Broadband P and S waves source spectra of 12 M_s≥5.0 earthquakes of the 1997 Jiashi, Xinjiang, China. earthquake swarm recorded at 13 GDSN stations have been analyzed. Rupture size and static stress drop of these ear...Broadband P and S waves source spectra of 12 M_s≥5.0 earthquakes of the 1997 Jiashi, Xinjiang, China. earthquake swarm recorded at 13 GDSN stations have been analyzed. Rupture size and static stress drop of these earthquakes have been estimated through measuring the corner frequency of the source spectra. Direction of rupture propaga- tion of the earthquake faulting has also been inferred from the azimuthal variation of the comer frequency. The main results are as follows: ① The rupture size of M_s≥6.0 strong earthquakes is in the range of 10~20 km, while that of Ms_=5.0~5.5 earthquakes is 6~10 km. ② The static stress drop of the swarm earthquakes is rather low, being of the order of 0.1 MPa. This implies that the deformation release rate in the source region may be low. ③ Stress drop of the earthquakes appears to be proportional to their seismic moment, and also to be dependent on their focal mechanism. The stress drop of normal faulting earthquakes is usually lower than that of strike-slip type earth quakes. ④ For each M_s≥6.0 earthquake there exists an apparent azimuthal variation of the comer frequencies. Azimuthally variation pattern of comer frequencies of different earthquakes shows that the source rupture pattern of the Jiashi earthquake swarm is complex and no uniform rupture expanding direction exists.展开更多
We computed source parameters for 143 earthquakes with M_L≥ 1. 0 occurring from January,2011 to March,2014 using waveform data recorded by the Nuozhadu and Jinghong Reservoir Seismic Networks. Then,the variation of s...We computed source parameters for 143 earthquakes with M_L≥ 1. 0 occurring from January,2011 to March,2014 using waveform data recorded by the Nuozhadu and Jinghong Reservoir Seismic Networks. Then,the variation of seismic activity and the characteristics of source parameters before and after the impoundment of the reservoir were investigated. The results show that:( 1) the seismic activity increased obviously after the impoundment,especially during the 3- 4 months after impoundment;( 2) the focal depths of the earthquakes occurring in the reservoir area are shallower than the earthquakes occurring outside the reservoir area in the initial stage of impoundment,but after a time,the difference was gradually reduced;( 3) corner frequency varies with the seismic moment and the log-linear relationship is more obvious after impounding;( 4)stress drop and apparent stress increase with increasing seismic moment,moreover they are lower for the earthquakes occurring in the reservoir area after impounding than those occurring outside the reservoir area or before impounding with the same seismic moment;( 5) the effect of reservoir impoundment on an earthquake can reach a depth of 10 km,and the maximum effect is seen at a depth of 3km- 6km,and the differences of seismic activity and average apparent stress between the inside and outside of the reservoir are significant.展开更多
文摘Broadband P and S waves source spectra of 12 M_s≥5.0 earthquakes of the 1997 Jiashi, Xinjiang, China. earthquake swarm recorded at 13 GDSN stations have been analyzed. Rupture size and static stress drop of these earthquakes have been estimated through measuring the corner frequency of the source spectra. Direction of rupture propaga- tion of the earthquake faulting has also been inferred from the azimuthal variation of the comer frequency. The main results are as follows: ① The rupture size of M_s≥6.0 strong earthquakes is in the range of 10~20 km, while that of Ms_=5.0~5.5 earthquakes is 6~10 km. ② The static stress drop of the swarm earthquakes is rather low, being of the order of 0.1 MPa. This implies that the deformation release rate in the source region may be low. ③ Stress drop of the earthquakes appears to be proportional to their seismic moment, and also to be dependent on their focal mechanism. The stress drop of normal faulting earthquakes is usually lower than that of strike-slip type earth quakes. ④ For each M_s≥6.0 earthquake there exists an apparent azimuthal variation of the comer frequencies. Azimuthally variation pattern of comer frequencies of different earthquakes shows that the source rupture pattern of the Jiashi earthquake swarm is complex and no uniform rupture expanding direction exists.
基金funded by the National Natural Science Foundation of China(Grant No.41174051)the National Science and Technology Pillar Program of the 12th"Five-year Plan"of China(Grant No.2012BAK19B02)
文摘We computed source parameters for 143 earthquakes with M_L≥ 1. 0 occurring from January,2011 to March,2014 using waveform data recorded by the Nuozhadu and Jinghong Reservoir Seismic Networks. Then,the variation of seismic activity and the characteristics of source parameters before and after the impoundment of the reservoir were investigated. The results show that:( 1) the seismic activity increased obviously after the impoundment,especially during the 3- 4 months after impoundment;( 2) the focal depths of the earthquakes occurring in the reservoir area are shallower than the earthquakes occurring outside the reservoir area in the initial stage of impoundment,but after a time,the difference was gradually reduced;( 3) corner frequency varies with the seismic moment and the log-linear relationship is more obvious after impounding;( 4)stress drop and apparent stress increase with increasing seismic moment,moreover they are lower for the earthquakes occurring in the reservoir area after impounding than those occurring outside the reservoir area or before impounding with the same seismic moment;( 5) the effect of reservoir impoundment on an earthquake can reach a depth of 10 km,and the maximum effect is seen at a depth of 3km- 6km,and the differences of seismic activity and average apparent stress between the inside and outside of the reservoir are significant.