The Sichuan-Yunnan region hosts numerous large active faults with complex spatial distributions and intricate intersections,where moderate-to-strong earthquakes occur frequently.Obtaining source mechanism solutions fo...The Sichuan-Yunnan region hosts numerous large active faults with complex spatial distributions and intricate intersections,where moderate-to-strong earthquakes occur frequently.Obtaining source mechanism solutions for these earthquakes is not only essential for analyzing the regional crustal stress regime,fault geometries,activity behaviors and seismic potentials,but also is critical for assessing seismic hazards.Previous studies have obtained source mechanism catalogs of regional historical moderate-to-strong earthquakes based on 1D crustal velocity models,or inverted source mechanisms for few representative events based on 3D velocity models incorporating lateral variations.However,a systematic source mechanism inversion framework,which integrates regional high-resolution 3D velocity models with significant topographic relief,still remains absent for the Sichuan-Yunnan region.Using the high-resolution 3D velocity model SWChinaCVM-2.0 with regional topographic relief,we first construct a comprehensive strain Green's tensor library for the 181 permanent broadband seismic stations across the Sichuan-Yunnan region.In particular,the forward modeling employs the spectral element method(SEM)with source-receiver reciprocity,followed by highly efficient compression of the computed library.Subsequently,a systematic source mechanism inversion is conducted for the 563 M_(L)≥4 earthquakes occurring in the region during 2009-2021 using full waveform matching.With the derived solutions of fault planes,full moment tensors and moment magnitudes,a new-generation,accurate source mechanism catalog for moderate-to-strong earthquakes in the Sichuan-Yunnan region is obtained.This catalog can provide essential data for future geoscience studies in the Sichuan-Yunnan region,and is a foundational geophysical work driven by new techniques and methods.In the future,the inversion framework can also be applied to areas with high seismic risks such as North China and Xinjiang,providing essential supports for rapid and accurate determination of source parameters and assessment of seismic hazards.展开更多
The mechanisms of the February 3, 1996 Lijiang main shock, Yunnan Province, are estimated by using the principle to inverse the mechanisms of two point sources simultaneously. The results are that the main shock of Li...The mechanisms of the February 3, 1996 Lijiang main shock, Yunnan Province, are estimated by using the principle to inverse the mechanisms of two point sources simultaneously. The results are that the main shock of Lijiang consists of two large ruptures, the time difference and the distance between the two ruptures are about 12 s (by the inversion) and about 26 km respectively. An extensional normal with strike-slip fault in about the north-south direction was formed by the first rupture, the mechanism of the second rupture is to be further studied. The method to inverse mechanisms of two point sources at the same time and the results obtained by directly analyzing P waveform records of the main shock are introduced, some related problems are also discussed. The Wuding earthquakes of October, 1995 and the Lijiang earthquake are considered to be the manifestation of the same dynamic process at different temporal and spatial points and the occurrence order of the two earthquakes is related to the direction of dynamics transmission.展开更多
Twenty-two earthquakes (ML=2.2-3.7) in the joint region of Xianshuihe, Longmenshan and An'ninghe faults are studied in this paper. The source mechanism solutions of these events are obtained using P-wave first mot...Twenty-two earthquakes (ML=2.2-3.7) in the joint region of Xianshuihe, Longmenshan and An'ninghe faults are studied in this paper. The source mechanism solutions of these events are obtained using P-wave first motion method, and the characteristics of the source stress field and rupture in the joint region are summarized preliminarily with some results of other researchers. Being strongly extruded by the approximately horizontal regional stress with the direction from north-west to south-east and the effect of the complex tectonics in the region, the source stress field has complex and variable characteristics. The earthquakes mainly show normal or strike-slip faults in Yajiang, North-triangle and west of Chengdu-block areas, indicating that the vertical forces have been playing an important role in the source stress fields, while the earthquakes mainly show reverse or strike-slip faults in Baoxing-Tianquan area, with the horizontal components of the principal pressure stress axes identical to the south-west direction to which the shallow mass is moving. We think that the manifold combinations of earthquake faults are the micro-mechanism based upon which the large regional shallow crust mass has been moving continually.展开更多
基金supported by the National Key Research and Development Project of China(Grant No.2021YFC3000600)the National Natural Science Foundation of China(Grant Nos.U2139204,42488301)。
文摘The Sichuan-Yunnan region hosts numerous large active faults with complex spatial distributions and intricate intersections,where moderate-to-strong earthquakes occur frequently.Obtaining source mechanism solutions for these earthquakes is not only essential for analyzing the regional crustal stress regime,fault geometries,activity behaviors and seismic potentials,but also is critical for assessing seismic hazards.Previous studies have obtained source mechanism catalogs of regional historical moderate-to-strong earthquakes based on 1D crustal velocity models,or inverted source mechanisms for few representative events based on 3D velocity models incorporating lateral variations.However,a systematic source mechanism inversion framework,which integrates regional high-resolution 3D velocity models with significant topographic relief,still remains absent for the Sichuan-Yunnan region.Using the high-resolution 3D velocity model SWChinaCVM-2.0 with regional topographic relief,we first construct a comprehensive strain Green's tensor library for the 181 permanent broadband seismic stations across the Sichuan-Yunnan region.In particular,the forward modeling employs the spectral element method(SEM)with source-receiver reciprocity,followed by highly efficient compression of the computed library.Subsequently,a systematic source mechanism inversion is conducted for the 563 M_(L)≥4 earthquakes occurring in the region during 2009-2021 using full waveform matching.With the derived solutions of fault planes,full moment tensors and moment magnitudes,a new-generation,accurate source mechanism catalog for moderate-to-strong earthquakes in the Sichuan-Yunnan region is obtained.This catalog can provide essential data for future geoscience studies in the Sichuan-Yunnan region,and is a foundational geophysical work driven by new techniques and methods.In the future,the inversion framework can also be applied to areas with high seismic risks such as North China and Xinjiang,providing essential supports for rapid and accurate determination of source parameters and assessment of seismic hazards.
文摘The mechanisms of the February 3, 1996 Lijiang main shock, Yunnan Province, are estimated by using the principle to inverse the mechanisms of two point sources simultaneously. The results are that the main shock of Lijiang consists of two large ruptures, the time difference and the distance between the two ruptures are about 12 s (by the inversion) and about 26 km respectively. An extensional normal with strike-slip fault in about the north-south direction was formed by the first rupture, the mechanism of the second rupture is to be further studied. The method to inverse mechanisms of two point sources at the same time and the results obtained by directly analyzing P waveform records of the main shock are introduced, some related problems are also discussed. The Wuding earthquakes of October, 1995 and the Lijiang earthquake are considered to be the manifestation of the same dynamic process at different temporal and spatial points and the occurrence order of the two earthquakes is related to the direction of dynamics transmission.
文摘Twenty-two earthquakes (ML=2.2-3.7) in the joint region of Xianshuihe, Longmenshan and An'ninghe faults are studied in this paper. The source mechanism solutions of these events are obtained using P-wave first motion method, and the characteristics of the source stress field and rupture in the joint region are summarized preliminarily with some results of other researchers. Being strongly extruded by the approximately horizontal regional stress with the direction from north-west to south-east and the effect of the complex tectonics in the region, the source stress field has complex and variable characteristics. The earthquakes mainly show normal or strike-slip faults in Yajiang, North-triangle and west of Chengdu-block areas, indicating that the vertical forces have been playing an important role in the source stress fields, while the earthquakes mainly show reverse or strike-slip faults in Baoxing-Tianquan area, with the horizontal components of the principal pressure stress axes identical to the south-west direction to which the shallow mass is moving. We think that the manifold combinations of earthquake faults are the micro-mechanism based upon which the large regional shallow crust mass has been moving continually.
