rocks that yield 40Ar/39Ar ages between 22.878 ± 0.051 Ma and 11.399 ± 0.041 Ma. Miocene rocks are unconformably overlain by an extensive sequence of Pliocene basalt and andesite lava flows and cinder cones that yield 40Ar/39Ar ages between 3.606 ± 0.060 Ma and 2.996 ± 0.027 Ma. The Pliocene sequence is, in turn, unconformably overlain by Quaternary tuffs and sedimentary rocks. This sequence of rocks is cut by NS- to NW-striking normal faults across the Volcanic Tableland that transition northward into NS-striking normal faults across the Black Mountain area and that, in turn, transition northward into NW-striking dextral and NE-striking sinistral faults in the River Spring area. A range of geologic markers were used to measure offset across the faults in the VBR, and combined with the age of the markers, yield minimum ∼EW-extension rates of ∼0.5 mm/yr across the Volcanic Tableland and Black Mountain regions, and minimum NW-dextral slip and NE-sinistral slip rates of ∼0.7 and ∼0.3 mm/yr, respectively, across the River Spring region. In the River Spring area, our preferred minimum dextral slip and sinistral slip rates are 0.8–0.9 mm/yr and 0.7–0.9 mm/yr, respectively. We propose three kinematic fault slip models, two irrotational and one rotational, whereby the VBR region transfers a portion of dextral Owens Valley fault slip northwestward into the Mina deflection. In irrotational model 1, Owens Valley fault slip is partitioned into two components, one northeastward onto the White Mountain fault zone and one northwestward into the Volcanic Tableland. Slip from the two zones is then transferred northward into the southwestern Mina deflection. In irrotational model 2, Owens Valley fault slip is partitioned into three components, with the third component partitioned west-northwest onto the Sierra Nevada frontal fault zone. In the rotational model, predicted sinistral slip rates across the southwestern Mina deflection are at least 115% greater than our observed minimum slip rates, implying our minimum observed rates underestimate true sinistral slip rates. A comparison of summed geologic fault slip rates, parallel to motion of the Sierra Nevada block relative to the central Great Basin, from the Sierra Nevada northeastward across the VBR region and into western Nevada are the same as geodetic rates, if our assumptions about the geologic slip rate across the dextral White Mountain fault zone is correct.

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Yang, Jiuyuan, Caijun Xu, Yangmao Wen, and Guangyu Xu. "The July 2020 Mw 6.3 Nima Earthquake, Central Tibet: A Shallow Normal-Faulting Event Rupturing in a Stepover Zone." Seismological Research Letters 93, no. 1 (November 3, 2021): 45–55. http://dx.doi.org/10.1785/0220210057.

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Abstract On 22 July 2020, an Mw 6.3 earthquake with a predominantly normal-faulting mechanism struck the Yibug Caka fault zone, central Tibet, where the overall tectonic environment is characterized by left-lateral strike-slip motion. This event offers a chance to gain insight into the tectonic deformation and the cause of shallow normal-faulting earthquakes in this little studied region. Here, we use Sentinel-1A/B Interferometric Synthetic Aperture Radar data to investigate the coseismic and postseismic deformation related to this earthquake. The earthquake ruptured a previously mapped West Yibug Caka fault and is dominated by normal slip with a peak value of 1.9 m at depth of 6.9 km. Postseismic deformation analysis indicates that the observed subsidence signals of up to ∼4.7 cm are a consequence of afterslip. Most of the afterslip is confined at depths between 0.8 and 8.4 km, peaking at 0.27 m at depth of 6.1 km. The significant coseismic slip and afterslip involved in the earthquake highlights a complex interaction between the major normal fault and the secondary synthetic fault. By an integrated analysis of the inversions, regional geology geomorphology, fault kinematics, and seismicity background, we propose a tectonic model that attributes the occurrence of this normal-faulting event to the release of extensional stress in a stepover zone controlled by the northeast-striking sinistral strike-slip Riganpei Co fault and Bu Zang Ai fault. Compared with that the structural stepover often acts as a barrier to affect the propagation of earthquake rupture, our study demonstrates that the failure of a stepover may potentially induce the occurrence of earthquake along the bounding strike-slip faults.

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Zhu, Liangyu, Lingyun Ji, Chuanjin Liu, Jing Xu, Xinkai Liu, Lei Liu, and Qiang Zhao. "The 8 January 2022, Menyuan Earthquake in Qinghai, China: A Representative Event in the Qilian–Haiyuan Fault Zone Observed Using Sentinel-1 SAR Images." Remote Sensing 14, no. 23 (November 30, 2022): 6078. http://dx.doi.org/10.3390/rs14236078.

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On 8 January 2022, a Ms 6.9 earthquake occurred in Menyuan, Qinghai, China. This event provided important geodetic data before and after the earthquake, facilitating the investigation of the slip balance along the seismogenic faults to understand seismogenic behavior and assess seismic risk. In this study, we obtained the interseismic (2016–2021) and coseismic deformation fields of the 2022 earthquake using Sentinel-1 synthetic aperture radar (SAR) images and estimated the slip rate, fault locking, and coseismic slip of the seismogenic faults. The results indicated that the seismogenic fault of the 2022 Menyuan earthquake, i.e., the Tuolaishan–Lenglongling Fault, had shallow locked areas before the earthquake; its long-term slip rate could reach 6 ± 1.2 mm/yr. The earthquake ruptured a sinistral strike-slip fault with a high dip angle; the maximum slip magnitude reached 3.47 m, with a moment magnitude of 6.6. The area of coseismic slip > 1.5 m was equivalent to the range of the isoline, with a locking value of 0.6. The interseismic locking region can limit the approximate scope of the coseismic slip distribution. The 2022 Menyuan earthquake released energy that had accumulated over 482 years in the stepover region between the Lenglongling and Tuolaishan faults. The accumulated elastic strain power of the Tuolaishan Fault was equivalent to an Mw 6.79 earthquake. These circumstances in terms of the strain energy balance demonstrate that interseismic locking, as constrained from the geodetic data, and the elapsed time from the previous paleoseismic event are useful for earthquake location and energy predictions.

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TUTKUN, Z., and S. PAVLIDES. "Small scale contractional-extensional structures and morphotectonics along the fault traces of Izmit-Cocaeli (Turkey) 1999 earthquake." Bulletin of the Geological Society of Greece 34, no. 1 (January 1, 2001): 345. http://dx.doi.org/10.12681/bgsg.17033.

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The Mw=7.4 Izmit (Kocaeli) earthquake of August 17, 1999 (Turkey) ruptured 100 km at least surface faults on land along the northwestern branch of the North Anatolian Fault Zone (NAFZ). Although the preexisting structures of NAFZ has been divided into segments, showing stepover and pull apart geometry, the earthquake ruptures are generally linear, E-W striking (N80°-100°), right-lateral. In small scale and on the recent sediments they show very typical strike-slip displacements (2 to 5m), pop-ups and pressure ridges (N 40- 70°), Ρ (N80°), R (N100-1100) and R' (~N350°) Riedel shears, extensional cracks (N115°-135°), restraining and releasing bends and small pull apart structures. In the epicentral area (Gölcük-Tepetarla) the seismic ruptures did not follow any known or previously mapped fault, but the morphology and the Digital Elevation Model (DEM) show typical and recognizable paleo-earthquake features. That is elongated valleys, shutter ridges, high angle slopes, scarplets, stream offset; while trenching tectonostratigraphy indicate palaeo sag-ponds (clayly deposits) and palaeo liquefaction (C14 dating-Holocene-historical deposits 200 to 11,000 yr. BP).

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Wen, Guisen, Xingxing Li, Yingwen Zhao, Yong Zhang, Caijun Xu, and Yuxin Zheng. "Kinematic Rupture Process and Its Implication of a Thrust and Strike-Slip Multi-Fault during the 2021 Haiti Earthquake." Remote Sensing 15, no. 7 (March 23, 2023): 1730. http://dx.doi.org/10.3390/rs15071730.

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A devasting Mw7.2 earthquake struck southern Haiti on 14 August 2021, leading to over 2000 casualties and severe structural failures. This earthquake, which ruptured ~70 km west of the 2010 Mw7.0 event, offers a rare opportunity to probe the mechanical properties of southern Haiti. This study investigates the kinematic multi-fault coseismic rupture process by jointly analyzing teleseismic and interferometric synthetic aperture radar (InSAR) datasets. We determined the optimal dip of different segment faults through finite-fault inversion, and the results show that the dips of the first, second and third faults are 62°, 76° and 76°, respectively, coinciding with the relocated aftershock distribution. The results estimated from our joint inversion revealed that the slip was dominated by reverse motion in the first segment and strike-slip motion in the second and third segments. Three slip patches were detected along the strike, with a peak slip of 3.0 m, and the rupture reached the surface at the second segment. The kinematic rupture process shows a unilateral rupture with a high centroid rupture velocity (5.5 km/s), and the rupture broke through the stepover and caused a cascade rupture. The rupture front experiences a directivity pulse of high ground motions with high amplitude and short duration, which may be an additional factor explaining the many landslides concentrated on the western end of the fault. The Coulomb failure stress change result indicates the increases in the probability of future events to the east and west of the 2021 main shock.

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Dorsey, Rebecca J., Brennan O’Connell, Kevin K. Gardner, Mindy B. Homan, Scott E. K. Bennett, Jacob O. Thacker, and Michael H. Darin. "Tectonostratigraphic record of late Miocene–early Pliocene transtensional faulting in the Eastern California shear zone, southwestern USA." Geosphere 17, no. 4 (May 14, 2021): 1101–25. http://dx.doi.org/10.1130/ges02337.1.

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Abstract The Eastern California shear zone (ECSZ; southwestern USA) accommodates ~20%–25% of Pacific–North America relative plate motion east of the San Andreas fault, yet little is known about its early tectonic evolution. This paper presents a detailed stratigraphic and structural analysis of the uppermost Miocene to lower Pliocene Bouse Formation in the southern Blythe Basin, lower Colorado River valley, where gently dipping and faulted strata provide a record of deformation in the paleo-ECSZ. In the western Trigo Mountains, splaying strands of the Lost Trigo fault zone include a west-dipping normal fault that cuts the Bouse Formation and a steeply NE-dipping oblique dextral-normal fault where an anomalously thick (~140 m) section of Bouse Formation siliciclastic deposits filled a local fault-controlled depocenter. Systematic basinward thickening and stratal wedge geometries in the western Trigo and southeastern Palo Verde Mountains, on opposite sides of the Colorado River valley, record basinward tilting during deposition of the Bouse Formation. We conclude that the southern Blythe Basin formed as a broad transtensional sag basin in a diffuse releasing stepover between the dextral Laguna fault system in the south and the Cibola and Big Maria fault zones in the north. A palinspastic reconstruction at 5 Ma shows that the southern Blythe Basin was part of a diffuse regional network of linked right-stepping dextral, normal, and oblique-slip faults related to Pacific–North America plate boundary dextral shear. Diffuse transtensional strain linked northward to the Stateline fault system, eastern Garlock fault, and Walker Lane, and southward to the Gulf of California shear zone, which initiated ca. 7–9 Ma, implying a similar age of inception for the paleo-ECSZ.

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Kuşçu, İsmail, Makoto Okamura, Hiromi Matsuoka, Kunio Yamamori, Yasuo Awata, and Selim Özalp. "Recognition of active faults and stepover geometry in Gemlik Bay, Sea of Marmara, NW Turkey." Marine Geology 260, no. 1-4 (May 2009): 90–101. http://dx.doi.org/10.1016/j.margeo.2009.02.003.

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Wen, Yameng, Daoyang Yuan, Hong Xie, Ruihuan Su, Qi Su, Zhimin Li, Hao Sun, et al. "Typical Fine Structure and Seismogenic Mechanism Analysis of the Surface Rupture of the 2022 Menyuan Mw 6.7 Earthquake." Remote Sensing 15, no. 18 (September 6, 2023): 4375. http://dx.doi.org/10.3390/rs15184375.

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On 8 January 2022, a seismic event of significant magnitude (Mw 6.7, Ms 6.9) occurred in the northeastern region of the Tibetan Plateau. This earthquake was characterized by left-lateral strike-slip motion, accompanied by a minor reverse movement. The Menyuan earthquake resulted in the formation of two main ruptures and one secondary rupture. These ruptures were marked by a left-lateral step zone that extended over a distance of 1 km between the main ruptures. The length of the rupture zones was approximately 37 km. The surface rupture zone exhibited various features, including left-lateral offset small gullies, riverbeds, wire fences, road subgrades, mole tracks, cracks, and scarps. Through a comprehensive field investigation and precise measurement using unmanned aerial vehicle (UAV) imagery, 111 coseismic horizontal offsets were determined, with the maximum offset recorded at 2.6 ± 0.3 m. The analysis of aftershocks and the findings from the field investigation led to the conclusion that the earthquake was triggered by the Lenglongling fault and the Tuolaishan fault. These faults intersected at a release double-curved structure, commonly referred to as a stepover. During this particular process, the Lenglongling fault was responsible for initiating the coseismic rupture of the Sunan–Qilian fault. It is important to note that the stress applied to the Tuolaishan fault has not been fully relieved, indicating the presence of potential future hazards.

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Weidman, Luke, Jillian M. Maloney, and Thomas K. Rockwell. "Geotechnical data synthesis for GIS-based analysis of fault zone geometry and hazard in an urban environment." Geosphere 15, no. 6 (October 16, 2019): 1999–2017. http://dx.doi.org/10.1130/ges02098.1.

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Abstract Many fault zones trend through developed urban areas where their geomorphic expression is unclear, making it difficult to study fault zone details and assess seismic hazard. One example is the Holocene-active Rose Canyon fault zone, a strike-slip fault with potential to produce a M6.9 earthquake, which traverses the city of San Diego, California (USA). Several strands trend through densely populated areas, including downtown. Much of the developed environment in San Diego predates aerial imagery, making assessment of the natural landscape difficult. To comply with regulations on development in a seismically active area, geotechnical firms have conducted many private, small-scale fault studies in downtown San Diego since the 1980s. However, each report is site specific with minimal integration between neighboring sites, and there exists no resource where all data can be viewed simultaneously on a regional scale. Here, geotechnical data were mined from 268 individual reports and synthesized into an interactive geodatabase to elucidate fault geometry through downtown San Diego. In the geodatabase, fault segments were assigned a hazard classification, and their strike and dip characterized. Results show an active zone of discontinuous fault segments trending north-south in eastern downtown, including active faults outside the mapped regulatory Earthquake Fault Zone. Analysis of fault geometry shows high variability along strike that may be associated with a stepover into San Diego Bay. This type of geodatabase offers a method for compiling and analyzing a high volume of small-scale fault investigations for a more comprehensive understanding of fault zones located in developed regions.

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Liu, Xiaoli, Debeier Deng, Zhige Jia, Jing Liu-Zeng, Xinyu Mo, Yu Huang, Qiaozhe Ruan, and Juntao Liu. "Refined Coseismic Slip Model and Surface Deformation of the 2021 Maduo Earthquake: Implications for Sensitivity of Rupture Behaviors to Geometric Complexity." Remote Sensing 16, no. 4 (February 18, 2024): 713. http://dx.doi.org/10.3390/rs16040713.

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Geometric complexities of a fault system have a significant impact on the rupture behavior of the fault. The 2021 Mw7.4 Maduo earthquake occurred on a multi-segmented complex sinistral fault in the interior of the Bayan-Har block in the northern Tibetan Plateau. Here, we integrate centimeter-resolution surface rupture zones and Sentinel-2 optical displacement fields to accurately determine the geometric parameters of the causative fault in detail. An adaptive quadtree down-sampling method for interferograms was employed to enhance the reliability of the coseismic slip model inversion for interferograms. The optimal coseismic slip model indicated a complex non-planar structure with varying strike and dip angles. The largest slip of ~6 m, at a depth of ~7 km, occurred near a 6 km-wide stepover (a geometric complexity area) to the east of the epicenter, which occurred at the transition zone from sub-shear to super-shear rupture suggested by seismological studies. Optical and SAR displacement fields consistently indicated the local minimization of effective normal stress on releasing stepovers, which facilitated rupture through them. Moreover, connecting intermediate structures contributes to maintaining the rupture propagation through wide stepovers and may even facilitate the transition from subshear to supershear. Our study provides more evidence of the reactivation of a branched fault at the western end during the mainshock, which was previously under-appreciated. Furthermore, we found that a strong asymmetry in slip depth, stress drop, and rupture velocity east and west of the epicenter was coupled with variations in geometric and structural characteristics of fault segments along the strike. Our findings highlight the sensitivity of rupture behaviors to small-scale details of fault geometry.

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Oglesby, David D. "What Can Surface-Slip Distributions Tell Us about Fault Connectivity at Depth?" Bulletin of the Seismological Society of America 110, no. 3 (April 7, 2020): 1025–36. http://dx.doi.org/10.1785/0120190245.

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ABSTRACT Fault systems with stepovers and gaps along strike are ubiquitous in nature, and many modern earthquakes (e.g., 1992 Landers, 1999 Hector Mine, 2016 Kaikōura, and 2019 Ridgecrest) have shown that ruptures can readily propagate across some disconnections, while being halted by others. It is quite possible, however, that many faults that appear discontinuous at the surface are in fact connected at depth, facilitating throughgoing rupture, and potentially increasing earthquake size. The present work explores whether the mapped surface slip in an earthquake is indicative of the connectivity of the fault system at depth. If there is a signal of subsurface connectivity in the surface-slip pattern, then the connectivity of the system could potentially be inferred. Through 3D dynamic rupture modeling of faults with along-strike gaps of various depths, I explore whether the amplitude or the spatial distribution of slip after an earthquake could be used to diagnose fault connectivity at depth. I find that, in general, fault segments that are connected up to shallow depths of 1–2 km and are relatively long along strike compared to the seismogenic depth tend to have higher slip gradients at their edges than faults that are connected at greater depth, or that are disconnected to the bottom of the seismogenic zone. Systematic slip gradient differences at fault segment edges have been recorded in past earthquakes, giving hope that the modeled effect can be detected in many cases, even though mapped surface slip is affected by a number of different sources of heterogeneity. The results provide an alternative explanation for observations that stepovers that allow throughgoing rupture tend to have higher slip gradients than those at which rupture terminates: perhaps many such stepovers are connected at depth, which could persistently favor throughgoing rupture. There may be implications for interpretation of apparent fault discontinuities worldwide.

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Han, Longfei, Jing Liu-Zeng, Wenqian Yao, Wenxin Wang, Yanxiu Shao, Xiaoli Liu, Xianyang Zeng, Yunpeng Gao, and Hongwei Tu. "Discontinuous Surface Ruptures and Slip Distributions in the Epicentral Region of the 2021 Mw7.4 Maduo Earthquake, China." Remote Sensing 16, no. 7 (April 1, 2024): 1250. http://dx.doi.org/10.3390/rs16071250.

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Geometric complexities play an important role in the nucleation, propagation, and termination of strike-slip earthquake ruptures. The 2021 Mw7.4 Maduo earthquake rupture initiated at a large releasing stepover with a complex fault intersection. In the epicentral region, we conducted detailed mapping and classification of the surface ruptures and slip measurements associated with the earthquake, combining high-resolution uncrewed aerial vehicle (UAV) images and optical image correlation with field investigations. Our findings indicate that the coseismic ruptures present discontinuous patterns mixed with numerous lateral spreadings due to strong ground shaking. The discontinuous surface ruptures are uncharacteristic in slip to account for the large and clear displacements of offset landforms in the epicentral region. Within the releasing stepovers, the deformation zone revealed from the optical image correlation map indicates that a fault may cut diagonally across the pull-apart basin at depth. The left-lateral horizontal coseismic displacements from field measurements are typically ≤0.6 m, significantly lower than the 1–2.7 m measured from the optical image correlation map. Such a discrepancy indicates a significant proportion of off-fault deformation or the possibility that the rupture stopped at a shallow depth during its initiation phase instead of extending to the surface. The fault network and multi-fault junctions west and south of the epicenter suggest a possible complex path, which retarded the westward propagation at the initial phase of rupture growth. A hampered initiation might enhance the seismic ground motion and the complex ground deformation features at the surface, including widespread shaking-related fissures.

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Little, T. A., P. Morris, M. P. Hill, J. Kearse, R. J. Van Dissen, J. Manousakis, D. Zekkos, and A. Howell. "Coseismic deformation of the ground during large-slip strike-slip ruptures: Finite evolution of “mole tracks”." Geosphere 17, no. 4 (May 14, 2021): 1170–92. http://dx.doi.org/10.1130/ges02336.1.

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Abstract To evaluate ground deformation resulting from large (~10 m) coseismic strike-slip displacements, we focus on deformation of the Kekerengu fault during the November 2016 Mw 7.8 Kaikōura earthquake in New Zealand. Combining post-earthquake field observations with analysis of high-resolution aerial photography and topographic models, we describe the structural geology and geomorphology of the rupture zone. During the earthquake, fissured pressure bulges (“mole tracks”) initiated at stepovers between synthetic Riedel (R) faults. As slip accumulated, near-surface “rafts” of cohesive clay-rich sediment, bounded by R faults and capped by grassy turf, rotated about a vertical axis and were internally shortened, thus amplifying the bulges. The bulges are flanked by low-angle contractional faults that emplace the shortened mass of detached sediment outward over less-deformed ground. As slip accrued, turf rafts fragmented into blocks bounded by short secondary fractures striking at a high angle to the main fault trace that we interpret to have originated as antithetic Riedel (R′) faults. Eventually these blocks were dispersed into strongly sheared earth and variably rotated. Along the fault, clockwise rotation of these turf rafts within the rupture zone averaged ~20°–30°, accommodating a finite shear strain of 1.0–1.5 and a distributed strike slip of ~3–4 m. On strike-slip parts of the fault, internal shortening of the rafts averaged 1–2 m parallel to the R faults and ~1 m perpendicular to the main fault trace. Driven by distortional rotation, this contraction of the rafts exceeds the magnitude of fault heave. Turf rafts on slightly transtensional segments of the fault were also bulged and shortened—relationships that can be explained by a kinematic model involving “deformable slats.” In a paleoseismic trench cut perpendicular the fault, one would observe fissures, low-angle thrusts, and steeply dipping strike-slip faults—some cross-cutting one another—yet all may have formed during a single earthquake featuring a large strike-slip displacement.

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Styron, Richard, Julio García-Pelaez, and Marco Pagani. "CCAF-DB: the Caribbean and Central American active fault database." Natural Hazards and Earth System Sciences 20, no. 3 (March 25, 2020): 831–57. http://dx.doi.org/10.5194/nhess-20-831-2020.

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Abstract. A database of ∼250 active fault traces in the Caribbean and Central American regions has been assembled to characterize the seismic hazard and tectonics of the area, as part of the Global Earthquake Model (GEM) Foundation's Caribbean and Central American Risk Assessment (CCARA) project. The dataset is available in many vector GIS formats and contains fault trace locations as well as attributes describing fault geometry and kinematics, slip rates, data quality and uncertainty, and other metadata as available. The database is public and open source (available at: https://github.com/GEMScienceTools/central_am_carib_faults, last access: 23 March 2020), will be updated progressively as new data become available, and is open to community contribution. The active fault data show deformation in the region to be centered around the margins of the Caribbean plate. Northern Central America has sinistral and reverse faults north of the sinistral Motagua–Polochic fault zone, which accommodates sinistral Caribbean–North American relative motion. The Central Highlands in Central America extend east–west along a broad array of normal faults, bound by the Motagua–Polochic fault zone in the north and trench-parallel dextral faulting in the southwest between the Caribbean plate and the Central American forearc. Faulting in southern Central America is complicated, with trench-parallel reverse and sinistral faults. The northern Caribbean–North American plate boundary is sinistral off the shore of Central America, with transpressive stepovers through Jamaica, southern Cuba and Hispaniola. Farther east, deformation becomes more contractional closer to the Lesser Antilles subduction zone, with minor extension and sinistral shear throughout the upper plate, accommodating oblique convergence of the Caribbean and North American plates.

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Hodge, C. C. "SEISMIC EVIDENCE FOR REVERSE AND WRENCH FAULT TECTONICS—CLIFF HEAD OIL FIELD, PERTH BASIN." APPEA Journal 45, no. 1 (2005): 381. http://dx.doi.org/10.1071/aj04030.

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Seismic interpretation of the Cliff Head oil field has shown it to be structurally complex with reverse faults, wrench faults and listric faults mapped at both field and reservoir scale within the Permo-Triassic section.The Cliff Head field overlies the Abrolhos Transfer Zone and has strong similarity to the progressive evolution, internal structure and rhomboid map geometry in experimental models of restraining stepovers in strikeslip systems. It is concluded that the Cliff Head oil field is a pop-up structure formed during the Permian and early Cretaceous within a restrained convergent wrench system—the result of sinistral transpression.A similar style of faulting could be applied when mapping seismic data in other offshore areas and especially the onshore Perth Basin with its poorer seismic data quality.Interpretation of prospects with a strong reverse or wrench component has implications for the timing of hydrocarbon emplacement and the potential for seal breach and leakage. Furthermore, paleo-structural style will determine fracture density and orientation and may be critical in determining optimum design of producer and injection wells during field development.It is recommended that interpreters of seismic data in the Perth Basin treat the fault patterns and structural trends of the Permian and early Cretaceous as different structural packages. The two should only be linked when it is very clear that there is a strong early Cretaceous overprint.

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Lozos, J. C., D. D. Oglesby, and J. N. Brune. "The Effects of Fault Stepovers on Ground Motion." Bulletin of the Seismological Society of America 103, no. 3 (June 1, 2013): 1922–34. http://dx.doi.org/10.1785/0120120223.

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Westaway, Rob. "Deformation around stepovers in strike-slip fault zones." Journal of Structural Geology 17, no. 6 (June 1995): 831–46. http://dx.doi.org/10.1016/0191-8141(94)00098-k.

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Micklethwaite, S., A. Ford, W. Witt, and H. A. Sheldon. "The where and how of faults, fluids and permeability - insights from fault stepovers, scaling properties and gold mineralisation." Geofluids 15, no. 1-2 (September 24, 2014): 240–51. http://dx.doi.org/10.1111/gfl.12102.

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Lozos, J. C., J. H. Dieterich, and D. D. Oglesby. "The Effects of d0 on Rupture Propagation on Fault Stepovers." Bulletin of the Seismological Society of America 104, no. 4 (July 15, 2014): 1947–53. http://dx.doi.org/10.1785/0120130305.

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Li, Xing, Wenbin Xu, Sigurjón Jónsson, Yann Klinger, and Guohong Zhang. "Source Model of the 2014 Mw 6.9 Yutian Earthquake at the Southwestern End of the Altyn Tagh Fault in Tibet Estimated from Satellite Images." Seismological Research Letters 91, no. 6 (August 19, 2020): 3161–70. http://dx.doi.org/10.1785/0220190361.

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Abstract Multiple fault segments ruptured during the 2014 Yutian earthquake, but the detailed source parameters and the mechanism of rupture complexity remain poorly understood. Here, we use high-resolution TanDEM-X satellite data and Satellite Pour l’Observation de la Terre-6/7 images to map the coseismic ground deformation field of the event. We find that the majority of coseismic slip occurred in the upper 10 km with the maximum left-lateral fault slip of ∼2.5 m at ∼6 km depth. The fault ruptured across a large 4.5 km extensional stepover from one left-lateral fault segment to another, with some right-lateral relay faulting in between. We find that the earthquake was followed by shallow afterslip concentrating at the southwestern end of coseismic rupture, in an area of many aftershocks and positive Coulomb failure stress change. Our findings demonstrate the power of satellite remote sensing technology in constraining source geometry and slip model of complex earthquakes when ground measurements are limited.

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Agosta, Fabrizio, Angela Vita Petrullo, Vincenzo La Bruna, and Giacomo Prosser. "Cenozoic Fault Growth Mechanisms in the Outer Apulian Platform." Geosciences 13, no. 4 (April 19, 2023): 121. http://dx.doi.org/10.3390/geosciences13040121.

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This work focuses on a ca. 55 km-long extensional fault zone buried underneath the foredeep deposits of the southern Apennines, Italy, with the goal of deciphering the Cenozoic fault growth mechanisms in the Outer Apulian Platform. By considering public 2D seismic reflection profiles, well logs, and isochron maps data, the study normal fault zone is interpreted as made up of four individual fault segments crosscutting Top Cretaceous, Top Eocene, Top Miocene, and Top Pliocene chrono-stratigraphic surfaces. The computed cumulative throw profiles form either bell-shaped or flat-shaped geometries along portions of the single fault segments. The computed incremental throw profiles also show an initial fault segmentation not corresponding with the present-day structural configuration. Data are consistent with the initial, post-Cretaceous fault segments coalescing together during Miocene–Pliocene deformation and with fault linkage processes localizing at the stepover/relay zones. Pleistocene faulting determined the evolution of a coherent fault system. The computed n-values obtained for the single time intervals by considering the maximum fault throw–fault length relations indicate that the fault segments formed scale-dependent geometries. Variations of these computed values are interpreted as due to the higher degree of maturity reached by the entire fault system during Miocene to Pleistocene deformation.

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Hu, Feng, Jiankuan Xu, Zhenguo Zhang, Wei Zhang, and Xiaofei Chen. "Construction of equivalent single planar fault model for strike-slip stepovers." Tectonophysics 632 (September 2014): 244–49. http://dx.doi.org/10.1016/j.tecto.2014.06.025.

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Vegas, N., A. Aranguren, and J. M. Tubia. "Granites built by sheeting in a fault stepover (the Sanabria Massifs, Variscan Orogen, NW Spain)." Terra Nova 13, no. 3 (December 2001): 180–87. http://dx.doi.org/10.1046/j.1365-3121.2001.00343.x.

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Wang, Hui, Mian Liu, Jiyang Ye, Jianling Cao, and Yan Jing. "Strain partitioning and stress perturbation around stepovers and bends of strike-slip faults: Numerical results." Tectonophysics 721 (November 2017): 211–26. http://dx.doi.org/10.1016/j.tecto.2017.10.001.

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Lozos, Julian C., David D. Oglesby, James N. Brune, and Kim B. Olsen. "Rupture Propagation and Ground Motion of Strike‐Slip Stepovers with Intermediate Fault Segments." Bulletin of the Seismological Society of America 105, no. 1 (December 16, 2014): 387–99. http://dx.doi.org/10.1785/0120140114.

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Xu, Xiurong, Zhenguo Zhang, Feng Hu, and Xiaofei Chen. "Dynamic Rupture Simulations of the 1920 Ms 8.5 Haiyuan Earthquake in China." Bulletin of the Seismological Society of America 109, no. 5 (September 10, 2019): 2009–20. http://dx.doi.org/10.1785/0120190061.

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Abstract The Haiyuan fault is a major seismogenic fault on the northeastern edge of the Tibetan–Qinghai plateau. The 16 December 1920 Ms 8.5 Haiyuan, China, earthquake is the largest and most recent event along the eastern Haiyuan fault (the Haiyuan fault in the article). Because only a few near‐field seismic recordings are available, the rupture process remains unclear. To understand the source process and intensity distribution of the 1920 Haiyuan earthquake, we simulated the dynamic rupture and strong ground motion of said earthquake using the 3D curved‐grid finite‐difference method. Considering the differences in epicenter locations among various catalogs, we constructed two models with different source points. For each model, three versions with different fault geometries were investigated: one continuous fault model and two discontinuous fault models with different stepover widths (1.8 and 2.5 km, respectively). A dynamic rupture source model with a final slip distribution similar to that observed on the ground surface was found. The maximum displacement on the ground surface was ∼6.5 m. Based on the dynamic rupture model, we also simulated the strong ground motion and estimated the theoretical intensity distribution. The maximum value of the horizontal peak ground velocity occurs near Haiyuan County, where the intensity reaches XI. Without considering the site conditions, the intensity values in most regions, based on the dynamic scenarios, are smaller than the values from field investigation. In this work, we present physically based insights into the 1920 Haiyuan earthquake, which is important for understanding rupture processes and preventing seismic hazards on the northeastern boundary of the Tibetan plateau.

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Marliyani, G. I., T. K. Rockwell, N. W. Onderdonk, and S. F. McGill. "Straightening of the Northern San Jacinto Fault, California, as Seen in the Fault-Structure Evolution of the San Jacinto Valley Stepover." Bulletin of the Seismological Society of America 103, no. 3 (June 1, 2013): 2047–61. http://dx.doi.org/10.1785/0120120232.

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Seyitoglu, Gurol, Bahadir Aktug, Korhan Esat, and Bulent Kaypak. "Neotectonics of Turkey (Türkiye) and surrounding regions: a new perspective with block modelling." Geologica Acta 20 (April 28, 2022): 1–21. http://dx.doi.org/10.1344/geologicaacta2022.20.4.

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This paper aims to present a new neotectonic perspective concordant with the seismic activities in Turkey and surrounding regions. The neotectonic structures have been re-evaluated mainly by using focal mechanism solutions and high-resolution satellite (Google Earth) images. The Southeast Anatolian Wedge explains thrust/blind thrust and asymmetrical folding relationship in SE Turkey, Syria, and Northern Iraq. The neotectonic structures of the Turkish-Iranian Plateau are enlightened by the rhomboidal cell model which creates a base to determine multiple intersection points between the region-wide left- and right-lateral shear zones. The releasing stepover between the North Anatolian Fault Zone and Southeast Anatolian-Zagros Fault Zone plus their connections with the Northeast Anatolian Fault Zone and the East Anatolian Fault Zone are described in a more meaningful way with the Anatolian Diagonal concept. It also clarifies the role of left-lateral shear zone in the west-southwest movement of Anatolian plate and its relationship with the Aegean and Cyprus arcs. A neotectonic region under the influence of NW-SE contraction is determined between the North Anatolian, Eskişehir, and Kırıkkale-Erbaa fault zones in which the Elmadağ-Eldivan and Abdüsselam pinched crustal wedges and the Beypazarı Blind Thrust Zone are developed. A new route for the southern branch of the North Anatolian Fault Zone is determined between Bolu and Değirmenlik (Milos) Island in the Aegean Sea via Mudurnu, Bursa, Balıkesir, and İzmir. All main neotectonic structures mentioned in this paper are evaluated by the elastic dislocation modelling and new neotectonic provinces are suggested.

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White, Malcolm C. A., Hongjian Fang, Rufus D. Catchings, Mark R. Goldman, Jamison H. Steidl, and Yehuda Ben-Zion. "Detailed traveltime tomography and seismic catalogue around the 2019 Mw7.1 Ridgecrest, California, earthquake using dense rapid-response seismic data." Geophysical Journal International 227, no. 1 (June 8, 2021): 204–27. http://dx.doi.org/10.1093/gji/ggab224.

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SUMMARY We derive a detailed earthquake catalogue and Vp, Vs and Vp/Vs models for the region around the 2019 Mw 6.4 and Mw7.1 Ridgecrest, California, earthquake sequence using data recorded by rapid-response, densely deployed sensors following the Ridgecrest main shock and the regional network. The new catalogue spans a 4-month period, starting on 1 June 2019, and it includes nearly 95 000 events detected and located with iterative updates to our velocity models. The final Vp and Vs models correlate well with surface geology in the top 4 km of the crust and spatial seismicity patterns at depth. Joint interpretation of the derived catalogue, velocity models, and surface geology suggests that (i) a compliant low-velocity zone near the Garlock Fault arrested the Mw 7.1 rupture at the southeast end; (ii) a stiff high-velocity zone beneath the Coso Mountains acted as a strong barrier that arrested the rupture at the northwest end and (iii) isolated seismicity on the Garlock Fault accommodated transtensional-stepover strain triggered by the main events. The derived catalogue and velocity models can be useful for multiple future studies, including further analysis of seismicity patterns, derivations of accurate source properties (e.g. focal mechanisms) and simulations of earthquake processes and radiated seismic wavefields.

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Doskich, Sofiia, Stepan Savchuk, and Bohdan Dzhuman. "GEODYNAMICS." GEODYNAMICS 2(35)2023, no. 2(35) (December 2023): 89–98. http://dx.doi.org/10.23939/jgd2023.02.089.

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The purpose of research is to identify horizontal deformation of the Ukraine territory, using only proven and suitable for geodynamic interpretation GNSS stations. The initial data are observations from 30 GNSS stations for 2017 to 2020. Methodology. The methodology includes the analysis of modern Earth's crust deformations of Ukraine. As a result, for the first time the impact of the coordinates time series created by two different methods: Precise Point Positioning (PPP) and the classical differential method, on determining deformation processes was analysed. It was established that nowadays for the tasks of monitoring, including geodynamic, it is necessary to use the Precise Point Positioning (PPP) method, because the accuracy of determined velocities of the GNSS stations by this method was higher than in the classical differential method. Results. A map of horizontal Earth's crust deformations on the territory of Ukraine was created according to the coordinates time series of GNSS stations. The extension areas of Shepetivka-Starokostiantyniv Khmelnytsky region, Boryspil- Pryluky-Pereyaslav-Khmelnitsky Kyiv and Chernihiv region, as well as a compression area of the Earth's crust in Nizhyn - Stepovi Khutory - Kozelets of Chernihiv region was identified. Additionally, a map of horizontal displacements of the GNSS-stations was created, where the diverse of these displacements was observed, which is likely to be caused by the presence of modern subvertical and sub-horizontal faults and fault areas. For better interpretation of the obtained results, it is necessary to involve geological and geophysical data of tectonic activity of the Ukraine territory.

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Manaker, D. M. "Subsurface Structure and Kinematics of the Calaveras-Hayward Fault Stepover from Three-Dimensional Vp and Seismicity, San Francisco Bay Region, California." Bulletin of the Seismological Society of America 95, no. 2 (April 1, 2005): 446–70. http://dx.doi.org/10.1785/0120020202.

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34

Dembo, Neta, Yariv Hamiel, and Roi Granot. "The stepovers of the Central Dead Sea Fault: What can we learn from the confining vertical axis rotations?" Tectonophysics 816 (October 2021): 229036. http://dx.doi.org/10.1016/j.tecto.2021.229036.

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35

Irmak, Tahir Serkan, Seda Yolsal-Çevikbilen, Tuna Eken, Bülent Doğan, Ceyhun Erman, Evrim Yavuz, Hakan Alçık, Peter Gaebler, Ali Pınar, and Tuncay Taymaz. "Source characteristics and seismotectonic implications of the 26 September 2019 Mw 5.7 Silivri High-Kumburgaz Basin earthquake and evaluation of its aftershocks at the North Anatolian Fault Zone (Central Marmara Sea, NW Turkey)." Geophysical Journal International 227, no. 1 (June 16, 2021): 383–402. http://dx.doi.org/10.1093/gji/ggab233.

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SUMMARY The Central Marmara Sea region hosts the northwestern branch of the North Anatolian Fault Zone (NAFZ) with its known seismic gap between the 1912 Ganos (Mw 7.2) and 1999 Izmit (Mw 7.4) major devastating earthquakes and thus poses a significant seismic hazard potential for the megacity Istanbul. The 26 September 2019 Mw 5.7 Silivri High-Kumburgaz Basin (central Marmara Sea) earthquake ruptured a thrust fault with a minor strike-slip component at the north of the eastern end of this gap relatively in the shallow depth (h= 8 km) range. Thus, in this study, we examine source properties of the main shock activity and coseismic behaviour of the failure, and the pattern of post-seismic deformation based on the aftershock distribution to have an insight into the role of the subsidiary and main fault structures on the crustal kinematics along this complicated branch of the NAFZ. The relocated epicentres are aligned in the E–W direction and tend to propagate towards the segments to the east of the main shock. The detected aftershock activity appears to focus on the east side of the main shock and almost no seismic activity was observed to the west of the epicentre. Independent investigations from coda-wave fitting, point-source, and finite-fault slip modelling agree on the moment magnitude of Mw5.7 for the 26 September 2019 main shock. The kinematic rupture model of this event implied that the main rupture nucleated around the hypocentre, and then propagated bilaterally along the E–W direction but with significant progress towards the east. The distribution of the slip vectors indicates that the rupture evolved on a dextral thrust fault plane. The spatio-temporal behaviour of the overall aftershocks sequence, their focal mechanism solutions and our kinematic slip model clearly shows that the existing secondary structures developed in simple shear dextral deformation are likely responsible for the main shock activity. We conclude that such type of deformation model results in a motion in response to the thrust faulting with strike-slip component with an N89°W (271°) orientation and 33°NE dipping at left stepover transpressional region on the NAFZ.

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Woolery, E. W., and A. Almayahi. "Northeast-Oriented Transpression Structure in the Northern New Madrid Seismic Zone: Extension of a Shear Zone across the Reelfoot Fault Stepover Arm." Bulletin of the Seismological Society of America 104, no. 5 (September 9, 2014): 2587–96. http://dx.doi.org/10.1785/0120140066.

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Tréhu, Anne M., Bridget Hass, Alexander de Moor, Andrei Maksymowicz, Eduardo Contreras-Reyes, Emilio Vera, and Michael D. Tryon. "Geologic controls on up-dip and along-strike propagation of slip during subduction zone earthquakes from a high-resolution seismic reflection survey across the northern limit of slip during the 2010 Mw 8.8 Maule earthquake, offshore Chile." Geosphere 15, no. 6 (November 7, 2019): 1751–73. http://dx.doi.org/10.1130/ges02099.1.

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Abstract A grid of closely spaced, high-resolution multichannel seismic (MCS) reflection profiles was acquired in May 2012 over the outer accretionary prism up dip from the patch of greatest slip during the 2010 Mw 8.8 Maule earthquake (offshore Chile) to complement a natural-source seismic experiment designed to monitor the post-earthquake response of the outer accretionary prism. We describe the MCS data and discuss the implications for the response of the accretionary prism during the earthquake and for the long-term evolution of the margin. The most notable observation from the seismic reflection survey is a rapid north-to-south shift over a short distance from nearly total frontal accretion of the trench sediments to nearly total underthrusting of undeformed trench sediments that occurs near the northern edge of slip in the 2010 earthquake. Integrating our structural observations with other geological and geophysical observations, we conclude that sediment subduction beneath a shallow décollement is associated with propagation of slip to the trench during great earthquakes in this region. The lack of resolvable compressive deformation in the trench sediment along this segment of the margin indicates that the plate boundary here is very weak, which allowed the outer prism to shift seaward during the earthquake, driven by large slip down dip. The abrupt shift from sediment subduction to frontal accretion indicates a stepdown in the plate boundary fault, similar to the stepovers that commonly arrest slip propagation in strike-slip faults. We do not detect any variation along strike in the thickness or reflective character of the trench sediments adjacent to the change in deformation front structure. This change, however, is correlated with variations in the morphology and structure of the accretionary prism that extend as far as 40 km landward of the deformation front. We speculate that forearc structural heterogeneity is the result of subduction of an anomalously shallow or rough portion of plate that interacted with and deformed the overlying plate and is now deeply buried. This study highlights need for three-dimensional structural images to understand the interaction between geology and slip during subduction zone earthquakes.

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Ryan, Kenny J., and David D. Oglesby. "Modeling the Effects of a Normal-Stress-Dependent State Variable, Within the Rate- and State-Dependent Friction Framework, at Stepovers and Dip-Slip Faults." Pure and Applied Geophysics 174, no. 3 (January 19, 2017): 1361–83. http://dx.doi.org/10.1007/s00024-017-1469-2.

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Sun, Qingqing, Tailiang Fan, Robert E. Holdsworth, Zhiqian Gao, Jun Wu, Shichang Gao, Ming Wang, and Yaxuan Yuan. "The spatial characterization of stepovers along deeply-buried strike-slip faults and their influence on reservoir distribution in the central Tarim Basin, NW China." Journal of Structural Geology 170 (May 2023): 104849. http://dx.doi.org/10.1016/j.jsg.2023.104849.

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40

Fossen, Haakon, Richard A. Schultz, Egil Rundhovde, Atle Rotevatn, and Simon J. Buckley. "Fault linkage and graben stepovers in the Canyonlands (Utah) and the North Sea Viking Graben, with implications for hydrocarbon migration and accumulation." AAPG Bulletin 94, no. 5 (May 2010): 597–613. http://dx.doi.org/10.1306/10130909088.

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Odum, J. K., W. J. Stephenson, and R. A. Williams. "Multisource, High-resolution Seismic-reflection Imaging of Meeman-Shelby Fault and a Possible Tectonic Model for a Joiner Ridge-Manila High Stepover Structure in the Upper Mississippi Embayment Region." Seismological Research Letters 81, no. 4 (July 1, 2010): 647–63. http://dx.doi.org/10.1785/gssrl.81.4.647.

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PLUHAR, C., R. COE, J. LEWIS, F. MONASTERO, and J. GLEN. "Fault block kinematics at a releasing stepover of the Eastern California shear zone: Partitioning of rotation style in and around the Coso geothermal area and nascent metamorphic core complex." Earth and Planetary Science Letters 250, no. 1-2 (October 15, 2006): 134–63. http://dx.doi.org/10.1016/j.epsl.2006.07.034.

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43

Wang, Hu, Dongming Li, Kaijin Li, Lin Deng, and Peisheng Luo. "Late Quaternary Fault Activity of the Southern Segment of the Daliangshan Fault along the Southeastern Margin of the Tibetan Plateau and Its Implications for Fault Rupture Behaviour at Stepovers." Lithosphere 2022, no. 1 (September 2, 2022). http://dx.doi.org/10.2113/2022/9259647.

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Abstract Stepovers have been widely suggested to be important structural boundaries that control earthquake rupture extent and therefore the size of earthquakes. Previous studies suggested that ~4-5 km wide stepovers are likely to arrest fault rupture. However, recent earthquake cases show that even much wider stepovers (e.g., ≥7-8 km wide) sometimes may not effectively impede seismic rupture propagation, which requires us to further explore cascading rupture mechanism of large earthquakes at wider stepovers. Here, we constrained slip rates and paleoseismic earthquakes of two fault sections that bound a constraining stepover with width of approximately 7-8 km along the southern segment of the Daliangshan fault along the southeastern margin of the Tibetan Plateau. Multiple landform offset and radiocarbon dating results constrained that the two fault sections show a moderate slip rate at approximately 5 mm/yr. Moreover, three or four paleoseismic events Z through W, in 1489 AD, 620-515 BC, 4475-3700 BC, and 6265-4510 BC, were revealed on the Jiaojihe fault section. Based on the aforementioned results, we suggest that the most recent seismic event might exhibit a jump over the restraining stepover, whereas ruptures of the older events might be arrested by the stepover. Furthermore, we suggest that moderate slip-rate faults might have similar potential with that of high slip-rate faults to rupture through wider stepovers, which increases us in understanding the generation of cascading ruptures on strike-slip faults and is helpful for evaluating seismic hazards.

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Sahakian, Valerie J., Boe J. Derosier, Thomas K. Rockwell, and Joann M. Stock. "Shallow distributed faulting in the Imperial Valley, California, USA." Geology, March 8, 2022. http://dx.doi.org/10.1130/g49572.1.

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In the tectonically complex Imperial Valley, California (USA), the Imperial fault (IF) is often considered to be the primary fault at the U.S.-Mexico border; however, its strain partitioning and interactions with other faults are not well understood. Despite inferred evidence of other major faults (e.g., seismicity), it is difficult to obtain a holistic view of this system due to anthropogenic surface modifications. To better define the structural configuration of the plate-boundary strain in this region, we collected high-resolution shallow seismic imaging data in the All American Canal, crossing the Imperial, Dixieland, and Michoacán faults. These data image shallow (<25 m) structures on and near the mapped trace of the Imperial fault, as well as the Michoacán fault and adjacent stepover. Integration of our data with nearby terrestrial cores provides age constraints on Imperial fault deformation. These data suggest that the Michoacán fault, unmapped in the United States, is active and likely produces dynamic or off-fault deformation within its stepover to the Dixieland fault. Together, these data support more strain partitioning than previously documented in this region.

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Ben-Zion, Yehuda, Thomas K. Rockwell, Zheqiang Shi, and Shiqing Xu. "Reversed-Polarity Secondary Deformation Structures Near Fault Stepovers." Journal of Applied Mechanics 79, no. 3 (April 6, 2012). http://dx.doi.org/10.1115/1.4006154.

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We study volumetric deformation structures in stepover regions using numerical simulations and field observations, with a focus on small-scale features near the ends of rupture segments that have opposite-polarity from the larger-scale structures that characterize the overall stepover region. The reversed-polarity small-scale structures are interpreted to be generated by arrest phases that start at the barriers and propagate some distance back into the rupture segment. Dynamic rupture propagating as a symmetric bilateral crack produces similar (anti-symmetric) structures at both rupture ends. In contrast, rupture in the form of a predominantly unidirectional pulse produces pronounced reversed-polarity structures only at the fault end in the dominant propagation direction. Several observational examples at different scales from strike-slip faults of the San Andreas system in southern California illustrate the existence of reversed-polarity secondary deformation structures. In the examples shown, relatively-small pressure-ridges are seen only on one side of relatively-large extensional stepovers. This suggests frequent predominantly unidirectional ruptures in at least some of those cases, although multisignal observations are needed to distinguish between different possible mechanisms. The results contribute to the ability of inferring from field observations on persistent behavior of earthquake ruptures associated with individual fault sections.

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Brothers, Daniel S., Neal W. Driscoll, Graham M. Kent, Robert L. Baskin, Alistair J. Harding, and Annie M. Kell. "Seismostratigraphic analysis of Lake Cahuilla sedimentation cycles and fault displacement history beneath the Salton Sea, California, USA." Geosphere, June 17, 2022. http://dx.doi.org/10.1130/ges02468.1.

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The Salton Trough (southeastern California, USA) is the northernmost transtensional stepover of the Gulf of California oblique-divergent plate boundary and is also where the southern terminus of the San Andreas fault occurs. Until recently, the distribution of active faults in and around the Salton Sea and their displacement histories were largely unknown. Subbottom CHIRP (compressed high-intensity radar pulse) surveys in the Salton Sea are used to develop a seismic facies model for ancient Lake Cahuilla deposits, a detailed map of submerged active faults, and reconstructed fault displacement histories during the late Holocene. We observe as many as fourteen Lake Cahuilla sequences in the Salton Sea (last ~3 k.y.) and develop a chronostratigraphic framework for the last six sequences (last ~1200 yr) by integrating CHIRP data and cone penetrometer logs with radiocarbon-dated stratigraphy at an onshore paleoseismic site. The Salton Sea contains northern and southern subbasins that appear to be separated by a tectonic hinge zone, and a subsidence signal across hinge-zone faults of 6–9 mm/yr (since ca. A.D. 940) increases toward the south to >15 mm/yr. The faults mapped to the south of the hinge zone appear to accommodate transtension within the San Andreas–Imperial fault stepover. We identify 8–15 distinct growth events across hinge-zone faults, meaning growth occurred at least once every 100 yr since Lake Cahuilla sedimentation began. Several faults offset the top of the most recent Lake Cahuilla highstand deposits, and at least two faults have offset the Salton Sea flood deposits. Active faults and folds were also mapped to a limited extent within the northern subbasin and display growth, but their kinematics and rupture histories require further study. The broad distribution of active faulting suggests that strain between the San Andreas, San Jacinto, and Imperial faults is highly distributed, thus discrepancies between geologic and geodetic slip-rate estimates from these major fault systems are to be expected.

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Hauksson, Egill, and Lucile M. Jones. "Seismicity, Stress State, and Style of Faulting of the Ridgecrest-Coso Region from the 1930s to 2019: Seismotectonics of an Evolving Plate Boundary Segment." Bulletin of the Seismological Society of America, June 2, 2020. http://dx.doi.org/10.1785/0120200051.

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ABSTRACT Decadal scale variations in the seismicity rate in the Ridgecrest-Coso region, part of the Eastern California Shear Zone, included seismic quiescence from the 1930s to the early 1980s, followed by increased seismicity until the 2019 Mw 6.4 and 7.1 Ridgecrest sequence. This sequence exhibited complex rupture on almost orthogonal faults and triggered aftershocks over an area of ∼90 km long by ∼5–10 km wide, which is a fraction of the area of the previously seismically active Indian Wells Valley and Coso range region. During the last 40 yr, the seismicity has been predominantly the result of strike-slip motion, extending north from the Garlock fault, along the Little Lake and Airport Lake fault zones, and approaching the southernmost Owens Valley fault to the north. The Coso range forms an extensional stepover between these two strike-slip fault systems. This evolution of a plate boundary zone is driven by the northwestward motion of the Sierra Nevada, and crustal extension along the southwestern edge of the Basin and Range Province. Stress inversion of focal mechanisms shows that the postseismic stress state consists of almost horizontal σ1 and vertical σ2. The σ1 is spatially rotated across the Coso range stepover with σ1-trending ∼N17° E to the north, whereas, along the Mw 7.1 mainshock rupture, the trend is ∼N6° E. The friction angles as measured between fault strikes and the σ1 trends correspond to a frictional coefficient of 0.75, suggesting average fault strength. In comparison, the mature Garlock fault has a smaller frictional coefficient of 0.28, similar to weak faults like the San Andreas fault. Thus, it appears that the heterogeneously oriented and spatially distributed but strong Ridgecrest-Coso faults accommodate seismicity at seemingly random places and times within the region and are in the process of self-organizing to form a major throughgoing plate-boundary segment.

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Ji, Haomin, An Li, Shimin Zhang, Ji Zhang, and Qing Liu. "Geometric Distribution and Earthquake Rupture Characteristics of the Northern Anqiu–Juxian Fault in the Tan–Lu Fault Zone, Eastern China." Frontiers in Earth Science 10 (February 17, 2022). http://dx.doi.org/10.3389/feart.2022.766222.

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The Northern Anqiu–Juxian Fault (NAJF) is one of the most active faults in the Tan-Lu Fault Zone (TLFZ), which produced the Anqiu M 7 earthquake in 70 BC. However, there is no clear understanding of the surface rupture caused by this historical earthquake. In this study, we determined the earthquake rupture characteristics of the NAJF based on high-precision surveying, geophysical exploration and drilling profiles. Based on an analysis of 87 horizontal offsets of gullies, we estimated a characteristic offset of ∼ 5 m along the NAJF for a rupture length about 130 km. Geophysical exploration results revealed a shallow geometric distribution of stepovers in the NAJF. We concluded that the ∼ 5 m offset and the rupture length of about 130 km are both in agreement with an empirical relationship among the magnitude, offset, and rupture length and imply that the ∼ 1 km wide stepover could not have terminated ruptures in the Anqiu M 7 earthquake. The relationship among the coseismic offset, magnitude, and surface rupture length of a strike-slip fault show that the 70 BC Anqiu earthquake was more likely to have had a magnitude of M ∼ 7.5.

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49

Barbot, Sylvain. "A Spectral Boundary-Integral Method for Quasi-Dynamic Ruptures of Multiple Parallel Faults." Bulletin of the Seismological Society of America, April 20, 2021. http://dx.doi.org/10.1785/0120210004.

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ABSTRACT Numerical models of rupture dynamics provide great insights into the physics of fault failure. However, resolving stress interactions among multiple faults remains challenging numerically. Here, we derive the elastostatic Green’s functions for stress and displacement caused by arbitrary slip distributions along multiple parallel faults. The equations are derived in the Fourier domain, providing an efficient means to calculate stress interactions with the fast Fourier transform. We demonstrate the relevance of the method for a wide range of applications, by simulating the rupture dynamics of single and multiple parallel faults controlled by a rate- and state-dependent frictional contact, using the spectral boundary integral method and the radiation-damping approximation. Within the antiplane strain approximation, we show seismic cycle simulations with a power-law distribution of rupture sizes and, in a different parameter regime, sequences of seismogenic slow-slip events. Using the in-plane strain approximation, we simulate the rupture dynamics of a restraining stepover. Finally, we describe cycles of large earthquakes along several parallel strike-slip faults in three dimensions. The approach is useful to explore the dynamics of interacting or isolated faults with many degrees of freedom.

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50

Niu, Pengfei, Zhujun Han, Kechang Li, Lixing Lv, and Peng Guo. "The 2022 Mw 6.7 Menyuan Earthquake on the Northeastern Margin of the Tibetan Plateau, China: Complex Surface Ruptures and Large Slip." Bulletin of the Seismological Society of America, March 13, 2023. http://dx.doi.org/10.1785/0120220163.

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ABSTRACT On 8 January 2022, the Mw 6.7 Menyuan earthquake occurred near the stepover of the Lenglongling (LLLF) and Tuolaishan (TLSF) faults of the Qilian–Haiyuan fault zone in the middle of the northeastern Tibetan plateau. Field investigations and unmanned aerial vehicle-based photogrammetry revealed that the earthquake generated five surface rupture zones with different strikes and kinematic properties. Two large rupture zones, R1 (∼22.8 km long) and R2 (∼3.9 km long), occurred along the northern branch of the western LLLF and the eastern segment of TLSF, respectively, and featured left-lateral strike slips. Among the three small rupture zones, the left-lateral strike-slip-type R3 (0.6 km long) was located in the extension direction of R2, whereas the thrust-type R4 (∼3.3 km long) and R5 (∼1.1 km long) zones were located north of the central section of R1. These complex multifault ruptures were caused mainly by the rupture of strike-slip faults on both sides of the stepover structure. A small amount of compressive shortening strain was released during the earthquake due to regional oblique compression. The total length of the rupture zone was ∼31.7 km; the maximum left-lateral and vertical offsets were 3.5 ± 0.3 and 0.47 ± 0.04 m, respectively. Compared with the relationship observed between coseismic slips and magnitudes in historical and modern earthquakes in western China, the 2022 Menyuan earthquake produced a large coseismic slip in relation to its magnitude. The distribution characteristics of the aftershock belts and their relationship with rupture zones showed that the seismogenic fault of the earthquake was nearly east–west-striking TLSF, which may have triggered the rupture of the northern branch of the western LLLF. In addition, only a small segment of TLSF was ruptured, indicating that the accumulated strain could not be released completely during the earthquake and that this remains the most likely area for the occurrence of large earthquakes in the future.

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Journal articles on the topic 'Stepover faults'

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