From the 1960 s to 1970 s, North China has been hit by a series of large earthquakes. During the past half century,geophysicists have carried out numerous surveys of the crustal and upper mantle structure, and associa...From the 1960 s to 1970 s, North China has been hit by a series of large earthquakes. During the past half century,geophysicists have carried out numerous surveys of the crustal and upper mantle structure, and associated studies in North China.They have made significant progress on several key issues in the geosciences, such as the crustal and upper mantle structure and the seismogenic environment of strong earthquakes. Deep seismic profiling results indicate a complex tectonic setting in the strong earthquake areas of North China, where a listric normal fault and a low-angle detachment in the upper crust coexist with a high-angle deep fault passing through the lower crust to the Moho beneath the hypocenter. Seismic tomography images reveal that most of the large earthquakes occurred in the transition between the high-and low-velocity zones, and the Tangshan earthquake area is characterized by a low-velocity anomaly in the middle-lower crust. Comprehensive analysis of geophysical data identified that the deep seismogenic environment in the North China extensional tectonic region is generally characterized by a low-velocity anomalous belt beneath the hypocenter, inconsistency of the deep and shallow structures in the crust, a steep crustalal-scale fault,relative lower velocities in the uppermost mantle, and local Moho uplift, etc. This indicates that the lithospheric structure of North China has strong heterogeneities. Geologically, the North China region had been a stable craton named the North China Craton or in brief the NCC, containing crustal rocks as old as ～3.8 Ga. The present-day strong seismic activity and the lower velocity of the lower crust in the NCC are much different from typical stable cratons around the world. These findings provide significant evidence for the destruction of the NCC. Although deep seismic profiling and seismic tomography have greatly enhanced knowledge about the deep-seated structure and seismogenic environment, some fundamental issues still remain and require further work.展开更多
The MS6.4 Menyuan earthquake occurred on the northern side of the Lenglongling fault(LLLF) in the mid-western of the Qilian-Haiyuan fault zone on January 21, 2016. The earthquake epicenter was distant from the Minle-D...The MS6.4 Menyuan earthquake occurred on the northern side of the Lenglongling fault(LLLF) in the mid-western of the Qilian-Haiyuan fault zone on January 21, 2016. The earthquake epicenter was distant from the Minle-Damaying and Huangcheng-Shuangta faults, eastern of the Northern Qilian Shan fault zone. A near northwest-striking rupture plane intersects the two faults at a certain angle. The focal mechanism solution shows that this was a thrust-type earthquake, slightly different from the strike-slip movement with a thrust component of the LLLF. Field geological mapping, tectonic geomorphology analysis, trench excavation and 14 C dating reveal that(1) the LLLF has been obviously active since the Holocene, and may behave with characteristic slip behavior and produce M_W7.3–7.5 earthquakes;(2) the LLLF appears as a flower structure in terms of structure style, and dips NNE at a steep angle; and(3) the most recent earthquake event occurred after 1815–1065 a BP. An associated fault, the Northern Lenglongling fault(NLLLF), is located at the northwestern end of the LLLF. Consequently, the NLLLF was continually subject to tectonic pushing effects from the left-lateral shear at the end of the LLLF, and, accordingly, it bent and rotated outward tectonically.Subsequently, the fault deviated from the dominant rupture azimuth and activity weakened. In the late Quaternary, it behaved as a thrust fault with no obvious deformation at the surface. This is indicated by the arc shape, with a micro-protrusion northeastward,and no geologic or geomorphic signs of surface rupturing since the late Quaternary. However, such faults could still rupture at depth, producing moderate-strong earthquakes. The geometric and kinematic properties of the NLLLF are in good agreement with the occurrence and kinematic properties of nodal plane 2, and with the distribution characteristics of the aftershocks and seismic intensity. Therefore, the NLLLF is a more suitable seismogenic structure for the MS 6.4 Menyuan earthquake. In addition, the thrus展开更多
On August 8,2017,a magnitude 7.0 earthquake occurred in Jiuzhaigou County,Sichuan Province,China.The deep seismogenic environment and potential seismic risk in the eastern margin of Tibetan Plateau have once again att...On August 8,2017,a magnitude 7.0 earthquake occurred in Jiuzhaigou County,Sichuan Province,China.The deep seismogenic environment and potential seismic risk in the eastern margin of Tibetan Plateau have once again attracted the close attention of seismologists and scholars at home and abroad.The post-earthquake scientific investigation could not identify noticeable surface rupture zones in the affected area;the complex tectonic background and the reason(s)for the frequent seismicity in the Jiuzhaigou earthquake region are unclear.In order to reveal the characteristics of the deep medium and the seismogenic environment of the M7.0 Jiuzhaigou earthquake region,and to interpret the tectonic background and genesis of the seismicity comprehensively,in this paper,we have reviewed all available observation data recorded by the regional digital seismic networks and large-scale,dense mobile seismic array(China Array)for the northern section of the North-South Seismic Belt around Jiuzhaigou earthquake region.Using double-difference seismic tomography method to invert the three-dimensional P-wave velocity structure characteristics of the upper crust around the Jiuzhaigou earthquake region,we have analyzed and discussed such scientific questions as the relationship between the velocity structure characteristics and seismicity in the Jiuzhaigou earthquake region,its deep tectonic environment,and the ongoing seismic risk in this region.We report that:the P-wave velocity structure of the upper crust around the Jiuzhaigoug earthquake region exhibits obvious lateral inhomogeneity;the distribution characteristics of the shallow P-wave velocity structure are closely related to surface geological structure and formation lithology;the M7.0 Jiuzhaigou earthquake sequence is closely related to the velocity structure of the upper crust;the mainshock of the M7.0 earthquake occurred in the upper crust;the inhomogeneous variation of the velocity structure of the Jiuzhaigou earthquake area and its surrounding medium appears to be the deep s展开更多
The tectonic position of the southwest section of the Qinzhou Bay-Hangzhou Bay Tectonic Junction Zone(QHTJZ)can be determined by examining the Qinzhou-Fangcheng Junction Zone(QFJZ)in Guangxi.This zone is significant b...The tectonic position of the southwest section of the Qinzhou Bay-Hangzhou Bay Tectonic Junction Zone(QHTJZ)can be determined by examining the Qinzhou-Fangcheng Junction Zone(QFJZ)in Guangxi.This zone is significant because it was the location of the largest earthquake ever recorded in the inland region of South China,specifically the 1936 Lingshan M6^(3/4)earthquake in Guangxi.Therefore,this region serves as an optimal location for researching the origins of intraplate earthquakes in South China.This study presents a display of a broadband magnetotelluric(MT)prospecting profile that traverses the Guangxi QFJZ and the Lingshan earthquake zone,extending from the northwest(NW)to the southeast(SE).A resistivity structure model was generated using three-dimensional(3D)inversion technology along the profile.The main faults in QFJZ were analyzed in terms of their deep extension forms and tectonic attributes.This analysis was performed by integrating the results obtained from geology,gravity,wave velocity ratio,Global Position System(GPS),and geothermal flow.The results showed that(1)the Dongzhong-Xiaodong fault(DXf),the eastern Fangcheng-Lingshan fault(FLf2),and the eastern Hepu-Beiliu fault(HBf2)were all trans-crustal deep faults,and crust-mantle ductile shear zones developed in the deep part.Two electrical boundary zones,DXf and HBf2,were identified.DXf inclined towards the northwest,while HBf2 inclined towards the southeast.The FangchengLingshan fault(FLf)exhibits a tectonic style resembling a“flower”shape in the upper crust.In the deeper section,it is characterized by an electrical boundary zone that gradually slopes towards the southeast direction.(2)The Hunan-Guangxi Passive Continental Margin(HGPCM)on the NW side of DXf had a stratified resistivity structure and relatively stable Bouguer gravity anomalies,which conformed to the quasi-craton tectonic attribute of the local failure at the southeastern margin of the Yangtze Block(YB).The southeastern side of this block is marked by the presence of the QFJZ and 展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos. 91014006, 90914005 & 41474073)
文摘From the 1960 s to 1970 s, North China has been hit by a series of large earthquakes. During the past half century,geophysicists have carried out numerous surveys of the crustal and upper mantle structure, and associated studies in North China.They have made significant progress on several key issues in the geosciences, such as the crustal and upper mantle structure and the seismogenic environment of strong earthquakes. Deep seismic profiling results indicate a complex tectonic setting in the strong earthquake areas of North China, where a listric normal fault and a low-angle detachment in the upper crust coexist with a high-angle deep fault passing through the lower crust to the Moho beneath the hypocenter. Seismic tomography images reveal that most of the large earthquakes occurred in the transition between the high-and low-velocity zones, and the Tangshan earthquake area is characterized by a low-velocity anomaly in the middle-lower crust. Comprehensive analysis of geophysical data identified that the deep seismogenic environment in the North China extensional tectonic region is generally characterized by a low-velocity anomalous belt beneath the hypocenter, inconsistency of the deep and shallow structures in the crust, a steep crustalal-scale fault,relative lower velocities in the uppermost mantle, and local Moho uplift, etc. This indicates that the lithospheric structure of North China has strong heterogeneities. Geologically, the North China region had been a stable craton named the North China Craton or in brief the NCC, containing crustal rocks as old as ～3.8 Ga. The present-day strong seismic activity and the lower velocity of the lower crust in the NCC are much different from typical stable cratons around the world. These findings provide significant evidence for the destruction of the NCC. Although deep seismic profiling and seismic tomography have greatly enhanced knowledge about the deep-seated structure and seismogenic environment, some fundamental issues still remain and require further work.
基金supported by a Special Project on Earthquake Research, the China Active Fault Survey Project-The South-North Seismic Zone Northern Segment (Grant No. 201408023)Fundamental Research Funds in Institute of Crustal Dynamics, China Earthquake Administration (Grant No. ZDJ2015-16)
文摘The MS6.4 Menyuan earthquake occurred on the northern side of the Lenglongling fault(LLLF) in the mid-western of the Qilian-Haiyuan fault zone on January 21, 2016. The earthquake epicenter was distant from the Minle-Damaying and Huangcheng-Shuangta faults, eastern of the Northern Qilian Shan fault zone. A near northwest-striking rupture plane intersects the two faults at a certain angle. The focal mechanism solution shows that this was a thrust-type earthquake, slightly different from the strike-slip movement with a thrust component of the LLLF. Field geological mapping, tectonic geomorphology analysis, trench excavation and 14 C dating reveal that(1) the LLLF has been obviously active since the Holocene, and may behave with characteristic slip behavior and produce M_W7.3–7.5 earthquakes;(2) the LLLF appears as a flower structure in terms of structure style, and dips NNE at a steep angle; and(3) the most recent earthquake event occurred after 1815–1065 a BP. An associated fault, the Northern Lenglongling fault(NLLLF), is located at the northwestern end of the LLLF. Consequently, the NLLLF was continually subject to tectonic pushing effects from the left-lateral shear at the end of the LLLF, and, accordingly, it bent and rotated outward tectonically.Subsequently, the fault deviated from the dominant rupture azimuth and activity weakened. In the late Quaternary, it behaved as a thrust fault with no obvious deformation at the surface. This is indicated by the arc shape, with a micro-protrusion northeastward,and no geologic or geomorphic signs of surface rupturing since the late Quaternary. However, such faults could still rupture at depth, producing moderate-strong earthquakes. The geometric and kinematic properties of the NLLLF are in good agreement with the occurrence and kinematic properties of nodal plane 2, and with the distribution characteristics of the aftershocks and seismic intensity. Therefore, the NLLLF is a more suitable seismogenic structure for the MS 6.4 Menyuan earthquake. In addition, the thrus
基金This research was supported by the National Natural Science Foundation of China(No.41974066,No.41474057)ChinArray Project-Northern Section of South-North Seismic Belt(201308011)+1 种基金Project of Science for Earthquake Resilience(XH20051)the Science and Technology Innovation Fund of Sichuan Earthquake Administration(201804).
文摘On August 8,2017,a magnitude 7.0 earthquake occurred in Jiuzhaigou County,Sichuan Province,China.The deep seismogenic environment and potential seismic risk in the eastern margin of Tibetan Plateau have once again attracted the close attention of seismologists and scholars at home and abroad.The post-earthquake scientific investigation could not identify noticeable surface rupture zones in the affected area;the complex tectonic background and the reason(s)for the frequent seismicity in the Jiuzhaigou earthquake region are unclear.In order to reveal the characteristics of the deep medium and the seismogenic environment of the M7.0 Jiuzhaigou earthquake region,and to interpret the tectonic background and genesis of the seismicity comprehensively,in this paper,we have reviewed all available observation data recorded by the regional digital seismic networks and large-scale,dense mobile seismic array(China Array)for the northern section of the North-South Seismic Belt around Jiuzhaigou earthquake region.Using double-difference seismic tomography method to invert the three-dimensional P-wave velocity structure characteristics of the upper crust around the Jiuzhaigou earthquake region,we have analyzed and discussed such scientific questions as the relationship between the velocity structure characteristics and seismicity in the Jiuzhaigou earthquake region,its deep tectonic environment,and the ongoing seismic risk in this region.We report that:the P-wave velocity structure of the upper crust around the Jiuzhaigoug earthquake region exhibits obvious lateral inhomogeneity;the distribution characteristics of the shallow P-wave velocity structure are closely related to surface geological structure and formation lithology;the M7.0 Jiuzhaigou earthquake sequence is closely related to the velocity structure of the upper crust;the mainshock of the M7.0 earthquake occurred in the upper crust;the inhomogeneous variation of the velocity structure of the Jiuzhaigou earthquake area and its surrounding medium appears to be the deep s
基金supported by the Science for Earthquake Resilience Program of the China Earthquake Administration(Grant Nos.XH24033B,XH22004YA)the Guangxi Scientific Research and Technology Development Plan Project(Grant Nos.1377002,14124004-4-8)the Earthquake Prediction Open Fund Project of China Earthquake Administration(Grant No.2021EF0F02)。
文摘The tectonic position of the southwest section of the Qinzhou Bay-Hangzhou Bay Tectonic Junction Zone(QHTJZ)can be determined by examining the Qinzhou-Fangcheng Junction Zone(QFJZ)in Guangxi.This zone is significant because it was the location of the largest earthquake ever recorded in the inland region of South China,specifically the 1936 Lingshan M6^(3/4)earthquake in Guangxi.Therefore,this region serves as an optimal location for researching the origins of intraplate earthquakes in South China.This study presents a display of a broadband magnetotelluric(MT)prospecting profile that traverses the Guangxi QFJZ and the Lingshan earthquake zone,extending from the northwest(NW)to the southeast(SE).A resistivity structure model was generated using three-dimensional(3D)inversion technology along the profile.The main faults in QFJZ were analyzed in terms of their deep extension forms and tectonic attributes.This analysis was performed by integrating the results obtained from geology,gravity,wave velocity ratio,Global Position System(GPS),and geothermal flow.The results showed that(1)the Dongzhong-Xiaodong fault(DXf),the eastern Fangcheng-Lingshan fault(FLf2),and the eastern Hepu-Beiliu fault(HBf2)were all trans-crustal deep faults,and crust-mantle ductile shear zones developed in the deep part.Two electrical boundary zones,DXf and HBf2,were identified.DXf inclined towards the northwest,while HBf2 inclined towards the southeast.The FangchengLingshan fault(FLf)exhibits a tectonic style resembling a“flower”shape in the upper crust.In the deeper section,it is characterized by an electrical boundary zone that gradually slopes towards the southeast direction.(2)The Hunan-Guangxi Passive Continental Margin(HGPCM)on the NW side of DXf had a stratified resistivity structure and relatively stable Bouguer gravity anomalies,which conformed to the quasi-craton tectonic attribute of the local failure at the southeastern margin of the Yangtze Block(YB).The southeastern side of this block is marked by the presence of the QFJZ and
