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1
Revenaugh, Justin. « The relation of crustal scattering to seismicity in southern California ». Journal of Geophysical Research : Solid Earth 105, B11 (10 novembre 2000) : 25403–22. http://dx.doi.org/10.1029/2000jb900304.
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Liu, Su Mei, et Xiang Dong Xie. « Reservoir-Induced Seismicity in the Three Gorges Reservoir Area ». Applied Mechanics and Materials 501-504 (janvier 2014) : 1477–85. http://dx.doi.org/10.4028/www.scientific.net/amm.501-504.1477.
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As a region with little or very low level background seismicity, the impoundment of the Three Gorges Reservoir in June 2003 was related to increasing reservoir-induced seismicity. Analysis of the spatial pattern of seismicity showed that a majority of the seismicity was associated with the heavily fractured, deep crustal Jiuwanxi Fault, especially in regions of permeable Carbonate rocks formations. Analysis of the temporal pattern of the seismicity and a comparison with the filling history of the reservoir showed that the frequency and intensity of induced seismicity started at low level accompanying the impoundment of the Three Gorges Reservoir, and then increased with the increasing of water level and decreased thereafter. The amplitude of fluctuation of water level was found to be related to the frequency and intensity of induced seismicity. The pore pressure diffusion plays an important role in reservoir induced seismicity.
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Alber, M., R. Fritschen et M. Bischoff. « Strength constraints of shallow crustal strata from analyses of mining induced seismicity ». Solid Earth Discussions 5, no 1 (3 juin 2013) : 737–65. http://dx.doi.org/10.5194/sed-5-737-2013.
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Abstract. Stress redistributions around large underground excavations such as coal mines may lead to failure of the surrounding rock mass. Some of these failure processes were recorded as seismic events. In this paper the different failure processes such as rock mass failure or the reactivation of faults are delineated from the seismic records. These are substantiated by rock mechanical analyses including laboratory strength tests on coal measure rocks obtained from underground drilling. Additionally, shear tests on discontinuities in coal measure rocks (slickensides in shale and rough sandstone joints) were conducted to grasp the possible variation of strength properties of faults. Numerical modeling was employed to evaluate the state of stress at the locations where seismic events did occur.
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Choudhury, Swapnamita, Param K. Gautam et Ajay Paul. « Seismicity and reservoir induced crustal motion study around the Tehri Dam, India ». Acta Geophysica 61, no 4 (23 mai 2013) : 923–34. http://dx.doi.org/10.2478/s11600-013-0125-1.
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Goertz-Allmann, Bettina P., et Stefan Wiemer. « Geomechanical modeling of induced seismicity source parameters and implications for seismic hazard assessment ». GEOPHYSICS 78, no 1 (1 janvier 2013) : KS25—KS39. http://dx.doi.org/10.1190/geo2012-0102.1.
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We simulate induced seismicity within a geothermal reservoir using pressure-driven stress changes and seismicity triggering based on Coulomb friction. The result is a forward-modeled seismicity cloud with origin time, stress drop, and magnitude assigned to each individual event. Our model includes a realistic representation of repeating event clusters, and is able to explain in principle the observation of reduced stress drop and increased [Formula: see text]-values near the injection point where pore-pressure perturbations are highest. The higher the pore-pressure perturbation, the less critical stress states still trigger an event, and hence the lower the differential stress is before triggering an event. Less-critical stress states result in lower stress drops and higher [Formula: see text]-values, if both are linked to differential stress. We are therefore able to establish a link between the seismological observables and the geomechanical properties of the source region and thus a reservoir. Understanding the geomechanical properties is essential for estimating the probability of exceeding a certain magnitude value in the induced seismicity and hence the associated seismic hazard of the operation. By calibrating our model to the observed seismicity data, we can estimate the probability of exceeding a certain magnitude event in space and time and study the effect of injection depth and crustal strength on the induced seismicity.
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Delorey, Andrew A., Kevin Chao, Kazushige Obara et Paul A. Johnson. « Cascading elastic perturbation in Japan due to the 2012 Mw 8.6 Indian Ocean earthquake ». Science Advances 1, no 9 (octobre 2015) : e1500468. http://dx.doi.org/10.1126/sciadv.1500468.
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Since the discovery of extensive earthquake triggering occurring in response to the 1992 Mw (moment magnitude) 7.3 Landers earthquake, it is now well established that seismic waves from earthquakes can trigger other earthquakes, tremor, slow slip, and pore pressure changes. Our contention is that earthquake triggering is one manifestation of a more widespread elastic disturbance that reveals information about Earth’s stress state. Earth’s stress state is central to our understanding of both natural and anthropogenic-induced crustal processes. We show that seismic waves from distant earthquakes may perturb stresses and frictional properties on faults and elastic moduli of the crust in cascading fashion. Transient dynamic stresses place crustal material into a metastable state during which the material recovers through a process termed slow dynamics. This observation of widespread, dynamically induced elastic perturbation, including systematic migration of offshore seismicity, strain transients, and velocity transients, presents a new characterization of Earth’s elastic system that will advance our understanding of plate tectonics, seismicity, and seismic hazards.
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Long, Leland Timothy. « A Model for Major Intraplate Continental Earthquakes ». Seismological Research Letters 59, no 4 (1 octobre 1988) : 273–78. http://dx.doi.org/10.1785/gssrl.59.4.273.
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Abstract Traditional paradigms of continental seismicity assert the stationarity of the earthquake process and a causal association of earthquakes with active faults, increasing levels of stress, and crustal structures, in a framework of Plate Tectonics. I propose, instead, that the seismicity associated with a magnitude six or greater intraplate continental earthquake is a transient phenomenon responding to a perturbation in crustal strength independent of existing faults and crustal structures. Regional plate stress may still provide the driving energy, but the causative stress is released by a perturbation in crustal strength in the vicinity of a major earthquake. The timing of a major earthquake and the characteristics of the associated seismicity may then be described by a sequence of five phases which are as follows: (1) Initiation. A major intraplate continental earthquake is initiated with a disturbance in the hydraulic or thermal properties of the crust below the epicenter. Such disturbances could be induced by the intrusion of a sill or by partial melting. (2) Strength corrosion. A corrosion in crustal strength follows the upward migration of fluids or heat from the area of recent disturbance. (3) Stress concentration. As a weakened central zone deforms in response to tectonic plate stress, stresses are concentrated in the surrounding rigid crust. (4) Failure. A major earthquake occurs when the stress surrounding the weakened core exceeds the crustal strength, either because the concentrated stresses are anomalously high or because the dispersing fluids have spread beyond the core. (5) Crustal healing. The final phase in the occurrence of a major intraplate continental earthquake is an extended aftershock sequence which is concentrated along the rupture zone of the main event. The occurrence of a major intraplate earthquake as described above releases the strain energy in a perturbed area. Additional major events would be unlikely until the strength has recovered sufficiently to equalize intraplate stress and permit a repeat of the cycle.
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Mukhopadhyay, Manoj, Eslam Elawadi, Basab Mukhopadhyay et Saad Mogren. « Induced and Ambient Crustal Seismicity under the Ghawar Oil-Gas Fields, Saudi Arabia ». Journal of the Geological Society of India 91, no 4 (avril 2018) : 449–56. http://dx.doi.org/10.1007/s12594-018-0878-x.
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Molchanov, O. « About climate-seismicity coupling from correlation analysis ». Natural Hazards and Earth System Sciences 10, no 2 (17 février 2010) : 299–304. http://dx.doi.org/10.5194/nhess-10-299-2010.
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Abstract. We have analyzed together the slow climate temperature variations in the near-equatorial Pacific Ocean area (SSTOI indices) and crustal seismic activity in the same region during 1973–2008 time period using correlation analysis and found similarity in seismic and ENSO periodicities (the latter with time lag about 1.5 years). Trends of the processes are also similar showing about 2 times increase in average seismic energy release during the whole period of analysis and conventional 0.1 °C/(10 years) increase in SSTOI index anomalies. Our major conclusion is on real credibility of climate-seismicity coupling. It is rather probable that at least partially climate ENSO oscillations and temperature anomaly trends are induced by similar variation in seismicity.
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Zhai, Guang, Manoochehr Shirzaei, Michael Manga et Xiaowei Chen. « Pore-pressure diffusion, enhanced by poroelastic stresses, controls induced seismicity in Oklahoma ». Proceedings of the National Academy of Sciences 116, no 33 (29 juillet 2019) : 16228–33. http://dx.doi.org/10.1073/pnas.1819225116.
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Induced seismicity linked to geothermal resource exploitation, hydraulic fracturing, and wastewater disposal is evolving into a global issue because of the increasing energy demand. Moderate to large induced earthquakes, causing widespread hazards, are often related to fluid injection into deep permeable formations that are hydraulically connected to the underlying crystalline basement. Using injection data combined with a physics-based linear poroelastic model and rate-and-state friction law, we compute the changes in crustal stress and seismicity rate in Oklahoma. This model can be used to assess earthquake potential on specific fault segments. The regional magnitude–time distribution of the observed magnitude (M) 3+ earthquakes during 2008–2017 is reproducible and is the same for the 2 optimal, conjugate fault orientations suggested for Oklahoma. At the regional scale, the timing of predicted seismicity rate, as opposed to its pattern and amplitude, is insensitive to hydrogeological and nucleation parameters in Oklahoma. Poroelastic stress changes alone have a small effect on the seismic hazard. However, their addition to pore-pressure changes can increase the seismicity rate by 6-fold and 2-fold for central and western Oklahoma, respectively. The injection-rate reduction in 2016 mitigates the exceedance probability of M5.0 by 22% in western Oklahoma, while that of central Oklahoma remains unchanged. A hypothetical injection shut-in in April 2017 causes the earthquake probability to approach its background level by ∼2025. We conclude that stress perturbation on prestressed faults due to pore-pressure diffusion, enhanced by poroelastic effects, is the primary driver of the induced earthquakes in Oklahoma.
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Fuchs, K. « Intraplate seismicity induced by stress concentration at crustal heterogeneities—the Hohenzollern Graben, a case history ». Geological Society, London, Special Publications 24, no 1 (1986) : 119–32. http://dx.doi.org/10.1144/gsl.sp.1986.024.01.12.
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Assameur, Djamel M., et Jean-Claude Mareschal. « Stress induced by topography and crustal density heterogeneities : implication for the seismicity of southeastern Canada ». Tectonophysics 241, no 3-4 (janvier 1995) : 179–92. http://dx.doi.org/10.1016/0040-1951(94)00202-k.
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Moriya, Hirokazu. « Acoustic Emission/Seismicity at Depth Beneath an Artificial Lake after the 2011 Tohoku Earthquake ». Applied Sciences 8, no 8 (20 août 2018) : 1407. http://dx.doi.org/10.3390/app8081407.
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Acoustic emission (AE)/seismicity activity increased near the city of Sendai, Japan, after the 11 March 2011 Tohoku earthquake in a newly seismically active region near the Nagamachi-Rifu fault, which caused a magnitude 5.0 earthquake in 1998. The source of this activity was around 12 km beneath an artificial lake. At the same time, activity on the Nagamachi-Rifu fault nearly ceased. More than 1550 micro-earthquakes were observed between 11 March 2011 and 1 August 2012, of which 63% exhibited similar waveforms and defined 64 multiplets. It appears that crustal extension of about 2 m during the Tohoku earthquake and additional extension of about 1 m during the following year changed the stress field in this region, thus generating micro-earthquakes and controlling their frequency. However, it has been presumed that crustal movement during the Tohoku earthquake did not affect the direction of principal stress, and that these events induced repeated quasi-static slips at asperities and the resultant micro-earthquakes.
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Quinones, Louis, Heather R. DeShon, SeongJu Jeong, Paul Ogwari, Oner Sufri, Monique M. Holt et Kevin B. Kwong. « Tracking Induced Seismicity in the Fort Worth Basin : A Summary of the 2008–2018 North Texas Earthquake Study Catalog ». Bulletin of the Seismological Society of America 109, no 4 (11 juin 2019) : 1203–16. http://dx.doi.org/10.1785/0120190057.
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Abstract Since 2008, earthquake sequences within the Fort Worth basin (FWB), north Texas, have been linked to wastewater disposal activities related to unconventional shale‐gas production. The North Texas Earthquake Study (NTXES) catalog (2008–2018), described and included herein, uses a combination of local and regional seismic networks to track significant seismic sequences in the basin. The FWB earthquakes occur along discrete faults that are relatively far apart (>30 km), allowing for more detailed study of individual sequence development. The three largest sequences (magnitude 3.6+) are monitored by local seismic networks (<15 km epicentral distances), whereas basinwide seismicity outside these three sequences is monitored using regional distance stations. A regional 1D velocity model for the FWB reflects basinwide well log, receiver function, and regional crustal structure studies and is modified for the larger individual earthquake sequences using local well‐log and geology data. Here, we present an mb_Lg relationship appropriate for Texas and a basin‐specific ML relationship, both calculated using attenuation curves developed with the NTXES catalog. Analysis of the catalog reveals that the earthquakes generally occur within the Precambrian basement formation along steeply dipping normal faults, and although overall seismicity rates have decreased since 2016, new faults have become active. Between 2006 and 2018, more than 2 billion barrels of fluids were injected into the Ellenburger formation within the FWB. We observe strong spatial and temporal correlations between the earthquake locations and wastewater disposal well locations and injection volumes, implying that fluid injection activities may be the main driving force of seismicity in the basin. In addition, we observe seismicity occurring at greater distances from injection wells (>10 km) over time, implying that far‐field stress changes associated with fluid injection activities may be an important component to understanding the seismic hazard of induced seismicity sequences.
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Robinson, Regan, Aibing Li, Alexandros Savvaidis et Hongru Hu. « Complex Shear-Wave Anisotropy from Induced Earthquakes in West Texas ». Bulletin of the Seismological Society of America 110, no 5 (21 juillet 2020) : 2242–51. http://dx.doi.org/10.1785/0120200086.
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ABSTRACT We have analyzed shear-wave splitting (SWS) data from local earthquakes in the Permian basin in west Texas to understand crustal stress change and induced seismicity. Two SWS parameters, the fast polarization direction and the delay time, are computed using a semiautomatic algorithm. Most measurements are determined in the Delaware basin and the Snyder area. In both regions, SWS fast directions are mostly consistent with local SHmax at stations that are relatively far from the earthquake clusters. Varying fast directions at one station are related to different ray paths and are probably caused by heterogeneity. In the Snyder area, most northeast–southwest fast directions are from the events in the northern part of the cluster, whereas the northwest–southeast fast directions are mostly from the southern part. The northeast–southwest and northwest–southeast fast directions could be attributed to the northeast-trending normal faults and the northwest-trending strike-slip faults, respectively. SWS results in the Delaware basin have two unique features. First, most shallow earthquakes less than 4 km deep produce relatively large delay times. This observation implies that the upper crust of the Delaware basin is highly fractured, as indicated by the increasing number of induced earthquakes. Second, diverse fast directions are observed at the stations in the high-seismicity region, likely caused by the presence of multiple sets of cracks with different orientations. This situation is possible in the crust with high pore pressure, which is expected in the Delaware basin due to extensive wastewater injection and hydraulic fracturing. We propose that the diversity of SWS fast directions could be a typical phenomenon in regions with a high rate of induced seismicity.
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Bykov, Victor G., et Sergey V. Trofimenko. « Slow strain waves in blocky geological media from GPS and seismological observations on the Amurian plate ». Nonlinear Processes in Geophysics 23, no 6 (19 décembre 2016) : 467–75. http://dx.doi.org/10.5194/npg-23-467-2016.
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Abstract. Based on the statistical analysis of spatiotemporal distribution of earthquake epicenters and perennial geodetic observation series, new evidence is obtained for the existence of slow strain waves in the Earth. The results of our investigation allow us to identify the dynamics of seismicity along the northern boundary of the Amurian plate as a wave process. Migration of epicenters of weak earthquakes (2 ≤ M ≤ 4) is initiated by the east–west propagation of a strain wave front at an average velocity of 1000 km yr−1. We have found a synchronous quasi-periodic variation of seismicity in equally spaced clusters with spatial periods of 3.5 and 7.26° comparable with the length of slow strain waves. The geodetic observations at GPS sites in proximity to local active faults show that in a number of cases, the GPS site coordinate seasonal variations exhibit a significant phase shift, whereas the time series of these GPS sites differ significantly from a sinusoid. Based on experimental observation data and the developed model of crustal block movement, we have shown that there is one possible interpretation for this fact that the trajectory of GPS station position disturbance is induced by migration of crustal deformation in the form of slow waves.
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van Vliet-Lanoë, Brigitte, Christine Authemayou, Stéphane Molliex, Michael Hugh Field, Manfred Frechen, Pascal Le Roy, Julie Perrot, Valérie Andrieu-Ponel, Gwendoline Grégoire et Bernard Hallégouët. « Middle Pleistocene seismically induced clay diapirism in an intraplate zone, western Brittany, France ». Quaternary Research 91, no 1 (31 août 2018) : 301–24. http://dx.doi.org/10.1017/qua.2018.63.
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AbstractThe Brittany region of France is located in a low seismicity intraplate zone. Most of the instrumented earthquakes are limited to a shallow crustal depth without surface rupture. A paleoseismological analysis was performed on deposits on the Crozon Peninsula and in the Elorn estuary. We highlight hydroplastic deformations induced by liquefaction leading to clay diapirism, which were likely triggered by past earthquakes. This diapirism seems to be frequent in continental nonconsolidated sediments and to develop on the inherited tectonic structures, when a shallow water table and confining layers exist. Timing of deformation is dated using paleoenvironmental data, and electron spin resonance and infrared-stimulated luminescence dating methods. Two seismic periods were identified in western Europe during early Marine Oxygen Isotope Stage (MIS) 10 (~380 ka) and early MIS 8 (~280–265 ka). The lack of similar deformations affecting the Holocene tidal deposits in the Bay of Brest suggests that the magnitude of the triggering paleoearthquakes is probably higher (Mw~6) than the recent events (Mw5.4). These unusual intraplate major paleoearthquakes need specific factors affecting the far-field crustal stress loading to be triggered, such as a brief acceleration of the Africa-Eurasia lithospheric plate convergence, glacio-isostatic stress perturbations associated with the onset of major glaciations in northern Europe, or other processes induced by orbital forcing.
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López-Comino, J. A., S. Cesca, M. Kriegerowski, S. Heimann, T. Dahm, J. Mirek et S. Lasocki. « Monitoring performance using synthetic data for induced microseismicity by hydrofracking at the Wysin site (Poland) ». Geophysical Journal International 210, no 1 (17 avril 2017) : 42–55. http://dx.doi.org/10.1093/gji/ggx148.
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Abstract Ideally, the performance of a dedicated seismic monitoring installation should be assessed prior to the observation of target seismicity. This work is focused on a hydrofracking experiment monitored at Wysin, NE Poland. A microseismic synthetic catalogue is generated to assess the monitoring performance during the pre-operational phase, where seismic information only concerns the noise conditions and the potential background seismicity. Full waveform, accounting for the expected spatial, magnitude and focal mechanism distributions and a realistic local crustal model, are combined with real noise recording to produce either event based or continuous synthetic waveforms. The network detection performance is assessed in terms of the magnitude of completeness (Mc) through two different techniques. First, we use an amplitude threshold, taking into the ratio among the maximal amplitude of synthetic waveforms and station-dependent noise levels, for different values of signal-to-noise ratio. The detection probability at each station is estimated for the whole data set and extrapolated to a broader range of magnitude and distances. We estimate an Mc of about 0.55, when considering the distributed network, and can further decrease Mc to 0.45 using arrays techniques. The second approach, taking advantage on an automatic, coherence-based detection algorithm, can lower Mc to ∼ 0.1, at the cost of an increase of false detections. Mc experiences significant changes during day hours, in consequence of strongly varying noise conditions. Moreover, due to the radiation patterns and network geometry, double-couple like sources are better detected than tensile cracks, which may be induced during fracking.
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Mandal, Prantik. « Relocations and local earthquake tomography : Implications toward the mafic pluton induced crustal seismicity in Kachchh, Gujarat, India, for last 18 years ». Journal of Asian Earth Sciences 190 (avril 2020) : 104196. http://dx.doi.org/10.1016/j.jseaes.2019.104196.
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Mandal, Prantik. « Three-dimensional seismic velocity imaging of the Kachchh rift zone, Gujarat, India : Implications toward the crustal mafic pluton induced intraplate seismicity ». Journal of Asian Earth Sciences 192 (mai 2020) : 104226. http://dx.doi.org/10.1016/j.jseaes.2020.104226.
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Kühn, Daniela, Sebastian Heimann, Marius P. Isken, Elmer Ruigrok et Bernard Dost. « Probabilistic Moment Tensor Inversion for Hydrocarbon-Induced Seismicity in the Groningen Gas Field, The Netherlands, Part 1 : Testing ». Bulletin of the Seismological Society of America 110, no 5 (11 août 2020) : 2095–111. http://dx.doi.org/10.1785/0120200099.
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ABSTRACT Since 1991, induced earthquakes have been observed and linked to gas production in the Groningen field. Recorded waveforms are complex, resulting partly from a Zechstein salt layer overlying the reservoir and partly from free-surface reverberations, internal multiples, interface conversions, guided waves, and waves diving below the reservoir. Therefore, picking of polarities or amplitudes for use in moment tensor inversion is problematic, whereas phase identification may be circumvented employing full waveform techniques. Although moment tensors have become a basic tool to analyze earthquake sources, their uncertainties are rarely reported. We introduce a method for probabilistic moment tensor estimation and demonstrate its use on the basis of a single event within the Groningen field, concentrating on detailed tests of input data and inversion parameters to derive rules of good practice for moment tensor estimation of events recorded in the Groningen field. In addition to the moment tensor, event locations are provided. Hypocenters estimated simultaneously with moment tensors are often less sensitive to uncertainties in crustal structure, which is pertinent for the application to the Groningen field, because the task of relating earthquakes to specific faults hitherto suffers from a limited resolution of earthquake locations. Because of the probabilistic approach, parameter trade-offs, uncertainties, and ambiguities are mapped. In addition, the implemented bootstrap method implicitly accounts for modeling errors affecting every station and phase differently. A local 1D velocity model extracted from a full 3D velocity model yields more consistent results than other models applied previously. For all velocity models and combinations of input data tested, a shift in location of 1 km to the south is observed for the test event compared to the public catalog. A full moment tensor computed employing the local 1D velocity model features negative isotropic components and may be interpreted as normal fault and collapse at reservoir level.
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Mameri, Lucan, Andréa Tommasi, Javier Signorelli et Riad Hassani. « Olivine-induced viscous anisotropy in fossil strike-slip mantle shear zones and associated strain localization in the crust ». Geophysical Journal International 224, no 1 (25 août 2020) : 608–25. http://dx.doi.org/10.1093/gji/ggaa400.
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SUMMARY We propose that strain localization in plate interiors, such as linear belts of intraplate seismicity, may arise from spatial variations in viscous anisotropy produced by preferred orientation of olivine crystals (CPO or texture) inherited from previous deformation episodes in the lithospheric mantle. To quantify this effect, we model the deformation of a plate containing a fossil strike-slip mantle shear zone at different orientations relative to an imposed horizontal shortening, but no initial heterogeneity in the crust. The fossil shear zone is characterized by different orientation and intensity of the olivine CPO relatively to the surrounding mantle, which is isotropic in most simulations. The anisotropy in viscosity produced by the CPO, which remains fixed throughout the simulations, is described by an anisotropic (Hill) yield function parametrized based on second-order viscoplastic self-consistent (SO-VPSC) models. The results indicate that lateral variations in viscous anisotropy in the mantle affect the strain distribution in the entire lithosphere. Reactivation of the strike-slip mantle shear zone and strain localization in the crust above it occur for horizontal compression at 35–55° to the fossil shear plane, with a maximum at 45°. The magnitude of strain localization depends on (i) the contrast in viscous anisotropy and, hence, on the variations in CPO orientation and intensity in the mantle, (ii) the boundary conditions and (iii) the feedbacks between mantle and crustal deformation. For a strong olivine CPO, when the boundary conditions do not hinder shear parallel to the fossil mantle shear zone, strain rates within it are up to a factor 30 higher than in an isotropic surrounding mantle or up to a factor 200 when the surrounding mantle is anisotropic, which results in strain rates up to a factor 10 or up to a factor 100 higher in the crust right above the fossil shear zone. Frictional weakening in the crust faults increases strain localization in the entire lithospheric column. High strength contrasts between the mantle and the ductile crust result in less efficient mechanical coupling, with strong localization in the mantle and lower crust, but weak in the brittle upper crust. Decrease in the crust–mantle strength contrast enhances the coupling and produces more homogenous strain distribution with depth, as well as a time-dependent evolution of strain localization, which reaches a peak and decreases before attaining steady-state. Comparison of seismic anisotropy, regional stress and focal mechanism data in linear arrays of intraplate seismicity, like the New Madrid and South Armorican seismic zones, to our models' predictions corroborates that olivine CPO preserved in fossil lithospheric-scale shear zones may be key for the development of such structures.
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Klinger, Adam G., et Maximilian J. Werner. « Stress drops of hydraulic fracturing induced microseismicity in the Horn River basin : challenges at high frequencies recorded by borehole geophones ». Geophysical Journal International 228, no 3 (15 novembre 2021) : 2018–37. http://dx.doi.org/10.1093/gji/ggab458.
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SUMMARY The ground motions caused by seismicity associated with fluid injection can pose a significant hazard. Borehole geophone arrays can provide access to tiny seismic events, which can extend the investigated magnitude range. However, the high frequency phase arrivals (i.e., >100 Hz) also present challenges associated with high frequency cut-offs (fmax), stronger attenuation and resonances within geophones. These effects limit our ability to accurately constrain attenuation models and high frequency source parameters. We investigate 112 −0.6 $\le \, M_{\rm w}\, \le$ 0.7 seismic events and calculate corner frequencies and stress drops from 90 of these events recorded during hydraulic fracturing treatment in the Horn River basin, British Columbia. High frequency resonances (>250 Hz) caused by spurious frequency excitation and/or coupling issues can significantly distort the shape of phase arrival spectra and affect source parameter estimates. Critically, resonances vary in strength between (nearly) colocated events, which may compromise the validity of a spectral ratio approach. For stations showing the cleanest spectra, the Brune model provides a decent fit to the displacement spectra. However, bandwidth limitations, low signal-to-noise ratios, high frequency cut-offs and significant attenuation still hinder our ability to retrieve high frequency source parameters. We find that a frequency independent Qp = 180 ± 40 provides a reasonable model for crustal attenuation but the large uncertainty caused by resonances prevents a robust constraint. From those events that show the best fits, we find a mean Madariaga corner frequency of 210 Hz ± 30 from P-phase arrivals, which is in the range of expected values if self-similarity extends into negative magnitudes. We also calculate a mean stress drop of 1.6 MPa ± 1.2, which is within the tectonic range but slightly lower than other deeper regional studies, which can be explained by lower effective stresses and/or a lower crustal shear strength. We find no evidence for a change in stress drop with depth or distance from the point of injection. A plausible explanation is that effective stresses are lowered relatively quickly over the entire fault zone via direct hydraulic connections. However, the large uncertainties make it difficult to interpret source parameter variability in detail. For high resolution monitoring and source properties of microseismicity, there is an urgent need for high quality high frequency recordings unaffected by spurious frequencies.
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Boroń, Paweł, Joanna Maria Dulińska et Dorota Jasińska. « Advanced Model of Spatiotemporal Mining-Induced Kinematic Excitation for Multiple-Support Bridges Based on the Regional Seismicity Characteristics ». Applied Sciences 12, no 14 (12 juillet 2022) : 7036. http://dx.doi.org/10.3390/app12147036.
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In the paper, an advanced model of spatiotemporal mining-induced kinematic excitation (SMIKE) for multiple-support bridges exposed to mining-induced seismicity is proposed. The uniqueness of this model results from the possibility of its application in any region of mining activity, as it is based on empirical regression functions characterizing such regions. In the model, the loss of coherency resulting from the scattering of waves in the heterogeneous ground, the wave-passage effect originating in different arrival times of waves to consecutive supports, and the site-response effect depending on the local soil conditions are taken into account. The loss of coherency of mining-induced seismic waves is obtained by applying a random field generator based on a spatial correlation function to produce time histories of accelerations on consecutive structure supports based on an originally recorded shock. The deterministic approach is used to account for temporal wave variability. The proposed SMIKE model is applied to assess the dynamic performance of a five-span bridge under a mining-induced shock recorded in the Upper Silesian Coal Basin (USCB), Poland. The first model’s parameter (space scale parameter) is identified on the basis of regression curves defined for the USCB region. The estimation of the second parameter (the mean apparent wave passage velocity) is based on discrete experimental data acquired via the vibroseis excitation registered in the in situ experiment. The impact of the model application on the dynamic performance of the bridge is assessed by comparing the dynamic response levels under SMIKE excitations, classic uniform excitations, and the “traveling wave” model—accounting only for the wave passage effect. The influence of wave velocity occurs to be crucial, modifying (either amplifying or reducing, depending on the location of the analyzed point) the dynamic response level up to a factor of two. The introduction of the space scale parameter changes the results by 20% in relation to the outcomes obtained for the “traveling” wave only.
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Xu, Song, Xiaoming Tang, Yuanda Su et Chunxi Zhuang. « Seismic shear wave anisotropy of an anisotropic rock containing aligned cracks : theory and applications to experiment and field data ». Geophysical Journal International 220, no 1 (12 octobre 2019) : 404–14. http://dx.doi.org/10.1093/gji/ggz456.
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SUMMARY Cracks universally exist in Earth's crustal rocks. Many rocks are intrinsically anisotropic, which, when coupled with crack-induced anisotropy, significantly affect seismic wave propagation through the rocks. Using the method of sphere equivalency of effective scattering, we have developed a technique to model the effective moduli of transversely isotropic (TI) media containing cracks. The modelling results show that the wave characteristics are significantly affected by the interaction of the two anisotropy mechanisms. To validate the validity and accuracy, the theory was applied to a recent experiment made with a vertical transverse isotropy (VTI) medium containing cracks and shows significantly better agreement with the data. For a more realistic situation, the new modelling was applied to interpret the borehole acoustic anisotropy measurement results from a fractured VTI formation, showing that the theory can adequately explain the anisotropic characteristics of the field data. With the validation and testing, the theoretical results advocated in this study can be used with confidence.
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Clemente-Chavez, A., A. Figueroa-Soto, F. R. Zúñiga, M. Arroyo, M. Montiel et O. Chavez. « Seismicity in northeast edge of the Mexican Volcanic Belt (MVB), activation of an undocumented fault : the Peñamiller earthquake sequence of 2011, Queretaro, Mexico ». Natural Hazards and Earth System Sciences Discussions 1, no 1 (21 février 2013) : 323–52. http://dx.doi.org/10.5194/nhessd-1-323-2013.
Texte intégralRésumé :
Abstract. The Peñamiller town, in the Queretaro state, Mexico is located at the northeast border of the seismogenic zone known as the Mexican Volcanic Belt (MVB), which covers a central fringe of Mexico with east-west orientation. In this town, a sequence of small earthquakes occurred during the end of 2010 and beginning of 2011. Seismicity frequent in of the continental regimen of central Mexico are not common, however, it is known that there are precedents of large earthquakes (Mw magnitude greater than 6.0) occurring in this zone. In order to enrich seismic information, which has not been analyzed nor documented until this moment, is presented this work. This will contribute to gain more insight into the tectonic situation of the central Mexico region. Twenty-four shallow earthquakes records of the Peñamiller, Queretaro seismic sequence of 2011 were recorded by a provisional accelerograph network from the Universidad Autonoma de Queretaro (UAQ). The data were analysed in order to determine the source locations and for the estimation of the source parameters. The study was carried out through an inversion process and by spectral analysis. The results show that the largest earthquake, occurred on 8 February 2011 at 19:53:48.6 UTC, had a moment magnitude Mw = 3.5, and was located at latitude 21.039° and longitude −99.752°, at a depth of 5.6 km. This zone is located less than 7 km away in south-east direction from downtown Peñamiller. The focal mechanisms are mostly normal faults with a small lateral component. This feature is consistent with the extensional regimen of the southern extension of the Basin and Range (BR) province. The source area of the largest event was estimated to have a radius of 0.5 km, which corresponds to a normal fault with azimuth of 174° and an almost pure dip slip; this caused Peak Ground Acceleration (PGA) of up to 100 cm s−2 in the horizontal direction. It is evident that the shallow earthquakes induced by crustal faulting can present a potential seismic risk and hazard within the MVB and considering the population growth, the necessity to enrich seismic information in this zone is very important; which at most urban sites in the region might even be greater than the risk posed by subduction earthquakes.
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Clemente-Chavez, A., A. Figueroa-Soto, F. R. Zúñiga, M. Arroyo, M. Montiel et O. Chavez. « Seismicity at the northeast edge of the Mexican Volcanic Belt (MVB) and activation of an undocumented fault : the Peñamiller earthquake sequence of 2010–2011, Querétaro, Mexico ». Natural Hazards and Earth System Sciences 13, no 10 (14 octobre 2013) : 2521–31. http://dx.doi.org/10.5194/nhess-13-2521-2013.
Texte intégralRésumé :
Abstract. The town of Peñamiller in the state of Querétaro, Mexico, is located at the northeast border of the seismogenic zone known as the Mexican Volcanic Belt (MVB), which transects the central part of Mexico with an east–west orientation. In the vicinity of this town, a sequence of small earthquakes occurred during the end of 2010 and beginning of 2011. Seismicity in the continental regimen of central Mexico is not too frequent; however, it is known that there are precedents of large earthquakes (Mw magnitude greater than 6.0) occurring in this zone. Three large earthquakes have occurred in the past 100 yr: the 19 November 1912 (MS = 7.0), the 3 January 1920 (MS = 6.4), and the 29 June 1935 (MS = 6.9) earthquakes. Prior to the instrumental period, the earthquake of 11 February 1875, which took place near the city of Guadalajara, caused widespread damage. The purpose of this article is to contribute to the available seismic information of this region. This will help advance our understanding of the tectonic situation of the central Mexico MVB region. Twenty-four shallow earthquakes of the Peñamiller seismic sequence of 2011 were recorded by a temporary accelerograph network installed by the Universidad Autónoma de Querétaro (UAQ). The data were analyzed in order to determine the source locations and to estimate the source parameters. The study was carried out through an inversion process and by spectral analysis. The results show that the largest earthquake occurred on 8 February 2011 at 19:53:48.6 UTC, had a moment magnitude Mw = 3.5, and was located at latitude 21.039° and longitude −99.752°, at a depth of 5.6 km. This location is less than 7 km away in a south-east direction from downtown Peñamiller. The focal mechanisms are mostly normal faults with small lateral components. These focal mechanisms are consistent with the extensional regimen of the southern extension of the Basin and Range (BR) province. The source area of the largest event was estimated to have a radius of 0.5 km, which corresponds to a normal fault with azimuth of 174° and an almost pure dip slip. Peak ground acceleration (PGA) was close to 100 cm s−2 in the horizontal direction. Shallow earthquakes induced by crustal faulting present a potential seismic risk and hazard within the MVB, considering the population growth. Thus, the necessity to enrich seismic information in this zone is very important since the risk at most urban sites in the region might even be greater than that posed by subduction earthquakes.
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Röth, Joschka, et Ralf Littke. « Down under and under Cover—The Tectonic and Thermal History of the Cooper and Central Eromanga Basins (Central Eastern Australia) ». Geosciences 12, no 3 (2 mars 2022) : 117. http://dx.doi.org/10.3390/geosciences12030117.
Texte intégralRésumé :
The Cooper subregion within the central Eromanga Basin is the Swiss army knife among Australia’s sedimentary basins. In addition to important oil and gas resources, it hosts abundant coal bed methane, important groundwater resources, features suitable conditions for enhanced geothermal systems, and is a potential site for carbon capture and storage. However, after seven decades of exploration, various uncertainties remain concerning its tectonic and thermal evolution. In this study, the public-domain 3D model of the Cooper and Eromanga stacked sedimentary basins was modified by integrating the latest structural and stratigraphic data, then used to perform numerical basin modelling and subsidence history analysis for a better comprehension of their complex geologic history. Calibrated 1D/3D numerical models provide the grounds for heat flow, temperature, thermal maturity, and sediment thickness maps. According to calibrated vitrinite reflectance profiles, a major hydrothermal/magmatic event at about 100 Ma with associated basal heat flow up to 150 mW/m2 caused source rock maturation and petroleum generation and probably overprinted most of the previous hydrothermal events in the study area. This event correlates with sedimentation rates up to 200 m/Ma and was apparently accompanied by extensive crustal shear. Structural style and depocentre migration analysis suggest that the Carboniferous–Triassic Cooper Basin initially has been a lazy-s shaped triplex pull-apart basin controlled by the Cooper Basin Master Fault before being inverted into a piggy-back basin and then blanketed by the Jurassic–Cretaceous Eromanga Basin. The interpreted Central Eromanga Shear Zone governed the tectonic evolution from the Triassic until today. It repeatedly induced NNW-SSE directed deformation along the western edge of the Thomson Orogen and is characterized by present-day seismicity and distinct neotectonic features. We hypothesize that throughout the basin evolution, alternating tectonic stress caused frequent thermal weakening of the crust and facilitated the establishment of the Cooper Hot Spot, which recently increased again its activity below the Nappamerri Trough.
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Varadan, Vijay K., Akhlesh Lakhtakia, Vasundara V. Varadan et Charles A. Langston. « Radiation characteristics of elastodynamic line sources buried in layered media with periodic interfaces. II. P- and SV-wave analysis ». Bulletin of the Seismological Society of America 77, no 6 (1 décembre 1987) : 2192–211. http://dx.doi.org/10.1785/bssa0770062192.
Texte intégralRésumé :
Abstract A method for determining for determining the elastodynamic (P and SV waves) radiation characteristics of finite-size sources buried in horizontally layered media, having periodically corrugated interfaces, is described. In particular, the example problem chosen to illustrate the procedure is as follows: a solid plate lies on top of a solid half-space; the solid-solid interface has been taken to be planar, but traction-free conditions prevail on the other boundary of the elastic plate, which surface is also periodically corrugated; and the source has been taken to be an isotropic, P-wave line source located inside the elastic plate. The technique presented utilizes the plane wave spectral decomposition of the relevant fields within the framework of the extended boundary condition method or the T matrix method. Since the T-matrix method is a matrix approach, it is very attractive computationally and is certainly more tractable than a method based on the direct solution of the integral equations involved in the scattering problem. Numerical results are given to delineate the various features of the field diffracted into the elastic half-space, as well as the displacement field induced on the traction-free boundary of the elastic plate. The specific example examined is directly related to regional wave propagation in a continental crustal wave guide.
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Muluneh, Ameha A., Derek Keir et Giacomo Corti. « Thermo-Rheological Properties of the Ethiopian Lithosphere and Evidence for Transient Fluid Induced Lower Crustal Seismicity Beneath the Ethiopian Rift ». Frontiers in Earth Science 9 (3 mai 2021). http://dx.doi.org/10.3389/feart.2021.610165.
Texte intégralRésumé :
Lower crustal earthquakes at plate boundaries and intraplate settings occur at depth where deformation is normally expected to occur in a ductile manner. Here we use the available earthquake catalogs and compute theoretical predictions for a range of conditions for the occurrence of lower crustal earthquakes beneath the Main Ethiopian Rift (MER) and adjacent north-western (NW) plateau. Yield strength envelops are constructed using information on geothermal gradient, strain rate, and composition constrained by geophysical observations. Our models suggest that away from the MER beneath the NW plateau the depth distribution of earthquakes in the lower crust is best explained by strong mafic lower crustal rheology and hydrostatic fluid pore pressure conditions. In the same region the effective elastic thickness is similar to seismogenic thickness showing that the lower crust has long-term strength and hence can physically support brittle deformation. On the contrary, in the central MER the seismogenic thickness is much larger than the effective elastic layer thickness implying that the lower crust has no long-term strength. Here our models show that both hydrostatic and near-lithostatic fluid pore pressures fail to explain the observed seismicity and instead a combination of near-lithostatic pore fluid pressure and transient high strain rate due to the movement of fluids provide a plausible mechanism for the occurrence of seismicity in the lower crust. Our interpretations are supported by occurrence of swarms of deep earthquakes beneath the MER, as opposed to more continuous background deep seismicity away from the rift. Using time-depth progression of earthquakes, we estimate permeability values of 5.9 × 10−15 m2 and 1.8 × 10−14 m2 at lower crustal depth. The range of permeability implies that seismicity can be induced by pore-pressure diffusion, likely from fluids sourced from the mantle that reactivate preexisting faults in the lower crust. Our thermo-rheological models explain the first order differences in lower crustal earthquakes both directly beneath and outboard of the rift valley.
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Zhao, Rong, Jing Xue et Kai Deng. « Modelling seismicity pattern of reservoir induced earthquakes including poroelastic stressing and nucleation effects ». Geophysical Journal International, 15 septembre 2022. http://dx.doi.org/10.1093/gji/ggac361.
Texte intégralRésumé :
Summary Abnormal seismic activities near reservoirs usually show a strong spatiotemporal correlation with the water filling history. Reservoir induced seismicity are thought to be related to crustal pore pressure and stress changes caused by water impounded behind the dams. Though the Coulomb-type stress analysis helps illuminate areas that would be under risk following reservoir impoundment, it lacks the ability to explain the temporal characteristics of reservoir induced seismicity. We present a numerical investigation of the seismicity rate evolution of reservoir induced earthquakes. Our modelling employs a fully coupled two-dimensional poroelastic model to calculate the pore pressure and stress changes caused by water impoundment and incorporates the rate-and-state dependent friction law to investigate the seismicity rate. We demonstrate that shallow earthquakes are mainly caused by pore pressure increase while poroelastic stress transfer takes the dominant role at depth. Whether a fault would be brought close to failure depends on its geometrical properties and its relative location to the reservoir. The temporal evolution of reservoir induced earthquakes are primarily controlled by tectonic environment instead of the diffusion of pore pressure.
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Maurer, Jeremy, Deborah Kane, Marleen Nyst et Jessica Velasquez. « Risk from Oklahoma’s Induced Earthquakes : The Cost of Declustering ». Bulletin of the Seismological Society of America, 7 avril 2020. http://dx.doi.org/10.1785/0120190268.
Texte intégralRésumé :
ABSTRACT The U.S. Geological Survey (USGS) has for each year 2016–2018 released a one-year seismic hazard map for the central and eastern United States (CEUS) to address the problem of induced and triggered seismicity (ITS) in the region. ITS in areas with historically low rates of earthquakes provides both challenges and opportunities to learn about crustal conditions, but few scientific studies have considered the financial risk implications of damage caused by ITS. We directly address this issue by modeling earthquake risk in the CEUS using the 1 yr hazard model from the USGS and the RiskLink software package developed by Risk Management Solutions, Inc. We explore the sensitivity of risk to declustering and b-value, and consider whether declustering methods developed for tectonic earthquakes are suitable for ITS. In particular, the Gardner and Knopoff (1974) declustering algorithm has been used in every USGS hazard forecast, including the recent 1 yr forecasts, but leads to the counterintuitive result that earthquake risk in Oklahoma is at its highest level in 2018, even though there were one-fifth as many earthquakes as occurred in 2016. Our analysis shows that this is a result of (1) the peculiar characteristics of the declustering algorithm with space-varying and time-varying seismicity rates, (2) the fact that the frequency–magnitude distribution of earthquakes in Oklahoma is not well described by a single b-value, and (3) at later times, seismicity is more spatially diffuse and seismicity rate increases are closer to more populated areas. ITS in Oklahoma may include a combination of swarm-like events with tectonic-style events, which have different frequency–magnitude and aftershock distributions. New algorithms for hazard estimation need to be developed to account for these unique characteristics of ITS.
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Luca D’Auria, Antonietta M. Esposito, Domenico Lo Bascio, Patrizia Ricciolino, Flora Giudicepietro, Marcello Martini, Teresa Caputo et al. « The recent seismicity of Mt. Vesuvius : inference on seismogenic processes ». Annals of Geophysics 56, no 4 (11 novembre 2013). http://dx.doi.org/10.4401/ag-6448.
Texte intégralRésumé :
<p>We have analyzed the recent seismicity of Mt. Vesuvius, with particular emphasis on the period 1999-2012. Since 1972 continuous observations with electromagnetic seismometers allowed the compilation of a detailed earthquake catalogue for the station OVO. Furthermore since 1999 another, more complete, catalogue for the station BKE, closer to the crater, is available. The Gutenberg-Richter distribution of magnitudes shows a temporal decrease of the b-value since 1985, with current values close to 1.0. The temporal pattern of the strain release shows a non-stationary behavior with periods of increased release rates (as in 1989-1990, 1995-1996 and 1999-2000). The spatial distribution of the seismicity consists in two main seismogenic volumes, one with hypocenters clustered below the Mt. Vesuvius crater at depths mostly between 1-6 km, and another with hypocenters clustered within the Gran Cono volcanic edifice, with depths above the sea level. We compare the statistical properties of the seismicity occurring within these two volumes and their spatial and temporal patterns. Moreover we analyze the statistical distribution of focal mechanisms for each volume. Our results point to gravity-induced stresses as the source of the shallow seismicity and of a combined effect of crustal heterogeneities, regional stress and hydrothermal dynamics for the deeper seismicity. Finally we discuss possible future developments of the seismic monitoring system in the light of the past and current seismicity.</p>
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Herath, Pasan, Januka Attanayake et Kalpna Gahalaut. « A reservoir induced earthquake swarm in the Central Highlands of Sri Lanka ». Scientific Reports 12, no 1 (29 octobre 2022). http://dx.doi.org/10.1038/s41598-022-22791-z.
Texte intégralRésumé :
AbstractAn anomalous seismic sequence of five small (MW < 3) felt earthquakes occurred between 29 August 2020 and 05 December 2020 around the Victoria Reservoir in the central highlands of Sri Lanka that clearly exceeded the established national background seismic rate. Using seismic waveform template-matching and a newly developed single-station earthquake location method based on travel-time back-projection, we detected an additional co-located 23 microseismic events, of which 18 occurred within the same period as the felt events. This hitherto undetected seismic swarm defines a seismogenic zone beneath the western flank of the reservoir between 1.5 and 3 km depths. The reservoir-induced peak stresses, resolved on E-W striking faults, predicted from the poroelastic theory that include both drained and undrained crustal responses are ~ 15 kPa in an area overlapping the seismogenic zone, which, together with the physical and spatio-temporal characteristics of the seismic swarm, establish a causal link between reservoir-induced stresses and the earthquake swarm with implications to seismic hazard. This is the first record of induced seismicity in Sri Lanka. The newly developed efficient computational workflows with minimal operational costs described in our study provide a blueprint for monitoring reservoir-induced seismicity in developing countries with severe resource limitations.
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Obermann, Anne, Sin-Mei Wu, Thorbjörg Ágústsdóttir, Alejandro Duran, Tobias Diehl, Pilar Sánchez-Pastor, Sigridur Kristjansdóttir, Vala Hjörleifsdóttir, Stefan Wiemer et Gylfi Páll Hersir. « Seismicity and 3-D body-wave velocity models across the Hengill geothermal area, SW Iceland ». Frontiers in Earth Science 10 (20 décembre 2022). http://dx.doi.org/10.3389/feart.2022.969836.
Texte intégralRésumé :
We image shallow crustal structures and analyze seismicity patterns in the Hengill high-enthalpy geothermal area in SW Iceland, exploiting a temporary densification of the seismic network 2018 to 2020. Using a subset of 6,300 high-quality manually picked P- and S-phases, we compute a minimum 1-D model for the region. Our results suggest that the most consistent and accurate hypocenter locations are derived from a joint inversion of P and S arrival times for the Hengill area. We demonstrate that this minimum 1-D model in combination with SeisComP detection and location algorithms can be used to produce fully-automated yet high-quality earthquake catalogs. Our analysis established that both the induced and natural seismicity in the Hengill area occurs in several distinct, spatially constrained clusters. In production and injection areas, the depth of the clusters is at about 2 km, near the bottom of the production and injection wells. These are most likely triggered by the injection and induced by the production, respectively. Outside of these clusters, the seismicity is generally deeper, with the depth of the deepest seismicity indicating the brittle-ductile transition zone. This zone is encountered at about 4 km near the center of the Hengill volcanic area and deepens with increasing distance from its volcanic center, to about 7 km in the southernmost region. A spatial analysis of b-values shows slightly increased values in areas with numerous injection wells and slightly decreased values in production areas. Three-dimensional crustal imaging of VP, VS, VP/VS shows a SE-NW trending fast velocity that extends, at 1–3 km depth between the extinct Grensdalur volcanic center and the presently active Hengill volcanic center. The fastest velocities are found in the NW corner of the Grensdalur volcanic center coinciding with a gravity high and probably reflecting dense solidified magmatic intrusion(s). This trend coincides with traces of geothermal surface manifestations, a shallow lying low resistivity anomaly and an aero-magnetic low. All these anomalies are caused by high temperature at some point in the geological history of the area and are most likely due to migration of the crustal accretion and volcanic activity between the two volcanic centers. Below-average VP/VS ratios at similar depth, coincide with the main production field. We suggest that this anomaly is caused by the extensive fluid extraction, which lowers the pore-pressure in the field and consequently increases the steam dominated zone, leading to lower Vp/Vs ratios. Most of the earthquakes are within the Vp/Vs low and at the boundary of the high and low Vp/Vs anomalies, which might indicate a region of good permeability.
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Arai, Ryuta. « Characteristics of seismicity in the southern Okinawa Trough and their relation to back-arc rifting processes ». Earth, Planets and Space 73, no 1 (10 août 2021). http://dx.doi.org/10.1186/s40623-021-01491-4.
Texte intégralRésumé :
AbstractThe southern part of the Okinawa Trough forms a narrow back-arc rift basin where evidence for submarine volcanoes and active hydrothermal venting is observed. The region is also known to cause large crustal earthquakes frequently which often accompany a rapid increase in seismicity rate. Although such swarm-like activities are common in active volcanic regions and are considered to be primarily induced by crustal fluid flows, potential interactions between tectonic, magmatic and hydrologic processes have been poorly examined in the southern Okinawa Trough despite these processes happening in the proximity. Here, I report the spatial and statistical characteristics of seismic activity in the southern Okinawa Trough and discuss their relation to other rifting-related phenomena. Most of the earthquakes with magnitude greater than 5 are localized around the rift axes (the Yaeyama Rift and the Yonaguni Rift) where seismic reflection data indicated the presence of solidified magmatic intrusions into the shallow sedimentary layers. I found the areas around the rift axes show low b values of < 0.8 and suggest that stress changes directly induced by dike intrusions beneath the rift axes control the occurrence of swarm activities. On the contrary, regions with high b values (> 1.2) are found around the Ishigaki Knoll and the Hatoma Knoll. These two areas are located between the rift axes and the Ryukyu Islands and correspond to potential submarine volcanoes proposed by seafloor bathymetry and seismic reflection images. This result may constrain the location of the volcanic front in the region.
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Plümper, Oliver, David Wallis, Floris Teuling, Evangelos Moulas, Stefan M. Schmalholz, Hamed Amiri et Thomas Müller. « High-magnitude stresses induced by mineral-hydration reactions ». Geology, 20 octobre 2022. http://dx.doi.org/10.1130/g50493.1.
Texte intégralRésumé :
Fluid-rock interactions play a critical role in Earth’s lithosphere and environmental subsurface systems. In the absence of chemical mass transport, mineral-hydration reactions would be accompanied by a solid-volume increase that may induce differential stresses and associated reaction-induced deformation processes, such as dilatant fracturing to increase fluid permeability. However, the magnitudes of stresses that manifest in natural systems remain poorly constrained. We used optical and electron microscopy to show that one of the simplest hydration reactions in nature [MgO + H2O = Mg(OH)2] can induce stresses of several hundred megapascals, with local stresses of as much as ~1.5 GPa. We demonstrate that these stresses not only cause fracturing but also induce plastic deformation with dislocation densities (1015 m–2) exceeding those typical of tectonically deformed rocks. If these reaction-induced stresses can be transmitted across larger length scales, they may influence the bulk stress state of reacting regions. Moreover, the structural damage induced may be the first step toward catastrophic rock failure, triggering crustal seismicity.
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Anyiam, Uzonna Okenna, Haijiang Zhang, Yuyang Tan, Jiawei Qian, Lei Gao, Ying Liu, Kezhen Zuo et Cuiping Zhao. « Enhanced 3D velocity structure, seismicity relocation and basement characterization of Changning shale gas and salt mining regions in southern Sichuan basin ». Frontiers in Earth Science 10 (19 janvier 2023). http://dx.doi.org/10.3389/feart.2022.1082122.
Texte intégralRésumé :
Current extensive seismicity in southern Sichuan Basin is ascribed to the reactivation of pre-existing faults, as a result of prolonged fluid injection for salt mining and shale gas development, respectively. However, the structural framework of the region remains poorly understood. Here, we apply Vp/Vs consistency-constrained double-difference seismic tomography to high quality phase data from 36,314 earthquakes jointly recorded by our local array and a regional seismic network to determine high-resolution velocity models. Earthquake relocations reveal shallow hypocenters for the Ms>5.0 earthquakes and two distinct seismogenic zones corresponding to the salt mine and shale gas regions, with most induced seismic events forming widespread lineaments some of which extend to the basement and are remarkably similar to the fault and fracture trends interpreted on reflection seismic and outcrops, respectively. Our 3-D crustal velocity analyses show that seismicity beneath the Changing salt mining area is associated with a combination of relatively low Vp/Vs (1.6–1.74) and high Vp/Vs (1.75–1.86) expressions, while most of small earthquakes within the Xingwen shale gas block are associated with relatively high Vp/Vs values (1.77–1.87), indicating the earthquakes in these two areas are caused by unique inducing mechanisms. The two moderately strong 2018 Xingwen Ms5.7 and 2019 Gongxian Ms5.3 earthquakes in the Xingwen shale gas block are located around low Vp/Vs. zones, suggesting they could be structurally controlled. In comparison, the 2019 Changning Ms6.0 earthquake in the Changning salt mining area is associated with high Vp/Vs. expression, suggesting its occurrence is related to fluid injections. In addition, top of the crystalline early Neoproterozoic (pre-Sinian) Sichuan basement is characterized by the 6.5 km/s Vp contour, which is new for earthquake tomographic studies in the region. Combined with outcrop analysis, we are able to construct a structural framework for induced seismicity in southern Sichuan basin, which unravels the structural architecture of induced seismicity.
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Olugboji, T., Manoochehr Shirzaei, Yingping Lu, A. A. Adepelumi et F. Kolawole. « On the Origin of Orphan Tremors and Intraplate Seismicity in Western Africa ». Frontiers in Earth Science 9 (20 septembre 2021). http://dx.doi.org/10.3389/feart.2021.716630.
Texte intégralRésumé :
On September 5–7, 2018, a series of tremors were reported in Nigeria’s capital city, Abuja. These events followed a growing list of tremors felt in the stable intraplate region, where earthquakes are not expected. Here, we review available seismological, geological, and geodetic data that may shed light on the origin of these tremors. First, we investigate the seismic records for parent location of the orphan tremors using a technique suitable when a single-seismic station is available such as the Western Africa region, which has a sparse seismic network. We find no evidence of the reported tremors within the seismic record of Western Africa. Next, we consider the possibility of a local amplification of earthquakes from regional tectonics, reactivation of local basement fractures by far-field tectonic stresses, post-rift crustal relaxation, landward continuation of oceanic fracture zones, or induced earthquakes triggered by groundwater extraction. Our assessments pose important implications for understanding Western Africa’s intraplate seismicity and its potential connection to tectonic inheritance, active regional tectonics, and anthropogenic stress perturbation.
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Barberio, Marino Domenico, Francesca Gori, Maurizio Barbieri, Andrea Billi, Antonio Caracausi, Gaetano De Luca, Stefania Franchini, Marco Petitta et Carlo Doglioni. « New observations in Central Italy of groundwater responses to the worldwide seismicity ». Scientific Reports 10, no 1 (20 octobre 2020). http://dx.doi.org/10.1038/s41598-020-74991-0.
Texte intégralRésumé :
Abstract Chemical and physical responses of groundwater to seismicity have been documented for thousands of years. Among the waves produced by earthquakes, Rayleigh waves can spread to great distances and produce hydrogeological perturbations in response to their passage. In this work, the groundwater level, which was continuously recorded in a monitoring well in Central Italy between July 2014 and December 2019, exhibited evident responses to dynamic crustal stress. In detail, 18 sharp variations of the groundwater level due to worldwide Mw ≥ 6.5 earthquakes were observed. Apart from earthquakes that occurred in Papua New Guinea and those with a hypocentral depth > 150 km, all far away Mw ≥ 7.6 earthquakes produced impulsive oscillations of groundwater. As the earthquake magnitude decreased, only some earthquakes with 6.5 ≤ Mw < 7.6 caused groundwater level perturbations, depending on the data acquisition frequency and epicentral distance from the monitoring well. A clear correlation between earthquake distance and magnitude in hydrogeological responses was found. Our results shed light on the hydrosensitivity of the study site and on the characteristics of fractured aquifer systems. Detecting the water table variations induced by distant earthquakes is another step towards a correct identification of (preseismic) hydrogeological changes due to near-field seismicity.
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De Landro, G., O. Amoroso, G. Russo, N. D’Agostino, R. Esposito, A. Emolo et A. Zollo. « Decade-long monitoring of seismic velocity changes at the Irpinia fault system (southern Italy) reveals pore pressure pulsations ». Scientific Reports 12, no 1 (24 janvier 2022). http://dx.doi.org/10.1038/s41598-022-05365-x.
Texte intégralRésumé :
AbstractSeveral studies have monitored crustal seismic velocity changes and attempted to relate them to the stress state and physical properties in volume embedding fault systems. The aim is to provide constraints on fault system dynamics and earthquake triggering mechanisms. Here, we reconstruct the spatiotemporal (4D) seismic velocity images of volume embedding the Irpinia fault system (IFS, South Italy), which originated the 1980 Ms 6.9 multi-segmented ruptures. By inverting data from more than ten years of continuous seismicity monitoring, we retrieved time-constant velocity anomalies, whose shapes correlate well with crustal lithology, while time-changing (up to 20%) velocity anomalies are mapped in the central region. Here, the Vp-to-Vs changes at depths of 1–5 km and 8–12 km correlate well with groundwater recharge and geodetic displacement during the same time interval. This correlation provides evidence for the existence of pulsating, pore pressure changes induced by groundwater recharge processes in a deep volume (8–12 km of depth), fractured and saturated with a predominant gas phase (likely CO2). We suggest that tomographic measurements of the Vp-to-Vs spatiotemporal changes are a suitable proxy to track the pore pressure evolution at depth in highly sensitive regions of fault systems.
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García-Hernández, Rubén, Luca D’Auria, José Barrancos, Germán D. Padilla et Nemesio M. Pérez. « Multiscale Temporal and Spatial Estimation of the b-Value ». Seismological Research Letters, 19 mai 2021. http://dx.doi.org/10.1785/0220200388.
Texte intégralRésumé :
Abstract The estimation of the b-value of the Gutenberg–Richter law is of great importance in different seismological applications. However, its estimate is strongly dependent upon selecting a proper temporal and spatial scale, due to the multiscale nature of the seismicity. For this reason, we propose a novel approach (MUltiscale Spatial and Temporal estimation of the B-value [MUST-B]), which allows consistent estimation of the b-value, avoiding subjective “a priori” choices, by considering simultaneously different temporal or spatial scales. A reliable appraisal of the b-value is obtained by applying a robust median over the estimates computed over all the considered scales. We validate the method using a synthetic dataset, showing its superior performances, compared to traditional approaches, in detecting sharp changes in the b-value as well as inconsistently mapping it for highly heterogeneous catalogs. We apply MUST-B to study the temporal and spatial variations of the b-value during the complex 2016–2017 seismic sequence in central Italy, revealing various interesting patterns. In particular, we observe a marked drop of the b-value after the Accumoli (24 August 2016 M 6.0) mainshock. The drop is also observed when realizing a tridimensional mapping of the b-values, showing the drop occurs mainly in the proximity of major earthquake hypocenters. In accordance with previous studies, we interpret these variations as the effect of the release of crustal fluids following the major earthquakes. We maintain that MUST-B can also be applied to other contexts, such as volcanic and induced seismicity, because of its capacity of dealing consistently with highly heterogeneous seismicity patterns.
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Wan, Bo, Xinshui Wang, Xijun Liu, Keda Cai, Wenjiao Xiao et Ross N. Mitchell. « Long-lived seamount subduction in ancient orogens : Evidence from the Paleozoic South Tianshan ». Geology, 21 décembre 2020. http://dx.doi.org/10.1130/g48547.1.
Texte intégralRésumé :
Along the present-day circum-Pacific subduction girdle, seamount subduction is known to have significant effects on subduction dynamics including on seismicity and arc magmatism. Because seamount subduction should have occurred throughout much of Earth history, its effects on orogenesis in the overriding plate should be identifiable in ancient orogens. In this study, we investigate the Paleozoic South Tianshan orogen of Central Asia, for which abundant evidence of seamount subduction exists, further bolstered by the continuation of a long-lived plume-induced large igneous province on the subsequently accreted Tarim craton. We find that semi-continuous seamount subduction from ca. 400 to 330 Ma temporarily shut down arc magmatism, and once the seamounts were completely subducted, then arc magmatism resumed and eclogites were quickly exhumed. If such an orogenic fingerprint of seamount subduction can be identified in ancient orogens, a much more complete picture of plume-subduction interaction and its influence on both crustal and mantle processes can be developed.
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Mukuhira, Yusuke, Masaoki Uno et Keisuke Yoshida. « Slab-derived fluid storage in the crust elucidated by earthquake swarm ». Communications Earth & ; Environment 3, no 1 (19 novembre 2022). http://dx.doi.org/10.1038/s43247-022-00610-7.
Texte intégralRésumé :
AbstractSlab-derived fluids control crustal dynamics in the subduction zone. However, the slab-derived fluid budget has never been quantified beyond a geophysical and geological spatiotemporal resolution. Here, we target an intense earthquake swarm associated with the M9 Tohoku earthquake, which represented the critical dynamic behavior of slab-derived fluid. The fluid volume involved has been quantified, with a plausible range of 106−108 m3, by utilizing injection-induced seismicity insights. Comparisons with geological proxies suggest that the estimated fluid volume can be accumulated via supply from the lower crust within 102–104 y. Our study demonstrated such amount of aqueous fluid stored at the midcrustal level, which triggered consecutive swarm activity for ~2 y with the Tohoku earthquake, suggesting a possible link between earthquake swarms to M9 class earthquakes (103 y cycle) and mineral veins and deposits. This study has shed light on the quantitative understanding of the dynamic slab-derived fluid budget.
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Aziz Zanjani, Farzaneh, et Guoqing Lin. « Double Seismic Zones along the Eastern Aleutian-Alaska Subduction Zone Revealed by a High-Precision Earthquake Relocation Catalog ». Seismological Research Letters, 5 juillet 2022. http://dx.doi.org/10.1785/0220210348.
Texte intégralRésumé :
Abstract The Eastern Aleutian-Alaska Subduction Zone (EAASZ) manifests significant along-strike variations in structure and geometry. The limited spatial resolution in intermediate-depth earthquake locations precludes investigation of small-scale variations in seismic characteristics. In this study, we use an existing 3D seismic velocity model and waveform cross-correlation data to relocate the earthquakes in 2016 near the EAASZ. Our improved absolute and relative earthquake locations reveal complex spatial characteristics of double seismic zones (DSZs). There are significant variations in location, depth, layer separation, and length of the DSZs along the EAASZ. We also observe nonuniform layer separations along the slope of the subducting slab that may imply either rheological or crustal thickness variations. In addition, our results suggest a triple seismic zone (TSZ) beneath Kenai. The interplay among different factors, including dehydration of metamorphic facies, intraslab stress, preexisting structures, and abrupt changes in slab geometry, may explain the observed variations in seismogenesis of the DSZs and TSZs. The comparison of our relocated seismicity with the thermal model for the slab beneath Cook Inlet shows that the intermediate-depth earthquakes occur between 500°C and 900°C isotherms. The 2016 Mw 7.1 Iniskin earthquake and its aftershocks are located at ∼800°C–900°C. The intricate small-scale variations in different characteristics of the DSZs and intermediate-depth seismicity and their correlations with major geometrical and physical controls can provide insight into what governs the seismogenesis of subduction-induced earthquakes.
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Ge, Jin, Xuhua Shi, Hanlin Chen, Xiubin Lin, Weipeng Ge, Xiaochun Wei, Feng Li et al. « Two kinematic transformations of the Pamir salient since the Mid-Cenozoic : Constraints from multi-timescale deformation analysis ». Frontiers in Earth Science 10 (1 septembre 2022). http://dx.doi.org/10.3389/feart.2022.967529.
Texte intégralRésumé :
The Pamir salient is a key part of the Himalayan–Tibetan Plateau orogenic system and has undergone intense tectonic deformation during the India–Asian collision. Delineating the Cenozoic kinematics and geodynamics of the Pamir salient requires a comprehensive understanding of the active arcuate structures along its frontal margin, from the perspective of the multi-spatiotemporal evolution of deformation patterns. Here, we reviewed the deformation rates of the major structures at different timescales, reanalyzed the published Global Positioning System velocities, and examined the present-day seismicity to constrain the kinematics of the Pamir salient since the Late Cenozoic. Integrated with the crustal evolution history during the Middle–Late Cenozoic and the deep structure, we proposed a new model to explain the multi-stage kinematics and associated geodynamics of the Pamir salient. During ∼37–24 Ma, the initial Pamir salient moved northward via radial thrusting that rotated the basins on both sides, which was driven by the continuous compression of the Indian slab after the breakoff of its oceanic part. During ∼23–12 Ma, the gravitational collapse of the Central and South Pamir crusts, which was induced by the breakoff of the continental part of the Indian slab, triggered the extension within the Pamir and foreland-ward movement of the upper crust. The upper crustal materials moved in varying directions due to the differential strength of the foreland areas, transforming the crustal kinematics from radial thrusting into a combination of radial thrusting and transfer faulting. Since the coupling of the Indian and Pamir slabs at ∼12–11 Ma, the deformation propagation towards the forelands accelerated, after which the kinematics of the Pamir salient exhibited asymmetric radial thrusting that has been sustained until the present. The asymmetric radial thrusting was likely driven by the compressive stress effect of the lithospheric basal shear generated by the underthrusting of the cratonic Indian lithosphere, which further led to the rollback of the Pamir slab and the consequent migratory extension in the South Pamir.
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Berbellini, Andrea, Lucia Zaccarelli, Licia Faenza, Alexander Garcia, Luigi Improta, Pasquale De Gori et Andrea Morelli. « Effect of Groundwater on Noise-Based Monitoring of Crustal Velocity Changes Near a Produced Water Injection Well in Val d'Agri (Italy) ». Frontiers in Earth Science 9 (1 avril 2021). http://dx.doi.org/10.3389/feart.2021.626720.
Texte intégralRésumé :
We study the crustal velocity changes occurred at the restart of produced water injection at a well in the Val d'Agri oil field in January–February 2015 using seismic noise cross-correlation analysis. We observe that the relative velocity variations fit well with the hydrometric level of the nearby Agri river, which may be interpreted as a proxy of the total water storage in the shallow aquifers of the Val d'Agri valley. We then remove from the relative velocity trend the contribution of hydrological variations and observe a decrease in relative velocity of ≈ 0.08% starting seven days after the injection restart. In order to investigate if this decreasing could be due to the water injection restart, we compute the medium diffusivity from its delay time and average station-well distance. We found diffusivity values in the range 1–5 m2/s, compatible with the observed delay time of the small-magnitude (ML ≤ 1.8) induced seismicity occurrences, triggered by the first injection tests in June 2006 and with the hydraulic properties of the hydrocarbon reservoir. Our results show that water storage variations can not be neglected in noise-based monitoring, and they can hide the smaller effects due to produced water injection.
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Lognonné, P., W. B. Banerdt, J. Clinton, R. F. Garcia, D. Giardini, B. Knapmeyer-Endrun, M. Panning et W. T. Pike. « Mars Seismology ». Annual Review of Earth and Planetary Sciences 51, no 1 (28 février 2023). http://dx.doi.org/10.1146/annurev-earth-031621-073318.
Texte intégralRésumé :
For the first time, from early 2019 to the end of 2022, Mars’ shallow and deep interiors have been explored by seismology with the InSight mission. Thanks to the performances of its seismometers and the quality of their robotic installation on the ground, 1,319 seismic events have been detected, including about 90 marsquakes at teleseismic distances, with Mw from 2.5 to 4.7 and at least 6 impacts, the largest ones with craters larger than 130 m. A large fraction of these marsquakes occur in Cerberus Fossae, demonstrating active regional tectonics. Records of pressure-induced seismic noise and signals from the penetration of a heat flow probe have provided subsurface models below the lander. Deeper direct and secondary body wave phase travel time, receiver function, and surface wave analysis have provided the first interior models of Mars, including crustal thickness and crustal layering, mantle structure, thermal lithospheric thickness, and core radius and state. ▪ With InSight's SEIS (Seismic Experiment for Interior Structure of Mars) experiment and for the first time in planetary exploration, Mars’ internal structure and seismicity are constrained. ▪ More than 1,300 seismic events and seismic noise records enable the first comparative seismology studies together with Earth and lunar seismic data. ▪ Inversion of seismic travel times and waveforms provided the first interior model of another terrestrial planet, down to the core. ▪ Several impacts were also seismically recorded with their craters imaged from orbit, providing the first data on impact dynamic on Mars. Expected final online publication date for the Annual Review of Earth and Planetary Sciences, Volume 51 is May 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
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Petrini, Claudio, Claudio Madonna et Taras Gerya. « Inversion in the permeability evolution of deforming Westerly granite near the brittle–ductile transition ». Scientific Reports 11, no 1 (décembre 2021). http://dx.doi.org/10.1038/s41598-021-03435-0.
Texte intégralRésumé :
AbstractFluid flow through crustal rocks is controlled by permeability. Underground fluid flow is crucial in many geotechnical endeavors, such as CO2 sequestration, geothermal energy, and oil and gas recovery. Pervasive fluid flow and pore fluid pressure control the strength of a rock and affect seismicity in tectonic and geotechnical settings. Despite its relevance, the evolution of permeability with changing temperature and during deformation remains elusive. In this study, the permeability of Westerly granite at an effective pressure of 100 MPa was measured under conditions near its brittle–ductile transition, between 650 °C and 850 °C, with a strain rate on the order of 2·10–6 s−1. To capture the evolution of permeability with increasing axial strain, the samples were continuously deformed in a Paterson gas-medium triaxial apparatus. The microstructures of the rock were studied after testing. The experiments reveal an inversion in the permeability evolution: an initial decrease in permeability due to compaction and then an increase in permeability shortly before and immediately after failure. The increase in permeability after failure, also present at high temperatures, is attributed to the creation of interconnected fluid pathways along the induced fractures. This systematic increase demonstrates the subordinate role that temperature dilatancy plays in permeability control compared to stress and its related deformation. These new experimental results thus demonstrate that permeability enhancement under brittle–ductile conditions unveils the potential for EGS exploitation in high-temperature rocks.
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King, Thomas, Luca De Siena, Philip Benson et Sergio Vinciguerra. « Mapping Faults in the Laboratory with Seismic Scattering 1 : The Laboratory Perspective ». Geophysical Journal International, 20 octobre 2022. http://dx.doi.org/10.1093/gji/ggac409.
Texte intégralRésumé :
Summary Seismic waves produced by stressed and deforming rocks lose coherence when they cross regions of high heterogeneity. The delay in the arrival of maximum seismic energy amplitude (peak delay), an essential attribute to model earthquake source characteristics, is increasingly used to map complex crustal geology, heterogeneous reservoirs, and fault networks. However, no laboratory calibration for the sensitivity of this parameter to fractures is currently available due to both experimental challenges and the difficulty in modelling wavefields in the near field. In this study, peak delays have been measured and mapped in space in the frequency range 50 kHz to 1 MHz using Acoustic Emission (AE) data recorded during a triaxial deformation experiment of Darley Dale Sandstone (DDS). Peak delays can increase dramatically throughout the experiment, but their behaviour depends on frequency and, especially, anomalous azimuth-dependent scattering. The frequency-dependence highlights dependence on strain. At low frequencies, peak delays are sensitive to surface waves generated at the sample boundaries, but they also mark the zones of shadow and intense/intermediate strains expected for an heterogeneous sample. At high frequencies, peak delays detect the zone of intense strain corresponding to the post-deformation shear zone. Temporal variations of peak delays show a frequency-dependent sensitivity to fracture nucleation, fault coalescence and sample failure. Scattering from these heterogeneities produces waves reverberating through seismic coda if the source-station path is close to an acoustic boundary, such as the fault zone or the sample boundaries. Our results confirm that peak delay has notable sensitivity to heterogeneity and can map and monitor structural- and deformation-induced changes in the near-field. The companion modelling paper tests this sensitivity and the corresponding imaging potential.