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1
Cooke, Michele L., Kevin Toeneboehn, and Jennifer L. Hatch. "Onset of slip partitioning under oblique convergence within scaled physical experiments." Geosphere 16, no. 3 (March 10, 2020): 875–89. http://dx.doi.org/10.1130/ges02179.1.
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Abstract Oblique convergent margins host slip-partitioned faults with simultaneously active strike-slip and reverse faults. Such systems defy energetic considerations that a single oblique-slip fault accommodates deformation more efficiently than multiple faults. To investigate the development of slip partitioning, we record deformation throughout scaled experiments of wet kaolin over a low-convergence (<30°), obliquely slipping basal dislocation. The presence of a precut vertical weakness in the wet kaolin impacts the morphology of faults but is not required for slip partitioning. The experiments reveal three styles of slip partitioning development delineated by the order of faulting and the extent of slip partitioning. Low-convergence angle experiments (5°) produce strike-slip faults prior to reverse faults. In moderate-convergence experiments (10°–25°), the reverse fault forms prior to the strike-slip fault. Strike-slip faults develop either along existing weaknesses (precut or previous reverse-slip faults) or through the coalescence of new echelon cracks. The third style of local slip partitioning along two simultaneously active dipping faults is transient while global slip partitioning persists. The development of two active fault surfaces arises from changes in off-fault strain pattern after development of the first fault. With early strike-slip faults, off-fault contraction accumulates to produce a new reverse fault. Systems with early lobate reverse faults accommodate limited strike-slip and produce extension in the hanging wall, thereby promoting strike-slip faulting. The observation of persistent slip partitioning under a wide range of experimental conditions demonstrates why such systems are frequently observed in oblique convergence crustal margins around the world.
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Utkin, V. P., A. N. Mitrokhin, P. L. Nevolin, and Y. P. Yushmanov. "Strike-slip fault tectogenesis in formation of the East Sikhote-Alin volcano-plutonic belt: Structural and dynamic analysis." LITHOSPHERE (Russia) 20, no. 4 (August 31, 2020): 528–41. http://dx.doi.org/10.24930/1681-9004-2020-20-4-528-541.
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Study object. The role of strike-slip fault tectogenesis in magmatism of the large (North Eastern Primorye) fragment of the Eastern Sikhote-Alin volcano-plutonic belt (ESAVPB) is studied. Materials and methods. The materials of geological mapping and field geostructural thematic-line research are used. Study methods are based on the concept of the geostructural patterns being formed by lateral, namely, strike-slip movements of crustal blocks. Results. There is recognized the system of the NE-trending sinistral faults, whose activation taken place during two stages. The pre-Late-Cretaceous fold-and-strike-slip-fault (orogenic) stage is characterized by the widely developed fold system within the stratified formations covering active strike-slip faults of the pre-Mesozoic consolidated basement. By the Late Cretaceous, the strike-slip faults cut the fold system into narrow blocks, creating the preconditions for the strike-slip faults’ activation during the next destructionand-strike-slip-fault (riftogenic) stage (Late Cretaceous – Cenozoic). During the latter, the strike-slip faults were activated under transtension (strike slip with extension) with formation of volcano-tectonic extension structures (VTES) nearcrosswise the strike-slip faults. The VTES played, on the one hand, the role of magma-feeding channels. On the other hand, the extension caused preconditions for formation of the depression subsidences that accumulated large volumes of the volcanics covering and «crosslinking» the VTES, resulting in wide development of volcanic covers within the ESAVPB. Conclusion. The VTES’ opening is thereby the effect of lateral (strike-slip) displacements of continental geoblocks that is not consistent with a priori ideas of the development of the East Sikhote-Alin volcano-plutonic belt under the oceanic plates’ subduction. The resulting materials complement the formulations according to which the East Asian volcanic belt formed under the structural-and-dynamic conditions being caused by the evolution of the East Asian global strike-slip fault zone resulting from displacement of the Asian continent to the south-west under the Earth’s rotational geodynamics.
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Chen, Peng, Bing Yan, and Yuan Liu. "Active Strike-Slip Faulting and Systematic Deflection of Drainage Systems along the Altyn Tagh Fault, Northern Tibetan Plateau." Remote Sensing 13, no. 16 (August 6, 2021): 3109. http://dx.doi.org/10.3390/rs13163109.
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Systematic deflection of drainage systems along strike-slip faults is the combination of repeated faulting slipping and continuous headward erosion accumulated on the stream channels. The measurement and analysis of systematically deflected stream channels will enhance our understanding on the deformational behaviors of strike-slip faults and the relationship between topographic response and active strike-slip faulting. In this study, detailed interpretation and analysis of remote sensing images and DEM data were carried out along the Altyn Tagh Fault, one typical large-scale strike-slip fault in the northern Tibetan Plateau, and together with the statistical results of offset amounts of 153 stream channels, revealed that (i) the drainage systems have been systematically deflected and/or offset in sinistral along the active Altyn Tagh Fault; (ii) The offset amounts recorded by stream channels vary in the range of 7 m to 72 km, and indicate a positively related linear relationship between the upstream length L and the offset amount D, the channel with bedrock upstream generally has a better correlation between L and D than that of non-bedrock upstream; (iii) River capture and abandonment are commonly developed along the Altyn Tagh Fault, which probably disturbed the continuous accumulation of offset recorded on individual stream channel, suggesting that the real maximum cumulative displacement recorded by stream channels might be larger than 72 km (lower bound) along the Altyn Tagh Fault. Along with the cumulative displacements recorded by other regional-scale strike-slip faults in the Tibetan Plateau, these results demonstrate that the magnitude of tectonic extrusion along these first-order strike-slip faults after the collision of India–Asia plates might be limited.
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BARTOV, YUVAL, and AMIR SAGY. "Late Pleistocene extension and strike-slip in the Dead Sea Basin." Geological Magazine 141, no. 5 (September 2004): 565–72. http://dx.doi.org/10.1017/s001675680400963x.
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A newly discovered active small-scale pull-apart (Mor structure), located in the western part of the Dead Sea Basin, shows recent basin-parallel extension and strike-slip faulting, and offers a rare view of pull-apart internal structure. The Mor structure is bounded by N–S-trending strike-slip faults, and cross-cut by low-angle, E–W-trending normal faults. The geometry of this pull-apart suggests that displacement between the two stepped N–S strike-slip faults of the Mor structure is transferred by the extension associated with the normal faults. The continuing deformation in this structure is evident by the observation of at least three deformation episodes between 50 ka and present. The calculated sinistral slip-rate is 3.5 mm/yr over the last 30 000 years. This slip rate indicates that the Mor structure overlies the currently most active strike-slip fault within the western border of the Dead Sea pull-apart. The Mor structure is an example of a small pull-apart basin developed within a larger pull-apart. This type of hierarchy in pull-apart structures is an indication for their ongoing evolution.
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Thanh, Bui Nhi, Nguyen Van Luong, Duong Quoc Hung, Nguyen Van Diep, and Mai Duc Dong. "Recent geodynamic characteristics of the Southern Central coast and the relations with geological hazards." Tạp chí Khoa học và Công nghệ biển 19, no. 3B (October 21, 2019): 125–36. http://dx.doi.org/10.15625/1859-3097/19/3b/14520.
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Recent geodynamic characteristics of the Southern Central coast are analyzed on the basis of vertical and horizontal displacement velocities along active fault zones. The horizontal displacement velocity varies in magnitude from this fault system to another fault system, from 0.11–0.3 mm/year on the strike-slip - normal faults to 0–0.058 mm/year on the strike-slip faults and normal faults. The subsidence velocity changes complicatedly, different from one fault to another fault, depending on the mechanism of faults. On the continental shelf, most of the values of high subsidence’s velocity are related to the normal and strike-slip faults. Subsidence activities make the sea level increase highly, the subsidence activity makes the sea level rise at structures that fall close to the shore, reach about 0.2–0.48 mm/year in late Pleistocene - Holocene. The increase of sea level directly affects the intensity of erosion, flood, salinity and land loss events in coastal lowlands. Slippage of the seabed, earthquakes, volcanoes are geological hazards directly related to the geodynamic regime of the Southern Central coast.
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Rondoyanni, Th, Ch Georgiou, D. Galanakis, and M. Kourouzidis. "EVIDENCES OF ACTIVE FAULTING IN THRACE REGION (NORTHEASTERN GREECE)." Bulletin of the Geological Society of Greece 36, no. 4 (January 1, 2004): 1671. http://dx.doi.org/10.12681/bgsg.16572.
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Active oblique to strike-slip faults were identified in southern Thrace (northeastern Greece), on the basis of field observations, geological mapping, analysis of geometrical and dynamic characteristics of recent tectonic structures as well as evaluation of their seismic potential. The seismic activity refers mainly to strong earthquakes occurring under the sea, while a minor number of seismic epicenters have been registered on land. According to the historic and recent data, most seismic destructions in this region are due to the influence of the North Anatolian Fault and North Aegean Trough system. The diachronic activity of several faults and the changes in the movement type from clearly normal to oblique-normal or strike-slip, have left clear signs on the existing polished fault planes. Among the numerous faults determined in Thrace, some of them can be characterized as active, according to their geological and morphotectonic characteristics. Taking in to account the faults length, the specific seismotectonic conditions prevailing over the Hellenic territory and the existed empirical relationships, the maximum displacement in case of seismic reactivation was estimated.
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Pu, RenHai, KunBai Li, Machao Dong, ZiCheng Cao, and Pengye Xu. "The 3D seismic characteristics and significance of the strike-slip faults in the Tazhong area (Tarim Basin, China)." Interpretation 7, no. 1 (February 1, 2019): T1—T19. http://dx.doi.org/10.1190/int-2016-0135.1.
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The eastern part of Tazhong area in the Tarim Basin consists of three sets of vertical strike-slip faults oriented in north–northeast (36°azimuth), east–northeast (68° azimuth), and west–northwest (126°azimuth) directions that cut the strata from Cambrian to Carboniferous. The fault belts indicate significant horizon upwarp and downwarp deformations and variations in their stratigraphic thickness on seismic profiles. Through detailed interpretation of the 3D seismic data, we consider that these phenomena reflect the different stress properties and active stages of the faults. The horizon upwarp and downwarp within the fault belts correlated respectively to the decrease and increase in stratigraphic thickness within the fault belts in comparison to the coeval counterpart of the bilateral fault blocks. For the same fault, different stratigraphic intervals express different types of horizon deformation and thickness changes. The horizon downwarp and the contemporaneous stratigraphic thickening inside the fault belts suggest the transtensional actions of the fault. The horizon upwarp and the contemporaneous thinning within the fault belts suggest transpressional actions of the fault. Based on this, we inferred the active periods of the three sets of strike-slip faults. The north–northeast-striking faults were formed in the late Ordovician Sangtamu Formation. This set of faults experienced four stages, i.e., sinistral transpression, sinistral transtension, static, and transtension. The east–northeast and west–northwest-striking faults initiated in the mid-Cambrian period as coupled transtension. Activity ceased in the west–northwest faults after the mid-Cambrian and in the east–northeast faults during the late Ordovician. The three sets of strike-slip faults all affect the formation of the hydrothermal dissolution reservoirs that are distributed in the Ordovician carbonate rocks.
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Sakellariou, D., H. Sigurdsson, M. Alexandri, S. Carey, G. Rousakis, P. Nomikou, P. Georgiou, and D. Ballas. "ACTIVE TECTONICS IN THE HELLENIC VOLCANIC ARC: THE KOLUMBO SUBMARINE VOLCANIC ZONE." Bulletin of the Geological Society of Greece 43, no. 2 (January 23, 2017): 1056. http://dx.doi.org/10.12681/bgsg.11270.
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This paper studies the rupture system of the Anydhros Basin, northeast of Thera island, and its relationship to the submarine volcanic activity along the Kolumbo line. Anydhros Basin is a N45o E trending elongate basin bounded by the Ios-Fault-Zone (IFZ) towards NW and by the AnydhrosFault-Zone (AFZ) towards SE. The AFZ continues southwestwards, crosscutting Thera Island. Swath bathymetry and seismic profiling data indicate that the Anydhros basin sedimentary infill is fractured by vertical, predominantly strike-slip faults, parallel to which the volcanic cones are aligned. We propose that the “KameniKolumbo Line” is an active, 40km-long, strike-slip fault zone. The KameniKolumbo strike slip runs through the volcanoes of Nea Kameni and Kolumbo and controls the spatial distribution of the volcanic cones along the axis of Anyhdros basin.
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Allanic, Cécile, and Charles Gumiaux. "Are there any active faults within the Lepontine dome (central Alps)?" Bulletin de la Société Géologique de France 184, no. 4-5 (July 1, 2013): 427–40. http://dx.doi.org/10.2113/gssgfbull.184.4-5.427.
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Abstract In metamorphic chain areas characterized by low seismicity, the evidence of neotectonic activity is generally very poor. However, direct evidences of seismogenic faults are reported hereafter in the Lepontine dome (Central Alps) considered in the literature as tectonically quiescent. Identification of aligned cluster of microseismic events guided morphotectonic researches. The latter revealed clear clues of recent faulting, i.e. marked scarps, perturbation of the drainage system or shift of terminal moraines. Thus, thanks to combination of seismological, geological and morphological data, we accurately locate four seismogenic faults and determine precisely their kinematic from fault-stria data and focal mechanisms. Three roughly NW-SE seismogenic dextral-normal faults were evidenced: the first close to the Simplon fault zone, the second in the middle northern part of the dome and the third one to the north of Bellinzona. They are part of a regional Riedel-shear zone system linked to the Insubric line. Dextral strike-slip component increases when strike of fault planes approaches the E-W orientation (corresponding to pure strike-slip) and respectively normal component increases when strike of fault planes is close to NW-SE. The second system highlighted corresponds to WSW-ENE normal faults mainly distributed on the whole northern flank of the dome along a zone of 10 km wide. They are roughly parallel to the Rhône and Bedretto valleys and exploit pre-existing basement fabric. These data coherent at all scales provide new constraints on the current stress regime going on in the Lepontine Dome and could have implications for future seismic hazard studies in the broader area.
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Hussain, Hamid, and Zhang Shuangxi. "Structural Evolution of the Kohat Fold and Thrust Belt in the Shakardarra Area (South Eastern Kohat, Pakistan)." Geosciences 8, no. 9 (August 21, 2018): 311. http://dx.doi.org/10.3390/geosciences8090311.
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The Kohat fold and thrust belt, located in North-Western Pakistan, is a part of Lesser Himalaya developed due to the collision between the Indian and Eurasian plates. The structural evolution records of this area indicate that it consists of tight anticlines and broad syncline structures. Previous studies show that the structural pattern of this area has been produced due to multiple episodes of deformation. In the present research, 2D seismic data has been integrated with our field surveys to clarify the role of active strike-slip faulting in reshaping the surface structures of Shakardarra, Kohat. At the surface, doubly plunging anticlines and synclines are evolved on evaporites as detachment folds, truncated by thrust faults along their limbs. Seismic data show that the thrust faults originate from basal detachment located at the sedimentary-crystalline interface and either cut up section to the surface or lose their displacement to splay or back thrusts. At the surface, the Shakardarra Fault, the Tola Bangi Khel Fault, the Chorlaki Fault, and the axial trend of fold change their strike from EW to NS showing that the thrust and axial trend of folds are rotated along the vertical axis by the influence of the Kalabagh strike-slip fault. Strike-slip motion dominates the style of deformation at the northern segment. The current deformation is concentrated on the splay faults in the northern segment of the Kalabagh Fault. We propose that Shakardarra is sequentially evolved in three episodes of deformation. In the first phase, the detachment folds developed on Eocene evaporites, which are truncated by thrust faults originated from the basal detachment in the second phase. In the third phase, early formed folds and faults are rotated along the vertical axis by the influence of Kalabagh strike-slip fault.
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Struik, Lambertus C. "Intersecting intracontinental Tertiary transform fault systems in the North American Cordillera." Canadian Journal of Earth Sciences 30, no. 6 (June 1, 1993): 1262–74. http://dx.doi.org/10.1139/e93-108.
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In central British Columbia, north-trending dextral strike-slip faults that cut Late Eocene granite also truncate northwest-trending dextral strike-slip faults. The northwest-trending strike-slip faults bound the Wolverine Metamorphic Complex (Wolverine Complex), which has been uplifted primarily by northwest–southeast Eocene crustal extension and somewhat by Late Eocene northerly extension. The crustal extension is indicated by shallow-dipping extensions faults, dyke complexes, and stretching lineations. The Wolverine Complex and its bounding faults define a crustal pull-apart in an en echelon dextral transform. The northwest- and north-trending dextral strike-slip faults in central British Columbia are the continuations of faults that transect the interior of the North American Cordillera, and they represent at least two distinct plate boundaries intermittently active during the Early to Middle Eocene, and the Late Eocene to Early Oligocene. Each of these systems consists of en echelon strike-slip faults linked by extensional pull-aparts, locally represented by metamorphic core complexes. These two plate-boundary systems represent two distinct plate-motion configurations between the North American and Kula–Pacific plates. The older plate boundary is truncated and disrupted by the younger one. These two systems may in turn be disrupted by a younger and different plate-motion configuration represented by the transverse Basin and Range extension complex and its northern and southern transform boundary faults.
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Handayani, Lina. "Active Fault Zones of The 2006 Yogyakarta Earthquake Inferred from Tilt Derivative Analysis of Gravity Anomalies." RISET Geologi dan Pertambangan 29, no. 1 (June 27, 2019): 1. http://dx.doi.org/10.14203/risetgeotam2019.v29.1018.
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The 2006 Yogyakarta Earthquake had caused a disaster in Bantul area. Several institutions had reported different results for the epicenter location. However, aftershocks studies indicated that the rupture area was at about 10 km east of Opak Fault. Analysis of gravity anomaly, including several degrees of residual anomalies and tilt derivative, facilitated this regional tectonic study to determine the structural constraints on the main earthquake and its aftershocks. The Yogyakarta area was primarily characterized by several SW-NE faults; one of them is the Opak Fault. Among those faults,, there are a series of WNW-ESE faults. Several groups of these lineations indicated a presence of some pairs of parallel strike-slips faults that formed pull-a-part basins. The obtained structural pattern has signified the dynamic response of the force from the subduction of the Australian Plate toward Sunda (Eurasia) Plate. The subduction force produced the strike-slip fault in a parallel direction of subduction, and subsequently, the faults caused the formation of thrust structures that are perpendicular to them.Gempabumi Yogyakarta pada tahun 2006 telah menyebabkan bencana di daerah Bantul dan sekitarnya. Lokasi episenter yang ditentukan oleh beberapa lembaga menunjukkan hasil yang berbeda. Tetapi analisa gempabumi susulan telah menunjukkan daerah pegerakan hingga 10 km ke sebelah timur dari Sesar Opak. Analisa anomali gayaberat yang terdiri dari perhitungan anomali sisa dan turunan kemiringan (tilt derivative) diharapkan dapat membantu studi tektonik regional dalam menentukan batasan struktur yang menyebabkan kejadian gempabumi di daerah Yogyakarta. Daerah ini dicirikan oleh sesar-sesar berarah BD (Barat daya)-TL (Timur laut), yang salah satunya adalah Sesar Opak. Di antara sesar-sesar tersebut, terdapat pula deretan sesar-sesar berarah BBL (Barat barat laut)-TTG (Timur tenggara). Beberapa kelompok kelurusan-kelurusan membentuk kemungkinan adanya cekungan pull-a-part, yang terbentuk karena adanya deretan sesar-sesar strike-slip. Pola struktur yang diperoleh menunjukkan respon dinamik dari subduksi Lempeng Australia terhadap Lempeng Eurasia (Sunda). Tekanan dari gaya subduksi menyebabkan terbentuknya sesar-sesar strike-slip. Kemudian sesar-sesar tersebut menyebabkan adanya struktur sesar naik yang tegak lurus terhadapnya.
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Zuza, Andrew V., An Yin, Jessica Lin, and Ming Sun. "Spacing and strength of active continental strike-slip faults." Earth and Planetary Science Letters 457 (January 2017): 49–62. http://dx.doi.org/10.1016/j.epsl.2016.09.041.
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YANG, KENN-MING, RUEY-JUIN RAU, HAO-YUN CHANG, CHING-YUN HSIEH, HSIN-HSIU TING, SHIUH-TSANN HUANG, JONG-CHANG WU, and YI-JIN TANG. "The role of basement-involved normal faults in the recent tectonics of western Taiwan." Geological Magazine 153, no. 5-6 (August 5, 2016): 1166–91. http://dx.doi.org/10.1017/s0016756816000637.
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AbstractIn the foreland area of western Taiwan, some of the pre-orogenic basement-involved normal faults were reactivated during the subsequent compressional tectonics. The main purpose of this paper is to investigate the role played by the pre-existing normal faults in the recent tectonics of western Taiwan. In NW Taiwan, reactivated normal faults with a strike-slip component have developed by linkage of reactivated single pre-existing normal faults in the foreland basin and acted as transverse structures for low-angle thrusts in the outer fold-and-thrust belt. In the later stage of their development, the transverse structures were thrusted and appear underneath the low-angle thrusts or became tear faults in the inner fold-and-thrust belt. In SW Taiwan, where the foreland basin is lacking normal fault reactivation, the pre-existing normal faults passively acted as ramp for the low-angle thrusts in the inner fold-and-thrust belt. Some of the active faults in western Taiwan may also be related to reactivated normal faults with right-lateral slip component. Some main earthquake shocks related to either strike-slip or thrust fault plane solution occurred on reactivated normal faults, implying a relationship between the pre-existing normal fault and the triggering of the recent major earthquakes. Along-strike contrast in structural style of normal fault reactivation gives rise to different characteristics of the deformation front for different parts of the foreland area in western Taiwan. Variations in the degree of normal fault reactivation also provide some insights into the way the crust embedding the pre-existing normal faults deformed in response to orogenic contraction.
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Pérez-López, Raúl, José F. Mediato, Miguel A. Rodríguez-Pascua, Jorge L. Giner-Robles, Adrià Ramos, Silvia Martín-Velázquez, Roberto Martínez-Orío, and Paula Fernández-Canteli. "An active tectonic field for CO<sub>2</sub> storage management: the Hontomín onshore case study (Spain)." Solid Earth 11, no. 2 (April 30, 2020): 719–39. http://dx.doi.org/10.5194/se-11-719-2020.
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Abstract. One of the concerns of underground CO2 onshore storage is the triggering of induced seismicity and fault reactivation by the pore pressure increasing. Hence, a comprehensive analysis of the tectonic parameters involved in the storage rock formation is mandatory for safety management operations. Unquestionably, active faults and seal faults depicting the storage bulk are relevant parameters to be considered. However, there is a lack of analysis of the active tectonic strain field affecting these faults during the CO2 storage monitoring. The advantage of reconstructing the tectonic field is the possibility to determine the strain trajectories and describing the fault patterns affecting the reservoir rock. In this work, we adapt a methodology of systematic geostructural analysis to underground CO2 storage, based on the calculation of the strain field from kinematics indicators on the fault planes (ey and ex for the maximum and minimum horizontal shortening, respectively). This methodology is based on a statistical analysis of individual strain tensor solutions obtained from fresh outcrops from the Triassic to the Miocene. Consequently, we have collected 447 fault data in 32 field stations located within a 20 km radius. The understanding of the fault sets' role for underground fluid circulation can also be established, helping further analysis of CO2 leakage and seepage. We have applied this methodology to Hontomín onshore CO2 storage facilities (central Spain). The geology of the area and the number of high-quality outcrops made this site a good candidate for studying the strain field from kinematics fault analysis. The results indicate a strike-slip tectonic regime with maximum horizontal shortening with a 160 and 50∘ E trend for the local regime, which activates NE–SW strike-slip faults. A regional extensional tectonic field was also recognized with a N–S trend, which activates N–S extensional faults, and NNE–SSW and NNW–SSE strike-slip faults, measured in the Cretaceous limestone on top of the Hontomín facilities. Monitoring these faults within the reservoir is suggested in addition to the possibility of obtaining a focal mechanism solutions for micro-earthquakes (M<3).
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Mountrakis, D., A. Kilias, A. Pavlaki, C. Fassoulas, E. Thomaidou, C. Papazachos, C. Papaioannou, Z. Roumelioti, C. Benetatos, and D. Vamvakaris. "Neotectonic analysis, active stress field and active faults seismic hazard assessment in Western Crete." Bulletin of the Geological Society of Greece 47, no. 2 (January 24, 2017): 582. http://dx.doi.org/10.12681/bgsg.11085.
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Within the framework of this study the complicated fault system of Western Crete was napped in detail and its kinematic and dynamic setting was analysed in order to distinguish 13 major active and possible active fault zones, the seismic potential of which was assessed. Moreover, kinematic data and striations were used to estimate the corresponding stress field geometry. Two stress phases were recognized: 1st the N-S extension phase (D1) in Mid-Upper Miocene to Lower Pliocene times forming E-W normal faults that bound the Neogene basins; 2nd the E-W extension phase (D2) in Late Pliocene-recent times forming N-S trending active normal faults. Smaller, mainly NE-SW trending faults, with significant strike-slip component, indicate a kinematic compatibility to the D2 phase, acting as transfer faults between larger N-S fault zones. The faults were incorporated in a detailed seismic hazard analysis together with the available seismological data, involving both probabilistic and deterministic approaches, for seismic hazard assessment of several selected sites (municipalities).
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Krapez, B., and M. E. Barley. "Archaean strike-slip faulting and related ensialic basins: evidence from the Pilbara Block, Australia." Geological Magazine 124, no. 6 (November 1987): 555–67. http://dx.doi.org/10.1017/s0016756800017386.
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AbstractArchaean sedimentary and volcanic successions in the Lalla Rookh Basin andc. 2950 Ma old Whim Creek Belt in the Pilbara Block, Western Australia, were deposited in basins with roughly the same configuration as their present outcrop. Basins were fault-bounded and developed in an ensialic setting, overlying older (3500 to 3300 Ma old); deformed and metamorphosed supracrustal rocks and granitoids. The basin margin faults are now part of a pattern of strike–slip faults which were active during the later stages of regional batholith emplacement. In both cases, structural patterns and style of basin filling are similar to younger basins related to strike–slip faulting. The Lalla Rookh Basin was dominated by coarse clastic sedimentation, comprising alluvial–fan, braided–stream, fan–delta and lacustrine facies. The Whim Creek Belt contains bimodal volcanics and clastic sediments, which comprise alluvial, subaqueous fanglomerate, submarine-fan and basinal facies. Regional strike–slip faulting and the development of the Lalla Rookh Basin and Whim Creek Belt, in response to externally imposed deformation, records an important step in the cratonization of the Pilbara Block. Late Archaean sedimentary basins, dominated by coarse clastic facies and situated adjacent to major strike–slip faults, in other cratons may have a similar origin.
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Andreani, Louis, Claude Rangin, Juventino Martínez-Reyes, Charlotte Le Roy, Mario Aranda-García, Xavier Le Pichon, and Rolando Peterson-Rodriguez. "The Neogene Veracruz fault: evidences for left-lateral slip along the southern Mexico block." Bulletin de la Société Géologique de France 179, no. 2 (March 15, 2008): 195–208. http://dx.doi.org/10.2113/gssgfbull.179.2.195.
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Abstract Structural data combined with analysis of satellite images and seismic profiles show that a major left-lateral strike-slip fault affects the Veracruz basin and post-5 Ma volcanic rocks of the Los Tuxtlas volcanic field (LTVF). The main volcanic alignment of the LTVF is located along this fault. Additional structural data collected in the Trans-Mexican volcanic belt (areas of Xalapa, Teziutlán and Huauchinango) show that the shear zone affects Pliocene Trans-Mexican volcanic rocks. Low seismicity associated to faulted Quaternary markers such as alluvial fans, alluvial terraces and volcanoes argue for active faulting in this area. Plio-Quaternary strike-slip faulting in the Veracruz basin and in the eastern Trans-Mexican volcanic belt is important because it connects two important structural provinces: the left-lateral strike-slip faults province to the south and the left-lateral transtensive faulting that affects the central part of the Trans-Mexican volcanic belt. These three active deformation zones constitute the boundary between the southern Mexico block and the North American plate. It is generally assumed that strike-slip faulting along the Trans-Mexican and Central America volcanic arcs is the result of oblique subduction of the Cocos plate under the North American and Caribbean plates. However slip vectors along the Middle America trench are almost perpendicular to the trench. This Neogene sinistral strike-slip motion could be partially driven by the eastward motion of the Caribbean plate rather than by strain partitioning along the oblique Middle America trench subduction zone.
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Karakostas, V. G., E. E. Papadimitriou, M. D. Tranos, and C. B. Papazachos. "ACTIVE SEISMOTECTONIC STRUCTURES IN THE AREA OF CHIOS ISLAND, NORTH AEGEAN SEA, REVEALED FROM MICROSEISMICITY AND FAULT PLANE SOLUTIONS." Bulletin of the Geological Society of Greece 43, no. 4 (January 25, 2017): 2064. http://dx.doi.org/10.12681/bgsg.11396.
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Data from a digital seismological network operating during April–July 2002 were used for the microseismicity study of the area around Chios Island (East Aegean Sea, Greece). Numerous microearthquakes were detected and more than 950 well–located hypocenters were obtained along with 96 reliably determined focal mechanisms. The epicentral distribution and focal mechanisms of several earthquakes revealed that the NE–SW striking dextral strike–slip faults dominate in the study area as is the dominant pattern in North Aegean Sea. An earthquake swarm near Psara Island and a cluster offshore the west coast of Chios Island are associated with NW–SE trending left–lateral strike–slip faults, orthogonal to the dextral ones. Near the west coast of the Island the microseismicity evidences that oblique faulting dominates, whereas onshore and offshore the North Chios Island, clusters of events manifest the activation of either E–W or N–S striking normal faults. This complex deformation pattern is the manifestation of the dextral strike–slip faulting termination against conjugate sinistral ones, the transition from strike–slip to normal through the oblique faulting, as well as the activation of biaxial normal faulting in places.
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KOKKALAS, S., and A. AYDIN. "Is there a link between faulting and magmatism in the south-central Aegean Sea?" Geological Magazine 150, no. 2 (August 29, 2012): 193–224. http://dx.doi.org/10.1017/s0016756812000453.
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AbstractA distinct spatial relationship between surface faulting, magmatic intrusions and volcanic activity exists in the Aegean continental crust. In this paper, we provide detailed structural observations from key onshore areas, as well as compilations of lineament maps and earthquake locations with focal plane solutions from offshore areas to support such a relationship. Although pluton emplacement was associated with low-angle extensional detachments, the NNE- to NE-trending strike-slip faults also played an important role in localizing the Middle Miocene plutonism, providing ready pathways to deeper magma batches, and controlling the late-stage emplacement and deformation of granites in the upper crust. Additionally, the linear arrangements of volcanic centres, from the Quaternary volcanoes along the active South Aegean Volcanic Arc, are controlled primarily by NE-trending faults and secondarily by NW-trending faults. These volcanic features are located at several extensional settings, which are associated with the main NE-trending faults, such as (i) in the extensional steps or relay zones between strike-slip and oblique-normal fault segments, (ii) at the overlap zones between oblique-normal faults associated with an extensional strike-slip duplex and (iii) at the tip zone of a NE-trending divergent dextral strike-slip zone. The NE trend of volcano-tectonic features, such as volcanic cone alignments, concentration of eruptive centres, hydrothermal activity and fractures, indicates the significant role of tectonics in controlling fluid and magma pathways in the Aegean upper crust. Furthermore, microseismicity and focal mechanisms of earthquakes in the area confirm the activity and present kinematics of these NE- trending faults.
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Cape, C. D., R. M. O'Connor, J. M. Ravens, and D. J. Woodward. "Seismic expression of shallow structures in active tectonic settings in New Zealand." Exploration Geophysics 20, no. 2 (1989): 287. http://dx.doi.org/10.1071/eg989287.
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Late Cenozoic deformation along the Australian/Pacific plate boundary is seen in onshore New Zealand as zones characterised by extension- or transcurrent- or contraction-related structures. High-resolution multichannel seismic reflection data were acquired in several of these tectonic zones and successfully reveal the shallow structures within them. Thirty kilometres of dynamite reflection data in the Rangitaiki Plains, eastern Bay of Plenty, define a series of NE-trending normal faults within this extensional back-arc volcanic region. The data cross surface ruptures activated during the 1987 Edgecumbe earthquake. In the southern North Island, a 20 km Mini-Sosie? seismic profile details the Quaternary sedimentation history and reveals the structure of the active strike-slip and thrust fault systems that form the western and eastern edges of the Wairarapa basin, respectively. This basin is considered to sit astride the boundary between a zone of distributed strike-slip faults and an active accretionary prism. In the Nelson area, northwestern South Island, previously unrecognised low-angle thrust faults of Neogene or Quaternary age are seen from Mini-Sosie data to occur at very shallow depths. Crustal shortening here was previously thought to arise from movement on high-angle reverse faults, and the identification of these low-angle faults has prompted a reassessment of that model. A grid of 18 km of Mini-Sosie seismic data from the central eastern South Island delineates Neogene or Quaternary thrust faults in Cenozoic sediments. The thrusts are interpreted as reactivated Early Eocene normal faults, and the thrust fault geometry is dominated by these older structures.
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Rodríguez-Pradilla, Germán, and David W. Eaton. "Automated Microseismic Processing and Integrated Interpretation of Induced Seismicity during a Multistage Hydraulic-Fracturing Stimulation, Alberta, Canada." Bulletin of the Seismological Society of America 110, no. 5 (August 18, 2020): 2018–30. http://dx.doi.org/10.1785/0120200082.
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ABSTRACT The development of organic-rich, low-permeability formations for hydrocarbon production requires the use of unconventional techniques such as multiwell pad drilling of horizontal wells and massive multistage hydraulic-fracturing stimulations. However, proliferation of these unconventional development methods has been linked to localized cases of fault reactivation during or shortly after hydraulic fracturing. In the Duvernay formation, located in Alberta, Canada, induced seismicity from hydraulic fracturing has occurred on nearly vertical strike-slip faults that are difficult to detect with conventional seismic exploration methods. In such cases, faults may only be discernible from seismic events with precise and accurate locations, which generally requires dense seismic monitoring arrays deployed near the stimulated wells. In this study, we introduce a new, semiautomated workflow for processing passive seismic data from a dense array and then integrate it with a 3D seismic dataset to characterize seismicity clusters related to hydraulic fracturing and pre-existing faults. The reactivated faults inferred from the distribution of the microseismic events directly overlie a system of incised, middle Devonian channels below the Duvernay formation observed in time slices extracted from the 3D seismic data. The channel system exhibits a set of lateral offsets, interpreted as ancient strike-slip fault displacements, the detection of which is further enhanced by use of a similarity attribute calculated from the 3D seismic data. Taken together, integrated interpretation of induced seismicity and 3D seismic data support a model of a regional left-lateral strike-slip fault system that was active during the middle Devonian and reactivated in a reverse sense (right-lateral strike slip) during hydraulic-fracturing operations.
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Kamra, Charu, Sumer Chopra, Ram Bichar Singh Yadav, and Vishwa Joshi. "Characterization of Major Fault Systems in the Kachchh Intraplate Region, Gujarat, India, by Focal Mechanism and Source Parameters." Seismological Research Letters 91, no. 6 (September 9, 2020): 3496–517. http://dx.doi.org/10.1785/0220200005.
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Abstract The focal mechanism and source parameters of 41 local earthquakes (Mw 4.0–5.1) that occurred in the Kachchh rift basin, which is seismically one of India’s most active intraplate regions, are determined to characterize various active fault systems in that region. The tectonics in the rift basin are heterogeneous and complex. In the present study, it was found that one-third of the earthquakes exhibit reverse mechanism and three-fourth are either strike slip or have some components of strike slip. Thus, we conclude that transverse tectonics are currently dominant in the Kachchh rift. These transverse faults are preferably oriented in the northeast–southwest and northwest–southeast directions in the eastern and western parts of the rift, respectively. The movement is sinistral and dextral on faults that are oriented in the northeast–southwest and northwest–southeast directions, respectively. These transverse faults are almost vertical (dip>70°) and mostly blind with no surface expressions. Most of the significant faults that strike east–west dip toward the south and are listric. The stress drop of these 41 earthquakes ranges between 2.3 and 10.39 MPa. It was found that the stress drop of earthquakes may depend on the focal mechanism and is independent of focal depths. The average stress drop is found to be the highest (7.3 MPa) for the earthquakes that show a dominant normal mechanism accompanied by strike slip (5.4 MPa) and reverse (4.7 MPa). The average stress drop of the Kachchh intraplate region is 5.3 MPa, which is consistent with other intraplate regions of the world. A conceptual model of the fault system in the Kachchh region is proposed, based on the results obtained in the present study.
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El Ghali, Abdessalem, Claude Bobier, and Noureddine Ben Ayed. "Significance of the E-W fault system in the geodynamic evolution of the Tunisian Alpine Chain foreland. Example of the Sbiba-Cherichira fault system in Central Tunisia." Bulletin de la Société Géologique de France 174, no. 4 (July 1, 2003): 373–81. http://dx.doi.org/10.2113/174.4.373.
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Abstract The recent sedimentary basins in Central Tunisia correspond to a set of depocenters with complex geometry which are bounded by E-W, N070 and N-S brittle structures. These bordering faults, active during Eocene and Cretaceous times, have been rejuvenated at the end of the Neogene and during Quaternary in a relay pattern system associated with compressive and extensive deformations according to the alternance of extension and compression phases (Tortonian Atlasic Phase of compression, post tectonic top Miocene-early Pleistocene extension associated to the rifting of the Tyrrhenian Basin, and Pleistocene Phase of compression). These tectonic regime changes involve subsidence inversions. Moreover, the neotectonic study carried out along the strike-slip faults corridories and their associated structures enable us : – to precise the timing of the tectonic deformations ; – to establish tectono-sedimentary relationships of Mio-Plio-Quaternary age. Introduction : geodynamical context and objectives of the study. – In Central Tunisia as in the whole Maghreb [Piqué et al., 1998 ; Piqué et al., 2002], the Mesozoic and Cenozoic evolution of sedimentary basins is largely controlled by tectonic heredity due to rejuvenation of basement discontinuities. In fact, previous studies have shown that the normal kinematics activity of The Sbiba-Cherichira fault has governed the opening and the distribution of the Cretaceous and the Eocene basins evolving in a globally extensive tectonic regime [Boltenhagen, 1981 ; El Ghali, 1993]. These old tectonics is proven, also, by the interpretation of NNE-SSW seismic profiles through this collapsed zone [Ben Ayed, 1986, fig. 3] and who reveal that subsidence had been active during the Lower Cretaceous and continued up to the Albian. In the late Miocene and early Quaternary, following the Langhian collision of Sardinia against the Northern Platform of Tunisia [Cohen et al., 1980], the Atlasic and Villafranchian Phases of compression are the most important. They were responsible for the formation of important N040° to N070°E Atlasic folds , N040° to N090°E thrusts , the opening of N120° to N150° E basins parallel to the shortening axis and E-W strike slip fault [Burollet, 1956 ; Ben Ayed, 1986]. In this paper, we present and discuss results of research carried out in the Sbiba-Cherichira area. This research combines interpretation of sedimentological observations and microtectonic or structural field studies [El Ghali et Batik, 1992] carried out along and near the Sbiba-Cherichira faults system, which corresponds to two separated master faults (fig. 2): – the « Southern Sbiba Fault » developed to the west with a direction N090°E which acted as is the southern boundary of the “Sbiba Trough” subsident area as early as the Albian (fig. 3) ; – the “Cherichira Fault” developed to the north-east with a direction N070°E. These faults are connected by the N040°E Labaied-Trozza Fault. Tortonian tectonic activity. – During Tortonian compression (orientation of the shortening axis N120°to N140°E) [Burollet, 1956 ; Ben Ayed, 1986 ; Philip et al., 1986 ; Martinez et al., 1990], many transformations were induced in the studied area (fig. 4a). In fact, the E-W faults of Sbiba and the N070 to N90°E faults of Cherichira, disposed in left relay, were reactivated as dextral strike-slip faults inducing simultaneous distensive deformations (normal faults, grabens, half-grabens…) and compressive ones (folds, reverse faults, overlappings….) localised at fracturing extremity [El Ghali, 1993]. Compressive structures. – The brittle structures are associated with ductile deformations of two types : *The first one corresponds to en echelon folds including : – to the south of the E-W Sbiba Fault, in J. Tiouacha and J. Labaied, Eocene and Neogene strata which are involved in hectometric folds with a N040° to N060°E axial direction (fig. 4a) and an axial westward dip changing from 05° to 60°E ; – to the west of the J. Rebeiba fault, Lutetian and Oligocene to Lower Miocene Strata which are affected by hectometric folds with a N070° to N090°E direction (fig. 4a) and an axial westward dip, changing from 05°to 20°E [El Ghali, 1993]. All these folds are abruptly cut up by the master faults and they can be interpreted as en echelon fault propagation folds. * The second includes plurikilometric folds parallel to the strike slip faults : – the E-W anticline of J. Labaied due to the transpression responsible for reactivation of the southern Sbiba Fault with a dextral strike slip component (fig. 4a); – the N040°E anticline of J. Trozza and the N070°E anticline of J. Cherichira respectively associated with the Trozza-Labaied fault and the Cherichira fault. Because of their orientation approximatively normal to the shortening axis, these faults are reactivated reversed faults giving fault-bend folds [Suppe, 1983] thrusted to the SE with a decollement level in Triassic evaporites extruded along the fault between J. M’Rhila and J. Cherichira (fig. 4a). Distensive structures : syntectonic depocenters associated to dextral strike-slip faults. – The dextral strike-slip faults extremities develop as normal faults N140 to N160°E in the dampening zone (fig. 4a). The east and west endings of Sbiba strike slip fault are two distensive extremities the opening mecanism of which is compatible with that of a megasplit basin at a strike-slip extremity [Harding, 1973 ; Odonne, 1981 ; Granier, 1985 ; Faugère et al., 1986…]. Top Miocene to early Pleistocene tectonic activity. – During upper top Miocene and early Pleistocene times, the Sbiba Trough was characterized by a subsidence more important than in any other place in Tunisia and was filled by continental deposits of the Segui Formation (conglomerates, sands, black clays and lacustrine limestones, fig. 5). Subsidence (500m near Haffouz, 3000m in Sbiba Trough, fig. 4b) was controlled by the activity of synsedimentary normal and strike-slip faults, forming small grabens, monoclinal grabens N090° to N130°E trending often cut by the Sbiba Fault (figs. 4b and 7). This extension can be considered as a post-tectonic extension relative to the Atlasic phase of compression, the orientation of the tensile axis being the same. Pleistocene tectonic activity. – In Central Tunisia, a NNW-SSE compressive phase, intervening in early Quaternary, has been demonstrated out [Burollet, 1956 ; Ben Ayed, 1986 ; Philip et al., 1986]. This “Villafranchian phase” follows distensive strike-slip tectonics of top Miocene Lowermost Pleistocene [El Ghali, 1993] and involves subsidence inversion. This phase is manifested by reverse dextral strike-slip faults on E-W segments (Sbiba and Ain Grab faults, fig. 4c) and by SE vergence overlappings on the NE-SW segments of J. Trozza (fig. 6) and N070°E ones of Cherichira (fig. 8). In other places the top Miocene-early Pleistocene deposits of the Segui Formation are folded, producing in the Sbiba basin N070° to N090°E en echelon folds (fig. 4c) with westward or eastward axial dipping between 05° and 15°. In Jebel Ain Grab area, the folds are overturned and locally thrusted northwards producing a morphostructural dam. This latter limits to the south a sag filled with fluviatile and lacustrine deposits (fig. 9). Comparison with neighbouring regions and conclusions. – The Sbiba-Cherichira faults system correspond to an en-echelon strike slip fault inherited from a basement discontinuity. It recorded most of the main tectonic processes which affected the southern margin of the Tethys. In Central Tunisia, this faults system constitutes an evolution model of one of the major scars which affects the sedimentary cover and controls basins distribution and evolution since the Cretaceous to the Quaternary. * The Tortonian compressional episode corresponding to the Compression Atlasic Phase described from the Rif in Morocco to northern Tunisia [Viguier et al., 1980 ; Philip, 1983 ; Ben Ayed, 1986 ; Morel, 1989 ; Aite, 1995 ; Piqué et al., 2002]. The N120° to N130°E orientation of the shortening axis induced the most important transpression which has triggered the rejuvenation of the Sbiba-Cherichira system as a very active fault driving halokinesis of Triassic evaporites and large development of brittle and folded structures associated to wrench faulting activity as in the eastern platform of Tunisia (fig. 10) [Ellouz, 1984]. * During the top Miocene-early Pleistocene postectonic extension, the rejuvenation of older faults generated a multidirectional extension near the Sbiba-Cherichira faults system as in northern Tunisian platform [Tricart et al., 1994] or in the north-eastern platform and in the strait of Sicily [Bobier et Martin, 1976 ; Ellouz, 1984]. In the Sbiba and Haffouz basins, the multidirectional extension is responsible for the development, along the N070°E dextral strike slip faults and N120°E left lateral strike slip faults, of depocenters for the Segui Formation which is superimposed to Middle Cretaceous subident areas [El Ghali, 1993]. * The Upper-Pleistocene episode which corresponds to the Villafranchian Phase with a N170° to N180°E shortening axis in agreement with the convergence of the European and African Plate and very well documented from the southern margin of Grande Kabilie [Aite, 1995] to northern Tunisia [Ben Ayed, 1986]. Near Sbiba it induced formation of folds, thrusts or reversed faults forming morphostructural dams in which fluvio-lacustrine deposits are accumulated.
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Witter, Robert C., Adrian M. Bender, Katherine M. Scharer, Christopher B. DuRoss, Peter J. Haeussler, and Richard O. Lease. "Geomorphic expression and slip rate of the Fairweather fault, southeast Alaska, and evidence for predecessors of the 1958 rupture." Geosphere 17, no. 3 (May 6, 2021): 711–38. http://dx.doi.org/10.1130/ges02299.1.
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Abstract Active traces of the southern Fairweather fault were revealed by light detection and ranging (lidar) and show evidence for transpressional deformation between North America and the Yakutat block in southeast Alaska. We map the Holocene geomorphic expression of tectonic deformation along the southern 30 km of the Fairweather fault, which ruptured in the 1958 moment magnitude 7.8 earthquake. Digital maps of surficial geology, geomorphology, and active faults illustrate both strike-slip and dip-slip deformation styles within a 10°–30° double restraining bend where the southern Fairweather fault steps offshore to the Queen Charlotte fault. We measure offset landforms along the fault and calibrate legacy 14C data to reassess the rate of Holocene strike-slip motion (≥49 mm/yr), which corroborates published estimates that place most of the plate boundary motion on the Fairweather fault. Our slip-rate estimates allow a component of oblique-reverse motion to be accommodated by contractional structures west of the Fairweather fault consistent with geodetic block models. Stratigraphic and structural relations in hand-dug excavations across two active fault strands provide an incomplete paleoseismic record including evidence for up to six surface ruptures in the past 5600 years, and at least two to four events in the past 810 years. The incomplete record suggests an earthquake recurrence interval of ≥270 years—much longer than intervals <100 years implied by published slip rates and expected earthquake displacements. Our paleoseismic observations and map of active traces of the southern Fairweather fault illustrate the complexity of transpressional deformation and seismic potential along one of Earth's fastest strike-slip plate boundaries.
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Qu, Shao Dong, Chi Yang Liu, Li Jun Song, Hui Deng, Long Zhang, and Guang Zhou Mao. "Structure Evolution of Qinjiatun-Qindong Fault System in Lishu Subbasin." Advanced Materials Research 734-737 (August 2013): 170–77. http://dx.doi.org/10.4028/www.scientific.net/amr.734-737.170.
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Three-dimensional(3-D) seismic data and structure analysis of the Lishu subasin in Songliao basin indicates that Qinjiatun fault zone is composed of two faults: East-Qin and West-Qin fault. This fault system initially formed at Huoshiling stage, peaked at Shahezi stage and faded dramatically from Yingcheng stage. The Qinjiatun fault was important in controlling strata thickness and distribution of the Huoshiling formation. Qindong fault, a typical strike-slip fault, developed relatively later, cutting the Qinjiatun fault, The major active stage was in Denglouku-Quantou stage, and weakened in the end of late Cretaceous. Qinjiatun fault zone was reversed at Denglouku stage when the regional stress went compressive, generating a structure nose that was potentially beneficial for hydrocarbon to accumulate. The strike-slip Qindong fault became active relatively later, cutting through the previous strata and proving pathways for both accumulation and effusion of hydrocarbon.
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Wu, Chenglong, Xiaobo Tian, Tao Xu, Xiaofeng Liang, Yun Chen, Gaohua Zhu, José Badal, Zhiming Bai, Guiping Yu, and Jiwen Teng. "Upper‐Crustal Anisotropy of the Conjugate Strike‐Slip Fault Zone in Central Tibet Analyzed Using Local Earthquakes and Shear‐Wave Splitting." Bulletin of the Seismological Society of America 109, no. 5 (August 27, 2019): 1968–84. http://dx.doi.org/10.1785/0120180333.
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Abstract Remarkable V‐shaped conjugate strike‐slip faults extend along the Bangong–Nujiang suture in central Tibet. Motions of these faults are considered to accommodate ongoing east–west extension and north–south contraction. Fabrics within the fault zone that are anisotropic to seismic waves can provide clues as to the unusual scale and style of lithospheric deformation. With the goal of determining the upper‐crustal anisotropy pattern in central Tibet, we measured shear‐wave splitting parameters (fast wave polarization direction and delay time) using waveforms generated by 194 local earthquakes recorded by 49 stations of the SANDWICH network. Stations located in eastern and western zones of the study area show anisotropy directions that agree well with the maximum horizontal compressive stress direction. The fast polarization directions at stations near active strike‐slip faults generally run parallel to the strikes of these faults. Pervasive inactive thrust faults caused by Cretaceous–Tertiary shortening in central Tibet also clearly correlate with the anisotropy detected at nearby stations. These results demonstrate that both local structures and stress contribute to upper‐crustal anisotropy in the region. Combining the new results with previous SKS‐wave splitting results and other seismic evidence, we propose that deformation in the upper crust is mechanically decoupled from that in the upper mantle, due to eastward middle‐lower crustal flow. This crustal flow causes basal shearing required for the formation of conjugate strike‐slip faults in central Tibet.
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Reicherter, K. R., and S. Reiss. "The Carboneras Fault Zone (southeastern Spain) revisited with Ground Penetrating Radar – Quaternary structural styles from high-resolution images." Netherlands Journal of Geosciences 80, no. 3-4 (December 2001): 129–38. http://dx.doi.org/10.1017/s0016774600023799.
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AbstractThe Carboneras Fault Zone (CFZ) represents an active set of sinistral strike-slip faults in the Betic Cordilleras of southeastern Spain. It constitutes a major segment of the ‘Trans-Alboran shear zone’ during the Cenozoic, striking NE-SW. The CFZ separates the Cabo de Gata Block (Neogene volcanics) against Neogene basinal sediments and the metamorphic basement of the Alpujarride Complex.Three sites along the CFZ were examined with Ground Penetrating Radar techniques. Radar surveying was complemented by structural studies. Shallow-depth high-resolution imaging of Tyrrhenian beach terraces exhibited both vertical and minor horizontal offsets in the Rambla Morales site in the south. A sinistral strike-slip fault associated with minor thrust faults in a positive flower structure was detected in the middle segment along the La Serrata ridge, sealed by a caliche of late Pleistocene age (> 10 ka). The Playa de Bolmayor section yielded sub-surface evidence for several faults probably related to recent activity of individual fault strands. Our results suggest a distributed tectonic activity of the CFZ during the Late Quaternary.
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Duvall, Michael J., John W. F. Waldron, Laurent Godin, and Yani Najman. "Active strike-slip faults and an outer frontal thrust in the Himalayan foreland basin." Proceedings of the National Academy of Sciences 117, no. 30 (July 13, 2020): 17615–21. http://dx.doi.org/10.1073/pnas.2001979117.
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The Himalayan foreland basin formed by flexure of the Indian Plate below the advancing orogen. Motion on major thrusts within the orogen has resulted in damaging historical seismicity, whereas south of the Main Frontal Thrust (MFT), the foreland basin is typically portrayed as undeformed. Using two-dimensional seismic reflection data from eastern Nepal, we present evidence of recent deformation propagating >37 km south of the MFT. A system of tear faults at a high angle to the orogen is spatially localized above the Munger-Saharsa basement ridge. A blind thrust fault is interpreted in the subsurface, above the sub-Cenozoic unconformity, bounded by two tear faults. Deformation zones beneath the Bhadrapur topographic high record an incipient tectonic wedge or triangle zone. The faults record the subsurface propagation of the Main Himalayan Thrust (MHT) into the foreland basin as an outer frontal thrust, and provide a modern snapshot of the development of tectonic wedges and lateral discontinuities preserved in higher thrust sheets of the Himalaya, and in ancient orogens elsewhere. We estimate a cumulative slip of ∼100 m, accumulated in <0.5 Ma, over a minimum slipped area of ∼780 km2. These observations demonstrate that Himalayan ruptures may pass under the present-day trace of the MFT as blind faults inaccessible to trenching, and that paleoseismic studies may underestimate Holocene convergence.
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Hennings, Peter H., Jens‐Erik Lund Snee, Johnathon L. Osmond, Heather R. DeShon, Robin Dommisse, Elizabeth Horne, Casee Lemons, and Mark D. Zoback. "Injection‐Induced Seismicity and Fault‐Slip Potential in the Fort Worth Basin, Texas." Bulletin of the Seismological Society of America 109, no. 5 (July 23, 2019): 1615–34. http://dx.doi.org/10.1785/0120190017.
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Abstract The rate of seismicity in the hydrocarbon‐producing Fort Worth Basin of north‐central Texas, which underlies the Dallas–Fort Worth metropolitan area, increased markedly from 2008 through 2015, coinciding spatiotemporally with injection of 2 billion barrels of wastewater into deep aquifers. Although the rate of seismicity has declined with injection rates, some earthquake sequences remained active in 2018 and new clusters have developed. Most of this seismicity occurred away from regionally mapped faults, challenging efforts to constrain the continuing hazards of injection‐induced seismicity in the basin. Here, we present detailed new models of potentially seismogenic faults and the stress field, which we use to build a probabilistic assessment of fault‐slip potential. Our new fault map, based on reflection seismic data, tens of thousands of well logs, and outcrop characterization, includes 251 basement‐rooted normal faults that strike dominantly north‐northeast, several of which extend under populated areas. The updated stress map indicates a relatively consistent north‐northeast–south‐southwest azimuth of the maximum horizontal principal stress over seismically active parts of the basin, with a transition from strike‐slip faulting in the north to normal faulting in the southeast. Based on these new data, our probabilistic analysis shows that a majority of the total trace length of the mapped faults have slip potential that is equal to or higher than that of the faults that have already hosted injection‐induced earthquake sequences. We conclude that most faults in the system are highly sensitive to reactivation, and we postulate that many faults are still unidentified. Ongoing injection operations in the region should be conducted with these understandings in mind.
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Ganas, A., V. Spina, N. Alexandropoulou, A. Oikonomou, and G. Drakatos. "THE CORINI ACTIVE FAULT IN SOUTHWESTERN VIOTIA REGION, CENTRAL GREECE: SEGMENTATION, STRESS ANALYSIS AND EXTENSIONAL STRAIN PATTERNS." Bulletin of the Geological Society of Greece 40, no. 1 (June 8, 2018): 297. http://dx.doi.org/10.12681/bgsg.16561.
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The Corini normal fault is an active structure of Quaternary age in Southwestern Viotia. This is a region of low finite strain, located between the Quaternary rifts of the Gulf of Corinth and the Gulf of Evia. The fault is segmented into several segments with an average strike of N58°E and dip direction to the SE. The architecture of the fault zone is characterized by a 15 cm thick gouge rock, observed along the fault plane on the footwall side. At several localities along strike we observed a well-defined basal strip of un-eroded fault plane that represents the width (uplift) of the last co-seismic slip. The width of the strip ranges 20-30 cm. Slip inversion data show a mean orientation ofsigmaS (leastprincipal stress) as Ν328Έ which implies similar kinematics with the active faults of the south coast of the Gulf of Corinth.
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Pratt, Thomas L., James F. Dolan, Jackson K. Odum, William J. Stephenson, Robert A. Williams, and Mary E. Templeton. "Multiscale seismic imaging of active fault zones for hazard assessment: A case study of the Santa Monica fault zone, Los Angeles, California." GEOPHYSICS 63, no. 2 (March 1998): 479–89. http://dx.doi.org/10.1190/1.1444349.
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High‐resolution seismic reflection profiles at two different scales were acquired across the transpressional Santa Monica Fault of north Los Angeles as part of an integrated hazard assessment of the fault. The seismic data confirm the location of the fault and related shallow faulting seen in a trench to deeper structures known from regional studies. The trench shows a series of near‐vertical strike‐slip faults beneath a topographic scarp inferred to be caused by thrusting on the Santa Monica fault. Analysis of the disruption of soil horizons in the trench indicates multiple earthquakes have occurred on these strike‐slip faults within the past 50 000 years, with the latest being 1000 to 3000 years ago. A 3.8-km-long, high‐resolution seismic reflection profile shows reflector truncations that constrain the shallow portion of the Santa Monica Fault (upper 300 m) to dip northward between 30° and 55°, most likely 30° to 35°, in contrast to the 60° to 70° dip interpreted for the deeper portion of the fault. Prominent, nearly continuous reflectors on the profile are interpreted to be the erosional unconformity between the 1.2 Ma and older Pico Formation and the base of alluvial fan deposits. The unconformity lies at depths of 30–60 m north of the fault and 110–130 m south of the fault, with about 100 m of vertical displacement (180 m of dip‐slip motion on a 30°–35° dipping fault) across the fault since deposition of the upper Pico Formation. The continuity of the uncomformity on the seismic profile constrains the fault to lie in a relatively narrow (50 m) zone, and to project to the surface beneath Ohio Avenue immediately south of the trench. A very high‐resolution seismic profile adjacent to the trench images reflectors in the 15 to 60 m depth range that are arched slightly by folding just north of the fault. A disrupted zone on the profile beneath the south end of the trench is interpreted as being caused by the deeper portions of the trenched strike‐slip faults where they merge with the thrust fault.
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Gunawan, Endra. "An Assessment of Earthquake Scaling Relationships for Crustal Earthquakes in Indonesia." Seismological Research Letters 92, no. 4 (March 3, 2021): 2490–97. http://dx.doi.org/10.1785/0220200267.
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Abstract To estimate the hazard posed by active faults, estimates of the maximum magnitude earthquake that could occur on the fault are needed. I compare previously published scaling relationships between earthquake magnitude and rupture length with data from recent earthquakes in Indonesia. I compile a total amount of 13 literatures on investigating coseismic deformation in Indonesia, which then divided into strike-slip and dip-slip earthquake cases. I demonstrate that a different scaling relationship generates different misfit compared to data. For a practical practice of making seismic hazard model in Indonesia, this research shows the suggested reference for a scaling relationship of strike-slip and dip-slip faulting regime. On a practical approach in constructing a logic tree for seismic hazard model, using different weighting between each published earthquake scaling relationship is recommended.
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Dorsett, Jacob H., Elizabeth H. Madden, Scott T. Marshall, and Michele L. Cooke. "Mechanical Models Suggest Fault Linkage through the Imperial Valley, California, U.S.A." Bulletin of the Seismological Society of America 109, no. 4 (June 11, 2019): 1217–34. http://dx.doi.org/10.1785/0120180303.
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Abstract The Imperial Valley hosts a network of active strike‐slip faults that comprise the southern San Andreas fault (SAF) and San Jacinto fault systems and together accommodate the majority of relative Pacific–North American plate motion in southern California. To understand how these faults partition slip, we model the long‐term mechanics of four alternative fault networks with different degrees of connectivity through the Imperial Valley using faults from the Southern California Earthquake Center Community Fault Model version 5.0 (v.5.0). We evaluate model results against average fault‐slip rates from the Uniform California Earthquake Rupture Model v.3 (UCERF3) and geologic slip‐rate estimates from specific locations. The model results support continuous linkage from the SAF through the Brawley seismic zone to the Imperial and to the Cerro Prieto faults. Connected faults decrease surface strain rates throughout the region and match more slip‐rate data. Only one model reproduces the UCERF3 rate on the Imperial fault, reaching the lower bound of 15 mm/yr. None of the tested models reproduces the UCERF3 preferred rate of 35 mm/yr. In addition, high‐strain energy density rates around the Cerro Prieto fault in all models suggest that the UCERF3 preferred rate of 35 mm/yr may require revision. The Elmore Ranch fault‐slip rate matches the UCERF3 rate only in models with continuous linkage. No long‐term slip‐rate data are available for the El Centro and Dixieland faults, but all models return less than 2 mm/yr on the El Centro fault and 3.5–9.6 mm/yr on the Dixieland fault. This suggests that the Dixieland fault may accommodate a significant portion of plate‐boundary motion.
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Wang, Duo, Gong-Ming Yin, Xu-Long Wang, Chun-Ru Liu, Fei Han, and Jin-Hua Du. "OSL dating of the late Quaternary slip rate on the Gyaring co Fault in central Tibet." Geochronometria 43, no. 1 (January 1, 2016): 162–73. http://dx.doi.org/10.1515/geochr-2015-0040.
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Abstract The Gyaring Co Fault (GCF) is an active right-lateral strike-slip fault in central Tibet that accommodates convergence between India and Asia in the interior of the Tibetan Plateau. The average long-term slip rate of the fault remains controversial, given the absence of absolute age data of faulted geomorphic features. We have applied optically stimulated luminescence (OSL) dating to the northern segment of the GCF, revealing that the GCF has displaced alluvial fans at Aerqingsang by 500 ± 100 m since their deposition at ~109 ka, yielding a slip rate of 4.6 ± 1.0 mm/yr. A slip rate of 3.4 ± 0.4 mm/yr is inferred from analysis of an alluvial fan with an offset of 65 ± 5 m (~19 ka) at Quba site 1. The Holocene slip rate is estimated to be 1.9 ± 0.3 mm/yr, as inferred from the basal age (~8.3 ka) of terrace T1 that has a gully displacement of 16 ± 2 m at Quba site 2. These slip rates are generally lower early estimates (10–20 mm/yr), but are consistent with more recent results (2.2–4.5 mm/yr) and GPS data for other strike-slip faults in this region, indicating that deformation may be distributed across the entire Tibetan Plateau. Moreover, we suggest that the slip rate along the GCF may have decreased slightly during the late Quaternary.
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Duvall, Alison R., Sarah A. Harbert, Phaedra Upton, Gregory E. Tucker, Rebecca M. Flowers, and Camille Collett. "River patterns reveal two stages of landscape evolution at an oblique convergent margin, Marlborough Fault System, New Zealand." Earth Surface Dynamics 8, no. 1 (February 28, 2020): 177–94. http://dx.doi.org/10.5194/esurf-8-177-2020.
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Abstract. Here we examine the landscape of New Zealand's Marlborough Fault System (MFS), where the Australian and Pacific plates obliquely collide, in order to study landscape evolution and the controls on fluvial patterns at a long-lived plate boundary. We present maps of drainage anomalies and channel steepness, as well as an analysis of the plan-view orientations of rivers and faults, and we find abundant evidence of structurally controlled drainage that we relate to a history of drainage capture and rearrangement in response to mountain-building and strike-slip faulting. Despite clear evidence of recent rearrangement of the western MFS drainage network, rivers in this region still flow parallel to older faults, rather than along orthogonal traces of younger, active strike-slip faults. Such drainage patterns emphasize the importance of river entrenchment, showing that once rivers establish themselves along a structural grain, their capture or avulsion becomes difficult, even when exposed to new weakening and tectonic strain. Continued flow along older faults may also indicate that the younger faults have not yet generated a fault damage zone with the material weakening needed to focus erosion and reorient rivers. Channel steepness is highest in the eastern MFS, in a zone centered on the Kaikōura ranges, including within the low-elevation valleys of main stem rivers and at tributaries near the coast. This pattern is consistent with an increase in rock uplift rate toward a subduction front that is locked on its southern end. Based on these results and a wealth of previous geologic studies, we propose two broad stages of landscape evolution over the last 25 million years of orogenesis. In the eastern MFS, Miocene folding above blind thrust faults generated prominent mountain peaks and formed major transverse rivers early in the plate collision history. A transition to Pliocene dextral strike-slip faulting and widespread uplift led to cycles of river channel offset, deflection and capture of tributaries draining across active faults, and headward erosion and captures by major transverse rivers within the western MFS. We predict a similar landscape will evolve south of the Hope Fault, as the locus of plate boundary deformation migrates southward into this region with time.
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Vazouras, Polynikis, Spyros A. Karamanos, and Panos Dakoulas. "Mechanical behavior of buried steel pipes crossing active strike-slip faults." Soil Dynamics and Earthquake Engineering 41 (October 2012): 164–80. http://dx.doi.org/10.1016/j.soildyn.2012.05.012.
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Yaghoubi, Ali, SeyedBijan Mahbaz, Maurice B. Dusseault, and Yuri Leonenko. "Seismicity and the State of Stress in the Dezful Embayment, Zagros Fold and Thrust Belt." Geosciences 11, no. 6 (June 12, 2021): 254. http://dx.doi.org/10.3390/geosciences11060254.
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This study focuses on determining the orientation and constraining the magnitude of present-day stresses in the Dezful Embayment in Iran’s Zagros Fold and Thrust Belt. Two datasets are used: the first includes petrophysical data from 25 wells (3 to 4 km deep), and the second contains 108 earthquake focal mechanisms, mostly occurring in blind active basement faults (5 to 20 km deep). Formal stress inversion analysis of the focal mechanisms demonstrates that there is currently a compressional stress state (Aφ=2.0–2.2) in the basement. The seismologically determined SHmax direction is 37° ± 10°, nearly perpendicular to the strike of most faults in the region. However, borehole geomechanics analysis using rock strength and drilling evidence leads to the counterintuitive result that the shallow state of stress is a normal/strike-slip regime. These results are consistent with the low seismicity level in the sedimentary cover in the Dezful Embayment, and may be evidence of stress decoupling due to the existence of salt layers. The stress state situation in the field was used to identify the optimally oriented fault planes and the fault friction coefficient. This finding also aligns with the prediction Coulomb faulting theory in that the N-S strike-slip basement Kazerun Fault System has an unfavorable orientation for slip in a reverse fault regime with an average SW-NE SHmax orientation. These results are useful for determining the origin of seismic activity in the basin and better assessing fault-associated seismic hazards in the area.
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Egebjerg Mogensen, Tommy, and John A. Korstgård. "Triassic and Jurassic transtension along part of the Sorgenfrei–Tornquist Zone in the Danish Kattegat." Geological Survey of Denmark and Greenland (GEUS) Bulletin 1 (October 28, 2003): 437–58. http://dx.doi.org/10.34194/geusb.v1.4680.
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In the Kattegat area, Denmark, the Sorgenfrei–Tornquist Zone, an old crustal weakness zone, was repeatedly reactivated during Triassic, Jurassic and Early Cretaceous times with dextral transtensional movements along the major boundary faults. These tectonic events were minor compared to the tectonic events of the Late Carboniferous – Early Permian and the Late Cretaceous – Early Tertiary, although a dynamic structural and stratigraphic analysis indicates that the Sorgenfrei–Tornquist Zone was active compared to the surrounding areas. At the end of the Palaeozoic, the area was a peneplain. Regional Triassic subsidence caused onlap towards the north-east, where the youngest Triassic sediments overlie Precambrian crystalline basement. During the Early Triassic, several of the major Early Permian faults were reactivated, probably with dextral strike-slip along the Børglum Fault. Jurassic – Early Cretaceous subsidence was restricted primarily to the area between the two main faults in the Sorgenfrei–Tornquist Zone, the Grenå–Helsingborg Fault and the Børglum Fault. This restriction of basin development indicates a change in the regional stress field at the Triassic–Jurassic transition. Middle Jurassic and Late Jurassic – Early Cretaceous subsidence followed the Early Jurassic pattern with local subsidence in the Sorgenfrei–Tornquist Zone, but now even more restricted to within the zone. The subsidence showed a decrease in the Middle Jurassic, and increased again during Late Jurassic – Early Cretaceous times. Small faults were generated internally in the Sorgenfrei–Tornquist Zone during the Mesozoic with a pattern that indicates a broad transfer of strike-slip/oblique-slip motion from the Grenå–Helsingborg Fault to the Børglum Fault.
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Snyder, David B., Brian J. Roberts, and Steven P. Gordey. "Contrasting seismic characteristics of three major faults in northwestern Canada." Canadian Journal of Earth Sciences 42, no. 6 (June 1, 2005): 1223–37. http://dx.doi.org/10.1139/e05-027.
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The Lithoprobe Slave Northern Cordillera Lithospheric Evolution (SNORCLE) profiles crossed three major tectonic zones of the northwestern Canadian Shield and northern Canadian Cordillera that are diverse in age and in depth of penetration. The oldest (26302590 Ma), the Yellowknife River fault zone, formed as a strike-slip fault in a tensional strain regime. Reflector attenuation or truncations align vertically beneath the fault trace through much of the crust, implying a near-vertical fault plane. The youngest (6010 Ma), the Tintina fault zone, produced cumulative dextral strike-slip displacements of 425 km, perhaps 800 km. Tomographic velocity and ray-trace models of reflection data indicate that several fault splays form a tectonic zone 30 km wide at the surface, but truncations of deeper crustal reflections suggest that the zone thins in the mid-crust and widens near the Moho. This apparent variable width versus depth of the Tintina fault is atypical of major strike-slip faults worldwide. The Teslin fault was an active terrane boundary during accretion of terranes onto North America. Observed reflection geometries indicate that the juxtapositions of highly contrasting metamorphic grades across the Teslin fault are confined to the upper crust along SNORCLE line 3, implying that the fault soles eastward into a mid-crustal detachment at the interpreted top of North American crust. The limited depth extent of the Teslin fault zone is similar to some models of the San Andreas fault and may result from their similar histories as convergent margin structures.
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Falcucci, Emanuela, Maria Eliana Poli, Fabrizio Galadini, Giancarlo Scardia, Giovanni Paiero, and Adriano Zanferrari. "First evidence of active transpressive surface faulting at the front of the eastern Southern Alps, northeastern Italy: insight on the 1511 earthquake seismotectonics." Solid Earth 9, no. 4 (July 18, 2018): 911–22. http://dx.doi.org/10.5194/se-9-911-2018.
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Abstract. We investigated the eastern corner of northeastern Italy, where a system of NW–SE-trending dextral strike-slip faults of western Slovenia intersects the south-verging fold and thrust belt of the eastern Southern Alps. The area suffered the largest earthquakes of the region, among which are the 1511 (Mw 6.3) event and the two major shocks of the 1976 seismic sequence, with Mw = 6.4 and 6.1. The Colle Villano thrust and the Borgo Faris–Cividale strike-slip fault have been here first analyzed by interpreting industrial seismic lines and then by performing morphotectonic and paleoseismological analyses. These different datasets indicate that the two structures define an active, coherent transpressive fault system that was activated twice in the past two millennia, with the last event occurring around the 15th–17th century. The chronological information and the location of the investigated fault system suggest its activation during the 1511 earthquake.
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Andrews, Ronia, Kusala Rajendran, and N. Purnachandra Rao. "The 4 December 2015 Mw 7.1 Normal-Faulting Antarctic Plate Earthquake and Its Seismotectonic Implications." Bulletin of the Seismological Society of America 110, no. 3 (March 24, 2020): 1090–100. http://dx.doi.org/10.1785/0120190249.
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ABSTRACT Oceanic plate seismicity is generally dominated by normal and strike-slip faulting associated with active spreading ridges and transform faults. Fossil structural fabrics inherited from spreading ridges also host earthquakes. The Indian Oceanic plate, considered quite active seismically, has hosted earthquakes both on its active and fossil fault systems. The 4 December 2015 Mw 7.1 normal-faulting earthquake, located ∼700 km south of the southeast Indian ridge in the southern Indian Ocean, is a rarity due to its location away from the ridge, lack of association with any mapped faults and its focal depth close to the 800°C isotherm. We present results of teleseismic body-wave inversion that suggest that the earthquake occurred on a north-northwest–south-southeast-striking normal fault at a depth of 34 km. The rupture propagated at 2.7 km/s with compact slip over an area of 48×48 km2 around the hypocenter. Our analysis of the background tectonics suggests that our chosen fault plane is in the same direction as the mapped normal faults on the eastern flanks of the Kerguelen plateau. We propose that these buried normal faults, possibly the relics of the ancient rifting might have been reactivated, leading to the 2015 midplate earthquake.
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Jiao, L., and N. V. Koronovsky. "Geological background of the 12 May 2008 Wenchuan catastrophic earthquake (Longmen Shan, Western China)." Moscow University Bulletin. Series 4. Geology, no. 6 (December 28, 2016): 37–45. http://dx.doi.org/10.33623/0579-9406-2016-6-37-45.
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Longmen Shan fault zone is located in the special joint between the Triassic Songpan-Ganzi orogen of the Qinghai-Tibetan Plateau and the stable Sichuan basin of the Yangtze platform. In this region there are four major active faults and three tectonic nappes. According to the analysis of neotectonics and historical earthquakes the Longmen Shan fault zone is a dangerous earthquake belt. The rupture system of the Wenchuan earthquake is characterized by thrust and dextral strike-slip movement.
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ALEKSANDROWSKI, P., R. KRYZA, S. MAZUR, and J. ŻABA. "Kinematic data on major Variscan strike-slip faults and shear zones in the Polish Sudetes, northeast Bohemian Massif." Geological Magazine 134, no. 5 (September 1997): 727–39. http://dx.doi.org/10.1017/s0016756897007590.
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The still highly disputable terrane boundaries in the Sudetic segment of the Variscan belt mostly seem to follow major strike-slip faults and shear zones. Their kinematics, expected to place important constraints on the regional structural models, is discussed in some detail. The most conspicuous is the WNW–ESE Intra-Sudetic Fault Zone, separating several different structural units of the West Sudetes. It showed ductile dextral activity and, probably, displacement magnitude of the order of tens to hundreds kilometres, during late Devonian(?) to early Carboniferous times. In the late Carboniferous (to early Permian?), the sense of motion on the Intra-Sudetic Fault was reversed in a semi-brittle to brittle regime, with the left-lateral offset on the fault amounting to single kilometres. The north–south trending Niemcza and north-east–southwest Skrzynka shear zones are left-lateral, ductile features in the eastern part of the West Sudetes. Similarly oriented (northeast–southwest to NNE–SSW) regional size shear zones of as yet undetermined kinematics were discovered in boreholes under Cenozoic cover in the eastern part of the Sudetic foreland (the Niedźwiedź and Nysa-Brzeg shear zones). One of these is expected to represent the northern continuation of the major Stare Mesto Shear Zone in the Czech Republic, separating the geologically different units of the West and East Sudetes. The Rudawy Janowickie Metamorphic Unit, assumed in some reconstructions to comprise a mostly strike-slip terrane boundary, is characterized by ductile fabric developed in a thrusting regime, modified by a superimposed normal-slip extensional deformation. Thrusting-related deformational fabric was locally reoriented prior to the extensional event and shows present-day strike-slip kinematics in one of the sub-units. The Sudetic Boundary Fault, although prominent in the recent structure and topography of the region, was not active as a Variscan strike-slip fault zone. The reported data emphasize the importance of syn-orogenic strike-slip tectonics in the Sudetes. The recognized shear sense is compatible with a strike-slip model of the northeast margin of the Bohemian Massif, in which the Kaczawa and Góry Sowie Units underwent late Devonian–early Carboniferous southeastward long-distance displacement along the Intra-Sudetic Fault Zone from their hypothetical original position within the Northern Phyllite Zone and the Mid-German Crystalline High of the German Variscides, respectively, and were juxtaposed with units of different provenance southwest of the fault. The Intra-Sudetic Fault Zone, together with the Elbe Fault Zone further south, were subsequently cut in the east and their eastern segments were displaced and removed by the younger, early to late Carboniferous, NNE–SSW trending, transpressional Moldanubian–Stare Mesto Shear Zone.
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Bacon, Steven N., Thomas F. Bullard, Amanda K. Keen-Zebert, Angela S. Jayko, and David L. Decker. "Spatiotemporal patterns of distributed slip in southern Owens Valley indicated by deformation of late Pleistocene shorelines, eastern California." GSA Bulletin 132, no. 7-8 (July 1, 2020): 1681–703. http://dx.doi.org/10.1130/b35247.1.
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Abstract High-resolution elevation surveys of deformed late Pleistocene shorelines and new luminescence dating provide improved constraints on spatiotemporal patterns of distributed slip between normal and strike-slip faulting in southern Owens Valley, eastern California. A complex array of five subparallel faults, including the normal Sierra Nevada frontal fault and the oblique-normal Owens Valley fault, collectively form an active pull-apart basin that has developed within a dextral transtensional shear zone. Spatiotemporal patterns of slip are constrained by post–IR-IRSL (post-infrared–infrared stimulated luminescence) dating of a 40.0 ± 5.8 ka highstand beach ridge that is vertically faulted and tilted up to 9.8 ± 1.8 m and an undeformed suite of 11–16 ka beach ridges. The tectono-geomorphic record of deformed beach ridges and alluvial fans indicates that both normal and dextral faulting occurred between the period of ca. 16 and 40 ka, whereas dextral faulting has been the predominant style of slip since ca. 16 ka. A total extension rate of 0.7 ± 0.2 mm/yr resolved in the N72°E direction across all faults in Owens Lake basin is within error of geodetic estimates, suggesting extension has been constant during intervals of 101–104 yr. A new vertical slip rate of 0.13 ± 0.04 m/k.y. on the southern Owens Valley fault from deformed 160 ± 32 ka shoreline features also suggests constant slip for intervals up to 105 yr when compared to paleoseismic vertical slip rates from the same fault segment. This record supports a deformation mechanism characterized by steady slip and long interseismic periods of 8–10 k.y. where the south-central Owens Valley fault and Sierra Nevada frontal fault form a parallel fault system.
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Liu, Yajing, Jeffrey J. McGuire, and Mark D. Behn. "Aseismic transient slip on the Gofar transform fault, East Pacific Rise." Proceedings of the National Academy of Sciences 117, no. 19 (April 28, 2020): 10188–94. http://dx.doi.org/10.1073/pnas.1913625117.
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Oceanic transform faults display a unique combination of seismic and aseismic slip behavior, including a large globally averaged seismic deficit, and the local occurrence of repeating magnitude (M) ∼6 earthquakes with abundant foreshocks and seismic swarms, as on the Gofar transform of the East Pacific Rise and the Blanco Ridge in the northeast Pacific Ocean. However, the underlying mechanisms that govern the partitioning between seismic and aseismic slip and their interaction remain unclear. Here we present a numerical modeling study of earthquake sequences and aseismic transient slip on oceanic transform faults. In the model, strong dilatancy strengthening, supported by seismic imaging that indicates enhanced fluid-filled porosity and possible hydrothermal circulation down to the brittle–ductile transition, effectively stabilizes along-strike seismic rupture propagation and results in rupture barriers where aseismic transients arise episodically. The modeled slow slip migrates along the barrier zones at speeds ∼10 to 600 m/h, spatiotemporally correlated with the observed migration of seismic swarms on the Gofar transform. Our model thus suggests the possible prevalence of episodic aseismic transients in M ∼6 rupture barrier zones that host active swarms on oceanic transform faults and provides candidates for future seafloor geodesy experiments to verify the relation between aseismic fault slip, earthquake swarms, and fault zone hydromechanical properties.
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Mildon, Zoe K., Gerald P. Roberts, Joanna P. Faure Walker, and Francesco Iezzi. "Coulomb stress transfer and fault interaction over millennia on non-planar active normal faults: the Mw 6.5–5.0 seismic sequence of 2016–2017, central Italy." Geophysical Journal International 210, no. 2 (May 30, 2017): 1206–18. http://dx.doi.org/10.1093/gji/ggx213.
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Abstract In order to investigate the importance of including strike-variable geometry and the knowledge of historical and palaeoseismic earthquakes when modelling static Coulomb stress transfer and rupture propagation, we have examined the August–October 2016 A.D. and January 2017 A.D. central Apennines seismic sequence (Mw 6.0, 5.9, 6.5 in 2016 A.D. (INGV) and Mw 5.1, 5.5, 5.4, 5.0 in 2017 A.D. (INGV)). We model both the coseismic loading (from historical and palaeoseismic earthquakes) and interseismic loading (derived from Holocene fault slip-rates) using strike-variable fault geometries constrained by fieldwork. The inclusion of the elapsed times from available historical and palaeoseismological earthquakes and on faults enables us to calculate the stress on the faults prior to the beginning of the seismic sequence. We take account the 1316–4155 yr elapsed time on the Mt. Vettore fault (that ruptured during the 2016 A.D. seismic sequence) implied by palaeoseismology, and the 377 and 313 yr elapsed times on the neighbouring Laga and Norcia faults respectively, indicated by the historical record. The stress changes through time are summed to show the state of stress on the Mt. Vettore, Laga and surrounding faults prior to and during the 2016–2017 A.D. sequence. We show that the build up of stress prior to 2016 A.D. on strike-variable fault geometries generated stress heterogeneities that correlate with the limits of the main-shock ruptures. Hence, we suggest that stress barriers appear to have control on the propagation and therefore the magnitudes of the main-shock ruptures.
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Paul, Himangshu, M. Ravi Kumar, and Santosh Kumar. "Evidence for reactivation of new faults and seismicity migration away from the causative fault of the 2001 MW 7.7 Bhuj earthquake, western India." Geophysical Journal International 226, no. 3 (May 13, 2021): 1800–1813. http://dx.doi.org/10.1093/gji/ggab188.
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SUMMARY The Kachchh Rift Basin of western India that hosted the devastating 2001 MW 7.7 Bhuj earthquake has been witnessing minor to moderate seismicity since then. The genesis of these intraplate earthquakes and geometry of the causative faults is still elusive. In this study, we relocated all the earthquakes recorded between 2006 and 2018 and utilized a set of 4285 best located earthquakes to provide rare insights into the orientation and depth distribution of the currently active faults. We also analysed previously computed source mechanisms, in perspective of our location results. It is revealed that the present seismic activity is primarily aligned along two planes—one steeply dipping (∼60°) to the northeast with a NW–SE strike and the other gently (∼34°) dipping to the SSW, striking WNW–ESE. The traces of these fault surfaces coincide with the Kachchh Mainland fault (KMF) and the North Wagad Fault (NWF) when extrapolated to the surface, respectively. Activity along the NWF has been shown in earlier studies, however, clear evidence of activity along the steep north-dipping KMF is presented for the very first time. Thrust earthquakes dominate the NWF while strike-slip earthquakes are seen across the KMF. Our results show that the two fault surfaces converge between 70.30°E and 70.43°E longitudes in the depth range 22–32 km, however, there is large E–W offset between the northern and southern extremities of the fault-system. This convergence zone hosted the largest earthquakes (ML 4.7–5.1) between 2006 and 2018 and the hypocentre of 2001 main shock also coincide with it. The earthquakes occurring in the interfault region show major strike-slip motion and are probably influenced by the relative motion between the NWF and KMF. Consistent seismicity, assisted probably by high conducting material, is seen across the NWF while intermittent seismicity is revealed along the KMF. Scrutiny of earlier studies revealed that the 2001 main shock and first few weeks of aftershocks were hosted on another south-dipping fault, the South Wagad Fault (SWF), however, activity along the SWF is found to be meagre during 2006–2018. Instead, seismicity has currently migrated to faults north and south of the SWF. These currently active faults most likely were reactivated during/after the 2001 main shock.
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Kaneda, Heitaro. "Threshold of geomorphic detectability estimated from geologic observations of active low slip-rate strike-slip faults." Geophysical Research Letters 30, no. 5 (March 2003): n/a. http://dx.doi.org/10.1029/2002gl016280.
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Yalçın, H., A. Kürçer, M. Utkucu, and L. Gülen. "SEISMOTECTONICS OF THE SOUTHERN MARMARA REGION, NW TURKEY." Bulletin of the Geological Society of Greece 50, no. 1 (July 27, 2017): 173. http://dx.doi.org/10.12681/bgsg.11717.
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The Southern Marmara Region is an active deformation area, which is a transition zone between the strike-slip tectonics manifested by the North Anatolian Fault System and the N-S extensional regime of the Aegean Region. We have reviewed tectonic and geological structure of the region, based onseismological studies. We have obtained a total of 37 earthquake moment tensor solutions between 1953 and 2015. In addition, stress tensor analysis has been carried out using 37 earthquake moment tensor solutions. Also long term seismicity were investigated and a,b, Mc values were calculated and mapped. Moment tensor solutions indicate that the source of these earthquakes are mostly NE-trending dextral strike-slip faults and some of them are E-W trending dip-slip normal faults. The stress tensor analysis shows that the direction of the regional compressive stress is NW-SE. The temporal and spatial distrubution of the large earthquakes (1944, 1953, 1964) indicate that the ruptures unilaterally propagate from SW to NE. The 1855 earthquake had been occurred to the east of Manyas Lake. The elapsed time (160 year) and regional stress transfer suggest that the segments to the east of Manyas Lake form a probable seismic gap and this area has a high earthquake risk.