Left-lateral Strike-slip Component Research Articles

Structural geometry and active faulting along the southern segment of the Longmenshan thrust belt: Insights into the seismotectonics of the 1327 Tianquan and 2013 Lushan earthquakes (eastern Tibetan Plateau, China)

The 2008 Mw 7.9 Wenchuan and 2013 Mw 6.7 Lushan earthquakes ruptured the central and southern segments of the Longmenshan thrust belt on the eastern Tibetan Plateau, respectively. The ∼M 7 Tianquan earthquake in 1327 is also thought to have occurred on the southern segment with effects spatially overlapping those of the Lushan earthquake, but the deformation style and seismogenic mechanism of the segment remain poorly understood. Satellite image interpretation, field investigations, and trenching reveal that the Shuangshi-Dachuan fault (SDF) on the southern segment displaces landforms, dips southeast, and is dominated by thrust motion with a left-lateral strike-slip component. The latest and penultimate events along the fault occurred in 1085–1457 CE and 1215 BCE-104 CE, respectively. Some ancient landslides exits along the fault, and one of them formed close to 703 ± 17 yr BP. The ages of the latest event and of the landslide agree well with the occurrence of the Tianquan earthquake, indicating that the earthquake was most likely generated by the SDF. Magnetotelluric imaging and the aftershock belt of the Lushan earthquake show that the Longmen Shan forms a wedge-shaped high-resistivity body protruding eastward. The SDF corresponds well to the east-dipping upper electrical boundary of the wedge-shaped body and is interpreted as a shallow backthrust; the seismogenic fault of the Lushan earthquake corresponds to the west-dipping lower boundary and is interpreted as a blind thrust fault. The left-lateral slip component of the SDF may be a response to the lateral extension of the weak lower crust.

Structure and kinematics of active faulting in the northern domain of Western and Central Alborz, Iran and interpretation in terms of tectonic evolution of the region

Field evidence, seismicity, and geodetic data are combined to define the tectonic evolution along the northern domain of the Western and Central Alborz ranges, which have experienced significant earthquakes. One of our main focuses is to present the geometric-kinematic characteristics of active fault planes in the North Alborz fault zone and its subsidiary faults as a basis for seismic hazard assessment. To evaluate the seismotectonics in the region, three active segments of the seismic zone are identified. These segments primarily exhibit reverse mechanisms and left-lateral strike-slip components and act as the boundaries of neotectonic stress domains around the transition zone between Alborz and the South Caspian Basin. The spatial distribution of the strike-slip and dip-slip faulting over the Western and Central Alborz range supports our understanding of the geodynamic processes of the region. Our map of local active faults reveals five main systems with N–S, NE–SW, ENE–WSW, E–W, and NW–SE directions. Field studies indicate that strike-slip movements predominate and are consistent with a ∼WNW-ESE-oriented left-lateral wrench system. Pure left-lateral strike-slip faults trending E-W, extensional faults trending NE–SW, and compressional faults trending NW-SE are identified. Regional field investigations reveal spatial variations in the fault zone width of the northern domain of the Western and Central Alborz. The findings demonstrate that fault zone structures and their spatial distribution along the width of the area are strongly affected by the strain partitioning process in the transpressional zone. A spectacular well-exposed transpressional zone from the Western and Central Alborz region is described in detail, where outer domains are faults with a dominant reverse mechanism, and the inner domain is a wrench zone that includes faults with a dominant strike-slip mechanism. The seismic activity in the Northern Alborz region is mainly concentrated along the North Alborz fault zone and its subsidiary fault planes, of which some are identified for the first time in this research. Significant seismic events have occurred at locations where these newly identified fault planes interact. The maximum values of the geodetic strain axes in Western and Central Alborz are consistent with the area of high seismicity.

Coseismic deformation of the 2020 Yutian MW 6.4 earthquake from Sentinel-1A and the slip inversion

A remarkable earthquake struck Yutian, China on June 26th, 2020. Here, we use Sentinel-1 images to investigate the deformation induced by this event. We invert the InSAR observations using a two-step approach: a nonlinear inversion to constrain fault geometries with uniform slip based on the rectangular plane dislocation in an elastic half-space, followed by a linear inversion to retrieve the slip distribution on the fault plane. The results show that the maximum LOS displacement is 22.6 ​cm, and the fault accessed to the ruptured characteristics of normal faults with the minor left-lateral strike-slip component. The fault model indicates a 210° strike. The main rupture zone concentrates in the depth of 5–15 ​km, and the fault slip peaks at 0.89 ​m at the depth of 9 ​km. Then, we calculate the variation of the static Coulomb stress based on the optimal fault model, the results suggest that the Coulomb stress of the Altyn Tagh fault and other neighboring faults has increased and more attention should be paid to possible seismic risks.

Active Tectonics and Paleoseismicity of the Eastern Issyk-Kul Basin (Kyrgyzstan, Tien Shan)

Abstract—The Malyi Orgochor, Orgochor, Birbash, Sukhoi Ridge, Ichketosma, and Tosma uplifts in the eastern Issyk-Kul basin are fault-related anticlinal folds composed of Neogene and Quaternary sediments involved in tectonic movements. The folds have asymmetric transversal profiles, with low-angle southern limbs and steep northern limbs cut by segments of the South Issyk-Kul and Karkara reverse faults reactivated in the late Quaternary. The location and geometry of the two faults, which both show reverse and left-lateral strike slip components, correspond to neotectonic propagation of deformation from the Terskey-Ala-Too Range over almost the whole eastern Issyk-Kul basin. Judging by primary and secondary coseismic surface deformation in the area, the South Issyk-Kul and Karkara faults repeatedly generated large earthquakes (M ≥ 7, I ≥ 9) in the Late Pleistocene and Holocene. According to trenching results, the historical earthquakes that occurred in the first and 10–11th centuries accommodated motions on the South Issyk-Kul fault. The new seismotectonic and paleoseismicity data from the eastern Issyk-Kul basin provide updates to its seismic potential.

Penentuan Hiposenter Dan Mekanisme Fokus Gempa Bumi MLv4,8 1 Januari 2015 Di Sekitar Sesar Matano

Earthquake was recorded by BMKG on Thursday January 1, 2015 at 22:20:04.8 GMT or Friday January 2, 2015 at 06:20:04.8 Central Indonesia Time. Hypocenter located at 120.87 E, 2.22 S with depth of 17 km and magnitude M Lv 4.8. Purpose of this research is to study fault plane mechanism that cause this earthquake using hypocenter and focal mechanisms. This research used waveform M Lv 4.8 January 1, 2015 which recorded at BMKG earthquake observation stations. Waveform is processed to obtain arrival time P- and S-wave and polarity of arrival time P-wave. Method used to determine hypocenter is Geiger Method with input are arrival time P- and S-wave. Focal mechanisms determined using the first polarity of arrival P-wave and hypocenter from previous step. Hypocenter obtained from this research is located at 2.2073 S, 120.798 E and 10 km depth. RMS is 0.7391. Focal mechanism of this earthquake is oblique fault, is normal fault with left-lateral strike slip component. Parameters are strike 312 0 , dip 71 0 and rake -14 0 . This result is consistent with Matano Fault type as a continuation of Palu-Koro Fault. M Lv 4.8 January 1, 2015 earthquake occurred because Matano Fault activity. Research results can provide a basis form earthquake hazard mitigation along Matano Fault zone.

Joint Inversion of GPS, Leveling, and InSAR Data for The 2013 Lushan (China) Earthquake and Its Seismic Hazard Implications

On 20 April 2013, a moment magnitude (Mw) 6.6 earthquake occurred in the Lushan region of southwestern China and caused more than 190 fatalities. In this study, we use geodetic data from nearly 30 continuously operating global positioning system (GPS) stations, two periods of leveling data, and interferometric synthetic aperture radar (InSAR) observations to image the coseismic deformation of the Lushan earthquake. By using the Helmert variance component estimation method, a joint inversion is performed to estimate source parameters by using these GPS, leveling, and InSAR data sets. The results indicate that the 2013 Lushan earthquake occurred on a blind thrust fault. The event was dominated by thrust faulting with a minor left-lateral strike–slip component. The dip angle of the seismogenic fault was approximately 45.0°, and the fault strike was 208°, which is similar to the strike of the southern Longmenshan fault. Our finite fault model reveals that the peak slip of 0.71 m occurred at a depth of ~12 km, with substantial slip at depths of 6–20 km. The estimated magnitude was approximately Mw 6.6, consistent with seismological results. Furthermore, the calculated static Coulomb stress changes indicate that the 2013 Lushan earthquake may have been statically triggered by the 2008 Wenchuan earthquake.

Гагатлинский рой слабых землетрясений – проявление активности Андийского разлома

The swarm of more than a hundred weak earthquakes, the bulk of which occurred in the second decade of January 2019, was recorded at the end of 2018 and at the beginning of 2019 in the area of the western borders of the Dagestan salient. Refinement of the position of the epicenters of the swarm events by the method of double differences showed their compact location to the northeast of the village Gagatli on the eastern latitudinal branch of the Andean fault, known for left-lateral strike-slip and normal fault kinematics. According to the results of the study of the fault plane solutions of the five most strong earthquakes in the swarm, the type of movement was established - a left-lateral strike-slip and normal component, which allowed the investigated activation to be attributed to the discharge of accumulated stresses in the eastern part of the Andean fault. A characteristic feature of the recordings of these events by the nearest stations located in the territory of Dagestan and Chechnya was the similarity of the wave pattern, established when they correlated in different frequency bands (1-2 Hz, 1-3 Hz, 1-5 Hz). The correlation matrix of the records of 19 events filtered in the 1-3 Hz band was used to construct cluster analysis dendrograms showing different correlation of the events of the swarm and other earthquakes of Dagestan at a similar distance.

Source parameters and slip distribution of the 2018 Mw 7.5 Palu, Indonesia earthquake estimated from space-based geodesy

The 2018 Mw 7.5 Palu earthquake is one of the most geometrically complex events ever recorded on Central Sulawesi Island. It caused devastating tsunamis and landslides after the mainshock, resulting in great casualties and damages to the infrastructures in Palu city and surrounding areas. In this study, we combined far-field InSAR, near-field SAR and optical sub-pixel correlation data to determine the fault geometry, source parameters and fault-slip distribution of this event along the Palu-Koro fault zone. Our best-fitting fault model contains three fault segments with variable strike angles, showing that the coseismic rupture is dominated by a left-lateral strike-slip motion accompanied by minor normal-slip and reverse-slip components. On the onshore segments, the maximum slip is up to ∼ 8.4m with a left-lateral strike-slip component of ∼ 6.8m at a depth of 4km on the central segment near Palu city, a normal-slip component of ∼ 4.3m in the left releasing step-over and a reverse-slip component of ∼ 3.2m in the offshore area near the Palu bay. On the offshore segment, the maximum slip is up to ∼ 4.2m with a normal-slip component of ∼ 1.8m. We argue that the offshore reverse-slip motion might have played a key role in the generation of the Palu tsunami. We also suggest that the linking normal segment contributed to the rupture propagation across the left releasing step-over from the central segment to the southern segment, while the linking reverse segment arrested the rupture propagation across the right restraining step-over to north. The Coulomb stress change reveals that there is possibility of future great earthquakes occurring on several major faults in the northeast of Palu city. Our results have great significance to qualitatively assess the risk of future seismic hazards in such a geometrically complex fault system.

The cause of the 2011 Hawthorne (Nevada) earthquake swarm constrained by seismic and InSAR methods

We used both seismic and InSAR data to investigate the mechanism behind the 2011 Hawthorne (Nevada) earthquake swarm that occurred between March 15 and August 17, 2011. Regional seismic data were used to estimate the centroid depth and focal mechanism for nine earthquakes that occurred in this swarm, with magnitudes between $$M_w$$ 3.9 and $$M_w$$ 4.8. The inferred focal mechanisms indicate that the source of these earthquakes is normal faulting with a small left-lateral strike-slip component along the southwest direction. Three InSAR displacement maps covering the epicentral zone of the 2011 Hawthorne earthquakes were inverted to get a slip model. The slip distribution shows that the deformation source is characterized by normal faulting, consistent with our inferred focal mechanisms. Our results suggest that the seismogenic zone was in the tensile stress environment. The temporal and spatial evolutions of seismicity suggest that the 2011 Hawthorne swarm might be caused by aseismic slip. Therefore, the 2011 Hawthorne earthquake swarm may have been the result of aseismic slip under the regional tectonic stress, and had nothing to do with volcanic activity. However, the quantitative evidence for aseismic slip is limited to the indication that the geodetic moment is 15% greater than the seismic moment, which is near the level of uncertainty.

A NE-Trending Oblique-Slip Fault Responsible for the 2016 Zaduo Earthquake (Qinghai, China) Revealed by InSAR Data

Twelve Sentinel-1 images are used to measure the surface displacements caused by the Zaduo earthquake on 17 October 2016 in Qinghai, China. Comprehensive analysis of the local geologic structure, focal mechanisms, relocated aftershocks, and fault geometrical parameters from nonlinear inversions of the InSAR data indicates that a NE-trending fault with a strike of ~ 61°, namely the Aduo fault, was responsible for this event. Further geodetic inversions for finite fault models show that the dip angle of this fault is 75° to the SE. The majority of the slip occurred at the depth from 5 km to 17 km, and the normal-slip component was comparable to the strike-slip component. The peak slip of ~ 31 cm occurred at a depth of ~ 10 km. The InSAR determined moment is 9.61 × 1017 N m with a rigidity of 30 GPa, equivalent to Mw 5.9. The geological map reveals that the Aduo fault was characterized by a left-lateral strike-slip component in the past, as evidenced by the offset of Paleogene sedimentary rocks. Our results for the Zaduo earthquake suggest that the Qiangtang block probably consists of two or more sub-blocks with different eastward extrusion velocities and that the deformation of the Qiangtang block is occurring not only along its boundaries but also in its interior.

Micro-seismicity and seismotectonic study in Western Himalaya–Ladakh-Karakoram using local broadband seismic data

We document the seismic activity and fault plane solutions (FPSs) in the Western Himalaya, Ladakh and Karakoram using data from 16 broadband seismographs operated during June 2002 to December 2003. We locate 206 earthquakes with a local magnitude in the range of 1.5 to 4.9 and calculate FPSs of 19 selected earthquakes based on moment tensor solutions. The earthquakes are distributed throughout the study region and indicate active tectonics in this region. The observed seismicity pattern is quite different than a well-defined pattern of seismicity, along the Main Central Thrust zone, in the eastern side of the study region (i.e., Kumaon-Garhwal Himalaya). In the Himalaya region, the earthquakes are distributed in the crust and upper mantle, whereas in the Ladakh-Karakoram area the earthquakes are mostly confined up to crustal depths. The fault plane solutions show a mixture of thrust, normal and strike-slip type mechanisms, which are well corroborated with the known faults/tectonics of the region. The normal fault earthquakes are observed along the Southern Tibet Detachment, Zanskar Shear Zone, Tso-Morari dome, and Kaurik-Chango fault; and suggest E-W extension tectonics in the Higher and Tethys Himalaya. The earthquakes of thrust mechanism with the left-lateral strike-slip component are seen along the Kistwar fault. The right-lateral strike-slip faulting with thrust component along the bending of the Main Boundary Thrust and Main Central Thrust shows the transpressional tectonics in this part of the Himalaya. The observed earthquakes with right-lateral strike-slip faulting indicate seismically active nature of the Karakoram fault.

Source Process of the October 2016 Tottori-Chubu Earthquake(<i>M</i>j 6.6) and Relation with Near Source Strong Motions

A source process inversion for an Mj 6.6 earthquake which occurred on October 21, 2016 in central Tottori Prefecture, was performed using near-field strong motion waveforms. The results showed that a left-lateral strike-slip component was dominant on the fault plane, the strike of which was in a NNW-SSE direction and the dip almost vertical. The moment magnitude was estimated as 6.2. A large slip area (asperity) was determined around the hypocenter, including its northern shallow part, in which the maximum slip was nearly 1.2 m. Another small asperity was estimated also near the northern edge of the fault plane. These two asperities corresponded to the two distinct wave packets observed at the stations near the source region. Furthermore, the results suggested that a discrepancy in frequency characteristics between these asperities existed, by comparing them with waveforms obtained just above the source region. We also estimated the stress drop on the fault plane by the final slip distribution, and the maximum value was about 16 MPa. This result meant that the strong ground motion excitation of this earthquake was of an average level compared to past crustal earthquakes in Japan.

Evaluation of relative tectonic activity of Buin Zahra-Avaj area, northern Iran

Present active tectonics is affecting central Alborz and created various dynamic landforms in Buin Zahra-Avaj area, northern Iran. The area, located between the southern central Alborz and the edge of northwestern central Iran, is the result of both the Arabian–Eurasian convergence and clockwise rotation of the south Caspian Basin with respect to Eurasia in which most of the steep fault planes have a left lateral strike-slip component and most of the dip-slip faults are reverse, dipping SW. Since this region consists of several residential and industrial areas and includes several fault zones, the assessment of the structures of the present activity is vital. Six significant morphometric indices have been applied for this evaluation including stream length–gradient (SL), drainage basin asymmetry factor (Af), hypsometric integral (Hi), ratio of valley floor width to valley height (Vf), drainage basin shape (Bs), and mountain front sinuosity (Smf). The combined analyzed indices, represented through the relative tectonic activity (Iat), were used. The study area was divided into four regions according to the values of Iat. These classes include class 1 (very high activity,18%), class 2 (high, 20%), class 3 (moderate, 44%), and class 4 (low, 18%). The results of these indices are consistent with field observations on landforms and the deformation of Quaternary deposits.

Seismicity associated with magmatism, faulting and hydrothermal circulation at Aluto Volcano, Main Ethiopian Rift

The silicic volcanic centres of the Main Ethiopian Rift (MER) play a central role in facilitating continental rifting. Many of these volcanoes host geothermal resources and are located in heavily populated regions. InSAR studies have shown several are deforming, but regional seismic networks have detected little seismicity. A local network of 12 seismometers was deployed at Aluto Volcano from 2012 to 2014, and detected 2142 earthquakes within a 24-month period. We locate the events using a 1D velocity model that exploits a regional model and information from geothermal boreholes and calculate local magnitudes, b-values and focal mechanisms. Event depths generally range from the near surface to 15km with most of the seismicity clustering in the upper 2km. A significant amount of seismicity follows the Artu Jawa Fault Zone, which trends in alignment with the Wonji Fault Belt, NNE–SSW and is consistent with previous studies of strain localisation in the MER. Focal mechanisms are mostly normal in style, with the mean T-axes congruent to the orientation of extension in the rift at this latitude. Some show relatively small left-lateral strike-slip components and are likely associated with the reactivation of NE-ENE structures at the southern tip of the Aluto-Gedemsa segment. Events range from −0.40 to 2.98 in magnitude and we calculate an overall b-value of 1.40±0.14. This relatively elevated value suggests fluid-induced seismicity that is particularly evident in the shallow hydrothermal reservoir and above it. Subdividing our observations according to depth identifies distinct regions beneath the volcanic edifice: a shallow zone (−2–0km) of high seismicity and high b-values that corresponds to the hydrothermal system and is influenced by a high fluid saturation and circulation; a relatively aseismic zone (0–2km) with low b-values that is impermeable to ascending volatiles; a region of increased fluid-induced seismicity (2–9km) that is driven by magmatic intrusion from below and a deeper zone (below 9km) that is interpreted as a partially crystalline, magmatic mush. These observations indicate that both the magmatic and hydrothermal systems of Aluto volcano are seismically active and highlight the need for dedicated seismic monitoring at volcanoes in the MER.

Deformation style in the damage zone of the Mondy fault: GPR evidence (Tunka basin, southern East Siberia)

The Mondy strike-slip fault connects the W-E Tunka and N-S Hovsgol basins on the southern flank of the Baikal rift system. Ground penetrating radar (GPR) surveys in its damage zone provide constraints on thicknesses, dips, and plunges of fault planes, as well as on the amount and sense of vertical slip. Strike-slip faulting in the southern segment of the Mondy fault within the territory of Russia bears a normal slip component of motion along the W-E and NW planes. These motions have produced negative flower structures in shallow crust appearing as grabens upon Pleistocene fluvioglacial terraces. The amount of normal slip estimated from the displacement of reflection events varies over the area and reaches its maximum of 3.4 m near Mondy Village. In the Kharadaban basin link, left-lateral strike slip displaces valleys of ephemeral streams to 22 m, while normal slip detected by GPR reaches 2.2 m; this normal-to-strike slip ratio corresponds to a direction of ~6° to the horizon. The angles of dips of faults are in the range 75°-79°; the thicknesses of fault planes marked by low- or high-frequency anomalies in GPR records vary from 2.5 to 17.0 m along strike and decrease with depth within a few meters below the surface, which is common to near-surface coseismic motions. Many ruptures fail to reach the surface but appear rather as sinkholes localized mainly in fault hanging walls. The deformation style in the damage zone of the Mondy fault bears impact of the NW Yaminshin fault lying between its two segments. According to photoelasticity, the stress field changes locally at the intersection of the two faults, under NE compression at 38°, till the inverse orientations of principal compression and extension stresses. This stress pattern leads to a combination of normal and left-lateral strike slip components.

Transverse zones controlling the structural evolution of the Zipaquira Anticline (Eastern Cordillera, Colombia): Regional implications

We report paleomagnetic, magnetic fabric and structural results from 21 sites collected in Cretaceous marine mudstones and Paleogene continental sandstones from the limbs, hinge and transverse zones of the Zipaquira Anticline (ZA). The ZA is an asymmetrical fold with one limb completely overturned by processes like gravity and salt tectonics, and marked by several axis curvatures. The ZA is controlled by at least two (2) transverse zones known as the Neusa and Zipaquira Transverse Zones (NTZ and ZTZ, respectively). Magnetic mineralogy methods were applied at different sites and the main carriers of the magnetic properties are paramagnetic components with some sites being controlled by hematite and magnetite. Magnetic fabric analysis shows rigid-body rotation for the back-limb in the ZA, while the forelimb is subjected to internal deformation. Structural and paleomagnetic data shows the influence of the NTZ and ZTZ in the evolution of the different structures like the ZA and the Zipaquira, Carupa, Rio Guandoque, Las Margaritas and Neusa faults, controlling several factors as vergence, extension, fold axis curvature and stratigraphic detatchment. Clockwise rotations unraveled a block segmentation following a discontinuos model caused by transverse zones and one site reported a counter clockwise rotation associated with a left-lateral strike slip component for transverse faults (e.g. the Neusa Fault). We propose that diverse transverse zones have been active since Paleogene times, playing an important role in the tectonic evolution of the Cundinamarca sub-basin and controlling the structural evolution of folds and faults with block segmentation and rotations.

Middle Miocene–Pliocene activities of the North Altyn fault system: evidence from apatite fission track data

In this study, apatite fission track (AFT) analyses from opposite sides of the Jianglisai fault are used to constrain the timing of fault activity. Samples collected on the hanging wall have AFT ages between 10 ± 1 and 15 ± 2 Ma and a mean track length ranging from 13.1 ± 0.2 to 13.5 ± 0.2 μm. Samples collected on the footwall have AFT ages between 7.4 ± 0.6 and 9.0 ± 0.9 Ma and a relatively short mean track length that ranges from 11.3 ± 0.2 to 11.6 ± 0.2 μm. AFT modeling revealed that each side experienced two rapid cooling events that were related to tectonic stresses and deformation propagating in a northwestern direction. Combined with electron spin resonance dating constraints, we interpret the rapid cooling of the hanging wall during the Middle Miocene (17–14 Ma) as having recorded that the Jianglisai fault has been active at or prior to ~17 Ma. Both sides of the fault recorded the exhumation event that occurred at approximately 8 Ma, which is responsible for developing the fold-and-thrust belt along the mountain front. The Early Pliocene (about 5 Ma) cooling event indicated that the thrusting-related exhumation in the Jianglisai fault system was a continuously gradual intensified process. The North Altyn Tagh fault system was formed through stepwise thrusting from southeast to northwest during the Middle Miocene to Early Pliocene (17–5 Ma). Since then, the rigid Tarim plate provided constraint on the northward propagation, which likely caused the change from compressional thrusting to thrusting with a left-lateral strike-slip component of the North Altyn Tagh fault system.

Rupture Process of the 23 October 2011 Mw7.1 Van Earthquake in Eastern Turkey by Joint Inversion of Teleseismic, GPS and Strong-Motion Data

On 23 October 2011, a strong earthquake (Mw = 7.1) struck the Van (Eastern Turkey) region and its surrounding areas at 10:41:22 UTC (hereafter referred to as the Van earthquake), causing severe damage to the source region. Several studies have been carried out on the focal mechanism, seismic moment, focal depth and rupture model of this earthquake. However, there are still significant differences in the moment release, focal depth and slip asperities among these models. Since most of these models only used a single data set to investigate the source parameters, the reliability of these results is still a concern. In order to make clear the uncertainties and provide a reliable detailed rupture model for the mainshock, we investigated the rupture process of the Van earthquake by a joint inversion of teleseismic broadband seismograms, near-field static GPS displacement records and strong-motion data. The inversion results indicate that the mainshock was dominated by a thrust slip with a small part of a left-lateral strike-slip component below the hypocenter. The rupture initiated at a focal depth of 16 km and propagated to the surface with a relatively low average rupture velocity of ~1.8 km/s, suggesting that the major energy of the earthquake was released in a long-period band, which is the main reason why the seismic moments inverted by a long period or static signals are higher than those obtained by short-period data. Most of the slip occurred around the hypocenter with a maximum slip of more than 3.3 m, and the associated static stress drop was ~3 MPa. The total seismic moment of the whole fault was 5.76 × 1019 N·m, and most energy was released in the first 20 s, which is in the variation range of the released rupture models. The major slip was concentrated at deeper depth and extended to a depth of around 25 km. Meanwhile, the surface rupture was quite small, which explains why only weak ruptures were observed at the surface although caused by such a strong earthquake.

Earthquake mechanisms in the Gulfs of Gökova, Sığacık, Kuşadası, and the Simav Region (western Turkey): Neotectonics, seismotectonics and geodynamic implications

The mechanical behavior of continental lithosphere of Aegean region and western Turkey is one of the foremost interesting geological disputes in earth sciences. This region provides complex tectonic events which produced a strong heterogeneity in the crust as such in among most continental regions. The reasons of the ongoing lithospheric-scale extension within the Aegean region can be revealed by the correlation with the prevailing kinematic and dynamic factors such as roll-back of the subduction slab and back arc extension, westward extrusion of the Anatolian micro-plate, block rotations and transtensional transform faults. Seismological studies of earthquake source mechanisms and slip inversions play important roles on deciphering the current deformation and seismotectonic characteristics of the region. In recent years, several moderate earthquakes have occurred in the Gulfs of Gökova, Sığacık, Kuşadası, and Simav Graben. We studied source mechanisms and rupture histories of those earthquakes to retrieve the geometry of active faulting, source characteristics, kinematic and dynamic fault parameters and current deformations in western Turkey. We used teleseismic body-waveform inversions of long-period P- and SH-, and broad-band P-waveforms. We also checked first motion polarities of P-waves recorded at both regional and teleseismic stations. Inversion results revealed E–W striking normal faulting mechanisms with small amount of left-lateral strike-slip components in the Gulf of Gökova, and NE–SW oriented right-lateral strike-slip faulting mechanisms in the Gulf of Sığacık. In Simav Graben, earthquake source parameters show dominantly normal faulting mechanisms with strike-slip components. Our inversions resulted in focal depths for the earthquake ranging from 10 to 15km and NE–SW trending T-axes directions. The finite-fault slip distribution and rupture propagation models exhibit seismic moment releases and large displacement values which essentially occurred at hypocenters of the earthquakes. The overall results exhibited uniform and circular-shaped rupture propagations along dip directions of fault planes. Although most of the focal mechanism solutions show dominantly normal faulting mechanisms associated with the E–W oriented horst–graben structures in western Turkey, there are also strike-slip faulting mechanisms related to remarkable strike-slip faults which are capable of generating damaging earthquakes, particularly in the Gulf of Sığacık and Karaburun Peninsula. Thus, we suggest that present-day deformation in the Gulfs of Gökova, Sığacık, Kuşadası, and Simav Graben (western Turkey) is still mainly driven by the N–S extensional tectonics, but we tentatively further emphasize the importance of strike-slip faults in shaping tectonic structures in the Aegean region.

Structure formation in the zone of the northeastern fragment of the Kolumbe Fault in northern Sikhote-Alin

By the stress field’s reconstruction and the analysis of the distribution for the slickenside belts and the dike-hosting faults, the dominating left-lateral strike slip component is found for the Kolumbe Fault. This component is caused by the regional SES-NWN compression. The igneous rocks of the East Sikhote Alin volcanic-plutonic belt are considered as units synchronous with the regional displacement. Following the opinion of V.P. Utkin, the rift strike-slip-tension origin of these structures is suggested. Based on the structural-tectonic position of the volcanic rocks and the accompanying intrusive bodies and on the other geological data as well, several dislocation stages are distinguished in the Kolumbe Fault’s evolution. It is found that the dominating strike-slip motions along the main fault and its feathering faults changed to normal and reverse faulting deformations at the end of every stage.