Right-lateral Strike-slip Component Research Articles

Constraints on the 2013 Saravan intraslab earthquake using permanent GNSS, InSAR and seismic data

SUMMARY On 16 April 2013, an Mw = 7.7 earthquake struck the border of Iran and Pakistan in the central part of the Makran subduction zone with a reported depth of 80 km by USGS. This rare event in this poorly instrumented region helps to shed light on the kinematics of the subducting slab. We investigate source parameters of the Saravan intraslab normal earthquake using RADARSAT-2 SAR images in three ascending tracks, nine permanent GNSS sites and teleseismic data. The maximum coseismic displacement occurred at the SRVN GNSS station with 54.1 mm southeast horizontal and 42.7 mm upward vertical displacements. The coseismic ascending InSAR displacement maps illustrate a continuous and smooth NE-trending elliptical shape deformation pattern with a maximum of ∼29 cm of displacement away from the satellite. We use 25 broad-band teleseismic P-waveforms to estimate the focal mechanism of the main shock. A joint uniform inversion of InSAR, GNSS and teleseismic data reveals a NW-dipping SW-striking fault and a primarily normal-faulting earthquake with a minor right-lateral strike-slip component. The static slip distribution of the InSAR coseismic maps localizes variable slip at depths between 50 and 81 km with a maximum amplitude >3 m at 60–75.5 km depth, rupturing the oceanic crust of the subducted slab. The kinematic slip distribution exhibits a well-constrained slip pattern with a nucleation depth of 65 km. The source time function indicates that the earthquake reaches its maximum moment tensor release at ∼8 and ∼16 s. The NE-trend of the Saravan earthquake slip pattern, the orientation of the volcanic arc, and the distribution of the intraslab intermediate-depth normal earthquakes provide new insights into slab geometry in the central Makran subduction zone. We suggest that the slab bending at the hinge of subducting Arabian Plate is oblique along a NE–SW direction parallel to the volcanic arc rather than the shoreline or deformation front, and it is likely to be the reason for an oblique volcanic arc in the Makran subduction zone. These new constraints on the Makran slab geometry will help further studies in establishing realistic coupling maps for seismic hazard assessment.

Earthquake on January 24, 2024 near Krasnodar city, Mw=4.1, I0=5

The article presents instrumental and macroseismic data on the earthquake on January 24, 2024 at 11:19 (UTC), Mw=4.1, h=8 km. The earthquake parameters were determined using instrumental data from the network of regional seismic stations in the North Caucasus of the GS RAS. The earthquake parameters were determined from instrumental data from the network of regional seismic stations in the North Caucasus of the GS RAS. The source spectra of three regional seismic stations (GOYR, MRNR and GUZR) were calculated, from which the seismic moment М0, the stress drop Δσ and the source radius R were determined. The solution of the focal mechanism was obtained from the polarization in P-waves at 71 seismic stations and the type of source fault with a right-lateral strike-slip component. The epicentral zone of the earthquake on 24.01.2024 is located within the high-magnitude Akhtyrka zone of potential earthquake source zones (ESZ) with Mmax=6.5-6.8 and represents the boundary between the Northwestern part of the structures of the Greater Caucasus and the West Kuban trough. According to macroseismic survey in the regions, 300 respondents were interviewed in 20 settlements. The maximum observed intensity was I=V MSK-64.

Underground Water Level, Strain, and Tilt Changes Observed Around the Fault Near Tono Research Institute of Earthquake Science

Near the Tono Research Institute of Earthquake Science (TRIES), Mizunami City, Gifu, two 500 m- deep shafts with diameters of 4.5 m and 6.5 m were excavated by the Japan Atomic Energy Agency (JAEA). The 6.5 m shaft is crossed by an NNW-trending geological fault (NNW fault), which has a right-lateral strike-slip component and a dip-slip component. Since before the excavation TRIES has been performing observations by a comprehensive set of borehole crustal activity observation devices in deep boreholes and extensometers in a vault near the shafts to observe variations in, for example, strain, tilt, and groundwater level continuously. During the shaft excavation, groundwater inflow to the shafts was encountered. The water was twice pumped out. During the pumping and non-pumping periods, TRIES’s observation data such as the groundwater level, the strain, and the tilt showed anomalous variations. The analysis of them revealed relationships among the groundwater level, the fault, the strain and the tilt. Strain analysis of TGR350 borehole station showed that the direction of the maximum shear strain was parallel to strike of the NNW fault. In addition, when the water in the shafts was being pumped out, the groundwater level at TGR350 declined and the maximum shear strain showed a right-lateral strike-slip movement in the NNW direction. When pumping was paused, the groundwater level increased, and the maximum shear strain showed a left-lateral strike-slip movement in the NNW direction. On the other hand, strain analysis of TGR165 borehole station showed different behavior from that of TGR350 borehole station deeper than TGR165. Tilt analysis of TGR165 borehole station showed tilt changes nearly perpendicular to strike of the NNW fault corresponding to the pumping and the non-pumping periods. Tilt analysis of TGR350 borehole station showed tilt changes of E-W direction with much smaller amplitude than that of TGR165. Behavior of the strain and the tilt during the pumping and non-pumping periods can be attributed in part to differences in the response of the medium to groundwater fluctuations, due to differences in the number and distribution characteristics of the fractures in the medium where the observation instruments are installed. We also discussed the observation results from the viewpoint of poroelasticity.

Transtensional coseismic fault slip of the 2021 Mw 6.7 Turt Earthquake and heterogeneous tectonic stress surrounding the Hovsgol Basin, Northwest Mongolia

Knowledge of the regional crustal deformation and stress field is fundamental to understanding and constrain the ongoing evolution of Hovsgol basin, northwest Mongolia. The 2021 Mw 6.7 Turt earthquake provides an unprecedented opportunity to probe the local tectonic stress field and upper crust deformation. We investigate the coseismic surface displacements and invert fault slip models using Interferometric Synthetic Aperture Radar observations and teleseismic data. The mainshock occurred as a result of normal faulting with a right-lateral strike-slip component on an NW striking plane, which is consistent with the transtensive local stress field inverted from regional focal mechanisms. It is surrounded by transpressive and strike-slip stress fields proposed by previous studies indicating regional stress heterogeneity probably controlled by the distinct structure geometries in and around Hovsgol basin. Our results also suggest that the current deformation of the Hovsgol basin is dominated by half-graben forming. Seven historical strong earthquakes (M 7) may advance the 2021 Turt earthquake by ~12% recurrence interval, based on the assumption of equal stress release from recurrence earthquakes, meanwhile, the 2021 Turt earthquake may increase the potential seismic hazard on the neighbor Mondy and South Hovsgol faults, which deserves more attention.

Source Parameters and Slip Distribution of the 2019 Mw 5.8 Mirpur (Pakistan) Earthquake Inferred from the Corrected InSAR Observations

AbstractOn 24 September 2019, an Mw 5.8 earthquake occurred on the Mangla-Samwal anticline near Mirpur city, Pakistan. Because the seismogenic fault is hidden and the near-field seismic data are scarce, the magnitude and slip distribution of this earthquake are not determined. Furthermore, due to small deformation and significant atmospheric noise in the coseismic interferograms, it is difficult to accurately determine source parameters and slip distribution using the original single ascending and descending Interferometric Synthetic Aperture Radar observations. In this article, we used Sentinel-1A satellite Synthetic Aperture Radar data to generate 60 ascending and 56 descending coseismic interferograms and performed atmospheric error correction including Kriging interpolation correction and displacement stacking to obtain more accurate coseismic displacement fields for the 2019 Mw 5.8 Mirpur earthquake. Considering the local geological structures, focal mechanism solutions, and the optimal fault parameters obtained from the coseismic displacement inversion, we determine that the strike and dip of the fault of the 2019 Mirpur earthquake are 296.3° and 4.0°, respectively. Based on this fault model, the fault plane was extended to 12.0 km long and 11.0 km wide and divided into subfaults of 1.0×1.0 km2. We inverted the coseismic displacement fields to obtain slip distribution on the fault plane. Slip is mainly distributed at a depth of 4.7 ∼ 5.0 km, with a maximum of 0.95 m at a depth of 4.88 km. The slip distribution shows that this earthquake was a thrust event with right-lateral strike-slip components, which is consistent with the focal mechanism solution from the U.S. Geological Survey. The estimated geodetic moment is about 7.14×1017 N·m, equivalent to Mw 5.8.

Neotectonic Fault Pattern of the Salair Area (Southern West Siberia): Relation with the Pre-Cenozoic Tectonic Framework

Abstract —Neotectonic activity in the area of the Salair Ridge (southern West Siberia) rejuvenated a system of large arc-shaped faults separating the Salair tectonic arc from the adjacent tectonic units. These regional faults, which make up the general tectonic framework of the Altai–Sayan Folded Area, originated in the late Paleozoic and were repeatedly reactivated in the Mesozoic. The deformation within the major Salair thrust sheet is mainly brittle and follows small fault planes that crosscut the margins of Paleozoic thrusts. The neotectonic faulting has controlled the erosion pattern of the territory and produced a reticulate drainage system. The Salair tectonic unit is a single 80 × 250 km block consisting of multiple neotectonic blocks, with relative vertical offset no more than 100 m in the block interior and 100–200 m in its southern, northern, and eastern borders. The northwestern and southeastern border faults have reverse slip geometry, while the motions on the en-echelon northeastern fault boundary include reverse and right-lateral strike-slip components. The thickness of the Salair thrust sheet estimated from magnetotelluric (MT) data increases in the western direction from 5 to 15 km in the northern block part and from 10 to >20 km in the south. The allochthon base is delineated by a low-resistivity zone interpreted as a horizontal detachment. This boundary formed in the Mesozoic and was rejuvenated at the neotectonic stage. The lithology and deformation of Jurassic sediments filling piedmont basins around the Salair Ridge indicate that the Cenozoic fault pattern generally inherits the Mesozoic framework but differs in about ten times smaller vertical offset.

TECTONIC STRESS FIELD AT INTERMEDIATE DEPTHS OF THE SOUTHERN FLANK OF THE KURIL-KAMCHATKA SEISMIC ZONE

The study has been done on the orientation of the principal axes of tectonic stress field at intermediate depths of earthquakes of the southern flank of the Kuril-Kamchatka subduction system separately for the upper and lower double seismic focal zones. Use has been made of the NIED and GlobalCMT catalogue data. The computation-based results are presented on schemes of the stressed state of the investigated areas and in tables. In the context of the southern Kuril Islands, evidence has been provided for predominance of the maximum compressive stresses along the slab plane in the upper layer and minimal compressive stresses (deviation extension) in the lower layer. However, the principal axes of maximum and minimum compression are displaced in direction relative to the slab dip: by 30–40° counterclockwise for the compression axis in the upper layer, which coincides with the direction of plate movement, and clockwise for the extension axis in the lower layer. This might be caused by the right-lateral strike-slip component of the Pacific Plate subduction. Unlike the general trend, the orientation of the principal axes of the stress field beneath the central Hokkaido-related segments in the upper layer is almost identical to that in the lower layer. There have also been found the segments exposed to shear stress, with the most extensive located opposite the northern Kunashir Island and beneath the southern Hokkaido Island. The results obtained for major large groups of clusters show good accordance with those published by other authors. The discrepancies relate primarily to small groups of isolated clusters showing local stress field heterogeneities.

Plio–Quaternary Structural Evolution of the Outer Sector of the Marche Apennines South of the Conero Promontory, Italy

Some new results and preliminary remarks about the Plio–Quaternary structural and evolutionary characteristics of the outer Marche Apennines south in the Conero promontory are presented in this study. The present analysis is based on several subsurface seismic reflection profiles and well data, kindly provided by ENI S.p.A. and available on the VIDEPI list, together with surface geologic–stratigraphic knowledge of Plio–Quaternary evolution from the literature. Examples of negative vs. positive reactivation of inherited structures in fold and thrust belts are highlighted. Here, we present an example from the external domain of the Marche Apennines, which displays interesting reactivation examples from the subsurface geology explored. The study area shows significant evolutionary differences with respect to the northern sector of the Marche region previously investigated by the same research group. The areal distribution of the main structures changes north and south of the ENE–WSW oriented discontinuity close to the Conero promontory. Based on the old tripartite classification of the Pliocene, the results of this work suggest a strong differential subsidence with extension occurring during the Early Pliocene and principal compressive deformation starting from the Middle Pliocene and decreasing or ceasing during the Quaternary. The main structure in this area is the NNW–SSE Coastal Structure, which is composed of E-vergent shallow thrusts and high-angle deep-seated normal faults underneath. An important right-lateral strike–slip component along this feature is also suggested, which is compatible with the principal NNE–SSW shortening direction. As mentioned, the area is largely characterized by tectonic inversion. Starting from Middle Pliocene, most of the Early Pliocene normal faults became E-vergent thrusts.

KURIL-OKHOTSK REGION

The review of the Kuril-Okhotsk region seismicity in 2014 is presented. Earthquake parameters were obtained on the basis of the data of the seismic stations of Sakhalin branch GS RAS and the data of neighboring seismological Russian and foreign agencies. 83.6 % of earthquakes are located within the depth interval of h80 km, 13.5 %  within the intermediate layer h=81–300 km, 2.9 % of earthquakes have depths h>300 km; the maximum depth of the hypocenter was h=559 km. The analysis of the seismic situation in 2014 in comparison with the data for 2001–2013 is carried out, a description of the seismic situation in seismically active regions is given. For 30 earthquakes information was obtained on the macroseismic effect in Russia, the maximum intensity did not exceed Ii=5; for 50 earthquakes there was information on the intensity in the territory of the Japanese Islands, the maximum value was Ii =67 by the MSK-64 scale. The strongest earthquake in the region occurred in the central part of the Sea of Okhotsk on September 18 at 04h17m with h=529 km and MSH=6.2. Its focal mechanism is classified as an incision with a small right-lateral strike-slip component along a subvertical plane of north-eastern strike. The seismicity of the region in 2014 can be considered as a moderate, the number of earthquakes with a magnitude MP≥4.5 and their total seismic energy do not exceed the average values over a 13-year period, the level of seismicity of the region according to the SOUS’09 method is classified as а “background average”. The distribution of earthquake hypocenters and their focal mechanisms show that most of the earthquakes in the Kuril-Okhotsk region relate to the process of the subduction of the Pacific lithospheric plate under the Okhotsk Sea plate.

Cenozoic structural deformation in the Yuqia-Jiulongshan region, northern Qaidam Basin, China

Based on field geological survey, interpretation of seismic reflection profile and thermochronology dating, this paper systematically studied the structural deformation of the Yuqia-Jiulongshan region in northern Qaidam Basin during the Cenozoic. The results show that the area is primarily dominated by a large box-shaped anticline, with steep limbs and a wide and gently-deformed core. The Mahaigaxiu and Jiulongshan anticlines are secondary folds controlled by secondary faults in the limbs of the box-shaped anticline. Whereas the Yuqia and the Northern Yuqia anticlines are secondary folds within the wide core of the box-shaped anticline. The geometry of the box-shaped anticline is mainly controlled by some high-angle reverse faults with certain right-lateral strike-slip components, displaying distinct positive flower structures in section view. Combining the sedimentary correlation and detrital apatite fission track analysis, we believe that the Yuqia-Jiulongshan region was a paleo-uplift that developed slightly in the early Cenozoic, resulting in the relatively thin Cenozoic strata. The intense deformation that shaped the present-day structural framework occurred in or after the sedimentary period of Shizigou Formation. The Yuqia – Jiulongshan paleo-uplift is adjacent to the Sainan depression that is rich in Lower-Middle Jurassic source rocks, and thus has high potential for future hydrocarbon exploration.

Insight into the 2017 Mainling Mw 6.5 earthquake: a complicated thrust event beneath the Namche Barwa syntaxis

On November 18, 2017, the Mainling Mw 6.5 earthquake occurred on the northern Namche Barwa syntaxis and was the largest earthquake in the syntaxis and surrounding areas since the Zayu Mw 8.4 earthquake in 1950. Due to inconvenient access and the severe environment in the Namche Barwa syntaxis area, the motions and tectonic structures of most faults remain unclear. Sparsely distributed seismic observation stations make the seismogenic fault and focal mechanism of the Mainling earthquake controversial. We adopt interferometric synthetic aperture radar (InSAR) to invert the slip distribution of this event by defining the fault geometry with relocated aftershocks. Our preferred model suggests that the 2017 Mainling earthquake ruptured two blind faults beneath the Namche Barwa syntaxis. The ruptures were dominated by thrusts with slight right-lateral strike-slip components. The slips on the two faults are equivalent to moment magnitudes of Mw 6.12 and Mw 6.34, with maximum dislocation magnitudes of 0.36 m and 0.43 m, respectively. The model fits well with the InSAR observations and the distribution of aftershocks. The results from the Coulomb stress simulation indicate that the stress loading caused by strong historical events promoted the occurrence of the 2017 Mainling earthquake. Compared with the seismogenic faults of the Mainling earthquake, the larger thrust faults in the southern Namche Barwa syntaxis can generate larger earthquakes. Therefore, we assume that Mw > 6.5 earthquakes may occur beneath the Namche Barwa syntaxis and that the seismic risk has been further promoted by historical events.

Seismic interpretation for the Jurassic/Paleozoic reservoirs of QASR gas field, Shushan-Matrouh basin north Western Desert, Egypt

The QASR gas field lies in the northern part of Shushan-Matrouh Basin (northern part of the Western Desert). Jurassic (Lower Safa)/Paleozoic are a reservoir rocks, in which the gas is trapped in clastic Sandstone, depending on structural framework affecting it. The QASR field structure is one of the most complex structures in the Western Desert of Egypt. The Jurassic (Lower Safa) and Paleozoic formations are consists of sandstone, siltstone with some shale streaks, indicating shallow marine facies, its sequence may reach a maximum thickness of over 900 ft in the northeastern part of Shushan-Matrouh basin.The combination between well logs data and 3D seismic interpretation represent that the Jurassic (Lower Safa)/Paleozoic form a complex horst block, which is bounded by NE-SW trending deep-seated faults, with throws is excess of 300 ft. The migration of hydrocarbons into the QASR structure could either be laterally from source rocks that occur in the Shushan basin to the west, and vertically from the sub-basin to the north via the QASR-OZORIS bounding fault.Time and depth-structural maps of Jurassic (Lower Safa)/Paleozoic describe various structure aspects that play a vital role in the hydrocarbon potentialities and prospect identification in the area. One incipient element of exploration and development success is to detect the faults that provide structural closure and traps.Two major faults run in the NE-SW direction and configurator a manner of horst and graben blocks. In addition, NWSW trending faults cut these blocks and form a right-lateral strike-slip component of displacement. Four-way dip structural closure represents the fruitful locations for high production and new prospect wells in the QASR gas field and other similar setting elsewhere.

The 2016 Mw 6.5 Nura earthquake in the Trans Alai range, northern Pamir: Possible rupture on a back-thrust fault constrained by Sentinel-1A radar interferometry

On June 26, 2016 an Mw 6.5 earthquake occurred in the Trans-Alai Range, about 37 km west of a 2008 Mw 6.7 earthquake, both near the town of Nura, China. We use Interferometric Synthetic Aperture Radar (InSAR) images from Sentinel-1A to image coseismic surface displacements from the most recent Nura earthquake. We invert the interferograms for both fault geometry and slip distribution. We find that the InSAR data can be described by either a steeply north-dipping fault or shallowly south-dipping fault, although only when slip on the south-dipping fault is constrained to be blind. The InSAR misfit for the north-dipping fault plane is slightly lower, and the north-dipping fault better describes the gradient of deformation in the near-field. We prefer the north-dipping fault geometry (~67° dip and 266° strike) as the source for the 2016 Nura earthquake, not only due to the better fit to the InSAR, but the resulting coseismic slip model is more consistent with the focal mechanism solutions and regional seismogenic thickness; however, it is important to reiterate that the InSAR data cannot uniquely determine which model is the definitive representation of the Nura earthquake. The maximum inferred coseismic slip is about 0.75 m at ~14 km depth beneath the Trans Alai range, with the largest slip in the depth range of about 8–20 km. Slip does not reach the surface, and is dominated by thrust displacement with a right-lateral strike-slip component. The geodetic moment of our preferred slip model is 6.61 × 1018 N·m, equivalent to Mw 6.5. The surface projection of our preferred fault is to the south of the Pamir Frontal Thrust (PFT), and we argue it is a back-thrust of the listric PFT, suggesting that the Trans Alai range is a ‘pop-up’ structure.

Transient deformation during the Milashan Tunnel construction in northern Sangri-Cuona Rift, southern Tibet, China observed by Sentinel-1 satellites

Using 3-year Sentinel-1 C-band synthetic aperture radar (SAR) data, we observed prominent ground subsidence around the construction site of the Milashan Tunnel, which is on top of the northern Sangri-Cuona Rift (SCR) in southern Tibet. The most deformed area extends ∼7 km in the north-south direction and ∼6 km in the east-west direction, with a peak subsidence rate of over 10 mm/a in the line of sight direction of both the descending and ascending satellites. Aside from the long-term ground subsidence arising directly from underground water outflow and rock excavation, a regional aseismic fault slip episode is also evident. The aseismic slip event began in May 2016 and ended in July 2016. The surface aseismic displacements can be explained by normal faulting with mainly down-dip movement and a modest right-lateral strike-slip component on a nearly north-south trending fault. The aseismic deformation triggered by the Milashan Tunnel construction demonstrates the sensitive response of crustal-scale tectonics to human activity, which poses high seismic hazards for the heavily populated region.

The active Kalabsha Fault Zone in Southern Egypt: detecting faulting activity using field-structural data and EMR-technique, and implications for seismic hazard assessment

Since November 14, 1981 earthquake (ML 5.6), about 60 km southwest of Aswan High Dam, the seismic hazard raised and the Aswan Local Seismic Network (ALSN) has recorded and precisely monitored the seismic activity in the vicinity of the High Dam. The major source of seismic activity in this region is the active Kalabsha Fault Zone (KFZ). The focal mechanism solutions indicate that two nodal planes strike E to ENE, with subordinate right-lateral strike-slip component and N to NNW, with left-lateral movement. The directions of tectonic extension (T) and compression (P) are NNE-SSW and NNW-SSE, respectively. Structural investigations and application of the Electromagnetic Radiation (EMR) technique reveal ongoing activity on the KFZ. Kinematic evolution of the KFZ implies faulting events with a strong movement intervened with periods of severe crushing, grinding, and even pulverization. Such tectonic processes have resulted in fault-breccia and fault-gouge. Results obtained from the present study indicate that the KFZ is not a single transcurrent wrench fault with dextral sense of movement but, instead, it represents a major dextral transtensional shear or fault zone deforming southern Egypt and plays a significant role in the structural shaping of the area to the west of Nasser Lake. Furthermore, the activity on the KFZ is most probably controlling the seismic cycle in the area. Topographic expression of KFZ is evidently realized at Sinn El-Kaddab scarp, as well as at Gebel Marawa. Frequent surface rupturing and newly recorded strong seismic activity advocate faulting reactivation supported by the EMR data, which suggest an active fault system oriented ENE-WSW and NNW-SSE affecting the KFZ, with a maximum horizontal stress (σ1) perturbing between ENE and NNW directions.

Small Magnitude Co-Seismic Deformation of the 2017 Mw 6.4 Nyingchi Earthquake Revealed by InSAR Measurements with Atmospheric Correction

The Nyingchi Mw 6.4 earthquake on 17 November 2017 is the first large event since 1950 at the southeast end of the Jiali fault. This event was captured by interferometric synthetic aperture radar (InSAR) measurements from the European Space Agency (ESA) Sentinel-1A radar satellite, which provide the potential to determine the fault plane, as well as the co-seismic slip distribution, and understand future seismic hazards. However, due to the limited magnitude of surface displacements and the strong topography variations, InSAR-derived co-seismic signals are contaminated by strong tropospheric effects which makes it difficult (if not impossible) to determine the source parameters and co-seismic slip distribution. In this paper, we employ the Generic Atmospheric Correction Online Service for InSAR (GACOS) to generate correction maps for the co-seismic interferograms, and successfully extract co-seismic surface displacements for this large event. The phase standard deviation after correction for a seriously-contaminated interferogram reaches 0.8 cm, significantly improved from the traditional phase correlation analysis (1.13 cm) or bilinear interpolation (1.28 cm) methods. Our best model suggests that the seismogenic fault is a NW–SE striking back-thrust fault with a right-lateral strike slip component. This reflects the strain partitioning of NE shortening and eastward movement of the Eastern Tibetan plateau due to the oblique convergence between the Indian and Eurasian plates.

Chronological evolution of some morphological, tectonic and volcanic features in Lake Van, based on correlation of seismic and core data

The Lake Van is the largest Lake in Turkey and the fourth largest soda lake in the World. High resolution (HR) seismic data acquired during 2012 reveals sub-lacustrine terraces, delta clinoforms, channel-networks, active faults and volcanic edifices. The seismic data were correlated with the cores recovered during the 2008 coring and 2010 ICDP PaleoVan drilling campaigns, using synthetic seismograms produced from the MSCL data of the age-modelled cores, thus allowing to date seismic reflector surfaces and to discuss the temporal evolution of the some of the morphological features and structures. Sub-lacustrine channel-network systems are well developed on the shelf areas connect with the river drainage systems on land and extend to water depths of more than 100 m. These drainage systems developed during the major low-stand periods of Lake Van, the last two of which occurred during 15 ka BP and the Younger Dryas with water levels at −200 m and −70 m, respectively. High lake levels similar to today during the early Holocene were followed by lake level oscillations with some low-stands during the Late Holocene. The low stands are characterized by terraces and berms located at 15 m below lake surface (mbls), 25 mbls, 35 mbls and 60 mbls, 70 mbls and 105 mbls. They were most likely related to the rapid climate change (RCC) events such as the 4.2 ka aridity event, Dark Age Cold Period, Medieval Warm Period and Little Ice. The volcanic features are located along the Southern Boundary Fault (SBF). A significant NW-SE trending active fault in the eastern shelf left-laterally offsets a channel by about 500 m and has a small reverse component in the HR seismic profiles. This fault is considered to be the source of Mw = 5.7 Edremit Earthquake of 9 November 2011. NW-SE trending normal faults with a right-lateral strike slip component north of the Northern Basin provides extension in the area. Normal faults are also dominant in the Erciş Strait. Using ages of reflector surfaces we estimate a vertical slip rate of 0.40 mm/yr to ∼0.5 mm/yr on the normal faults in the shelf areas over the last 2–3 ka.

Coseismic Fault Slip of the September 16, 2015 Mw 8.3 Illapel, Chile Earthquake Estimated from InSAR Data

The complete surface deformation of 2015 Mw 8.3 Illapel, Chile earthquake is obtained using SAR interferograms obtained for descending and ascending Sentinel-1 orbits. We find that the Illapel event is predominantly thrust, as expected for an earthquake on the interface between the Nazca and South America plates, with a slight right-lateral strike slip component. The maximum thrust-slip and right-lateral strike slip reach 8.3 and 1.5 m, respectively, both located at a depth of 8 km, northwest to the epicenter. The total estimated seismic moment is 3.28 × 1021 N.m, corresponding to a moment magnitude Mw 8.27. In our model, the rupture breaks all the way up to the sea-floor at the trench, which is consistent with the destructive tsunami following the earthquake. We also find the slip distribution correlates closely with previous estimates of interseismic locking distribution. We argue that positive coulomb stress changes caused by the Illapel earthquake may favor earthquakes on the extensional faults in this area. Finally, based on our inferred coseismic slip model and coulomb stress calculation, we envision that the subduction interface that last slipped in the 1922 Mw 8.4 Vallenar earthquake might be near the upper end of its seismic quiescence, and the earthquake potential in this region is urgent.

Geodetic model of the 2015 April 25 Mw 7.8 Gorkha Nepal Earthquake and Mw 7.3 aftershock estimated from InSAR and GPS data

Abstract We map the complete surface deformation of 2015 Mw 7.8 Gorkha Nepal earthquake and its Mw 7.3 aftershock with two parallel ALOS2 descending ScanSAR paths’ and two ascending Stripmap paths’ images. The coseismic fault-slip model from a combined inversion of InSAR and GPS data reveals that this event is a reverse fault motion, with a slight right-lateral strike-slip component. The maximum thrust-slip and right-lateral strike-slip values are 5.7 and 1.2 m, respectively, located at a depth of 7–15 km, southeast to the epicentre. The total seismic moment 7.55 × 1020 Nm, corresponding to a moment magnitude Mw 7.89, is similar to the seismological estimates. Fault slips of both the main shock and the largest aftershock are absent from the upper thrust shallower than 7 km, indicating that there is a locking lower edge of Himalayan Main Frontal Thrust and future seismic disaster is not unexpected in this area. We also find that the energy released in this earthquake is much less than the accumulated moment deficit over the past seven centuries estimated in previous studies, so the region surrounding Kathmandu is still under the threaten of seismic hazards.

Holocene displacement field at an emerged oceanic transform-ridge junction: The Husavik-Flatey Fault – Gudfinnugja Fault system, North Iceland

Our research focuses on Holocene tectonics in a broad area surrounding the junction between the active NW–SE trending Husavik-Flatey transform fault (HFF) and the N–S Gudfinnugja normal fault (GF), an exceptional example of onshore transform-ridge intersection. We mapped 637 minor and major faults, and measured the dip-slip and strike-slip offset components on the major faults. We also mapped 1016 individual tension fractures, as well as opening directions on the most reliable ones. The results indicate that this portion of the HFF comprises major right-stepping segments, with both normal and right-lateral strike-slip components, linked by local normal faults. The entire GF always shows pure dip-slip normal displacements, with a strong decrease in offset at the junction with the HFF. Fissure opening directions are in the range N45°-65°E along the HFF, N90°E along the GF, and N110°E within the area south of the HFF and west of the GF. Fault kinematics and fissure openings suggest a displacement field in good agreement with most of present-day GPS measurements, although our data indicate the possible long-term Holocene effects of the superimposition of magma-related stresses on the regional tectonic stresses. The HFF and the GF work together as a structural system able to accommodate differential crustal block motion, and possibly past dyke intrusions.