Immediately following the MS7.0 Lushan earthquake on April 20,2013,using high-pass and lowpass filtering on the digital seismic stations in the Shanxi Province,located about 870–1,452 km from the earthquake epicenter...Immediately following the MS7.0 Lushan earthquake on April 20,2013,using high-pass and lowpass filtering on the digital seismic stations in the Shanxi Province,located about 870–1,452 km from the earthquake epicenter,we detected some earthquakes at a time corresponding to the first arrival of surface waves in high-pass filtering waveform.The earthquakes were especially noticed at stations in Youyu(YUY),Shanzizao(SZZ),Shanghuangzhuang(SHZ),and Zhenchuan(ZCH),which are located in a volcanic region in the Shanxi Province,but they were not listed in the Shanxi seismic observation report.These earthquakes occurred 4–50 min after the passage of the maximum amplitude Rayleigh wave,and the periods of the surface waves were mainly between 15 and20 s following.The Coulomb stresses caused by the Rayleigh waves that acted on the four stations was about0.001 MPa,which is a little lower than the threshold value of dynamic triggering,therefore,we may conclude that the Datong volcanic region is more sensitive to the Coulomb stress change.To verify,if the similar phenomena are widespread,we used the same filtering to observecontrastively continuous waveform data before,and 5 h after,the MS7.0 Lushan earthquake and MS9.0 Tohoku earthquake in 2011.The results show that the similar phenomena occur before the earthquakes,but the seismicity rates after the earthquakes are remarkably increased.Since these weak earthquakes are quite small,it is hard to get clear phase arrival time from three or more stations to locate them.In addition,the travel time differences between P waves and S waves(S–P)are all less than 4 s,that means the events should occur in 34 km around the stations in the volcanic region.The stress of initial dynamic triggering of the MS9.0 Tohoku earthquake was about0.09 MPa,which is much higher than the threshold value of dynamic triggering stress.The earthquakes after the MS9.0 Tohoku earthquake are related to dynamic triggering stress,but the events before the earthquake cannot be linked to seismic events,but may be related to the background seismicity or from other kinds of local sources,such as anthropogenic sources(i.e.,explosions).Using two teleseismic filtering,the small background earthquakes in the Datong volcanic region occur frequently,thus we postulate that previous catalog does not apply bandpass filter to pick out the weak earthquakes,and some of the observed weak events were not triggered by changes in the dynamic stress field.展开更多
At GMT time 13:19, August 8, 2017, an Ms7.0 earthquake struck the Jiuzhaigou region in Sichuan Province, China,causing severe damages and casualties. To investigate the source properties, seismogenic structures, and s...At GMT time 13:19, August 8, 2017, an Ms7.0 earthquake struck the Jiuzhaigou region in Sichuan Province, China,causing severe damages and casualties. To investigate the source properties, seismogenic structures, and seismic hazards, we systematically analyzed the tectonic environment, crustal velocity structure in the source region, source parameters and rupture process, Coulomb failure stress changes, and 3-D features of the rupture plane of the Jiuzhaigou earthquake. Our results indicate the following:(1) The Jiuzhaigou earthquake occurred on an unmarked fault belonging to the transition zone of the east Kunlun fault system and is located northwest of the Huya fault.(2) Both the mainshock and aftershock rupture zones are located in a region where crustal seismic velocity changes dramatically. Southeast to the source region, shear wave velocity at the middle to lower crust is significantly low, but it rapidly increases northeastward and lies close to the background velocity across the rupture fault.(3) The aftershock zone is narrow and distributes along the northwest-southeast trend, and most aftershocks occur within a depth range of 5–20 km.(4) The focal mechanism of the Jiuzhaigou earthquake indicates a left-lateral strike-slip fault, with strike, dip, and rake angles of 152°, 74° and 8°, respectively. The hypocenter depth measures 20 km, whereas the centroid depth is about 6 km. The co-seismic rupture mainly concentrates at depths of 3–13 km, with a moment magnitude(M_w) of 6.5.(5) The co-seismic rupture also strengthens the Coulomb failure stress at the two ends of the rupture fault and the east segment of the Tazang fault. Aftershocks relocation results together with geological surveys indicate that the causative fault is a near vertical fault with notable spatial variations: dip angle varies within 66°–89° from northwest to southeast and the average dip angle measures ~84°. The results of this work are of fundamental importance for further studies on the source characteristics, tectonic environment, and seismic hazard evaluation of the Jiuzhaigou earthquake.展开更多
基金supported by Office of Science and Technology in Shanxi province based on research Projects(2012011029)National Natural Science Foundation(41174086)+1 种基金Scientific and Technological Research Project in Shanxi province(20100311129-2,20090311084)the China Earthquake Administration Spark Project(XH1005,XH13004)
文摘Immediately following the MS7.0 Lushan earthquake on April 20,2013,using high-pass and lowpass filtering on the digital seismic stations in the Shanxi Province,located about 870–1,452 km from the earthquake epicenter,we detected some earthquakes at a time corresponding to the first arrival of surface waves in high-pass filtering waveform.The earthquakes were especially noticed at stations in Youyu(YUY),Shanzizao(SZZ),Shanghuangzhuang(SHZ),and Zhenchuan(ZCH),which are located in a volcanic region in the Shanxi Province,but they were not listed in the Shanxi seismic observation report.These earthquakes occurred 4–50 min after the passage of the maximum amplitude Rayleigh wave,and the periods of the surface waves were mainly between 15 and20 s following.The Coulomb stresses caused by the Rayleigh waves that acted on the four stations was about0.001 MPa,which is a little lower than the threshold value of dynamic triggering,therefore,we may conclude that the Datong volcanic region is more sensitive to the Coulomb stress change.To verify,if the similar phenomena are widespread,we used the same filtering to observecontrastively continuous waveform data before,and 5 h after,the MS7.0 Lushan earthquake and MS9.0 Tohoku earthquake in 2011.The results show that the similar phenomena occur before the earthquakes,but the seismicity rates after the earthquakes are remarkably increased.Since these weak earthquakes are quite small,it is hard to get clear phase arrival time from three or more stations to locate them.In addition,the travel time differences between P waves and S waves(S–P)are all less than 4 s,that means the events should occur in 34 km around the stations in the volcanic region.The stress of initial dynamic triggering of the MS9.0 Tohoku earthquake was about0.09 MPa,which is much higher than the threshold value of dynamic triggering stress.The earthquakes after the MS9.0 Tohoku earthquake are related to dynamic triggering stress,but the events before the earthquake cannot be linked to seismic events,but may be related to the background seismicity or from other kinds of local sources,such as anthropogenic sources(i.e.,explosions).Using two teleseismic filtering,the small background earthquakes in the Datong volcanic region occur frequently,thus we postulate that previous catalog does not apply bandpass filter to pick out the weak earthquakes,and some of the observed weak events were not triggered by changes in the dynamic stress field.
基金funded by the Seismological Bureau Spark Program Project(Grant No.XH15007)the National Natural Science Foundation of China(Grant Nos.41604058,41574057,41621091)the Sichuan-Yunnan National Seismological Monitoring and Prediction Experimental Station Project(Grant No.2016CESE0204)
文摘At GMT time 13:19, August 8, 2017, an Ms7.0 earthquake struck the Jiuzhaigou region in Sichuan Province, China,causing severe damages and casualties. To investigate the source properties, seismogenic structures, and seismic hazards, we systematically analyzed the tectonic environment, crustal velocity structure in the source region, source parameters and rupture process, Coulomb failure stress changes, and 3-D features of the rupture plane of the Jiuzhaigou earthquake. Our results indicate the following:(1) The Jiuzhaigou earthquake occurred on an unmarked fault belonging to the transition zone of the east Kunlun fault system and is located northwest of the Huya fault.(2) Both the mainshock and aftershock rupture zones are located in a region where crustal seismic velocity changes dramatically. Southeast to the source region, shear wave velocity at the middle to lower crust is significantly low, but it rapidly increases northeastward and lies close to the background velocity across the rupture fault.(3) The aftershock zone is narrow and distributes along the northwest-southeast trend, and most aftershocks occur within a depth range of 5–20 km.(4) The focal mechanism of the Jiuzhaigou earthquake indicates a left-lateral strike-slip fault, with strike, dip, and rake angles of 152°, 74° and 8°, respectively. The hypocenter depth measures 20 km, whereas the centroid depth is about 6 km. The co-seismic rupture mainly concentrates at depths of 3–13 km, with a moment magnitude(M_w) of 6.5.(5) The co-seismic rupture also strengthens the Coulomb failure stress at the two ends of the rupture fault and the east segment of the Tazang fault. Aftershocks relocation results together with geological surveys indicate that the causative fault is a near vertical fault with notable spatial variations: dip angle varies within 66°–89° from northwest to southeast and the average dip angle measures ~84°. The results of this work are of fundamental importance for further studies on the source characteristics, tectonic environment, and seismic hazard evaluation of the Jiuzhaigou earthquake.
