Right-lateral Strike-slip Fault Research Articles

Surface deformation and strike-slip faulting controlled by dyking and host rock lithology: A compendium from the Krafla Rift, Iceland

In the present work, we have obtained a detailed, complete view of surface deformation at a volcano-tectonic structure belonging to the Krafla Fissure Swarm (NE Iceland), through the integration of field mapping and the Aerial Structure from Motion technique (ASfM), as well as through orthomosaics and Digital Surface Models (DSMs). The documented, 2.5-km-long deformation zone is marked by a range of features, such as topographic bulging, parallel extension fractures, and narrow grabens affected by local floor uplift, which we have explained as the effect of the northward, shallow propagation of a dyke from the Krafla magma chamber. Our lithostratigraphic field survey of the area, at a 1: 5000 scale, indicates that major changes in the pattern of surface deformation take place across the contacts between deposits with different rheological properties. The transition from very stiff lavas to softer hyaloclastites produces changes from extensional fracturing to normal faulting, though the width of the deformation zone does not change. We have also documented a number of NE-SW, left-lateral and NNW-SSE, right-lateral strike-slip fault zones that are rotated in clockwise and anticlockwise sense to the main NNE-SSW graben trend, and extend outwards as much as about 17 m. The graben zone terminates to the north by splitting into two strike-slip fault zones. These were likely generated at the front of the dyke tip during its propagation, and were later on bypassed by the advancement of the dyke. As the dyke entered the soft hyaloclastites, propagation was slowed down and the dyke became thicker.

Transpression and Exhumation of Granitoid Plutons along the Northern Part of the Nehbandan Fault System in the Sistan Suture Zone, Eastern Iran

Geometry and kinematics of deformation across the Nehbandan Fault System (NFS) have been studied in the Bibimaryam and Damdameh areas in the Sistan Suture zone (SSZ). Nearly vertical fault planes with sub-horizontal lineations and correlation of these faults analysis with anisotropy of magnetic susceptibility (AMS) indicates a predominantly transpressive regime including right-lateral strike-slip faults with reverse components in the region. An assemblage of en-echelon and doubly plunging folds with slip indicators, such as duplexes in their limbs, confirms progressive transpressive deformation. Accompanying hydrothermal alteration has created ideal conditions for reactivating shear fractures during late Cenozoic times that record the last phase of tectonic activity. Intrusive bodies such as the Bibimaryam and Damdameh granitoid plutons are exposed along the NW‒SE faults that branch off the Nehbandan Fault System (NFS). Fault analysis there shows three directions for compression (σ1): N085°, N074°, and N024° from the Late Cretaceous to the Plio-Quaternary respectively, on the borders of the NFS. Our results are consistent with recent paleostress studies, which revealed counterclockwise rotation of σ1 during the Late Cenozoic in eastern Iran. Redistribution of σ1 directions along the NFS in the context of general N‒S striking indicates a decreasing pure shear component, and consequently an increasing simple shear component from the Late Cretaceous to Plio-Quaternary. This reconfiguration of σ1 likely triggered the exhumation of the Tertiary Bibimaryam and Damdameh granitoid plutons along the fault zones. Field evidence and lithofacies indicate that exhumation of the intrusive bodies cannot have preceded the late Eocene. Hence, the late Cenozoic uplift and exhumation of the Sistan Belt may largely have resulted from the development of a dextral transpressive regime along the NFS in the SSZ.

The geology and tectonic evolution of the northwest part of the Barberton Greenstone Belt, South Africa: A review

AbstractFormations on the northwestern flank of the Barberton Greenstone Belt have hosted over 85% of all the gold recovered from the ca. 3550 to 3000 Ma Barberton Supergroup since early discoveries in 1872. This sector of the greenstone belt also happens to coincide with a complex tectonic architecture resulting from successive stages of folding and faulting superimposed onto a complex lithostratigraphy. Of particular importance has been the influence of two diapiric granitoid intrusions that caused added structural complexity following their emplacement ca. 3227 to 3250 Ma. Of these the larger Kaap Valley Pluton invaded the area north of present day Barberton town causing the separation of the greenstones into a northern arm (Jamestown Schist Belt) and a southern sector which remained attached to the main greenstone belt (Moodies Hills). The ballooning pluton produced vertical as well as horizontal flattening stresses, the latter reactivating earlier high-angle faults and resulting in subhorizontal strike-slip movements, particularly along the Barbrook Fault Zone, which acted as a right-lateral strike-slip fault. Formations north of this fault were buckled, following progressive deformation in the region known as the Sheba Hills, into major synclinal folds (Eureka and Ulundi Synclines) with folded axial planes that dip steeply to the south, southeast or east. The second granitoid intrusion (Stentor Pluton), which has been extensively modified by subsequent magmatic events, caused significant flattening of greenstone belt rocks in the northeastern part of the Barberton Greenstone Belt (Three Sisters region) as well as in other areas rimming the granitic body. Combined, the two plutons produced a wide range of interference and reactivated structures particularly affecting a triangular region extending from the Jamestown Schist Belt into the area occupied by the New Consort Gold Mine and areas to the east. This paper attempts to outline, in the simplest manner, the geological and structural evolution of the main gold-producing region of the Barberton Goldfield. The principal aim is therefore to highlight the structural influence of the diapiric plutonism and the manner in which the plutons contributed significantly to the horizontal reactivation of pre-existing regional faults, which in turn, resulted in the progressive deformation of a heterogeneous lithological terrane.

The role of active strike-slip faults and opposite vertical axis rotations in accommodating eurasia-arabia shortening in central iran

In Central Iran, most of the Late Cenozoic to Present shortening has been accomplished in the Zagros, in the Alborz, and Kopeh-Dagh mountain ranges. Between these active mountain belts, a minor amount of shortening is observed and the deformation style is characterized by active strike-slip faults that bound relatively aseismic blocks. Two main strike-slip fault systems are presently active in different regions of Central Iran: South of latitude 34°N, active deformation is accommodated on ∼N–S oriented right-lateral strike-slip faults, and north of latitude 34°N, E–W left-lateral strike slip faults prevail.In this work, we investigated two different structures, representative of the two different strike-slip systems occurring in Central Iran: the Yazd fold system located in an area dominated by the occurrence of NNW-SSE oriented right-lateral strike slip faults, and the Ferdows fold system that developed at the western termination of the E–W left-lateral strike-slip Dasht-e-Bayaz fault. Paleomagnetic results show opposite vertical-axis rotations related to the different orientation and sense of movement of strike-slip fault systems, suggesting that in Central Iran the N–S oriented right-lateral and E–W oriented left-lateral strike-slip faults play significant roles in accommodating the Arabia-Eurasia convergence, by rotating counterclockwise and clockwise in the horizontal plane, respectively.

The role of Late Cretaceous wrench tectonics in hydrocarbon endowment in El-Gindi Basin, northern Western Desert, Egypt

Abstract Detailed subsurface mapping and structural analysis of El-Gindi basin indicate the hydrocarbon potentiality of the Cretaceous reservoirs. El-Gindi basin is a Late Cretaceous-Eocene basin located at El-Fayium district, northeastern Western Desert of Egypt. The overwhelming impact of the Late Cretaceous wrench tectonics was evident during the inversion of the Jurassic-Early Cretaceous rift-related basins along the North Western Desert of Egypt and subsequent deposition of a thick succession of Eocene sediments (~6000 ft Apollonia Formation) within El-Gindi Basin. These tectonic events were developing the oil maturity and trapping through the Late Cretaceous reservoir sequences, Upper Bahariya Formation (Cenomanian) and the Abu Roash “G” Member (Turonian). The Gindi Fault, however, is a NW-trending basement feature breaching El-Gindi basin and bounding several deeper half grabens in the western half of El-Fayium district. It has been reactivated during the Cretaceous, Eocene and probably Oligocene-Early Miocene times, where extended northwestward to the Qarun Field at the footslopes of the Kattaniya inverted basin forming several oil traps along its strike. The Late Cretaceous dextral wrenching developed a regional system of ENE-oriented structural ridges such as Kattaniya and Silah (bounded El-Gindi basin to the north and south, respectively), associated with a series of NE-to ENE- oriented right-lateral strike-slip faults enclosing some structural closures in between. The development of such ridges causing regional subsidence and subsequent deposition of the Apollonia Formation creating several structural hydrocarbon traps. In addition, the structural closures formed between the ends of right-lateral strike-slip faults at Silah High became potential sites for hydrocarbon accumulation. The thermal maturity model of El-Gindi basin suggests a phase of hydrocarbon expulsion occurred during or immediately after deposition of the Apollonia Formation, where the Lower and Upper Cretaceous sediments passing the oil window. According to the analysis of well cores, E-logs and seismic data, shallow marine to deltaic environments have been assigned for the Cenomanian-Turonian reservoir sediments. Moreover, the deposition within channels, point-bars and estuarine environments for the hydrocarbon bearing sandstone reservoirs within El-Gindi Basin was identified.

A NW-striking dextral strike-slip fault at the eastern end of the Altyn Tagh fault and its tectonic implications for northeastward growth of the Tibetan Plateau

The eastern end of the Altyn Tagh fault connects the western Qilian Shan thrust belt and its foreland basin, the Hexi Corridor, which contains numerous active faults with various strikes and kinematics. Although understanding of the geometry and kinematics of these active faults is increasing, the deformation pattern since the late Quaternary in the western end of the Hexi Corridor remains controversial. Studying the geometry and kinematics of these faults provides great benefit for understanding regional deformation patterns. The North Kuantan Shan fault (NKTSF) is located at the eastern end of the Altyn Tagh fault and the western end of the Hexi Corridor. Remote sensing images and field investigations suggest that the NKTSF strikes NW and acts as a right-lateral strike-slip fault with a reverse component. Optically stimulated luminescence (OSL) data combined with vertical offsets of the fault scarp imply a range of vertical slip rates of 0.015–0.093 mm/a, and cosmogenic 10Be ages and displacements of river terrace risers suggest a range of horizontal slip rates of 0.25–0.71 mm/a. The geometry and kinematics of the NKTSF enable us to estimate the deformation pattern in the western Hexi Corridor, which indicates that this area is undergoing northeastward compression related to the northern Tibetan Plateau (Qilian Shan). Active faults in the region are driven by the northeastward push of the Tibetan Plateau rather than the eastward extension of the Altyn Tagh fault.

Dynamics of the relief and sesmotectonic activity of the modern structures in the delta of the river lena

This paper presents seismogeodynamic analysis of modern structures located in the Lena river delta. These structures are key elements in the tectonic evolution of the shelf–continent transition zone in the Arctic segment of the boundary between the Eurasian and North American lithospheric plates. The geological structure of the Lena river delta is predetermined by the junction of the ancient Siberian platform and the Mesozoic Laptev Sea plate. These two large geoblocks of the crust, which differ in age, are separated by a fragment of the Kharaulakh segment of the Verkhoyansk fold system. In our study aimed to reveal regularities in seismotectonic destruction of the crust, we analyzed the geological and geophysical data on the crustal structure, active faults, modern structural plan, dynamic characteristics of the modern relief, and hydrological features characterizing of the flow redistribution in the Lena riverbed. A system of active faults identified in the Lena river delta shows a contrasting kinematic plan of the junction zone of the main geostructures. According to the analysis results, shear faulting is a dominant factor of impact on the morphologic features and seismogeodynamic activation of the modern structures. A regional right-lateral strike-slip fault of the sublatitudinal strike is traced as a major structural boundary that cuts the Lena river delta into several geodynamic segments. Seismotectonic destruction of the crust in the segments differs in types (transpression, transtension and compression). The above-mentioned fault is not only the main element of the kinematic plan of the newest structures in the Lena river delta – it controls the general structural pattern and seismotectonic parameters of active fault zones in the entire northern sector of the Verkhoyansk marginal suture. The seismogeodynamic analysis results obtained in our study provide a reliable basis for estimating potential seismic hazard of the modern structures in the Lena river delta and updating the available seismic zoning maps of the shelf–continent transition zone in the Arctic segment of the boundary between the Eurasian and North American lithospheric plates.

Dynamics of the Relief and Seismotectonic Activity of the Modern Structures in the Delta of the River Lena

The paper presents seismogeodynamic analysis of modern structures located in the Lena river delta. These structures are key elements in the tectonic evolution of the shelf–continent transition zone in the Arctic segment of the boundary between the Eurasian and North American lithospheric plates. The geological structure of the Lena river delta is predetermined by the junction of the ancient Siberian platform and the Mesozoic Laptev Sea plate. These two large geoblocks of the crust, which differ in age, are separated by a fragment of the Kharaulakh segment of the Verkhoyansk fold system. In our study aimed to reveal regularities in seismotectonic destruction of the crust, we analyzed the geological and geophysical data on the crustal structure, active faults, modern structural plan, dynamic characteristics of the modern relief, and hydrological features characterizing of the flow redistribution in the Lena riverbed. A system of active faults identified in the Lena river delta shows a contrasting kinematic plan of the junction zone of the main geostructures. According to the analysis results, shear faulting is a dominant factor of impact on the morphologic features and seismogeodynamic activation of the modern structures. A regional right-lateral strike-slip fault of the sublatitudinal strike is traced as a major structural boundary that cuts the Lena river delta into several geodynamic segments. Seismotectonic destruction of the crust in the segments differs in types (transpression, transtension and compression). The above-mentioned fault is not only the main element of the kinematic plan of the newest structures in the Lena river delta – it controls the general structural pattern and seismotectonic parameters of active fault zones in the entire northern sector of the Verkhoyansk marginal suture. The seismogeodynamic analysis results obtained in our study provide a reliable basis for estimating potential seismic hazard of the modern structures in the Lena river delta and updating the available seismic zoning maps of the shelf–continent transition zone in the Arctic segment of the boundary between the Eurasian and North American lithospheric plates.

Analysis of fault damage zones using three-dimensional seismic coherence in the Anadarko Basin, Oklahoma

Fault damage zones may significantly affect subsurface fluid migration and the development of unconventional resources. Most analyses of fault damage zones are based on direct field observations, and we expand these analyses to the subsurface by investigating the damage zone structure of an approximately 32-km (∼105-ft)-long right-lateral strike-slip fault in Oklahoma. We used the three-dimensional (3-D) seismic attribute of coherence to first define its regional and background levels, and then we evaluated the damage zone dimensions at multiple sites. We found damage zone thickness of approximately 1600 m (∼5300 ft) at a segment that is dominated by subsidiary faults, and it is slightly thicker at a segment with a pull-apart basin. The damage zone intensity decays exponentially with distance from the fault core, in agreement with field observations and distribution of seismic events. The coherence map displays a strong asymmetry of the damage zone between the two sides of the 3-D fault, which is related to the subsidiary structures of the fault zone. We discuss the effects of heterogeneous stress field on damage zone evolution through the detected subsidiary structures. It appears that seismic coherence is an effective tool for subsurface characterization of fault damage zones.

Groundwater system responses to the 2016 ML 5.8 Gyeongju earthquake, South Korea

The September 12, 2016 Gyeongju earthquakes (ML = 5.1 of foreshock and ML = 5.8 of mainshock) had significant effects on groundwater systems along the Yangsan Fault System composed of NNE-trending, right-lateral strike-slip faults in Korea. Hydrological changes induced by the earthquakes are important because no surface ruptures have been reported and few earthquakes usually occur in Korea. The main objective of this research was to propose a conceptual model interpreting the possible mechanisms of groundwater response to the earthquakes based on anomalous hydrogeochemical data including isotope concentrations with lithostratigraphic classification. For this, annual monitoring data (groundwater level, temperature, and electrical conductivity) and collected data (hydrochemical parameters, radon-222, and strontium isotopes) were used. Groundwater level anomalies could be attributed to the movement of the epicentral strike-slip fault. Radon concentration data showed the potential of groundwater mixing processes. Strontium anomalies could be related to the lithology and stratigraphy of the bedrock, reflecting the effect of water–rock interaction. Using a Self-Organizing Map (SOM) statistical analysis, associations of hydro-geochemical characteristics among groundwater wells were interpreted. By combining the grouped results of the SOM with lithostratigraphic unit data, 21 groundwater wells were classified into four groups, each corresponding to different hydrogeological behaviors. A new comprehensive conceptual model was developed to explain possible mechanisms for the hydrological and geochemical responses in each group, which have been respectively identified as water–rock interaction, mixing of shallow and deep aquifers via sea water intrusion, bedrock fracture opening related to strike-slip fault movement, and no response.

Damage induced by the 25 April 2015 Nepal earthquake in the Tibetan border region of China and increased post-seismic hazards

Abstract. The seismic effects in Nyalam, Gyirong, Tingri and Dinggye counties along the southern border of Tibet were investigated during 2–8 May 2015, a week after the great Nepal earthquake along the Main Himalaya Thrust. The intensity was VIII in the region and reached IX at two towns on the Nepal border, resulting in the destruction of 2700 buildings, seriously damaging over 40 000 others, while killing 27 people and injuring 856 in this sparsely populated region. The main geologic effects in this steep rugged region are collapses, landslides, rockfalls, and ground fissures, many of which are reactivations of older land slips. These did great damage to the buildings, roads, and bridges in the region. Most of the effects are along four incised valleys which are controlled by N-trending rifts and contain rivers that pass through the Himalaya Mountains and flow into Nepal; at least two of the larger aftershocks occurred along the normal faults. And, the damage is not related to the faulting of N-trending rifts but rather is distributed along the intensity of Nepal earthquake. Areas weakened by the earthquake pose post-seismic hazards. Another main characteristic of damage is the recurrence of the old landslide and rockfalls. In addition, there is an increased seismic hazard along active N-trending grabens in southern Tibet due to the shift in stress resulting from the thrust movement that caused the Nepal earthquake. NW-trending right-lateral strike-slip faults also may be susceptible to movement. The results of the findings are incorporated in some principle recommendations for the repair and reconstruction after the earthquake.

Revealing the Source of the 27 August 1810 Loreto, Baja California, Tsunami from Historical Evidence and Numerical Modelling

Historical documents revealed that on 27 August 1810 an earthquake affected the Loreto town and the surrounding region, along 200 km of the coast of Baja California, Mexico, and damage was considerable due to strong ground motions. However, the 1810 Loreto earthquake, unlike other earthquakes of the nineteenth and twentieth centuries, produced an extensive tsunami flooding on the eastern coast of Baja California, from Loreto to La Paz. We report here the historical account of this event and analyse the source of the related tsunami. Based on the historical record and the tectonic setting, we infer that this earthquake was produced along a transform fault, right-lateral strike slip fault, Farallon fault, on the Baja California Gulf. However, the associated tsunami was disproportionally large if compared with the earthquake intensity (IX) and approximate magnitude (7.4 Mw), fault style, and the relatively late tsunami arrival, i.e. an hour after the earthquake, suggesting that a submarine landslide, triggered by this earthquake, was the suspect source for the Loreto tsunami. We present here historical data and a numerical model of the Loreto 1810 tsunami to elucidate the source, using both the 1810 earthquake and a submarine landslide, and confirm that a submarine landslide is most likely the tsunami-triggering mechanism that followed the 1810 earthquake.

A TEST OF THE OBLIQUE-RIFTING MODEL FOR TRANSFER ZONE DEFORMATION IN THE NORTHERN FEN-WEI RIFT: IMPLICATIONS FROM THE 1989 M 6.1 DATONG-YANGGAO EARTHQUAKE SWARM

Tectonophysical experiments show that the evolution of the Fen-Wei Rift is controlled by oblique rifting. A key characteristic of the model in our study is that the western and eastern borders of the transfer zone between the adjacent NEE-striking extensional basins tend to form right-lateral strike-slip faults with slight normal slip as a result of the interaction between the adjacent NEE-striking extensional basins under oblique rifting. The current deformation of the Fen-Wei Rift can be clarified by testing this predicted deformation characteristic. Our analysis of the relocation and focal mechanism solutions of the 1989 M 6.1 Datong-Yanggao earthquake swarm, which was the largest earthquake that occurred in the Fen-Wei Rift in the last 200 years, suggests that the transfer zone between the Yangyuan and Hunyuan basins is bounded by the NNE-striking right-lateral strike-slip faults with slight normal slip at its eastern and western edges. This consistency between the model and the current tectonic activity in the study area indicates that oblique rifting still plays an important role in the current deformation of the northern Fen-Wei Rift.

The December 2nd, 2015 Bingöl, Eastern Anatolia-TURKEY, earthquake (Mw = 5.3): A rupture on optimally oriented fault plane

Eastern Anatolia is a ∼2 km high plateau shaped by the continent-continent collision of the Arabian and Eurasian plates. The left lateral East Anatolian Fault Zone, the right lateral North Anatolian Fault Zone and the Bitlis fold-thrust belt are the major tectonic boundaries of this convergence zone. The Arabian-Eurasian collision has resulted in high volcanism and well recorded seismic activity in Eastern Anatolia and its surroundings. Karlıova Junction is located at the intersection of these major fault systems and contains secondary faults such as the Karakoçan fault and the Sancak-Uzunpınar fault. We processed high quality waveform data collected from a recent seismic activity in the proximity of the city of Bingöl where the largest event is the moderate-size earthquake (Mw = 5.3) occurred on 2 December 2015. This event is located to the west of Karlıova Junction and to the northwest of Sancak-Uzunpınar fault. The spatial distribution of the aftershocks points out unmapped faults with NNW-SSE alignment towards the west of Sancak-Uzunpınar fault. Aftershock depth distribution indicates a nearly 15 km deep brittle seismogenic zone. The relocated aftershock distributions and seismic moment calculations yield a rupture area 9 km in length and 5 km in width with an average 8 cm of slip. The latest four earthquakes preceding the 2015 Eq with magnitudes larger than Mw > 6 enhanced the Coulomb stress failure in the 2015 Bingöl Earthquake rupture area. The ruptured fault plane is in-line with the optimally oriented right-lateral strike-slip faults.

Active strike-slip faulting in the Zagros Mountains: Geological and geomorphological evidence of the pull-apart Zaribar Lake basin, Zagros, NW Iran

The Zaribar Lake is situated along the Main Recent Fault, a dextral major strike-slip active fault system in the Zagros collision zone. The formation of the Zaribar Lake in Late Pleistocene is associated with the activities of the Main Zagros Reverse Fault, initiated in Late Oligocene, and with the Main Recent Fault, whose inception occurred about 5 Ma ago. Metamorphic, intrusive and ophiolitic rocks in the Zagros suture zone are affected by a normal fault system in the Zaribar area. Geometry and kinematics of these normal faults indicate that the Zaribar Lake is generated in a releasing zone. The strike of the Main Recent Fault varies from 300° to 330° along the Marivan fault segment. The releasing bend of the Marivan Fault around the Zaribar Lake has resulted in the extensional deformation by which the lake has been downdropped between two strike-slip faults. Besides the extensional mechanism of the main right-lateral strike-slip faults that has resulted in the formation of the Zaribar as a large-scale pull-apart basin, minor strike-slip faults have also produced specific landforms around the lake. Small-scale normal faults and large scale grabens developed around the lake are geological indicators of extensional areas. Geomorphological evidence also support the pull-apart origin for the Zaribar Lake. Beheaded rivers, numerous offsets in drainage system, half-broom shaped drainage pattern, sag ponds with different scales, linear and strike-parallel valleys and alluvial fan with high sweep angle and width/length ratio confirm the movements along right-lateral, strike slip faults around the Zaribar.

ACTIVE TECTONIC AND PALEOSEISMOLOGIC CHARACTERISTICS OF THE YENİCE-GÖNEN FAULT, NW TURKEY, IN LIGHT OF THE 18 MARCH 1953 YENİCE-GÖNEN EARTHQUAKE (Ms=7.2)

The Yenice-Gönen Fault (YGF) is located in the central part of the Biga Peninsula between Gönen and Yenice and is a right-lateral strike-slip active fault with general trending N65°E. On 18 March 1953 there was an earthquake on the YGF that died 263 people (Ms=7.2) and a 70 km surface rupture developed during this earthquake. In this study measurements of slip distribution were performed on the surface rupture of the Yenice-Gönen Earthquake (YGE) and the annual slip rate on the YGF was calculated. Right-lateral displacements of between 1.70±0.1 and 3.20±0.2 metres were measured on the surface rupture of the YGE. The maximum displacements were in an area close to the central part of the YGF (between Çakır and Karaköy village) and these values decreased relatively in NE and SW directions, documenting that was the bilaterally surface rupture propogation during the YGE. In the last 300.000 years, a total offset of 800±50 metres was measured on Gönen River and annual slip rate of 2.65±0.15 mm was calculated along the YGF. Current GPS studies show right-lateral strike-slip faults in the South Marmara region have slip rates of 6-8 mm/year. This slip rate is assessed as being partitioned between the YGF, Sarıköy Fault and Çan-Biga Fault zones which represent extensions of the North Anatolian Fault system within the South Marmara region. Paleoseismology studies determined that in the last 6200 years 6 earthquakes resulting in surface ruptures have occurred on the YGF, including the 1953 earthquake. According to the 14C and OSL dating results, the variable and irregular earthquake recurrence interval of YGF is ranging from 505 to 1793 years. In this study average earthquake recurrence interval of YGF was determined as 1180 years.

Co-seismic surface ruptures in Qiangtang Terrane: Insight into Late Cenozoic deformation of central Tibet

Recently large earthquakes mostly occurred at the plateau margins along major lithospheric faults. However, a co-seismic rupture has been discovered in central Tibet along the Burgar Co Fault (BGCF), a 150 km-long northwest-trending right-lateral strike-slip fault within the hinterland of the Qiangtang terrane, central Tibet. The activity of the BGCF is marked by a 50 km-long fresh surface rupture from 83°38′57″E, 33°58′54″N to 84°09′50″E, 33°47′42″N, restrained by a bend with a 17° counter-clockwise angle. Geomorphic offsets measured in the field and from high-resolution satellite images indicate the lateral displacements cluster at 1.4 ± 0.1 m, 2.7 ± 0.4 m, 5.4 ± 0.6 m, 9.2 ± 0.8 m and 12.5 ± 1 m. The smallest value (average 1.4 ± 0.1 m, maximum 1.8 m) is defined as the most recent co-seismic offset of a magnitude Mw = 7 earthquake. Other clusters are interpreted as the cumulative events which demonstrate that earthquakes frequently took place along the BGCF. The seismic behavior of the BGCF together with widespread sinuous north-trending grabens and NE, NW strike slip faults around western and central Qiangtang indicates that the most recent active structures have deformed scattered in the internal part of this terrane. Additionally, the conjugate strike slip fault systems along the Bangong-Nujiang Suture define an intangible southern boundary, altogether implying that the Qiangtang terrane has undergone significant deformation thus can no longer be treated as an integral block. Finally, compared with the continental slip in eastern Qiangtang, an alternative geodynamic model for Qiangtang is inferred: a weak channel flow decoupling the upper and middle-lower crust which facilitates the southeastwards extrusion as an entire block in the east, and continuous deformation as scattered small crustal wedges without expansive upper and middle-lower crust decoupling underground in the western and central areas. The Qiangtang terrane serves as the dominant place for extensive material to migrate eastward, accommodating simultaneous E-W extension and N-S compression.

Crustal deformation in the northern Andes – A new GPS velocity field

We present a velocity field for northwestern South America and the southwest Caribbean based on GPS Continuously Operating Reference Stations in Colombia, Panama, Ecuador and Venezuela. This paper presents the first comprehensive model of North Andean block (NAB) motion. We estimate that the NAB is moving to the northeast (060°) at a rate of 8.6 mm/yr relative to the South America plate. The NAB vector can be resolved into a margin-parallel (035°) component of 8.1 mm/yr rigid block motion and a margin-normal (125°) component of 4.3 mm/yr. This present-day margin-normal shortening rate across the Eastern Cordillera (EC) of Colombia is surprising in view of paleobotanical, fission-track, and seismic reflection data that suggest rapid uplift (7 km) and shortening (120 km) in the last 10 Ma. We propose a “broken indenter” model for the Panama-Choco arc, in which the Choco arc has been recently accreted to the NAB, resulting in a rapid decrease in shortening in the EC. The Panama arc is colliding eastward with the NAB at approximately 15–18 mm/yr, and the Panama-Choco collision may have been responsible for much of the uplift of the EC. The present on-going collision poses a major earthquake hazard in northwestern Colombia from the Panama border to Medellin area. Since the northeastward margin-parallel motion of the NAB is now greater than the rate of shortening in the EC, northeast trending right-lateral strike-slip faulting is the primary seismic hazard for the 8 million inhabitants of Bogota, the capital city of Colombia. There continues to be a high risk of a great megathrust earthquakes in southern Colombia along the Ecuador-Colombia trench. Trench earthquakes have only released a fraction of the energy accumulated in the Ecuador-Colombia trench since the 1906 Ecuador earthquake, and interseismic strain is accumulating rapidly at least as far north as Tumaco, the rupture area of the 1979 earthquake.

Structure of the Cenozoic Cover of the Sanjiang–Middle Amur Sedimentary Basin (Russia, China)

Based on the map of the gravitational-field anomalies with respect to the existing structural data, a single structural scheme of the Sanjiang–Middle Amur sedimentary basin is constructed. It reflects the Paleogene rift-related stage of the basin’s evolution, when numerous grabens oriented mostly to the northeast formed under the action of NW–SE tension forces. The regularities in the location of the grabens indicate that the basin formed under conditions of interaction of right-lateral northeastern and left-lateral sublatitudinal and west-northwestern strike-slip faults. The ancient northeastern faults activated in the Paleogene formed marginal Western and Eastern zones of right-lateral strike-slip faults. En-echelon series of grabens in the central part mark the position of the rudimentary zones of the left-lateral strike-slip faults. The internal structure of the grabens is analyzed using the materials of the previous and new seismic and well data. The common and individual features of their structures are revealed. The structure of the grabens of the western and eastern marginal zones is demonstrated. It is noted that some grabens are prospective for raw hydrocarbons. An analysis of the deep structure of the territory of East Asia, including the basin, assumes the presence of an upwelling zone by the results of geophysical studies of recent years, primarily seismotomography.

Coseismic displacement of the 5 April 2017 Mashhad earthquake (Mw 6.1) in NE Iran through Sentinel-1A TOPS data: New implications for the strain partitioning in the southern Binalud Mountains

The outward expansion of the northeastern Iranian Plateau is mainly accommodated by a series of widely distributed range-normal thrust and range-parallel strike-slip faults. However, the role of the strike-slip faults in this region's strain-partitioning kinematics remains unclear. The occurrence of the 5 April 2017 Mw 6.1 Mashhad earthquake provides us a rare opportunity to study this topic because this earthquake struck the southern Binalud Mountains, which are experiencing an oblique convergence between the northward-moving Lut Block and the NW-striking Binalud and Kopeh Dagh mountain ranges. We process two paired ascending and descending Sentinel-1A radar-image observations to determine the relative contributions from the dip and strike-dip subcomponents in such an oblique collisional domain. The interferograms along the line-of-sight direction and their converted horizontal and vertical displacements indicate that a thrust with a right-lateral strike-slip fault controlled the rupture process of the Mashhad earthquake, with the maximum dextral shearing and vertical displacements reaching 19.5 cm and 14 cm, respectively. Coseismic surface deformation measurements are also used to estimate the fault geometry and invert the slip distribution along the underlying seismogenic fault. Our best-fit faulting model suggests that the coseismic rupture occurred on a fault plane with a dip angle of 37.5° and strike angle of 324°. The strike-slip subcomponent was more significant than the dip-slip, approaching ∼95 cm, and the dip-slip varied from 10 cm to 47 cm. The seismic-moment release of our preferred fault model is 1.71 × 1018 Nm, equivalent to a Mw 6.16 earthquake event. We also use the preferred fault model to calculate the Coulomb failure stress (CFS) change at the nearby receiver faults. Combined with an analysis of historical earthquakes and the consistent dextral river deflections along the strike-slip fault systems of the southern Binalud and Kopeh Dagh Mountains, we speculate that the seismogenic structure that triggered the Mashhad earthquake should have been one strand fault of the NW–SE-striking Kashafrud fault system. The strike-slip faults in NE Iran play an important role in accommodating the lateral transport of crustal material from the convergence front of the Lut Block and Binalud fragments and providing commonly distributed anticlockwise rotation around a vertical axis.