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
Late at night on 17 June 2019,a magnitude 6.0 earthquake struck Shuanghe Town and its surrounding area in Changning County,Sichuan,China,becoming the largest earthquake recorded within the southern Sichuan Basin.A ser...Late at night on 17 June 2019,a magnitude 6.0 earthquake struck Shuanghe Town and its surrounding area in Changning County,Sichuan,China,becoming the largest earthquake recorded within the southern Sichuan Basin.A series of earthquakes with magnitudes up to 5.6 occurred during a short period after the mainshock,and we thus refer to these earthquakes as the Changning M6 earthquake sequence(or swarm).The mainshock was located very close to a salt mine,into which for^3 decades fresh water had been extensively injected through several wells at a depth of 2.7–3 km.It was also near(within^15 km)the epicenter of the 18 December 2018 M5.7 Xingwen earthquake,which is thought to have been induced by shale gas hydraulic fracturing(HF),prompting questions about the possible involvement of industrial activities in the M6 sequence.Following previous studies,this paper focuses on the relationship between injection and seismicity in the Shuanghe salt field and its adjacent Shangluo shale gas block.Except for a period of serious water loss after the start of cross-well injection in 2005–2006,the frequency of earthquakes shows a slightly increasing tendency.Overall,there is a good correlation between the event rate in the Shuanghe area and the loss of injected water.More than 400 M≥3 earthquakes,including 40 M≥4 and 5 M≥5 events,had been observed by the end of August 2019.Meanwhile,in the Shangluo area,seismicity has increased during drilling and HF operations(mostly in vertical wells)since about 2009,and dramatically since the end of 2014,coincident with the start of systematic HF in the area.The event rate shows a progressively increasing background with some fluctuations,paralleling the increase in HF operations.More than 700 M≥3 earthquakes,including 10 M≥4 and 3 M≥5 in spatially and temporally clustered seismic events,are correlated closely with active fracturing platforms.Well-resolved centroid moment tensor results for M≥4 earthquakes were shown to occur at very shallow depths around shale formations with active HF,in agreement with some of the clusters,which occurred within the coverage area of temporary or new permanent monitoring stations and thus have been precisely located.After the Xingwen M5.7 earthquake,seismic activity in the salt well area increased significantly.The Xingwen earthquake may have created a unidirectional rupture to the NNW,with an end point close to the NW-trending fault of the Shuanghe earthquake.Thus,a fault in the Changning anticline might have terminated the fault rupture of the Xingwen earthquake,possibly giving the Xingwen earthquake a role in promoting the Changning M6 event.展开更多
Hydraulic fracturing is a key technology in shale gas extraction,whether hydraulic fracturing induces earthquakes has become a hot topic in the public and the focus of scholars’research.The urgency of shale gas minin...Hydraulic fracturing is a key technology in shale gas extraction,whether hydraulic fracturing induces earthquakes has become a hot topic in the public and the focus of scholars’research.The urgency of shale gas mining and the catastrophic nature of earthquakes highlight the urgent need to study this issue.The Changning anticline at the southern margin of the Sichuan Basin is a key area for shale gas exploitation.Taking this as an example,this paper applies the velocity model of the study area to reposition the M5.7 magnitude earthquake on December 16,2018 and the M5.3 magnitude earthquake on January 03,2019 and their aftershock sequence in this area.Using shale gas exploration drilling and reflection seismic data to carry out structural analysis,and recovering the tectonic geological setting of earthquake occurrence by restoring the formation process of the Changning anticline,to further explore the seismic mechanism.Our results show that the Changning anticline is a large basement fault-bend fold,and the displacement of the fault forming the anticline is 18 km,and the Changning anticline absorbs 33%of the fault slip.The Silurian Longmaxi Formation of the Changning anticline experienced larger-parallel shearing along underlying basement faults,forming a micro-fracture system.The footwall ramp of the basement fault is reactivated at present,earthquakes in this area mostly occur along the footwall ramp of the basement fault and above and below it.The anticlinal and synclinal hinge zones are also the earthquake concentration areas,but the earthquake magnitude decreases upwards along the kink-band,and small earthquakes below M2.0 occur in the Silurian Longmaxi Formation.So far,the earthquake in the Changning anticline mainly occurred in the southern limb of the anticline,which is a natural earthquake formed along the footwall ramp of the basement fault.The earthquakes in the Changning area are possible related to the geo-tectonic setting for the southeast outward compression of the Qinghai-Tibet Plateau at present,the moderate or large-scale earthquakes in the southwest Sichuan Basin are mainly due to the reactivation during late Quaternary of the earlier formed faults.It is suggested to carry out scientific monitoring of seismic activities in shale gas development zones.展开更多
An M=6.0 earthquake occurred on February 23, 2001 in the western Sichuan Province, China. The macro seismic epicenter situated in the high mountain-narrow valley region between Yajiang and Kangding counties. According...An M=6.0 earthquake occurred on February 23, 2001 in the western Sichuan Province, China. The macro seismic epicenter situated in the high mountain-narrow valley region between Yajiang and Kangding counties. According to field investigation in the region, the intensity of epicentral area reached VIII and the areas with intensity VIII, VII and VI are 180 km2, 1 472 km2 and 3 998 km2, respectively. The isoseismals are generally in elliptic shape with major axis trending near N-S direction. The earthquake destroyed many buildings and produced some phenomena of ground failure and mountainous disasters in the area with intensity VIII. This event may be resulted from long-term activities of the Litang fault and Yunongxi fault, two main faults in the western Sichuan. The movements between the main faults made the crust stress adjusted and concentrated, and finally the earthquake on a secondary fault in the block released a quite large energy.展开更多
According to information from on-the-spot investigations, the tectonics of salt mining areas and digital seismic records, we studied the activity of earthquakes induced by water pumping in and out of the salt mines in...According to information from on-the-spot investigations, the tectonics of salt mining areas and digital seismic records, we studied the activity of earthquakes induced by water pumping in and out of the salt mines in Shuanghe town, Changning county, Sichuan Province. The study found that the rates of water injection and extraction in the Shuanghe salt mining region were evenly matched before April 2006 and earthquake activity was stable. On the other hand, shallow small and moderate earthquake numbers increased sharply after the water injection rate became much larger than the water extraction rate. Large injection over a long time may causes the permeation of water through pre-existing small fractures and micro-cracks in the Changning anticlinal and accelerate the rupture of micro tectonic formations in nearby regions, inducing small earthquake swarm activity. The Q value calculated by using digital earthquake records indicates a relatively inhomogeneous medium in this area. The results of the accurate location of small earthquakes show that sources are relatively shallow and are concentrated at a depth of 2km to 3km. Focal mechanism solutions reveal a normal dip-slip character of shallow earthquakes. All of these show certain characteristics of earthquake activity induced by water injection.展开更多
1研究背景。Hayakawa在1996年提出的地磁垂直强度极化方法在我国广泛应用。该方法通过数值模拟获知一次源来自高空电离层的极化值小于1,源自于震源的极化值大于或约等于1(Hayakawa et al,1996),Hayakawa利用该方法对1993年的关岛8级地...1研究背景。Hayakawa在1996年提出的地磁垂直强度极化方法在我国广泛应用。该方法通过数值模拟获知一次源来自高空电离层的极化值小于1,源自于震源的极化值大于或约等于1(Hayakawa et al,1996),Hayakawa利用该方法对1993年的关岛8级地震进行研究,发现震前垂直强度极化Yz h值逐渐增大直到发震时达最大值,震后恢复。近年我国学者研究发现地震往往发生在台站出现极化值高值异常后的1个月时间内(冯志生等,2010),发震地点在异常空间等值线的阈值线附近(冯丽丽等,2021),这种极化值异常与外空场活动无关(何畅等,2017)。展开更多
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 State Scholarship Fund of China (No. 201804190004)
文摘Late at night on 17 June 2019,a magnitude 6.0 earthquake struck Shuanghe Town and its surrounding area in Changning County,Sichuan,China,becoming the largest earthquake recorded within the southern Sichuan Basin.A series of earthquakes with magnitudes up to 5.6 occurred during a short period after the mainshock,and we thus refer to these earthquakes as the Changning M6 earthquake sequence(or swarm).The mainshock was located very close to a salt mine,into which for^3 decades fresh water had been extensively injected through several wells at a depth of 2.7–3 km.It was also near(within^15 km)the epicenter of the 18 December 2018 M5.7 Xingwen earthquake,which is thought to have been induced by shale gas hydraulic fracturing(HF),prompting questions about the possible involvement of industrial activities in the M6 sequence.Following previous studies,this paper focuses on the relationship between injection and seismicity in the Shuanghe salt field and its adjacent Shangluo shale gas block.Except for a period of serious water loss after the start of cross-well injection in 2005–2006,the frequency of earthquakes shows a slightly increasing tendency.Overall,there is a good correlation between the event rate in the Shuanghe area and the loss of injected water.More than 400 M≥3 earthquakes,including 40 M≥4 and 5 M≥5 events,had been observed by the end of August 2019.Meanwhile,in the Shangluo area,seismicity has increased during drilling and HF operations(mostly in vertical wells)since about 2009,and dramatically since the end of 2014,coincident with the start of systematic HF in the area.The event rate shows a progressively increasing background with some fluctuations,paralleling the increase in HF operations.More than 700 M≥3 earthquakes,including 10 M≥4 and 3 M≥5 in spatially and temporally clustered seismic events,are correlated closely with active fracturing platforms.Well-resolved centroid moment tensor results for M≥4 earthquakes were shown to occur at very shallow depths around shale formations with active HF,in agreement with some of the clusters,which occurred within the coverage area of temporary or new permanent monitoring stations and thus have been precisely located.After the Xingwen M5.7 earthquake,seismic activity in the salt well area increased significantly.The Xingwen earthquake may have created a unidirectional rupture to the NNW,with an end point close to the NW-trending fault of the Shuanghe earthquake.Thus,a fault in the Changning anticline might have terminated the fault rupture of the Xingwen earthquake,possibly giving the Xingwen earthquake a role in promoting the Changning M6 event.
基金Supported by the National Natural Science Foundation of China(41430316,40739906,41272237).
文摘Hydraulic fracturing is a key technology in shale gas extraction,whether hydraulic fracturing induces earthquakes has become a hot topic in the public and the focus of scholars’research.The urgency of shale gas mining and the catastrophic nature of earthquakes highlight the urgent need to study this issue.The Changning anticline at the southern margin of the Sichuan Basin is a key area for shale gas exploitation.Taking this as an example,this paper applies the velocity model of the study area to reposition the M5.7 magnitude earthquake on December 16,2018 and the M5.3 magnitude earthquake on January 03,2019 and their aftershock sequence in this area.Using shale gas exploration drilling and reflection seismic data to carry out structural analysis,and recovering the tectonic geological setting of earthquake occurrence by restoring the formation process of the Changning anticline,to further explore the seismic mechanism.Our results show that the Changning anticline is a large basement fault-bend fold,and the displacement of the fault forming the anticline is 18 km,and the Changning anticline absorbs 33%of the fault slip.The Silurian Longmaxi Formation of the Changning anticline experienced larger-parallel shearing along underlying basement faults,forming a micro-fracture system.The footwall ramp of the basement fault is reactivated at present,earthquakes in this area mostly occur along the footwall ramp of the basement fault and above and below it.The anticlinal and synclinal hinge zones are also the earthquake concentration areas,but the earthquake magnitude decreases upwards along the kink-band,and small earthquakes below M2.0 occur in the Silurian Longmaxi Formation.So far,the earthquake in the Changning anticline mainly occurred in the southern limb of the anticline,which is a natural earthquake formed along the footwall ramp of the basement fault.The earthquakes in the Changning area are possible related to the geo-tectonic setting for the southeast outward compression of the Qinghai-Tibet Plateau at present,the moderate or large-scale earthquakes in the southwest Sichuan Basin are mainly due to the reactivation during late Quaternary of the earlier formed faults.It is suggested to carry out scientific monitoring of seismic activities in shale gas development zones.
文摘An M=6.0 earthquake occurred on February 23, 2001 in the western Sichuan Province, China. The macro seismic epicenter situated in the high mountain-narrow valley region between Yajiang and Kangding counties. According to field investigation in the region, the intensity of epicentral area reached VIII and the areas with intensity VIII, VII and VI are 180 km2, 1 472 km2 and 3 998 km2, respectively. The isoseismals are generally in elliptic shape with major axis trending near N-S direction. The earthquake destroyed many buildings and produced some phenomena of ground failure and mountainous disasters in the area with intensity VIII. This event may be resulted from long-term activities of the Litang fault and Yunongxi fault, two main faults in the western Sichuan. The movements between the main faults made the crust stress adjusted and concentrated, and finally the earthquake on a secondary fault in the block released a quite large energy.
基金Key Project in the National Science and Technology Pillar Program in the Eleventh"Five-year Plan" Period (2006BA01B02-01-01)Project in the National Science and Technology Pillar Program(2006BAC01B04),China
文摘According to information from on-the-spot investigations, the tectonics of salt mining areas and digital seismic records, we studied the activity of earthquakes induced by water pumping in and out of the salt mines in Shuanghe town, Changning county, Sichuan Province. The study found that the rates of water injection and extraction in the Shuanghe salt mining region were evenly matched before April 2006 and earthquake activity was stable. On the other hand, shallow small and moderate earthquake numbers increased sharply after the water injection rate became much larger than the water extraction rate. Large injection over a long time may causes the permeation of water through pre-existing small fractures and micro-cracks in the Changning anticlinal and accelerate the rupture of micro tectonic formations in nearby regions, inducing small earthquake swarm activity. The Q value calculated by using digital earthquake records indicates a relatively inhomogeneous medium in this area. The results of the accurate location of small earthquakes show that sources are relatively shallow and are concentrated at a depth of 2km to 3km. Focal mechanism solutions reveal a normal dip-slip character of shallow earthquakes. All of these show certain characteristics of earthquake activity induced by water injection.
文摘1研究背景。Hayakawa在1996年提出的地磁垂直强度极化方法在我国广泛应用。该方法通过数值模拟获知一次源来自高空电离层的极化值小于1,源自于震源的极化值大于或约等于1(Hayakawa et al,1996),Hayakawa利用该方法对1993年的关岛8级地震进行研究,发现震前垂直强度极化Yz h值逐渐增大直到发震时达最大值,震后恢复。近年我国学者研究发现地震往往发生在台站出现极化值高值异常后的1个月时间内(冯志生等,2010),发震地点在异常空间等值线的阈值线附近(冯丽丽等,2021),这种极化值异常与外空场活动无关(何畅等,2017)。
