To reveal the geometry of the seismogenic structure of the Aug. 8, 2017 M_S 7.0 Jiuzhaigou earthquake in northern Sichuan,data from the regional seismic network from the time of the main event to Oct. 31, 2017 were us...To reveal the geometry of the seismogenic structure of the Aug. 8, 2017 M_S 7.0 Jiuzhaigou earthquake in northern Sichuan,data from the regional seismic network from the time of the main event to Oct. 31, 2017 were used to relocate the earthquake sequence by the tomoDD program, and the focal mechanism solutions and centroid depths of the M_L ≥ 3.5 events in the sequence were determined using the CAP waveform inversion method. Further, the segmental tectonic deformation characteristics of the seismogenic faults were analyzed preliminarily by using strain rosettes and areal strains(As). The results indicate:(1) The relocated M_S 7.0 Jiuzhaigou earthquake sequence displays a narrow ～ 38 km long NNW-SSE-trending zone between the NW-striking Tazang Fault and the nearly NSstriking Minjiang Fault, two branches of the East Kunlun Fault Zone. The spatial distribution of the sequence is narrow and deep for the southern segment, and relatively wide and shallow for the northern segment. The initial rupture depth of the mainshock is 12.5 km, the dominant depth range of the aftershock sequence is between 0 and 10 km with an average depth of 6.7 km. The mainshock epicenter is located in the middle of the aftershock region, showing a bilateral rupture behavior. The centroid depths of 32 M_L ≥ 3.5 events range from 3 to 12 km with a mean of about 7.3 km, consistent with the predominant focal depth of the whole sequence.(2) The geometric structure of the seismogenic fault on the southern section of the aftershock area(south of the mainshock) is relatively simple, with overall strike of ～150° and dip angle ～75°, but the dip angle and dip-orientation exhibit some variation along the segment. The seismogenic structure on the northern segment is more complicated; several faults, including the Minjiang Fault, may be responsible for the aftershock activities. The overall strike of this section is ～159° and dip angle is ～59°, illustrating a certain clockwise rotation and a smaller dip angle than the southern segment. The differences between the two segments demonstrate variation of the geometric structure along the seismogenic faults.(3) The focal mechanism solutions of 32 M_L ≥ 3.5 events in the earthquake sequence have obvious segmental characteristics. Strike-slip earthquakes are dominant on the southern segment, while 50% of events on the northern segment are thrusting and oblique thrusting earthquakes, revealing significant differences in the kinematic features of the seismogenic faults between the two segments.(4) The strain rosettes for the mainshock and the entire sequence of 31 M_L ≥ 3.5 aftershocks correspond to strike-slip type with NWW-SEE compressional white lobes and NNE-SSW extensional black lobes of nearly similar size. The strain rosette and As value of the entire sequence of 22 M_L ≥ 3.5 events on the southern segment are the same as those of the M_S 7.0 mainshock,indicating that the tectonic deformation here is strike-slip. However, the strain rosette of the entire sequence of 10 M_L ≥ 3.5 events on the northern segment show prominent white compressional lobes and small black extensional lobes, and the related As value is up to 0.52,indicating that the tectonic deformation of this segment is oblique thrusting with a certain strike-slip component. Differences between the two segments all reveal distinctly obvious segmental characteristics of the tectonic deformation of the seismogenic faults for the Jiuzhaigou earthquake sequence.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 structural factor controlling the spatial distribution of the mainshock and its sequence.The 3D P-wave velocity structure also suggests that the crustal low-velocity layer of northeastern SGB(Songpan-GarzêBlock)stretches into MSM(Minshan Mountain),and migrates to the northeast,but the tendency to emerge as a shallow layer is impeded by the high-velocity zone of Nanping Nappe tectonics and the Bikou Block.Our results reveal an uneven distribution of high-and low-velocity structures around the Tazang segment of the East Kunlun fault zone.Given that the rupture caused by the Jiuzhaigou earthquake has enhanced the stress fields at both ends of the seismogenic fault,it is very important to stay vigilant to possible seismic hazards in the large seismic gap at the Maqu-Maqên segment of the East Kunlun fault zone.展开更多
On Aug.8, 2017, an M_S 7.0 earthquake struck Jiuzhaigou, a county of Sichuan province, China. A number of investigations and studies have been conducted, some of which involved local velocity models. However, the suit...On Aug.8, 2017, an M_S 7.0 earthquake struck Jiuzhaigou, a county of Sichuan province, China. A number of investigations and studies have been conducted, some of which involved local velocity models. However, the suitability of these models has not been properly addressed. Here we collect 11 already-existing models, including those used in studies of the 2017 M_S 7.0 Jiuzhaigou earthquake,choose 10 local stations surrounding the earthquake, and employ the same technique(TRIT) to relocate the hypocenter. And furthermore, we choose a more suitable model from the 11 already-existed models by analyzing the relocation process and the relocated results for reasonability. Finally, our conclusion is that the model Fang 2018 is more suitable and the hypocenter parameters, 103.801°E,33.192°N and 15.8 km for longitude, latitude and depth, respectively, and 2017-08-08 13:19:46.66 for its origin time, based on this model should be recommended for the 2017 M_S7.0 Jiuzhaigou earthquake.展开更多
Jiuzhaigou is a world-heritage site located in the plateau area of Northwest Sichuan Province,China.Serious slope failures in the epicentral area were triggered by the Ms7.0 Jiuzhaigou earthquake occurred on August 8,...Jiuzhaigou is a world-heritage site located in the plateau area of Northwest Sichuan Province,China.Serious slope failures in the epicentral area were triggered by the Ms7.0 Jiuzhaigou earthquake occurred on August 8,2017.The source areas of the hazards are usually concentrated near ridge crests,revealingthe possible occurrence of ground motion amplification phenomena.To explore the role of the amplification of ground motions in the formation of earthquake-triggered slope failures,two seismometers were installed,on the next day after the main shock,at the bottom of the slopeof Jubao Mountain near the seismogenic fault.The two monitoring sites are located at elevations of 1414 m(J1)and 1551 m(J2,the top of the mountain).Five aftershocks were recorded by the monitoring instruments.We compared the mean levels of the peak ground acceleration(PGA)observed at different locations,and investigated the directional variations inthe shaking energy by analyzing the polar diagrams of the Arias intensity(Ia).Then,in order to identify the directional resonance phenomenonandtheir frequencies and amplification coefficients,we examined the horizontal-to-vertical spectral ratio(HVSR)and the standard spectral ratio(SSR).Polar diagrams of theArias intensity(Ia)indicated that the site response of Jubao Mountain showed a pronounced directivity(in theEW direction)with shaking maxima near the hill top oriented orthogonally to the elongation of the relief.We observed anobvious resonance phenomenonat site J2 at relatively low frequencies(2.5-9 Hz)and very weak spectral amplifications at site J1 at high frequencies(5-15 Hz),which suggested that the predominant frequency of monitoring site J2 was obviously attenuated and that the difference in the spectra was related to the influences of the local-scale site conditions of the whole mountain.The results of spectral ratio analyses(HVSR and SSR)showed that the direction of resonance was concentrated around an EW orientation,and the amplification factors near the hill top were larger than 2.It suggests that geologic factors also play a significant role in the anisotropic amplifications affecting the tops of slopes besides the topographic effects.展开更多
This paper introduces the response process of the Gansu Earthquake Agency during the Jiuzhaigou M_S7.0 earthquake in Sichuan Province,including earthquake emergency disposal procedures,information reports,disaster inv...This paper introduces the response process of the Gansu Earthquake Agency during the Jiuzhaigou M_S7.0 earthquake in Sichuan Province,including earthquake emergency disposal procedures,information reports,disaster investigation and intensity assessment,seismic monitoring and trend determination,and emergency dissemination. This paper reveals the characteristics of earthquake damage in the quake-hit areas of Gansu Province,draws some corresponding conclusions and summarizes the countermeasures for recovery and reconstruction in the quake-hit areas of Gansu Province.展开更多
This paper expounds the features of the buildings and analyzes the seismic disaster characteristics of the Jiuzhaigou M_S7. 0 earthquake in the area between Songpan and Jiuzhaigou. New buildings (especially the frame ...This paper expounds the features of the buildings and analyzes the seismic disaster characteristics of the Jiuzhaigou M_S7. 0 earthquake in the area between Songpan and Jiuzhaigou. New buildings (especially the frame structure) had good anti-seismic performance,but brick-wood structures and brick-concrete structures sustained large amounts of damage in the earthquake. By computing the seismic damage index,we found that the seismic damage index of the frame structure was far less than that of civil structures and brick-wood structures. The seismic damage index of frame structures were all zero in the Ⅵ area,and increased rapidly with the increase of intensity,but the increasing range was reduced. We also discussed how to evaluate the intensity in areas where there was a lack of buildings or there was only one structure type,which can be referenced in future field work.展开更多
After the occurrence of an earthquake,strong motion observation networks can record ground motion at distributed observation stations. Based on the ground motion parameters from these records,the spatial distribution ...After the occurrence of an earthquake,strong motion observation networks can record ground motion at distributed observation stations. Based on the ground motion parameters from these records,the spatial distribution of seismic intensity can be quickly determined,and the degree of damage in different areas can be estimated. This information provides the technical basis for the emergency response,so as to ensure that rescue teams can reach extreme earthquake areas and carry out the search and rescue operation in an accurate and timely manner to reduce casualties and property loss. In this paper,we introduced 7 intensity algorithms and compared the results with the records of the Jiuzhaigou M_S7. 0 earthquake. We found that the differences between the instrumental intensities calculated by each method and the macro intensities were within a 1-degree range,which suggested good practicality of these different methods. The results calculated by the industrial standards-based calculation method and the integrated test showed good consistency.展开更多
The M_S7. 0 Jiuzhaigou earthquake occurred on August 8,2017. The earthquake occurred in the vicinity of the Tazang fault,the Minjiang fault and the Huya fault,where the focal mechanism is of the strike slip type. The ...The M_S7. 0 Jiuzhaigou earthquake occurred on August 8,2017. The earthquake occurred in the vicinity of the Tazang fault,the Minjiang fault and the Huya fault,where the focal mechanism is of the strike slip type. The static and dynamic anomalies of the gravity field can provide important physical field information for studying the structural properties of deep crust. Multi-scale decomposition techniques are used to separate Bouguer gravity at different depths and give some explanation to gravity variations at different time space scales. The results indicate that the wavelet multi-scale results of the EGM2008 model and the measured gravity data are consistent. Through comparative analysis,it is found that the Jiuzhaigou earthquake occurred in the stress enhanced region. The variation of gravity field at different time scales has a certain scientific significance for further understanding potential earthquake risk trend.展开更多
基金supported by National Science Foundation of China(41574047)National Key R&D Program of China(2018YFC150330501)
文摘To reveal the geometry of the seismogenic structure of the Aug. 8, 2017 M_S 7.0 Jiuzhaigou earthquake in northern Sichuan,data from the regional seismic network from the time of the main event to Oct. 31, 2017 were used to relocate the earthquake sequence by the tomoDD program, and the focal mechanism solutions and centroid depths of the M_L ≥ 3.5 events in the sequence were determined using the CAP waveform inversion method. Further, the segmental tectonic deformation characteristics of the seismogenic faults were analyzed preliminarily by using strain rosettes and areal strains(As). The results indicate:(1) The relocated M_S 7.0 Jiuzhaigou earthquake sequence displays a narrow ～ 38 km long NNW-SSE-trending zone between the NW-striking Tazang Fault and the nearly NSstriking Minjiang Fault, two branches of the East Kunlun Fault Zone. The spatial distribution of the sequence is narrow and deep for the southern segment, and relatively wide and shallow for the northern segment. The initial rupture depth of the mainshock is 12.5 km, the dominant depth range of the aftershock sequence is between 0 and 10 km with an average depth of 6.7 km. The mainshock epicenter is located in the middle of the aftershock region, showing a bilateral rupture behavior. The centroid depths of 32 M_L ≥ 3.5 events range from 3 to 12 km with a mean of about 7.3 km, consistent with the predominant focal depth of the whole sequence.(2) The geometric structure of the seismogenic fault on the southern section of the aftershock area(south of the mainshock) is relatively simple, with overall strike of ～150° and dip angle ～75°, but the dip angle and dip-orientation exhibit some variation along the segment. The seismogenic structure on the northern segment is more complicated; several faults, including the Minjiang Fault, may be responsible for the aftershock activities. The overall strike of this section is ～159° and dip angle is ～59°, illustrating a certain clockwise rotation and a smaller dip angle than the southern segment. The differences between the two segments demonstrate variation of the geometric structure along the seismogenic faults.(3) The focal mechanism solutions of 32 M_L ≥ 3.5 events in the earthquake sequence have obvious segmental characteristics. Strike-slip earthquakes are dominant on the southern segment, while 50% of events on the northern segment are thrusting and oblique thrusting earthquakes, revealing significant differences in the kinematic features of the seismogenic faults between the two segments.(4) The strain rosettes for the mainshock and the entire sequence of 31 M_L ≥ 3.5 aftershocks correspond to strike-slip type with NWW-SEE compressional white lobes and NNE-SSW extensional black lobes of nearly similar size. The strain rosette and As value of the entire sequence of 22 M_L ≥ 3.5 events on the southern segment are the same as those of the M_S 7.0 mainshock,indicating that the tectonic deformation here is strike-slip. However, the strain rosette of the entire sequence of 10 M_L ≥ 3.5 events on the northern segment show prominent white compressional lobes and small black extensional lobes, and the related As value is up to 0.52,indicating that the tectonic deformation of this segment is oblique thrusting with a certain strike-slip component. Differences between the two segments all reveal distinctly obvious segmental characteristics of the tectonic deformation of the seismogenic faults for the Jiuzhaigou earthquake sequence.
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 structural factor controlling the spatial distribution of the mainshock and its sequence.The 3D P-wave velocity structure also suggests that the crustal low-velocity layer of northeastern SGB(Songpan-GarzêBlock)stretches into MSM(Minshan Mountain),and migrates to the northeast,but the tendency to emerge as a shallow layer is impeded by the high-velocity zone of Nanping Nappe tectonics and the Bikou Block.Our results reveal an uneven distribution of high-and low-velocity structures around the Tazang segment of the East Kunlun fault zone.Given that the rupture caused by the Jiuzhaigou earthquake has enhanced the stress fields at both ends of the seismogenic fault,it is very important to stay vigilant to possible seismic hazards in the large seismic gap at the Maqu-Maqên segment of the East Kunlun fault zone.
基金supported by the DQJB project (DQJB16B05) of the Institute of Geophysics,CEAthe NSFC project (41474046)
文摘On Aug.8, 2017, an M_S 7.0 earthquake struck Jiuzhaigou, a county of Sichuan province, China. A number of investigations and studies have been conducted, some of which involved local velocity models. However, the suitability of these models has not been properly addressed. Here we collect 11 already-existing models, including those used in studies of the 2017 M_S 7.0 Jiuzhaigou earthquake,choose 10 local stations surrounding the earthquake, and employ the same technique(TRIT) to relocate the hypocenter. And furthermore, we choose a more suitable model from the 11 already-existed models by analyzing the relocation process and the relocated results for reasonability. Finally, our conclusion is that the model Fang 2018 is more suitable and the hypocenter parameters, 103.801°E,33.192°N and 15.8 km for longitude, latitude and depth, respectively, and 2017-08-08 13:19:46.66 for its origin time, based on this model should be recommended for the 2017 M_S7.0 Jiuzhaigou earthquake.
基金financially supported by the National Natural Science Foundation of China(Grand Nos.41877235,1704243)the Funds for Creative Research Groups of China(Grant No.41521002)the Independent Fund of State Key Laboratory of Geohazard Prevention and Geoenvironment Protection(Grant No.SKLGP2015Z001)
文摘Jiuzhaigou is a world-heritage site located in the plateau area of Northwest Sichuan Province,China.Serious slope failures in the epicentral area were triggered by the Ms7.0 Jiuzhaigou earthquake occurred on August 8,2017.The source areas of the hazards are usually concentrated near ridge crests,revealingthe possible occurrence of ground motion amplification phenomena.To explore the role of the amplification of ground motions in the formation of earthquake-triggered slope failures,two seismometers were installed,on the next day after the main shock,at the bottom of the slopeof Jubao Mountain near the seismogenic fault.The two monitoring sites are located at elevations of 1414 m(J1)and 1551 m(J2,the top of the mountain).Five aftershocks were recorded by the monitoring instruments.We compared the mean levels of the peak ground acceleration(PGA)observed at different locations,and investigated the directional variations inthe shaking energy by analyzing the polar diagrams of the Arias intensity(Ia).Then,in order to identify the directional resonance phenomenonandtheir frequencies and amplification coefficients,we examined the horizontal-to-vertical spectral ratio(HVSR)and the standard spectral ratio(SSR).Polar diagrams of theArias intensity(Ia)indicated that the site response of Jubao Mountain showed a pronounced directivity(in theEW direction)with shaking maxima near the hill top oriented orthogonally to the elongation of the relief.We observed anobvious resonance phenomenonat site J2 at relatively low frequencies(2.5-9 Hz)and very weak spectral amplifications at site J1 at high frequencies(5-15 Hz),which suggested that the predominant frequency of monitoring site J2 was obviously attenuated and that the difference in the spectra was related to the influences of the local-scale site conditions of the whole mountain.The results of spectral ratio analyses(HVSR and SSR)showed that the direction of resonance was concentrated around an EW orientation,and the amplification factors near the hill top were larger than 2.It suggests that geologic factors also play a significant role in the anisotropic amplifications affecting the tops of slopes besides the topographic effects.
基金sponsored by the National Natural Science Foundation of China(51678545)
文摘This paper introduces the response process of the Gansu Earthquake Agency during the Jiuzhaigou M_S7.0 earthquake in Sichuan Province,including earthquake emergency disposal procedures,information reports,disaster investigation and intensity assessment,seismic monitoring and trend determination,and emergency dissemination. This paper reveals the characteristics of earthquake damage in the quake-hit areas of Gansu Province,draws some corresponding conclusions and summarizes the countermeasures for recovery and reconstruction in the quake-hit areas of Gansu Province.
基金sponsored by the Key Technology R&D Program of Jiangsu Province(BE2014731)the Earthquake Science and Technology Spark Plan,CEA(XH16014)
文摘This paper expounds the features of the buildings and analyzes the seismic disaster characteristics of the Jiuzhaigou M_S7. 0 earthquake in the area between Songpan and Jiuzhaigou. New buildings (especially the frame structure) had good anti-seismic performance,but brick-wood structures and brick-concrete structures sustained large amounts of damage in the earthquake. By computing the seismic damage index,we found that the seismic damage index of the frame structure was far less than that of civil structures and brick-wood structures. The seismic damage index of frame structures were all zero in the Ⅵ area,and increased rapidly with the increase of intensity,but the increasing range was reduced. We also discussed how to evaluate the intensity in areas where there was a lack of buildings or there was only one structure type,which can be referenced in future field work.
基金sponsored by the State Key Research and Development Program of China(2016YFC1402800)the Basic R&D Fund for Central Level Public Service Research Institute,China(DQJB17T01)the National Natural Foundation of China(U1434210,51421005)
文摘After the occurrence of an earthquake,strong motion observation networks can record ground motion at distributed observation stations. Based on the ground motion parameters from these records,the spatial distribution of seismic intensity can be quickly determined,and the degree of damage in different areas can be estimated. This information provides the technical basis for the emergency response,so as to ensure that rescue teams can reach extreme earthquake areas and carry out the search and rescue operation in an accurate and timely manner to reduce casualties and property loss. In this paper,we introduced 7 intensity algorithms and compared the results with the records of the Jiuzhaigou M_S7. 0 earthquake. We found that the differences between the instrumental intensities calculated by each method and the macro intensities were within a 1-degree range,which suggested good practicality of these different methods. The results calculated by the industrial standards-based calculation method and the integrated test showed good consistency.
基金funded by the National Key Research and Development Program of China(2018YFC1503305)the National Nature Science Foundation of China(41874092)
文摘The M_S7. 0 Jiuzhaigou earthquake occurred on August 8,2017. The earthquake occurred in the vicinity of the Tazang fault,the Minjiang fault and the Huya fault,where the focal mechanism is of the strike slip type. The static and dynamic anomalies of the gravity field can provide important physical field information for studying the structural properties of deep crust. Multi-scale decomposition techniques are used to separate Bouguer gravity at different depths and give some explanation to gravity variations at different time space scales. The results indicate that the wavelet multi-scale results of the EGM2008 model and the measured gravity data are consistent. Through comparative analysis,it is found that the Jiuzhaigou earthquake occurred in the stress enhanced region. The variation of gravity field at different time scales has a certain scientific significance for further understanding potential earthquake risk trend.
