Left-lateral Strike-slip Displacement Research Articles

Geometry, slip rate, and the latest earthquake of the Jinta Nanshan Fault: Interactions of the Altyn Tagh Fault and the Qilian Shan at the northern margin of the Tibetan Plateau

This work presents a study of late Quaternary activity on the Jinta Nanshan Fault (JTF), to constrain its properties including seismic hazard, and to understand the tectonic evolution of the northern edge of the Tibetan Plateau. The JTF has developed during northeastward growth of the Qilian fold-and-thrust belt and eastward growth of the Altyn Tagh Fault. Based on remotely-sensed image interpretation and field investigation, trench studies, high-resolution terrain construction and Optical Stimulated Luminescence dating, we study the fault geometry and slip motion, and constrain the slip rate and the latest earthquake for the JTF. The JTF continues as far southeast as the Heihe River and shows predominantly left-lateral strike-slip displacement. The left-lateral slip rate is 0.27–0.48 mm/yr since late Pleistocene, much larger than the vertical slip rate of 0.05 ± 0.01 mm/yr. The latest rupture event of the JTF is slightly before 1 ka, which could be related to the poorly-recorded 756 CE earthquake in Hexi Corridor, and is also associated with fresh offset during this earthquake in the geomorphology of the east segment of the JTF. Strike-slip offset in this earthquake is estimated as 3.2 ± 0.4 m, with a rupture length of at least ∼13 km, indicating a moment magnitude of 6.4–7.2. We estimate the recurrence interval as 8–13 ka, based on the size of the latest offset and the slip rate of 0.27–0.48 mm/yr. These results indicate that the strike-slip continuation of the Altyn Tagh Fault dominates the slip behaviour of the JTF. The small strike-slip rate, and the match between the strike-slip of the JTF and the vertical slip of the North-South Normal Faults (NSF) at its eastern end, permit the interpretation that the slip of Altyn Tagh Fault is completely accommodated by crustal extension at the NSF, and dies out at the eastern end of the Jinta Nanshan region.

3D Paleoseismology from iOS Lidar and Structure from Motion Photogrammetry: a case study on the Dog Valley fault, California

Measuring displacements of strike-slip paleoearthquakes from trenching excavations requires detailed 3D trenching excavations. Here a new methodology utilizing an iOS based laser scanner and structure-from-motion is used to reconstruct stratigraphy and trace a displaced fluvial channel sequence across the Dog Valley fault in Northeastern California. The Dog Valley fault is a left-lateral strike slip fault in the northern Walker Lane. The northern Walker Lane accommodates ~5-7 mm/yr of dextral shear; however, the relative rates of deformation and earthquake history of the fault have not been previously assessed. Here, we present geomorphic mapping observations and preliminary paleoseismic trenching results from the Dog Valley fault. Lidar data reveal a clear east-northeast striking fault trace that extends about ~25 km from the Prosser Creek drainage west of the Polaris Fault near Highway 89 to the northwest flank of Peavine Mountain. The main trace of the fault appears to project through Stampede dam. Youthful fault scarps are visible along much of the fault, with alternating northwest- and southeast-facing scarps. Clear lateral displacements are largely absent along the fault, however right-stepping fault strands, sidehill benches, linear valleys and ridges, and alternating scarp facing directions are all consistent with left-lateral strike slip displacement. Stratigraphic and structural relations exposed in the Dog Valley fault trench show clear truncations and tilting of bedded fluvial and peat deposits and provide evidence for the occurrence of two Holocene earthquakes: the most recent earthquake postdates ~8 ka, and an earlier earthquake is inferred to have occurred between 8491-8345 cal. ybp. Based on 3D excavations of a prominent channel margin, the most recent earthquake was associated with ~ 115 cm of left-lateral displacement, corresponding to an M6.7 earthquake.

A structural analysis of the Washita Valley Fault in the southeast Anadarko Basin

We propose that the Washita Valley Fault in the southeast Anadarko Basin originated when Precambrian-Cambrian preexisting rift-related faults became reactivated as a rotational stress field reached a favorable orientation for strike-slip displacement. During the Early to Middle Pennsylvanian, contractional deformation dominated as a Precambrian-Cambrian failed rift underwent structural inversion along a northeast-directed stress field. Structures that developed in the basin consisted primarily of thin-skinned fold-thrust structures resulting from slip along two main detachment levels. By the Late Pennsylvanian, stress rotated toward the east–northeast causing left-lateral strike-slip displacement along east–west-oriented structures. During this time, the Washita Valley Fault originated from an east–west-oriented preexisting basement fault. The Washita Valley Fault formed as a near-vertical segment cutting through the earlier fold-thrust structures. Movement was accompanied by oblique normal slip allowing grabens to develop that were subsequently filled with Virgilian-age sediment. A left step of the Washita Valley Fault allowed for a significant graben to develop near the east end of the study area resulting in a thick Virgilian-age growth section validating the timing of the fault movement. The Wichita Mountain Fault also underwent a component of left-lateral strike-slip displacement during the Late Pennsylvanian highlighting its continuous movement and deformation history in a rotating stress field. Although much of the published literature on the Washita Valley Fault is limited to the Arbuckle Uplift, our study documents its subsurface architecture, timing, and structural history in the southeast Anadarko Basin using a modern 3D seismic data set in relation to evolving Pennsylvanian tectonics.

Paleocene–early Eocene post-subduction magmatism in Sikhote-Alin (Far East Russia): New constraints for the tectonic history of the Izanagi-Pacific ridge and the East Asian continental margin

New isotopic, geochemical and geochronological data justify the widespread occurrence of middle Paleocene to early Eocene (60–53 Ma) post-subduction felsic magmatism across the entire Sikhote-Alin territory (southeastern Russia), conform with previous observations in Northeast China, the southern Korean Peninsula, and the Inner Zone of Japan. This igneous activity in East Asia coincided with the reactivation (after tectonic quiescence between ~93–60 Ma) of left-lateral strike-slip displacements along the Tan-Lu and Central Sikhote-Alin faults and with the post-60 Ma cessation of subduction/accretion recorded in the Shimanto belt of SW Japan. The Sikhote-Alin post-subduction igneous A-type rocks present diverse mineralogical and geochemical features that suggest interactions of the subducting plate with anhydrous mantle upwelling through slab tears in the continental margin. The middle Paleocene–early Eocene magmatism is not related to subduction but is synchronous with strike-slip tectonics and the termination of accretionary prism development, suggesting a shift in tectonic regime from oceanic plate subduction at a convergent margin to parallel sliding and initiation of a transform continental margin. These new observations are inconsistent with the current tectonic model of 60–50 Ma Izanagi-Pacific ridge subduction beneath East Asian continental margin.

Surface deformations of 24 January 2020 Sivrice (Elazığ)–Doğanyol (Malatya) earthquake (Mw = 6.8) along the Pütürge segment of the East Anatolian Fault Zone and its comparison with Turkey’s 100-year-surface ruptures

On Friday, January 24, 2020 at 20.55:11 local time (17:55 UTC), an earthquake with a magnitude of Mw = 6.8 has occurred in Sivrice district of Elazig (Eastern Turkey). Focal mechanism solution is consistent with pure left-lateral strike-slip faulting; the location of the epicenter and fault mechanism suggest deformation along the Puturge segment of the East Anatolian Fault Zone. A 10-day fieldwork was carried out along the Puturge segment to study surface deformation; the geometry of the surface rupture and other seismic geomorphological structures were mapped and studied in detail. The field data are also correlated with satellite images. This paper, therefore, presents classification of seismic geomorphological structures and discuss intimate relationship between fault geometry and stress field in the region. Seismic geomorphological deformation and related features of the Sivrice (Elazig) earthquake are observed in the area between Gezin (Elazig) and Ormanici (Puturge) villages; they are classified into two as seismotectonic and seismo-gravitational features. Field observations confirm that seismo-gravitational structures develop along both Gezin-Sivrice–Doganbagi and Doganbagi–Cevrimtas–Ilincak–Koldere–Ormanici sections of the Puturge segment, while surface rupture is mapped as seismotectonic structure only along the Doganbagi–Cevrimtas–Ilincak–Koldere–Ormanici section. Small-scale landslides, rock falls, feather cracks along asphaltic roads, and laterally discontinues ground failure-related features are common seismo-gravitational structures that developed along the fault zone. In addition, small-scale lateral spreading and liquefaction structures are common especially in areas where fault-perpendicular streams meet the Karakaya Dam reservoir. The surface rupture is mapped as stepping and overlapping en echelon fractures along elongated pressure ridges between Cevrimtas and Doganbag villages, to northwest of Ilincak village, along 1.5-km-long pressure ridge between Topalusagi and Doganyol, across the elongated hill that developed on an alluvial fan to the northwest of Doganyol and in the area between Koldere and Ormanici villages. Surface fractures deforming the pressure ridges are all aligned parallel to the long axes of the ridges and display reverse components that give rise to small-scale pop-up structures. Interferometric SAR (DInSAR) studies indicate a 10-cm uplift in the northwestern block of the fault and a 6-cm subsidence in the southeast block. The difference in vertical movements between two blocks of the fault is interpreted to suggest that at least 30-km-long section of the Puturge segment in the area between southwest of Sivrice and Puturge is broken during the main shock. Although the focal mechanism solution of the main shock gives pure left-lateral strike-slip faulting, there is no significant left-lateral displacement observed during the fieldwork. This can be explained by the following: (1) left-lateral strike-slip displacement was not able to reach the surface; (2) left-lateral torque movement of the fault around a vertical axis during the earthquake, (3) restraining bend nature of the Puturge segment, or (4) the presence of Puturge metamorphics along the fault strike. It is also important to note that along most part of the Puturge segment where surface rupture is observed, talus, colluvial or alluvial fan sediments are exposed; unconsolidated and/or poorly consolidated nature of these sediments may also be counted as one of the main reason for not observing horizontal displacement on the surface. When we compare these surface deformations with the surface ruptures that occurred in the last 100 years in Turkey, we suggest that the formation of the surface deformations is variable depending on: (1) the fault type and the state of regional stress, (2) the magnitude of the earthquake, (3) the duration time of the earthquake and (4) the geomorphologic feature of landscape in relation to the lithologic and structural features of the rock units along the active fault zone.

Seismotectonics of the 2017–2018 Songyuan Earthquake Sequence, Northeastern China: Passive Bookshelf Faulting and Block Rotation in the Songliao Basin

AbstractThe high frequency of earthquake clusters generated by pure strike-slip faulting over the past 3 yr (beginning in 2017 in the Songliao basin, northeastern China) has motivated us to consider why lateral strike slip and not extension determines the seismic activity within the Songliao basin. Precise location and characterization of relocated aftershocks, forward modeling of the coseismic displacement field, and Global Positioning System (GPS) monitoring data are combined to detect the possible seismogenic structures of the Songyuan earthquake sequence. The 2017 ML 5.3 aftershock cluster coincided with the northeast-striking Fuyu–Zhaodong fault (FZF), and the 2018 aftershock swarm followed the linear trend (N42°W) of the Songhuajiang fault (SHF). In addition, the forward modeling results indicate that during the earthquakes, right-lateral and left-lateral strike-slip displacements occurred simultaneously along the FZF and SHF, respectively. These two strike-slip faults joined to accommodate the intervening crustal blocks’ asymmetrical east–west convergence and a single northward extrusion. We also utilize 5 yr of GPS data to construct the regional strain-rate map for the basin. The measurements show that right-lateral transform motion along the immense northeast-striking right-lateral strike-slip faults, for example, the Tanlu fault zone and the FZF, impose a northeast-striking simple shear across the Songliao basin. This simple shear not only caused left-lateral movement on the minor northwest-striking left-lateral strike-slip faults such as the SHF but also rotated them ∼14° clockwise into their present orientations. The results of the proposed bookshelf faulting model in which the predominant northeast-striking parallel faults are initiated are consistent with the observed lineament orientations, focal mechanisms, and earthquake distributions. The sharp shift in the subduction direction of the Pacific plate seems to have had a considerable influence on the intracontinental deformation in China, at least throughout northeastern China.

Earthquake crisis unveils the growth of an incipient continental fault system

Large continental faults extend for thousands of kilometres to form boundaries between rigid tectonic blocks. These faults are associated with prominent topographic features and can produce large earthquakes. Here we show the first evidence of a major tectonic structure in its initial-stage, the Al-Idrissi Fault System (AIFS), in the Alboran Sea. Combining bathymetric and seismic reflection data, together with seismological analyses of the 2016 Mw 6.4 earthquake offshore Morocco – the largest event ever recorded in the area – we unveil a 3D geometry for the AIFS. We report evidence of left-lateral strike-slip displacement, characterise the fault segmentation and demonstrate that AIFS is the source of the 2016 events. The occurrence of the Mw 6.4 earthquake together with historical and instrumental events supports that the AIFS is currently growing through propagation and linkage of its segments. Thus, the AIFS provides a unique model of the inception and growth of a young plate boundary fault system.

Evolution of Riedel-shear pop-up structures during cumulative strike-slip faulting: A case study in the Misayama-Godo area, Fujimi Town, central Japan

Strike-slip faulting often develops en échelon faulting resulting from Riedel shears. When faulted basement rocks are covered by thick unconsolidated deposits, this en échelon faulting leads to the subsequent evolution of a series of pop-ups along the fault during cumulative displacement. Although previous sandbox experiments and numerical simulations have examined the evolutionary processes for Riedel-shear pop-up structure formation, few field examples have been reported until now concerning (1) the time-series of evolutionary processes of pop-up structure generation and (2) time periods necessary to reach the stage of a “throughgoing fault zone”. The Itoigawa-Shizuoka Tectonic Line (ISTL) fault zone is among the largest and fastest-slipping active fault zones in Japan, and a series of tectonic pop-ups related to left-lateral strike-slip displacement have developed in the Fujimi area in the central to southern part of the fault zone. This area is covered by thick (~820 m) unconsolidated deposits, which have resulted in Riedel-shear pop-up structures. We conducted a geomorphic analysis, an extensive drilling survey, and pit excavation survey on a pop-up in the Misayama-Godo area of Fujimi, and concluded that (1) the pop-up structures in the Misayama-Godo area have been built up by two marginal faults between ~100 ka and ~10–20 ka, and (2) the fault displacement at depth has been concentrated on the faults that run across the pop-up structures (corresponding to the “throughgoing fault zone”) since ~10–20 ka. One of the faults that run across the pop-up structures probably slipped during the most recent earthquake in the central to southern part of the ISTL fault zone. This study is presented as a robust field example of the evolution of Riedel-shear pop-up structures during cumulative strike-slip faulting.

Structure of the Northwestern Boundary of the Middle Amur Sedimentary Basin (Russian Far East) from Audiomagnetotelluric Sounding Data

This paper reports the data on the structure of the northwestern boundary of the Middle Amur sedimentary basin which were obtained after resumption of audiomagnetotelluric soundings. The geoelectric sections for two profiles across the basin strike are constructed, the sedimentary cover and basement structures are studied, and their electrical properties are determined. The compared data of the earlier and present studies show low-resistivity zones of 50–150 Ohm m beneath high-resistivity rocks of 500–1000 Ohm m in the northwestern part of the Ul’dura–Churki uplift at a 2–4 km depth, which are absent in the southwestern part of the uplift. This fact is related to strike-slip–overthrust processes due to graben formation in the area of junction with the Jiamusi–Bureya Massif in the Kur fault zone (YYilan–Yitong branch of the Tan-Lu fault zone) and also to global left-lateral strike-slip displacements and volcanic activity.

Satellite geodetic monitoring of the Vladikavkaz active fault zone: First results

A geodetic network of Global Satellite Navigation System (GNSS) observation sites was organized in 2014–2015 for studying the contemporary crustal motions in the zone of the Vladikavkaz deep fault (Milyukov et al., 2014; 2015). The measurements were conducted and the first velocity estimates obtained testifying to the consistency of crustal motions in the Vladikavkaz fault zone and the Ossetian region overall in the ITRG2008 system. The first results show that the velocities and directions of horizontal motions do not change upon the transition of the fault zone. In correspondence with the northeastern orientation of the site displacement vectors and sublatitudinal trend of the disjunctive zone, the presence of left-lateral strike-slip displacements along the branches of an active fault should be expected. However, the signs pointing to the activation of motion in the fault zone are absent. Besides, even the manifestation of weak seismicity has not been observed within the high-magnitude seismogenic Vladikavkaz zone associated with this fault for more than 25 years. This suggests the passive present state of this structure, one of the largest disjunctive structures of the Northern Caucasus. In order to verify this conclusion and revealing the kinematic pattern of the displacements associated with the fault structure it is reasonable to continue the measurements.

Structure and evolution of the Sura-Kama strike-slip zone in the Cenozoic (the Volga-Ural anteclise of the East European Platform)

The Sura-Kama zone (SKZ) complicates the central area of the Volga-Ural anteclise and extends sublaterally from the Sura River basin towards the Kama River at a distance of 700–750 km. Based on the analysis of geological-geophysical data and structural studies, a model for the tectonic structure and the evolution of the SKZ is developed. This is a deep tectonic fault that shows the features of long-term polystage development. During the latest Cimmerian-Alpine period of tectonic reactivation, the SKZ represented a zone of strike-slip and consecutive manifestation of early transpressional right-lateral strike-slip dislocations that changed to left-lateral strike-slip displacements under transtension settings as a result of kinematic inversion. Features of the heterogeneous structure of the SKZ are revealed. The segments formed by the system of strike-slip duplexes are alternated along the strike by the principle of rotation-fold and “domino” structures. The particular models of evolution of these segments are proposed by the examples of the widely known Karlin, Tetyushin, and Lower Kama dislocations. It is assumed that kinematic inversion and compression-decompression phenomena on the flanks of the SKZ, as well as the tectonic environments in the area of its dynamic influence were highly important for the development of the processes of migration and redistribution of hydrocarbon components.

Evidence of Large Scale Tectonic Processes on the Tharsis Rise, Mars

Past observations of Mars have led scientists to believe that tectonic kinematics stopped early in its planetary development. Recent exploration of Mars has led to new theories that support an active tectonic regime on the Tharsis rise. With the advancement of new satellite imagery and technologies such as Thermal Emission Imaging System, High Resolution Imaging Science Experiment satellite imagery, the Mars Orbital Laser Altimeter, and interactive software such as J-Mars and Esri GIS, we have identified additional large-scale surface features in the Tharsis Rise and surrounding areas. Large-scale Martian lineations, folds, and conjugate joints can be compared to similar structures on Earth to interpret potential plate boundaries. For example, a northeast-trending set of lineations with significant left-lateral strike-slip displacement and conjugate jointing located to the northeast of the Tharsis Rise could accommodate transform motion between two plates. Our observations allow the designation of multiple potential plate margins in the region. We propose a tectonic model showing relative motions along plate boundaries in a potentially active multiple-plate system on Mars.

Evolution of Strike-Slip Duplexes and Wrench-Related Folding in the Central Part of Al Jabal Al Akhdar, NE Libya

AbstractThe deformation in the central part of Al Jabal Al Akhdar, NE Libya, is dominated by E-W right-lateral strike-slip fault zones that form a conjugate system with the N-S left-lateral strike-slip faulting. The dextral wrench-dominated transpression is responsible for the formation of strike-slip duplexes, en echelon folds, and thrusts that deform the Cretaceous-Eocene sedimentary sequences. The strike-slip duplex is formed by the progressive linkage of horsetail-like structures at the western tip of the Al Bayda strike-slip fault that joined splays coming from other dextral strike-slip faults. The master linear fault branches into second-order dextral or sinistral faults that regroup into a linear single fault. Faults started from arrays of en echelon extensional/extensional-shear fractures that then coalesced into throughgoing strike-slip faults. Shortening was accompanied by significant N-S-striking left-lateral strike-slip displacements, with the development of NE- to ESE- and SW-plunging major f...

Correction to “Spatial and temporal patterns of exhumation across the Venezuelan Andes: Implications for Cenozoic Caribbean geodynamics”

[1] In the paper “Spatial and temporal patterns of exhumation across the Venezuelan Andes: Implications for Cenozoic Caribbean geodynamics” by Mauricio A. Bermúdez, Barry P. Kohn, Peter A. van der Beek, Matthias Bernet, Paul B. O'Sullivan, and Reginald Shagam (Tectonics, 29, TC5009, doi:10.1029/2009TC002635, 2010), there are corrections to Figure 9 caption and an additional reference. Figure 9. Possible kinematic configuration for the South American-Caribbean plate boundary zone during earliest Oligocene (Figure 9a), late Miocene (Figure 9b), and Pliocene times (Figure 9c). (a) Earliest Oligocene, widespread but relatively slow exhumation in the Venezuelan Andes, Eastern Cordillera of Colombia, and Perija range results from inversion of preexisting rift structures during regional compression, possibly related to initial subduction of Panama arc. (b) Late Miocene, rotation of the Maracaibo block (MB) is almost completed, left-lateral strike-slip displacement between the Maracaibo block and the South American plate is concentrated on the BFS, producing translation and minor rotation in the Trujillo block (TB) during its tectonic escape. Major exhumation of the SNB and SLCB occurs during this phase. (c) Pliocene, final closure of Panama arc is expressed by rapid localized exhumation in parts of the Venezuelan Andes (ECB) and Eastern Cordillera (Quetame Massif [Parra et al., 2009]). See text for more detailed discussion. Figures are modified from http://www.tectonicanalysis.com/site/caribbean/default.htm [see also Pindell and Kennan, 2009] with minor inputs from Montes et al. [2005], Corredor [2003], and Hoorn et al. [1995].

Co-seismic strike-slip surface rupture and displacement produced by the 2010 M W 6.9 Yushu earthquake, China, and implications for Tibetan tectonics

The magnitude (M W) 6.9 (M s 7.1) Yushu earthquake occurred on 14 April 2010 in the Yushu area, central Tibetan Plateau, causing widespread damage in high mountain regions. Field investigations reveal that the earthquake produced a 33-km-long surface rupture zone, with dominantly left-lateral strike-slip along the Yushu Fault of the pre-existing strike-slip Ganzi-Yushu Fault Zone. The co-seismic surface ruptures are characterized by discontinuous shear faults, right-stepping en echelon tensional cracks, and left-stepping mole track structures that indicate a left-lateral strike-slip shear sense for the seismic fault. Field measurements indicate co-seismic left-lateral strike-slip displacements of approximately 0.3–3.2 m (typically 1–2 m), accompanied by a minor vertical component of <0.6 m. The present results show that (i) the Yushu earthquake occurred upon the pre-existing active Ganzi-Yushu Fault Zone, which controlled the spatial distribution of co-seismic surface ruptures and displacements; (ii) the left-lateral strike-slip motion indicates that the Ganzi-Yushu Fault Zone partitions deformation into eastward extrusion of and northeastward shortening the central Tibetan Plateau to accommodate the continuing penetration of the Indian plate into the Eurasian plate.

Geophysical signature of the vien-type uranium mineralization of Wadi Eishimbai, Southern Eastern Desert, Egypt

The application of various geophysical tools with different responses succeeded in fixing U-mineralization in Wadi Eishimbai area. The area was studied using detailed ground spectrometric, magnetic, and filtered very low-frequency electromagnetic (VLF-EM) surveys. The interpretation of the obtained spectrometric maps clearly reflects the sharp increase of equivalent uranium (eU) content. Meanwhile, K and Th contents show sharp decreases. The eU/equivalent thorium (eTh) ratio correlates positively with eU concentrations and negatively with eTh concentrations, indicating an increase in U potentiality than the surrounding granite. The N–S shear zone displays an eU content ranging from 20 to 140 ppm. The ENE-trending lamprophyre is characterized by elongated uranium anomalies trending in the E–W direction, with values >90 ppm. Equivalent uranium content of the brecciated granite attains values up to 700 ppm. The ground magnetic and VLF-EM surveys played important roles in providing structural information which are proven useful in geological mapping and mineral exploration for the discovery of uranium mineralization in the study area. This study follows the expected subsurface extension of the Sela shear zone under Wadi sediments. The ground total magnetic intensity map shows a relatively narrow and an elongated shape for the lamprophyre anomaly extending for about 600 m in the Wadi toward the western direction. VLF-EM contour maps of the two used frequencies (17.1 and 28.5 kHz) show excellent agreement, indicating that the shear zone is distinguished with slightly strong conductivity westwards as an extension of the main shear zone. It is elongated in an ENE–WSW trend and extends in the western direction, referring to the existence of conductive materials. Most of the NW/SE-trending faults cause sudden changes in the magnetic and VLF-EM contour spacing over an appreciable distance, which suggests a discontinuity in depth due to their left-lateral strike-slip displacements. The interpreted faults, with an ENE–WSW trend representing the main trend of Sela shear zone through which hydrothermal solutions flowed, cause high alteration and uranium mineralization.

Complicated phenomena of the Beichuan-Yingxiu surface fracture zone during Wenchuan Ms8.0 earthquake in Sichuan Province, China

After Wenchuan Ms8.0 earthquake, the surface fractures have been investigated in Beichuan City and Yingxiu Town. It was found that the Beichuan-Yingxiu earthquake fracture zone trends northeastward, dipping to northwest. The earthquake fracture zone is mainly characterized by thrust faulting with small amounts of strike-slip movement, and demonstrating various complexities for different areas. The phenomena related to dextral strike-slip displacement are found in Beichuan City and those related to left-lateral strike-slip movement in Yingxiu Town. The compressive shortening of the two surface fracture zones in Beichuan City is 2.8–3.9 m and the left-lateral strike-slip displacement of the surface fractures in Yingxiu Town is 0.52 m.

Seismic deformation in the St. Simeon Monasteries (Qal'at Sim'an), Northwestern Syria

The St. Simeon Fault is 80 km long and stretches from the eastern side of the Al Ghab Depression to the north–east; it links the structures of the Levant and East-Anatolian active zones. Left-lateral strike-slip displacements and deformations of landforms cut by the fault have been recorded. The Sim'an Ridge is located between two branches of the fault and displaced by 1.2 km, overlapping a young depression. As the terminations of these branches at the site of their overlapping converge northerly, the mechanism of structural scissors considerably enhances the lateral extrusion of the Sim'an Ridge. The St. Simeon Monastery, built by the Byzantine in the 5th century AD, is situated on the top of the Sim'an Ridge. The main church of the St. Simeon Monastery has a cruciform shape, and its eastern wing is deflected by 3–9° to the north. The existing architectural explanation of this phenomenon assumes initial designing of this bend by the builders and contains many contradictions. Upon our study of active faults, specific features and traces of seismic impacts on the monastery structures, we suggest an alternative, seismic explanation. Our scenario interprets the curvatures of the monastery structures as a consequence of distributed co-seismic or post-seismic deformations in the intra-fault block delimited by the branches of the St. Simeon Fault.

ZARMITAN GRANITOID-HOSTED GOLD DEPOSIT, TIAN SHAN BELT, UZBEKISTAN

The 10-Moz Zarmitan gold deposit is located in the Nuratau region in central Uzbekistan. This area represents a part of the late Paleozoic Tian Shan orogenic belt. The belt formed as a result of a late Paleozoic orogenic collision between the Tarim-Karakum continent and the Kazakhstan-north Tian Shan plate and represents one of the richest gold provinces in the world. The Zarmitan deposit, containing 84 major orebodies and numerous smaller veins, is partially hosted by the Koshrabad granitoid intrusion, the geochemical characteristics of which indicate a late orogenic affinity. The gold-bearing veins are distributed as a complex anastomosing east-west–striking and concave to the north swarm. The strike length of this zone is approximately 7 km, and the thickness varies from 200 to 1,500 m. The total resource of the 84 major lodes is 32 million tonnes (Mt) at 9.8 g/t Au and 14.6 g/t Ag. Gold mineralization is associated with reverse vertical movement accompanied by left-lateral strike-slip displacement along high-angle faults, which represent splays off the Karaulkhana-Charmitan fault zone. This fault is one of the major structures in the Northern Nuratau area and is a major control on mineralization along the southern contact of the Koshrabad pluton, including the Zarmitan deposit. The highest gold grades and highest Au/Ag ratios are found in gold-bearing veins from the central part of the Zarmitan deposit, which is also characterized by abundant hydraulic breccias. This study considers new field and mine data from Zarmitan with earlier studies of the deposit and with recent models for intrusion-related gold deposits.

Evidence of coseismic ruptures along the Roum fault (Lebanon): a possible source for the AD 1837 earthquake

The Roum fault is the westernmost branch within the Lebanese restraining bend of the Dead Sea Transform Fault. This strike-slip fault extends for about 35 km from north of the Hula basin to the Awali river, and shows left-lateral strike-slip displacements (manifested as offset streams) and vertical movements. Recent seismic records indicate its seismogenic potential as the source of the double shock of 16 March 1956 (Ms 4.8, 5.1) earthquake. We studied the Roum fault using combined field investigations in geomorphology, structural geology, and palaeoseismology. Fresh fault scarps and pressure ridges visible along the fault trace attest to recent coseismic ruptures. A palaeoseismic trench investigation exposed a complex fault zone with several rupture strands and a minimum of four faulting episodes in the last ∼10,000 years, the most recent event being post 84–239 AD. According to historical records, the 1 January 1837 (Ms 7.1) earthquake, which induced severe damage in the region, is the most likely candidate. Our results assign a slip-rate of 0.86–1.05 mm/year along the Roum fault, which shows that it accommodates about 14% of the total predicted strike-slip motion within the Lebanese restraining bend, and it should be considered a potential seismogenic fault for seismic hazard estimates in Lebanon.