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On October 7, 2021, a magnitude 5.9 earthquake struck the Harnai (Baluchistan) region of Pakistan, causing several fatalities and injuries within the epicentral area. First-order tectonic deformation in this region is caused by the convergence of the Indian Plate with respect to the Eurasian Plate. The Katwaz Block hinders the motion of the Indian Plate, resulting in the formation of strike-slip faults. In this study, the P-wave first-motion polarity technique was used to determine the mainshock faulting style. Cyclic scanning of the polarity solutions was applied to determine the most suitable focal mechanism solution among the available solutions generated by the FOCMEC (focal mechanism) software. The nodal planes correspond to different faulting styles (i.e., thrust and strike-slip faulting). A nodal plane oriented in the NW-SE direction corresponded to a strike-slip mechanism, which was considered to be the fault plane. Tectonically, this earthquake was associated with the Harnai-Karahi strike-slip fault zone owing to the fault strike and direction of slip. The apparent stress drop, fault length, and moment magnitude of the Harnai earthquake were 35.4 bar, 6.1 km, and 5.9, respectively. A lower b-value for the Gutenberg-Richter law was observed prior to the earthquake. Higher α- than b-values (α > b) indicate that this earthquake was governed by large events as opposed to small-magnitude events. The Harnai sequence had a decay exponent close to unity, lasted for 145 days, and produced few aftershocks. The study will help the future hazard mitigation in the region.

On October 7, 2021, a magnitude 5.9 earthquake struck the Harnai (Baluchistan) region of Pakistan, causing several fatalities and injuries within the epicentral area. First-order tectonic deformation in this region is caused by the convergence of the Indian Plate with respect to the Eurasian Plate. The Katwaz Block hinders the motion of the Indian Plate, resulting in the formation of strike-slip faults. In this study, the P-wave first-motion polarity technique was used to determine the mainshock faulting style. Cyclic scanning of the polarity solutions was applied to determine the most suitable focal mechanism solution among the available solutions generated by the FOCMEC (focal mechanism) software. The nodal planes correspond to different faulting styles (i.e., thrust and strike-slip faulting). A nodal plane oriented in the NW-SE direction corresponded to a strike-slip mechanism, which was considered to be the fault plane. Tectonically, this earthquake was associated with the Harnai-Karahi strike-slip fault zone owing to the fault strike and direction of slip. The apparent stress drop, fault length, and moment magnitude of the Harnai earthquake were 35.4 bar, 6.1 km, and 5.9, respectively. A lower b-value for the Gutenberg-Richter law was observed prior to the earthquake. Higher α- than b-values (α > b) indicate that this earthquake was governed by large events as opposed to small-magnitude events. The Harnai sequence had a decay exponent close to unity, lasted for 145 days, and produced few aftershocks. The study will help the future hazard mitigation in the region. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Geodesy & Geodynamics (1671-5942) is the property of Editorial Board Journal of Geodesy & Geodynamics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Moment tensor inversion was performed for earthquake of moderate magnitude occurring in May 2022 near Khuzdar, Pakistan. According to local news agencies, the event caused damages to engineered structures and collapse of several mud houses. Faulting style depicted from inversion implies that the event may be associated with Ornach-Nal strike-slip fault which is part of western boundary of Indian plate. To understand the tectonic setting of the area, the present study was augmented by inclusion of results from similar studies. Principal stress axis (SHmax) was determined by performing stress inversion. Based on 38 events focal mechanism solutions from the global Harvard Centroid Moment Tensor (CMT) of the Khuzdar region depict NW–SE orientation of SHmax direction. On the basis of their stress homogeneity, reduced stress tensors obtained from formal stress inversion have been divided into two subsets resulting in thrust and strike-slip faulting. The present-day stress state conforms to the oblique convergence of Indian and Arabian plates beneath Eurasian. Shear strain produced by strike-slip movement of plate boundary (Chaman fault system) is being accommodated in Kirthar range within the Indian plate. Before this event, a lower b-value (0.7) and accelerated earthquake sequence were observed in the Khuzdar region, which is (in our view evidence of presence of stress loaded asperities along this fault system) representation of stress loaded asperities exist. The spatial distribution of b-value depicts the lowest value in this region before the occurrence of Awaran earthquake of 2013 that took place about 70 km west of the recent event. [ABSTRACT FROM AUTHOR]

Tectonic extrusion bypassing the eastern Himalayan syntaxis results in a significant increase in regional stress instability and the associated frequent occurrence of earthquakes in southern Yunnan, China. However, the stress field, and the relationship between the focal mechanism of earthquakes and stress evolution in southern Yunnan, remain enigmatic. In this paper, using a modified grid point test method, we calculated the focal mechanism of ML ≥ 2.5 earthquakes in southern Yunnan (22–25° N, 100–104° E) from January 2009 to June 2023. Utilizing the solutions of historical earthquake focal mechanisms, we obtained the present-day regional tectonic stress field in southern Yunnan via inversion. The results indicate complex and diverse seismic focal mechanisms, and the main types of earthquakes are strike-slip events, followed by normal fault and reverse fault events. The orientations of the maximum and minimum principal stress axes rotate in a clockwise direction from northeast to southwest. The internal stress orientation distribution of the rhombic Sichuan–Yunnan block in the study area is consistent, and the block boundary zone is the site where stress deflection occurs, and the regional tectonic stress field is influenced by the interaction among different blocks. The distribution of R-value in the Lamping–Simao block gradually increases from north to south, indicating that the compressive stress required for material transport becomes relatively small. Combined with the geological and tectonic background of the study area, our results suggest that the speed of block movement gradually decreases from north to south; the distribution of R-value in the South China block is significantly smaller than that of the interior of the Sichuan–Yunnan rhombus, and the proportion of compressive stresses is larger, indicating a stronger extrusion in this region, which may be related to the fact that the Sichuan–Yunnan rhombus is strongly resisted by the South China block in the east. [ABSTRACT FROM AUTHOR]

The Palu earthquake, with a magnitude of 7.5, severely devastated the region in Central Sulawesi, Indonesia, but the mechanism of dynamic rupture considering in-situ conditions is not well understood. The in-situ stress field and fault geometry play important roles in the evolution of the supershear rupture. This study investigated the in-situ stress field, critical factors including the inversion of principal stress orientation by the focal mechanism solution, and constraint magnitude using the improved lateral pressure coefficient polygon. Furthermore, the dynamic rupture process is simulated using the finite element method (FEM) considering the strike and in-situ stress magnitudes of the seismogenic fault. The result shows that the principal stress orientation rotates counterclockwise about 15° from north to south, and the northern part of the fault zone is less straight than the fault from Palu Bay to the south, which are two decisive factors for supershear in the north. The damage zones considering the peak acceleration and co-seismic displacement are enlarged in Palu City, which is attributed to the rupture mode. It provides plausible explanations for this supershear event and sheds light on different dynamic rupture processes and seismic hazards that can be predicted by fully understanding the regional in-situ stress field.

The Xiluodu (XLD) reservoir is the second largest reservoir in China and the largest in the Jinsha River basin. The occurrence of two M > 5 earthquakes after reservoir impoundment has aroused great interest among seismologists and plant operators. We comprehensively analyzed the seismicity of the XLD reservoir area using precise earthquake relocation results and focal mechanism solutions and found that the seismicity of this area was weak before impoundment. Following impoundment, earthquake activity increased significantly. The occurrence of M ≥ 3.5 earthquakes within five years of impoundment also appear to be closely related to rapid rises and falls in water level, though this correlation weakened after five years because earthquake activity was far from the reservoir area. Earthquakes in the XLD reservoir area are clustered; near the dam (Area A), small faults are intermittently distributed along the river, while Area B is composed of multiple NW-trending left-lateral strike-slip faults and a thrust fault and Area C is composed of a NW-trending left-lateral strike-slip main fault and a nearly EW-trending right-lateral strike-slip minor fault. The geometries of the deep and the shallow parts of the NW-trending fault differ. Under the action of the NW-trending background stress field, a series of NW-trending left-lateral strike-slip faults and NE-trending thrust faults in critical stress states were dislocated due to the stress caused by reservoir impoundment. The two largest earthquakes in the XLD reservoir area were tectonic earthquakes that were directly triggered by impoundment.

This paper briefly reviewed the initiation steps and developments of the South China Sea Region Tsunami Warning and Mitigation Systems. In addition, we highlighted the structure and basic functions of the earthquake monitoring and processing system of the Tsunami Warning Systems, such as earthquake location, source mechanism solution and finite fault model inversion using the real-time seismic waveform data from regional and global seismographic networks, that will result in the rapid source parameters estimation for a larger earthquake in tsunami warning. Numerous simulations and hands-on events have shown that the preliminary earthquake parameters could be determined in less than 8 minutes after earthquake. The W-phase method is able to produce rapid and reliable estimation of the moment magnitude and source mechanism for larger events within 10—15 minutes after the earthquake. A finite fault model can be acquired after the earthquake event via computing teleseismic body-wave inversion program. The earthquake monitoring and processing system provide accurate and reliable information in contributing to tsunami warning services.

Three representative small and medium earthquakes in Shanxi seismic belt in recent years were taken as examples. By using different methods, such as the first motion of P-wave, first motion of P-wave combining P/SV/SH amplitude ratio, CAP (Cut and Past), and moment tensor inversion, the reliability and stability of focal mechanism solutions of small and medium earthquakes were analyzed and verified by gradually increasing calculation stations and selecting different data types and data quantities. The results indicate that in practice, 1) for a stable and reliable solution based on P-wave first motions, at least more than eight P-wave polarity data with clear initial motion and good inclusion in the earthquake are required; 2) for small earthquakes with inadequate station records, increasing the amplitude ratio data improves constraints on the results to a certain extent, but increasing the amplitude ratio data often significantly increases the contradiction ratio, while the constraints on the results are not continuously improved; 3) for ML≈3.2 earthquakes, the CAP method gives stable and reliable results, and for medium earthquakes with larger magnitude, moment tensor inversion method is also suggested to be an ideal choice to obtain reliable focal mechanism solutions.

The North–South Seismic Belt produces the most frequent strong earthquakes in the Chinese continental region, such as the MS 8.0 Wenchuan earthquake on 12 May 2008 and Ms 7.0 Lushan earthquake on 20 April 2013. This seismicity results in significant hazards. Fault geometry modeling is crucial for analyzing earthquake preparation and trigger mechanisms, simulating and predicting strong earthquakes, inverting fault slip rates, etc. In this study, a novel method for obtaining geometric models of ruptured seismogenic faults over a large area is designed based on datasets from surface fault traces, fault orientations, focal mechanism solutions, and earthquake relocations. This method involves three steps. 1) An initial model of the fault geometry is constructed from the focal mechanism solution data. This initial model is used to select the earthquake relocation data related to the target fault. 2) Next, a fine model of the fault geometry with a higher resolution than that of the initial model is fitted based on the selected earthquake relocation data. 3) The minimum curvature interpolation method (Briggs, 2012) is adopted to build a 3D model of the subsurface fault geometry according to the three-dimensional coordinates of nodes on all profiles of each fault/segment. Based on this method and data collected in the North–South Seismic Belt, the fine morphologies of different faults along 1,573 transverse profiles were fitted, and a 3D model of 263 ruptured seismogenic faults or fault segments in the North–South Seismic Belt was built using the minimum curvature spatial interpolation method. Since the earthquake number decreases with increasing depth, the model uncertainty increases with increasing depth. Different ruptured faults have different degrees of seismicity, so different fault models may have different uncertainties. The overall fitting error of the model is 0.98 km with respect to the interpreted results, from six geophysical exploration profiles.

The goal of this paper is to describe cluster analyses of the focal mechanism solutions estimated from local and teleseismic measurements and stress inversions to support the recent and previously published studies in the investigated region, that is the Vrancea seismic zone. We have applied different established clustering methods—e.g. hierarchical density-based clustering for applications with noise (HDBSCAN) and agglomerative hierarchical analysis—to the geographical coordinates, focal depths and parameters of the focal mechanism solutions of the gathered seismic events. We have attempted to develop a fully automated algorithm for the classification of earthquakes and to support the further investigation of stress inversions. This algorithm does not call for the setting of hyper-parameters by the users, thus the contribution from any bias of the user can be reduced significantly and the time required to carry out the clustering can also be decreased. In most cases, the resulting stress tensors are in close agreement with those we found in the literature. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Geodesy & Geodynamics (1671-5942) is the property of Editorial Board Journal of Geodesy & Geodynamics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Tectonic extrusion bypassing the eastern Himalayan syntaxis results in a significant increase in regional stress instability and the associated frequent occurrence of earthquakes in southern Yunnan, China. However, the stress field, and the relationship between the focal mechanism of earthquakes and stress evolution in southern Yunnan, remain enigmatic. In this paper, using a modified grid point test method, we calculated the focal mechanism of ML ≥ 2.5 earthquakes in southern Yunnan (22–25° N, 100–104° E) from January 2009 to June 2023. Utilizing the solutions of historical earthquake focal mechanisms, we obtained the present-day regional tectonic stress field in southern Yunnan via inversion. The results indicate complex and diverse seismic focal mechanisms, and the main types of earthquakes are strike-slip events, followed by normal fault and reverse fault events. The orientations of the maximum and minimum principal stress axes rotate in a clockwise direction from northeast to southwest. The internal stress orientation distribution of the rhombic Sichuan–Yunnan block in the study area is consistent, and the block boundary zone is the site where stress deflection occurs, and the regional tectonic stress field is influenced by the interaction among different blocks. The distribution of R-value in the Lamping–Simao block gradually increases from north to south, indicating that the compressive stress required for material transport becomes relatively small. Combined with the geological and tectonic background of the study area, our results suggest that the speed of block movement gradually decreases from north to south; the distribution of R-value in the South China block is significantly smaller than that of the interior of the Sichuan–Yunnan rhombus, and the proportion of compressive stresses is larger, indicating a stronger extrusion in this region, which may be related to the fact that the Sichuan–Yunnan rhombus is strongly resisted by the South China block in the east.

Copyright of Journal of Geodesy & Geodynamics (1671-5942) is the property of Editorial Board Journal of Geodesy & Geodynamics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Geodesy & Geodynamics (1671-5942) is the property of Editorial Board Journal of Geodesy & Geodynamics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract The tectonic stress field was investigated in and around the aftershock area of the Hokkaido Eastern Iburi earthquake (M JMA = 6.7) occurred on 6 September 2018. We deployed 26 temporary seismic stations in the aftershock area for approximately 2 months and located 1785 aftershocks precisely. Among these aftershocks, 894 focal mechanism solutions were determined using the first-motion polarity of P wave from the temporary observation and the permanent seismic networks of Hokkaido University, Japan Meteorological Agency (JMA), and High Sensitivity Seismograph Network Japan (Hi-net). We found that (1) the reverse faulting and the strike-slip faulting are dominant in the aftershock area, (2) the average trend of P- and T-axes is 78° ± 33° and 352° ± 51°, respectively, and (3) the average plunge of P- and T-axes is 25° ± 16° and 44° ± 20°, respectively: the P-axis is close to be horizontal and the T-axis is more vertical than the average of the P-axes. We applied a stress inversion method to the focal mechanism solutions to estimate a stress field in the aftershock area. As a result, we found that the reverse fault type stress field is dominant in the aftershock area. An axis of the maximum principal stress (σ 1) has the trend of 72° ± 7° and the dipping eastward of 19° ± 4° and an axis of the intermediate principal stress (σ 2) has the trend of 131° ± 73° and the dipping southward of 10° ± 9°, indicating that both of σ 1- and σ 2-axes are close to be horizontal. An axis of the minimum principal stress (σ 3) has the dipping westward of 67° ± 6° that is close to be vertical. The results strongly suggest that the reverse-fault-type stress field is predominant as an average over the aftershock area which is in the western boundary of the Hidaka Collision Zone. The average of the stress ratio R = (σ 1 − σ 2)/(σ 1 − σ 3) is 0.61 ± 0.13 in the whole aftershock area. Although not statistically significant, we suggest that R decreases systematically as the depth is getting deep, which is modeled by a quadratic polynomial of depth.

Using the Cut And Paste (CAP) method, we invert the focal mechanism of 38 moderate earthquakes (MS ≥ 3.0) recorded by Yunnan seismic network and analyze the corresponding focal mechanism consistency based on the minimum spatial rotation angle. Our results indicate that the MS 6.4 mainshock is induced by a lateral strike slip fault (with a rake angle of ∼ −165°) and a little normal-faulting component event along a nearly vertical plane (dipping angle∼ 79° and strike ∼138°). Combining our results with high resolution catalog, we argue that the seismogenic fault of this earthquake sequence is a secondary fault western to the major Weixi-Qiaohou-Weishan fault. The focal mechanism evolution can be divided into three periods. During the first period, the foreshock sequence, the focal mechanism consistency is the highest (KA

Featured Application: This work is mainly applied to the analysis of relevant geophysical field changes caused by earthquakes. The tectonic processes leading up to an earthquake and the occurrence of the earthquake itself will cause local changes in the geophysical field (geomagnetic field, stress field, etc.). In this paper, the variation characteristics of the tectonic stress field (TSF) and local geomagnetic field (LGF) before and after the Yangbi Ms 6.4 earthquake are studied. The regional stress tensor damping inversion method was used to invert the TSF using focal mechanism solutions (FMSs). The change characteristics of the TSF before and after the earthquake were analyzed. An annual variation model of the LGF was constructed, and the variation of the horizontal vector was analyzed. The azimuth and plunge of the maximum principal compressive stress axis of the TSF in the epicentral region before and after the earthquake were −4.4° and 2.7°, 172.7° and 6.6°, respectively. The variations in the declination, inclination and total intensity of the epicenter one year before and one month after the earthquake were −0.20′ (0.07′), 0.29′ (−0.12′), and −1.7 nT (−1.9 nT), respectively. The epicenter is located at the boundary of the "weak variation region" of the horizontal vector. This research is of great significance concerning the TSF background and incubation mechanism of earthquakes. [ABSTRACT FROM AUTHOR]

The June 17, 2019, MS 6.0 Changning earthquake is the largest recorded event in the Sichuan basin, spatiotemporal variations of stress field may shed light on the seismogenic mechanism of the earthquake. We determined the focal mechanism solutions (FMSs) of 124 earthquakes with MS ≥ 3.0 occurring in the Changning area from April 1, 2007, to February 29, 2020, and analyzed changes of FMSs and stress field before and after Changning earthquake. The Changning aftershocks were predominantly thrust fault earthquakes, followed by strike slip. The P-axis azimuths of the aftershock FMSs were oriented predominantly in the NEE direction, notably differing from the NWW-oriented P-axis azimuths of pre-earthquake FMSs; it shows the rotation of local stress field before and after the Changning earthquake, it is speculated that the change of stress field in Changning area may be caused by long-term water injection and salt mining activities. From the southeast to the northwest of the aftershock zone, the azimuths of principal compressive stress (S1) change from NEE to near-EW in both horizontal and vertical planes. Significant changes occurred in the FMS types and stress field of the aftershock zone following the Changning earthquake, the FMSs became diverse, the S1 azimuth of the Changning area changed from NWW to NEE, and then EW, the plunge and stress tensor variances increased, it reflects that the stress field of the Changning area adjusts continually with time.

On September 8, 2018, an MS 5.9 earthquake struck Mojiang, a county in Yunnan Province, China. We collect near-field seismic recordings (epicentral distances less than 200 km) to relocate the mainshock and the aftershocks within the first 60 hours to determine the focal mechanism solutions of the mainshock and some of the aftershocks and to invert for the finite-fault model of the mainshock. The focal mechanism solution of the mainshock and the relocation results of the aftershocks constrain the mainshock on a nearly vertical fault plane striking northeast and dipping to the southeast. The inversion of the finite-fault model reveals only a single slip asperity on the fault plane. The major slip is distributed above the initiation point, ~14 km wide along the down-dip direction and ~14 km long along the strike direction, with a maximal slip of ~22 cm at a depth of ~6 km. The focal mechanism solutions of the aftershocks show that most of the aftershocks are of the strike-slip type, a number of them are of the normal-slip type, and only a few of them are of the thrust-slip type. On average, strike-slip is dominant on the fault plane of the mainshock, as the focal mechanism solution of the mainshock suggests, but when examined in detail, slight thrust-slip appears on the southwest of the fault plane while an obvious part of normal-slip appears on the northeast, which is consistent with what the focal mechanism solutions of the aftershocks display. The multiple types of aftershock focal mechanism solutions and the slip details of the mainshock both suggest a complex tectonic setting, stress setting, or both. The intensity contours predicted exhibit a longer axis trending from northeast to southwest and a maximal intensity of Ⅷ around the epicenter and in the northwest.

Abstract The Hokkaido Eastern Iburi earthquake (M JMA = 6.7) occurred on September 6, 2018, in the Hokkaido corner region where the Kurile and northeastern Japan island arcs meet. We relocated aftershocks of this intraplate earthquake immediately after the main shock by using data from a permanent local seismic network and found that aftershock depths were concentrated from 20 to 40 km, which is extraordinarily deep compared with other shallow intraplate earthquakes in the inland area of Honshu and Kyushu, Japan. Further, we found that the aftershock area consists of three segments. The first segment is located in the northern part of the aftershock area, the second segment lies in the southern part, and the third segment forms a stepover between the other two segments. The hypocenter of the main shock, from which the rupture initiated, is located on the stepover segment. The centroid moment tensor solution for the main shock indicates a reverse faulting, whereas the focal mechanism solution determined by using the first-motion polarity of the P wave indicates strike-slip faulting. To explain this discrepancy qualitatively, we present a model in which the rupture started as a small strike-slip fault in the stepover segment of the aftershock area, followed by two large reverse faulting ruptures in the northern and southern segments.

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 3 February 2020 MS 5.1 Qingbaijiang earthquake, southwestern China, is the closest recorded MS ≥ 5.0 event to downtown Chengdu City to date, with an epicentral distance of only 38 km. Here we analyze seismic data from the Sichuan and Chengdu regional seismic networks, and employ a multi-stage location method to relocate the earthquakes that have occurred along the central and northern segments of the Longquanshan fault zone since 2009, including the MS 5.1 Qingbaijiang earthquake sequence, to investigate the seismogenic structure of the region. The relocation results indicate that the seismicity along the central and northern segments of the Longquanshan fault zone has occurred mainly along the eastern branch since 2009, with the hypocentral distribution along a vertical cross-section illustrating a steep, NW-dipping parallel imbricate structure. The terminating depth of the eastern branch is about 12 km. The distribution of the MS 5.1 Qingbaijiang earthquake sequence is along the NE–SW-striking Longquanshan fault zone. The aftershock focal depths are in the 3–6 km range, with the mainshock located at 104.475°E, 30.73°N. Its initial rupture depth of 5.2 km indicates that the earthquake occurred above the shallow decollement layer of the upper crust in this region. The hypocentral distribution along the long axis of the aftershock area highlights that this earthquake sequence occurred along a fault dipping at 56° to the NW. Our surface projection of the inferred fault plane places it near the eastern branch of the Longquanshan fault zone. We infer the MS 5.1 mainshock to be a thrust faulting event based on the focal mechanism solution via the cut-and-paste waveform inversion method, with strike/dip/rake parameters of 22°/36°/91° and 200°/54°/89° obtained for nodal planes I and II, respectively. We identify that the seismogenic fault of the MS 5.1 Qingbaijiang earthquake lies along the eastern branch of the Longquanshan fault zone, and nodal plane II represents the coseismic rupture plane, based on a joint analysis of the event relocation results, mainshock focal mechanism, and regional geological information. Our study provides vital information for assessing the seismic hazard of the Longquanshan fault zone near Chengdu City.

NW Iran-SE Turkey is a tectonically active zone related to the Arabia-Eurasia convergence, but the active stress state in this zone has not yet been clearly studied. To improve the knowledge of present-day stress state in this region, optimum reduced stress tensor was analysed. For this, a large number of earthquake focal mechanisms (277) were collected. The analyses show most mechanisms exhibit strike-slip to thrust faulting. These data indicate that this region is dominated by an N158° maximum horizontal compressive stress (SHmax) belonging to a transpressional tectonic regime. In the scale of the study area, the relative magnitude of the intermediate and minimum principal stress axes do not differ much (ϕ = 0.09). Brittle deformation in this area is dominantly accommodated by a combination of strike-slip and thrust faulting (Aϕ = 1.82 to 2.30). The analyses reveal that two sets of faults show a high tendency to slip and reactivate. These sets contain NW-SE-striking right-lateral and NNE-SSW-striking left-lateral faults. The results of this study may help to study the active seismicity, tectonic activity, and seismic risk in this region. [ABSTRACT FROM AUTHOR]

The tectonic stress field was investigated in and around the aftershock area of the Hokkaido Eastern Iburi earthquake (MJMA = 6.7) occurred on 6 September 2018. We deployed 26 temporary seismic stations in the aftershock area for approximately 2 months and located 1785 aftershocks precisely. Among these aftershocks, 894 focal mechanism solutions were determined using the first-motion polarity of P wave from the temporary observation and the permanent seismic networks of Hokkaido University, Japan Meteorological Agency (JMA), and High Sensitivity Seismograph Network Japan (Hi-net). We found that (1) the reverse faulting and the strike-slip faulting are dominant in the aftershock area, (2) the average trend of P- and T-axes is 78° ± 33° and 352° ± 51°, respectively, and (3) the average plunge of P- and T-axes is 25° ± 16° and 44° ± 20°, respectively: the P-axis is close to be horizontal and the T-axis is more vertical than the average of the P-axes. We applied a stress inversion method to the focal mechanism solutions to estimate a stress field in the aftershock area. As a result, we found that the reverse fault type stress field is dominant in the aftershock area. An axis of the maximum principal stress (σ1) has the trend of 72° ± 7° and the dipping eastward of 19° ± 4° and an axis of the intermediate principal stress (σ2) has the trend of 131° ± 73° and the dipping southward of 10° ± 9°, indicating that both of σ1- and σ2-axes are close to be horizontal. An axis of the minimum principal stress (σ3) has the dipping westward of 67° ± 6° that is close to be vertical. The results strongly suggest that the reverse-fault-type stress field is predominant as an average over the aftershock area which is in the western boundary of the Hidaka Collision Zone. The average of the stress ratio R = (σ1 − σ2)/(σ1 − σ3) is 0.61 ± 0.13 in the whole aftershock area. Although not statistically significant, we suggest that R decreases systematically as the depth is getting deep, which is modeled by a quadratic polynomial of depth. [ABSTRACT FROM AUTHOR]

The tectonic processes leading up to an earthquake and the occurrence of the earthquake itself will cause local changes in the geophysical field (geomagnetic field, stress field, etc.). In this paper, the variation characteristics of the tectonic stress field (TSF) and local geomagnetic field (LGF) before and after the Yangbi Ms 6.4 earthquake are studied. The regional stress tensor damping inversion method was used to invert the TSF using focal mechanism solutions (FMSs). The change characteristics of the TSF before and after the earthquake were analyzed. An annual variation model of the LGF was constructed, and the variation of the horizontal vector was analyzed. The azimuth and plunge of the maximum principal compressive stress axis of the TSF in the epicentral region before and after the earthquake were −4.4° and 2.7°, 172.7° and 6.6°, respectively. The variations in the declination, inclination and total intensity of the epicenter one year before and one month after the earthquake were −0.20′ (0.07′), 0.29′ (−0.12′), and −1.7 nT (−1.9 nT), respectively. The epicenter is located at the boundary of the “weak variation region” of the horizontal vector. This research is of great significance concerning the TSF background and incubation mechanism of earthquakes.

The medium-small earthquakes that occurred in the middle part of Tibetan Plateau (32°N–36°N, 90°E–93°E) from August 2016 to June 2017 were relocated using the absolute earthquake location method Hypo2000. Compared to the reports of Chinese Seismological Networks, our relocation results are more clustered on the whole, the horizontal location differences exceed 10 km, and the focal depths are concentrated in 0–8 km, which indicates that the upper crust inside the Tibetan Plateau is tectonically active. In June 2017 altogether eight earthquakes above magnitude 3.0 took place; their relocated epicenters are concentrated around Gêladaindong. The relocation results of M

Here, we show the present-day tectonic stress field and regional GPS velocity and strain rate fields in Hubei Province, central China. Our results are calculated based on the digital observation data from 01 January 2010, to 31 December 2017, by using the seis-CAP, P-wave first motion, and grid search methods and the software GAMIT/GLOBK10.4. The results show that the P axis azimuths of focal mechanism solutions, the principal compressional stress field, and the regional velocity and strain rate fields are conformably compressional in a NW–SE direction. The regional stress shape ratio R values are relatively low, and the faults are dominantly compressive-shear or compresso-shear faults. The average velocity modulus value for the GPS observation stations in western Hubei is 6.1 mm/a, which is higher than that in eastern Hubei (5.4 mm/a). The average velocity modulus value in the Jianghan Basin interior is relatively low (4.4 mm/a), while that in the northwestern Jianghan Basin is higher (7.6 mm/a). The strain rate field is characterized by NW–SE compression accompanied by NE–SW tension. The results suggest that the present-day crustal movement in Hubei Province is mainly controlled by collisions with the Indian Plate in the west and the Philippine Plate in the east and the consequent crustal shortening induced by western Hubei wedging into the Jianghan Basin. Further, the resistance by the thrust-and-fold belt in eastern Hubei contributes to the principal compressional movement in the study area. The T axis azimuth of focal mechanism solutions is consistent with the principal extensional stress field direction. In the central and northern Jianghan Basin, the R values are relatively high, the faults are mainly transtensional, and the crustal deformation is mainly extensional, which may be affected by the denudation, thinning and rapid rebound of the Dabie Orogen, resulting in tectonic extrusion and flow in the Jianghan Basin to both the NE and SW sides. [ABSTRACT FROM AUTHOR]

Focal depths of the 2008 MS6.1 Panzhihua earthquake sequence and tectonic stress field in the source area are investigated. Source depths of 24 earthquakes in Panzhihua earthquake sequence with a magnitude M≥3.0 were determined using the seismic depth phase sPL; additionally, the focal depths of 232 earthquakes were measured by fitting the three-component waveforms of the P and S waves. The source depth of the main shock is ~12 km. The majority of the aftershocks with magnitude M≥3.0 occurred in the brittle upper crust at the depths range of 12–18 km. Further, the Source mechanisms of the 232 events around the Panzhihua earthquake source area were determined, and the results show that the earthquakes have predominantly strike-slip mechanisms in the Dianzhong Block, but display complexity of the focal mechanisms outside and near the boundary of the Dianzhong block. The 232 earthquake mechanisms from this study are combined with the solutions from the Global Centroid Moment Tensor (GCMT) catalog to derive 2D stress field. The inversion results show that the Dianzhong block is predominantly under a strike slip faulting regime and the direction of the maximum principal compression σ1 is northwest-southeast (NW-SE)-trending. The distribution is coincide with GPS velocity field. However, orientations of principal stress axes as well as the faulting types change outside and near the Dianzhong block. The results show that the tectonic stress field in the study area is predominantly controlled by the southeast (SE)-trending horizontal movement and clockwise rotation of the Dianzhong block as a result of the eastward movement of eastern Tibetan meeting the old and rigid South China block (SCB). The Panzhihua earthquake ruptured at ~12 km depth where the tectonic stress regime is under the SE-direction horizontal compression and the NE-direction horizontal extension. [ABSTRACT FROM AUTHOR]

Nowadays, the already-existing earthquake catalogs are abundant, which can be used as the basic statistics for the research and prediction of aftershocks. There is plenty of information on the radiation of earthquake energy and the focal mechanism solution. Moreover, it contains a lot of seismic time and space correlation, most of which is hidden, unprecedented, and very hard to be described by geophysical formulas directly. Firstly, this study proposed a block supported vector regression algorithm in order to artificially study the correlation between main-shock parameters (magnitude, radiation energy, main-shock apparent stress, main-shock seismic moment, earthquake field, etc.) and aftershock parameters (magnitude, time, and space distance). Secondly, an interactive aftershock prediction software has been developed based on the C# language to conduct the research of aftershock prediction and application on real-time level. [ABSTRACT FROM AUTHOR]

• Extensional strains around the Longquan Shan fault zone were observed through GPS. • 12 out of 21 earthquakes (M > 3.0) in the Sichuan Basin are normal earthquakes. • The Longquan Shan fault zone is a deep-buried fault zone that reaches the Moho. The Longquan Shan fault zone (LQSF) locates in the Sichuan Basin of China, parallel to the well-known Longmen Shan fault zone. Different models for the LQSF indicate different understanding of the geological evolution of the Tibetan Plateau. In this paper, we provide evidences which demonstrate that the LQSF is a normal and deep-buried fault zone. Firstly, we find distinct extensional strains around the LQSF based on Global Positioning System (GPS) observations. We also find that the downward GPS velocities across the LQSF decrease suddenly from 4 to 5 mm/yr at the west to roughly zero at the east. Secondly, we collate focal mechanism solutions to earthquakes of M ≥ 3.0 in the Sichuan Basin and find that 12 out of 21 earthquakes are normal earthquakes. The surrounding extensional strains and the high proportion of normal earthquakes indicate that the shallow part of the LQSF is normal at present. Thirdly, based on the migration section obtained from deep seismic reflection profiling, we outline the geometric structure of the LQSF. It is a deep-buried fault zone that reaches the Moho, with two branches at the top. Such a fault model corresponds with the realities of the low seismic activities around the Longquan Shan anticline, and the scattered earthquakes beneath the Chengdu plain. Finally, we propose a three-stage evolutional model about the Longquan Shan fault system, which includes the formation of anticline in Late Triassic, the uplift of the Mountain in Oligence, and the stage of normal characteristics of the fault zone from Late Miocene. [ABSTRACT FROM AUTHOR]

We used 1‐D and 3‐D velocity models to determine focal mechanism solutions (FMSs) of 349 crustal earthquakes (M 2.7–7.3) and stress tensors in the source area of the 2016 Kumamoto earthquake (M 7.3) that occurred on the Futagawa‐Hinagu fault zone in Kyushu, Southwest Japan. There are some differences in the FMSs determined with the 1‐D and 3‐D velocity models. The use of the 3‐D velocity model leads to better results of stress tensors, which are determined by inverting the FMSs. The orientation of the minimum stress (σ3) axis is more accurately determined, which trends NNW‐SSE to N‐S nearly horizontally. In contrast, the axes of the maximum and intermediate stresses (σ1 and σ2) trend WSW‐ENE to E‐W with wide ranges. Significant spatiotemporal variations of the stress field are revealed in the Kumamoto source zone, indicating a small magnitude of deviatoric stress. The friction coefficient of the faults is estimated to be relatively small (~0.4), indicating that the seismogenic faults in central Kyushu are weak. The fault weakening may be caused by fluids beneath the source area and arc magma under the nearby Aso active volcano. Key Points: Focal mechanism solutions and stress tensors in the 2016 Kumamoto earthquake area are determined with a 3‐D velocity modelThe 3‐D velocity model leads to better results of stress tensorsSeismogenic faults in the source area are weak due to the effect of arc magma and fluids [ABSTRACT FROM AUTHOR]

Abstract: The process of the lead up and development of a catastrophic seismic event that affected the Earth's crust and the upper mantle, which led to a change in the natural environment in the western part of the Zagros folded mountain belt, is analyzed. The macroseismic effect, the focal mechanism, the aftershock sequence, the seismotectonic position of the epicentral area, and other parameters characterizing the features of the zone of this catastrophic earthquake with magnitude М = 7.4 that occurred near the Iran-Iraq border on November 12, 2017, are described. In one settlement (Iraq, the city of Dzharband khan), a macroseismic effect corresponding to 9-points according to the Modified Mercalli Intensity scale is recorded. An area of about 150 × 100 km2 underwent impacts of 7-8 points, tremors with the intensity of 5-6 points covered an extensive area of about 800 × 700 km2, and 4- to 5-point impacts were observed all over western Iran and eastern Iraq and appeared in major cities such as Tehran, Baghdad, Kirkuk, Ahvad, and Pasht. In the period from November 12, 2017, until January 21, 2018, more than 50 aftershocks with magnitude mb = 4.2-5.6 were registered in the epicenter zone of the earthquake according to data from the Federal Research Center Geophysical Survey of the Russian Academy of Sciences (RAS). Their epicentral area extended in the near-meridional direction along the Iraq-Iran border, primarily to the south from the epicenter of the main shock. Its length reached about 210 km and width was about 60 km. The position of the epicentral field of the aftershocks makes it possible to associate the earthquake focus of November 12, 2017, with the Khanaqin fault zone of the meridional strike and dextral strike-slip kinematics. The fault crosses Zagros diagonally near the Iran-Iraq border. Given that the size of the earthquake focus is established by the distribution of epicenters of the aftershocks, it covered the Khanaqin fault zone almost over its entire length. Sufficient attention is paid to the identified prognostic effects. The data of observations from geophysical observatories reflecting the processes of earthquake lead up and development are presented. Before the earthquake of November 12, 2017, the information and measuring systems of the North Caucasus geophysical observatory of Schmidt Institute of Physics of the Earth, RAS, had recorded gravitomagnetic disturbances of the ultralow frequency range. These prognostic effects appeared a few hours before the main shock. The conditions of the origination and development of seismogravity and gravitomagnetic disturbances are specified. In light of the presented material, it becomes clear that the experimental study of a separate class of fundamental gravitomagnetism problems identified in recent years is a defining problem of geophysics today. The gravitomagnetic disturbances in the lithosphere and other geospheres of the Earth recorded at large distances from the focal area can be considered a source of information on the time of appearance of the main high-magnitude shock. To use these effects for a real prediction of the expected magnitude and location and time of the pending earthquake, it is apparently necessary to develop a monitoring network at the observatory equipped with specialized measuring systems that can detect weak gravitomagnetic and seismogravity signals in the high-interference signaling environment on the Earth. [ABSTRACT FROM AUTHOR]

The majority of published in-situ stress information in the Australian continent is confined to petroleum provinces where industry technologies facilitate the capture of contemporary crustal stress information. In contrast, the stress pattern of non-petroleum regions such as the Flinders and Mount Lofty Ranges in South Australia, where intraplate deformation is localised, has not been investigated comprehensively so far. The ongoing activities of the mining industry in South Australia has enabled us to access recently drilled boreholes for image logging techniques that have typically been under-utilised by the mineral sector. Herein, we conduct stress analysis by analysing borehole image logs from 16 boreholes in the basement rocks of South Australia as well as two geothermal wells and one coal seam gas well in South Australia's northern Flinders Ranges, the Gawler Craton and the Eyre Peninsula. The resulting dataset of stress orientations is further accomplished by including recent seismological observations, which provide crustal stress information derived from focal mechanism solutions. The results of this study suggest a regional E-W orientation of the maximum horizontal compressive stress that is consistent with numerous observed neotectonic structures in this region. The focal mechanism solutions in this study suggest that the majority of events occur in a thrust faulting stress regime, which is consistent with the observed Quaternary fault scarps. However, our data compilation also indicates the presence of strike-slip and normal faulting stress regimes in the region, which has not been suggested extensively before this study. [ABSTRACT FROM AUTHOR]

This study comprises a new focal mechanism solution (OMÇ) program that can be used for scientific research and educational purposes. In addition, results of applied researches performed in the frame of this study, are also given using this software which is called WinFOC. In order to compute fault plane solutions and investigate kinematics of different fault systems, it is used WinFOC that accepts P-wave first motion polarity technique. In this way, 7 different earthquakes that occurred in our country were analyzed by using this program and obtained results were compared with findings reported by different institutions. The calculations performed with WinFOC were made using interactive graphical interface. In this context, we have determined P- and T-axes with azimuth (ф), dip (£) and rake (δ) angles of fault planes. Dip-directions (σ) were also identified on fault planes with availability of dip-slip faults. Compression and dilatation zones were manually separated from each other by meridians with different range of steps varying in different degrees. In order to interpret beach-balls with kinematics of fault ruptures that are responsible of earthquakes, the program is also capable to plot most acceptable 3-D bloc-diagram with appropriate scale according to slip-rate of dominant strike-type. [ABSTRACT FROM AUTHOR]

The focal mechanism solutions of the M5. 1 Badong earthquake and subsequent 34 aftershocks at ML 2. 0 or more were calculated using the P-wave first motion method; the main earthquake was normal fault dip slip type, and the slip types of the seismogenic rupture surfaces of the subsequent aftershocks primarily include normal dip slip (14 times), reverse dip slip (9 times), normal strike slip (9 times) and reverse strike slip (2 times). The M5. 1 Badong earthquake activities may be related to the stress adjustment caused by the rise of the groundwater level and the decrease of the frictional resistance betvveen structural planes of rock formations due to the effect of reservoir water penetration, and related to the joint activities of the NE-strike Gaoqiao fault and the near EW-strike Daping fault.

Northwestern Iran is one of the seismically active regions with a high seismic risk in the world. This area is a part of the complex tectonic system due to the interaction between Arabia, Anatolia and Eurasia. The purpose of this study is to deduce the stress regimes in the northwestern Iran and surrounding regions from stress inversion of earthquake focal mechanisms. We compile 92 focal mechanisms data from the Global CMT catalogue and other sources and also determine the focal mechanisms of 14 earthquakes applying the moment tensor inversion. We divide the studied region into 9 zones using similarity of the horizontal GPS velocities and existing focal mechanisms. We implement two stress inversion methods, Multiple Inverse Method and Iterative Joint Inversion Method, which provide comparable results in terms of orientations of maximum horizontal stress axes SHmax. The similar results of the two methods should make us more confident about the interpretations. We consider zones of exclusion surrounding all the earthquakes according to independent focal mechanisms hypothesis. The hypothesis says that the inversion should involve events that are far enough from each other in order that any previous event doesn't affect the stress field near the earthquake under consideration. Accordingly we deal with the matter by considering zones of exclusion around all the events. The result of exclusion is only significant for eastern Anatolia. The stress regime in this region changes from oblique to strike slip faulting because of the exclusion. In eastern Anatolia, the direction of maximum horizontal stress is nearly north-south. The direction alters to east-west in Talesh region. Errors of σ 1 are lower in all zones comparing with errors of σ 2 and σ 3 and there is a trade-off between data resolution and covariance of the model. The results substantiate the strike-slip and thrust faulting stress regimes in the northwest of Iran. [ABSTRACT FROM AUTHOR]

In this paper, the relationships of the plunges and azimuths of T and P axes versus the strikes, dips, and rakes of two seismic nodal planes were derived to provide reference for earthquake researchers. The independence of the plunges and azimuths of T, B, and P axes in focal mechanism solution was discussed, and it was concluded that three parameters, i.e., the azimuths of T, B and P axes, are completely independent. The focal mechanism solution representation based on Euler rotation was introduced, using three Euler angles in place of the plunges and azimuths of T, B, and P axes, and three focal mechanism solution representations were briefly compared and analyzed in respect of accuracy on the basis of the assumption of rounding; it was concluded that the Euler angle representation has better accuracy, compared with the azimuth representation and the traditional representation with T, B, and P axes. [ABSTRACT FROM AUTHOR]

The M S 6.4 earthquake occurred in Yangbi County, Yunnan Province, China, on 21 May, 2021. The earthquake is located on the west side of the Red River fault, the western boundary of the Sichuan-Yunnan block in the SE margin of the Tibetan Plateau. The Yangbi M S 6.4 earthquake has aroused great concern due to its unique geographical location and frequent strong earthquakes in Yunnan. In this study, a total of 4695 local earthquakes of the Yangbi M S 6.4 earthquake sequence are relocated using the double-difference location method, including the mainshock source location of 99.879°E, 25.687°N, and depth of 9.67 km. The mainshock has a moment magnitude of 6.1, and one of the fault-plane solutions is 137°, 83° and − 163° in strike, dip, rake respectively. Combined with the relocation and focal mechanism solutions results, it is suggested that the seismogenic fault of the Yangbi M S 6.4 earthquake is a NW-SE trending fault on the southwest side of the Weixi-Qiaohou fault (WQF), with high dip of SW, which is a previously-unknown blind fault. The regional 2D stress field shows that the principal compressive stress around the Yangbi earthquake is NNW-SSE and nearly N-S direction, which appears to be deflected counterclockwise by a small angle on its east side and changed to N-S and NNE-SSW direction on its west side, while both the north and south sides of the Yangbi earthquake show directional coherence. Strong differential deformation distorts in the upper crust to the northeast of the seismic source as reflected by tectonic stress field and the upper crust seismic anisotropy, indicating strong influence of Lijiang-Xiaojinhe fault (LXF). The stress field in the source area is jointly controlled by southeastward movement of southeastern margin of Tibetan Plateau, the northeastward movement of Indian plate and the differential movement between the different tectonic blocks. • The Yangbi M s6.4 earthquake sequences are relocated to reveal two burst areas of small earthquakes. The seismogenic fault is a blind fault. • The new detailed 2D stress field is released, and a model of stress field is reported around the source area. • Strong differential deformation distorts in the upper crust to the northeast of the source area. [ABSTRACT FROM AUTHOR]

Pakistan is situated very close to the subduction zone of Indian-Arabian plates and Indian-Eurasian plates. Thus, it is a country with moderate to high seismicity with a large number of major earthquakes. Therefore, the severity of seismic hazards of major earthquakes is not ignorable. The seismicity of northern areas of Pakistan (33-37°N and 70-76°E), which are the part of North West Himalaya, is studied. Three earthquake catalogues are selected and then completed for this purpose. The spatial distribution of their epicenters, as a function of depth, shows that most of the earthquakes (about 84 %) occurred in shallow to intermediate depths. Relationship between major faults and their source mechanism is also investigated. The Focal mechanism solutions of 39 significant earthquakes in this area, occurred in the period of 1976-2014 with magnitude M > 5.0, are also analyzed. The focal depth of these events is in the range of 10-244 km. Among 39 focal mechanisms, the majority of them located in lower crust. Global centroid moment tensor solutions indicate that the majority of the seismic events show strike-slip faulting with a left-lateral sense of motion, followed by thrust and normal faulting. Most of these focal mechanisms located in the Hindu-Kush, a most seismically active, region. The major source of these events and thrusting is the subduction of the Indian plate under the Eurasian Plate. At shallow to intermediate depth, low-to-intermediate angle thrust faulting is dominant. It is seen that in a large number of seismic events the compressive stress is acting nearly in NNW-SSE to N-S directions. [ABSTRACT FROM AUTHOR]

We applied the gCAP algorithm to determine 239 focal mechanism solutions (3:0≤MW ≤6:0) with records of dense ChinArray stations deployed in Yunnan, and then inverted 686 focal mechanisms (including 447 previous results) for the regional crustal stress field with a damped linear inversion. The results indicate dominantly strike-slip environment in Yunnan as both the maximum (σ1) and minimum (σ3) principal stress axes are sub-horizontal. We further calculated the horizontal stress orientations (i.e., maximum and minimum horizontal compressive stress axes: SH and Sh, respectively) accordingly and found an abrupt change near ∼26°N. To the north, SH aligns NW-SE to nearly E-W while Sh aligns nearly N-S. In contrast, to the south, both SH and Sh rotate laterally and show dominantly fan-shaped patterns. The minimum horizontal stress (i.e., maximum strain axis) Sh rotates from NW-SE to the west of Tengchong volcano gradually to nearly E-W in west Yunnan, and further to NE-SW in the South China block in the east. The crustal strain field is consistent with the upper mantle strain field indicated by shear-wave splitting observations in Yunnan but not in other regions. Therefore, the crust and upper mantle in Yunnan are coupled and suffering vertically coherent pure-shear deformation in the lithosphere. [ABSTRACT FROM AUTHOR]