On September 16,2021,a MS6.0 earthquake struck Luxian County,one of the shale gas blocks in the Southeastern Sichuan Basin,China.To understand the seismogenic environment and its mechanism,we inverted a fine three-dim...On September 16,2021,a MS6.0 earthquake struck Luxian County,one of the shale gas blocks in the Southeastern Sichuan Basin,China.To understand the seismogenic environment and its mechanism,we inverted a fine three-dimensional S-wave velocity model from ambient noise tomography using data from a newly deployed dense seismic array around the epicenter,by extracting and jointly inverting the Rayleigh phase and group velocities in the period of 1.6–7.2 s.The results showed that the velocity model varied significantly beneath different geological units.The Yujiasi syncline is characterized by low velocity at depths of~3.0–4.0 km,corresponding to the stable sedimentary layer in the Sichuan Basin.The eastern and western branches of the Huayingshan fault belt generally exhibit high velocities in the NE-SW direction,with a few local low-velocity zones.The Luxian MS6.0 earthquake epicenter is located at the boundary between the high-and low-velocity zones,and the earthquake sequences expand eastward from the epicenter at depths of 3.0–5.0 km.Integrated with the velocity variations around the epicenter,distribution of aftershock sequences,and focal mechanism solution,it is speculated that the seismogenic mechanism of the main shock might be interpreted as the reactivation of pre-existing faults by hydraulic fracturing.展开更多
Based on the seismic data recorded by the China Earthquake Networks Center(CENC) in the Luxian area from January 2009 to October 2021,the 3D V_P,V_S, V_P/V_S structures and seismic locations of the area are obtained b...Based on the seismic data recorded by the China Earthquake Networks Center(CENC) in the Luxian area from January 2009 to October 2021,the 3D V_P,V_S, V_P/V_S structures and seismic locations of the area are obtained by joint inversion using the V_P/V_S model consistency-constrained double-difference tomography method(tomoDDMC).The earthquakes in the study area are mainly concentrated at a depth of 2-6 km,and the focal depth is generally shallow.The Ms 6.0 Luxian earthquake occurred at the transition zone of high-and low-velocity anomalies and the aftershock sequence was distributed along the edge of the low-V_P zone.A small number of foreshocks occurred on the west side of the M_S 6.0 Luxian earthquake,while most of the aftershocks were distributed on the east side of the M_S 6.0 Luxian earthquake.The aftershock sequence consisted of three seismic bands with different trends,and the overall distribution was in a NWW direction,which was inconsistent with the spatial distribution of the main active faults nearby.In addition,the spatiotemporal distribution of earthquakes and the variation of b-values are closely related to the industrial water injection activities in the study area,reflecting the activation of pre-existing hidden faults under certain tectonic and stress environments leading to seismic activities in the area.展开更多
In this article,we review the general characteristics of seismicity in and around China and the overall statistics of earthquake damage in 2021,focusing on several significant events and related scientific topics.Amon...In this article,we review the general characteristics of seismicity in and around China and the overall statistics of earthquake damage in 2021,focusing on several significant events and related scientific topics.Among them,the largest event is the M_(S)7.4 Madoi earthquake in Qinghai Province,northwest China.The event marks another M_(S)≥7 earthquake occurring near the boundary of the Bayan Har Block that has ended a remarkable quiescence of the M_(S)≥7 earthquakes within the Chinese mainland.In addition,the M_(S)6.4 Yangbi earthquake in Yunnan Province,southwest China draws the most attention because of its abundant foreshocks,which are well recorded by the densely distributed seismic stations in the surrounding regions.Regarding this event,we review several recent publications focusing on the Gutenberg-Richter b-value change and the physical mechanism of foreshocks associated with this sequence.The M_(S)6.0 Luxian earthquake in Sichuan Province,southwest China has caused serious damage with a relatively low magnitude,partly because the focal depth of the mainshock is relatively shallow (3.5 km).It is another strong earthquake occurring within the southeast Sichuan basin with low historical seismicity yet has increased significantly since 2015,probably due to shale gas development and associated hydraulic fracturing.展开更多
基金This work was supported by the Special Fund of the Institute of Geophysics,China Earthquake Administration(Nos.DQJB22B19,DQJB22R29 and DQJB22B26)the National Natural Science Foundation of China(Nos.41974066,U1839209 and 42074053)。
文摘On September 16,2021,a MS6.0 earthquake struck Luxian County,one of the shale gas blocks in the Southeastern Sichuan Basin,China.To understand the seismogenic environment and its mechanism,we inverted a fine three-dimensional S-wave velocity model from ambient noise tomography using data from a newly deployed dense seismic array around the epicenter,by extracting and jointly inverting the Rayleigh phase and group velocities in the period of 1.6–7.2 s.The results showed that the velocity model varied significantly beneath different geological units.The Yujiasi syncline is characterized by low velocity at depths of~3.0–4.0 km,corresponding to the stable sedimentary layer in the Sichuan Basin.The eastern and western branches of the Huayingshan fault belt generally exhibit high velocities in the NE-SW direction,with a few local low-velocity zones.The Luxian MS6.0 earthquake epicenter is located at the boundary between the high-and low-velocity zones,and the earthquake sequences expand eastward from the epicenter at depths of 3.0–5.0 km.Integrated with the velocity variations around the epicenter,distribution of aftershock sequences,and focal mechanism solution,it is speculated that the seismogenic mechanism of the main shock might be interpreted as the reactivation of pre-existing faults by hydraulic fracturing.
基金supported by the Fundamental Research Funds for the Institute of Earthquake Forecasting, China Earthquake Administration(CEAIEF20220211 and CEAIEF20220401)。
文摘Based on the seismic data recorded by the China Earthquake Networks Center(CENC) in the Luxian area from January 2009 to October 2021,the 3D V_P,V_S, V_P/V_S structures and seismic locations of the area are obtained by joint inversion using the V_P/V_S model consistency-constrained double-difference tomography method(tomoDDMC).The earthquakes in the study area are mainly concentrated at a depth of 2-6 km,and the focal depth is generally shallow.The Ms 6.0 Luxian earthquake occurred at the transition zone of high-and low-velocity anomalies and the aftershock sequence was distributed along the edge of the low-V_P zone.A small number of foreshocks occurred on the west side of the M_S 6.0 Luxian earthquake,while most of the aftershocks were distributed on the east side of the M_S 6.0 Luxian earthquake.The aftershock sequence consisted of three seismic bands with different trends,and the overall distribution was in a NWW direction,which was inconsistent with the spatial distribution of the main active faults nearby.In addition,the spatiotemporal distribution of earthquakes and the variation of b-values are closely related to the industrial water injection activities in the study area,reflecting the activation of pre-existing hidden faults under certain tectonic and stress environments leading to seismic activities in the area.
基金the Spark Program of Earthquake Sciences(XH20072)the National Natural Science Foundation of China(U2039202).
文摘In this article,we review the general characteristics of seismicity in and around China and the overall statistics of earthquake damage in 2021,focusing on several significant events and related scientific topics.Among them,the largest event is the M_(S)7.4 Madoi earthquake in Qinghai Province,northwest China.The event marks another M_(S)≥7 earthquake occurring near the boundary of the Bayan Har Block that has ended a remarkable quiescence of the M_(S)≥7 earthquakes within the Chinese mainland.In addition,the M_(S)6.4 Yangbi earthquake in Yunnan Province,southwest China draws the most attention because of its abundant foreshocks,which are well recorded by the densely distributed seismic stations in the surrounding regions.Regarding this event,we review several recent publications focusing on the Gutenberg-Richter b-value change and the physical mechanism of foreshocks associated with this sequence.The M_(S)6.0 Luxian earthquake in Sichuan Province,southwest China has caused serious damage with a relatively low magnitude,partly because the focal depth of the mainshock is relatively shallow (3.5 km).It is another strong earthquake occurring within the southeast Sichuan basin with low historical seismicity yet has increased significantly since 2015,probably due to shale gas development and associated hydraulic fracturing.