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
In accordance with the requirements of the National Key Technology R＆D Program of the 11th ＂Five-year Plan＂, a densified seismic network consisting of 26 seismic stations was established at the Three Gorges Reservo...In accordance with the requirements of the National Key Technology R＆D Program of the 11th ＂Five-year Plan＂, a densified seismic network consisting of 26 seismic stations was established at the Three Gorges Reservoir area in the section of Hubei Province in March 2009 （21 short-period seismographs, 5 broadband digital seismographs）. From March to December, 2009, a total of 2,995 ML -0. 8 - 2. 9 earthquakes were detected during the trial impounding of the Three Gorges Reservoir （ water level rose from 145 m to 172.8m）. Using the double difference earthquake location algorithm, 2,837 earthquakes were precisely re-located. The results show that the pattern of small local earthquake swarms in the Three Gorges Reservoir area took on a linear distribution or mass-like cluster distribution, the mass-like clusters of events were generally within a distance of 5 km from waterfront, and the linear distribution of the earthquakes could be extended to a distance of 16 km away from the waterfront. In the Hubei section of the Three Gorges Reservoir, earthquakes were mainly concentrated in the northern end of the Xiannvshan and Jiuwanxi faults near the Xiangxihe River, and along the banks of the Yangtze River at the west of Xietan township and the Shenlongxi area on the northern bank in the Badong region, with focal depths less than 10km, and 4km in average. Earthquake frequency in the reservoir region had a positive correlation with reservoir water level fluctuations, indicating that the seismicity belongs to reservoir induced earthquakes. Along the Shenlong River in the reservoir area, earthquakes showed three linear distributions in the northern Badong county, and distributed according to Karst distribution. There are underground rivers in the carbonate strata. When the reservoir was impounded, water permeated into the underground rivers, thus inducing earthquakes. Earthquakes in the areas on the crossriver segment of Xiannvshan fault, the Jiuwanxi fault and at the areas west of Xietan, Shazhen and Xizhen, may be related to the softening of discontinuities, such as the Nukou fault, the Xiannvshan fault, or the bedding joints, which would lead to failure of rock masses, thus, inducing earthquakes. However, convincing conclusions about the triggering mechanism still need further study. Additionally, near the areas south of Wenhua and Yanglin of Zigui county and at Rangkou town east of Badong county, mininginduced earthquakes occurred at the mines nearby, and on the shores of the reservoir are some collapse earthquakes.展开更多
Based on other previous researches, we recalculate the micro-displacement along the Heizi fault with recent deformation data of the Heizi reservoir. The result shows that activity characteristics of Heizi fault has ch...Based on other previous researches, we recalculate the micro-displacement along the Heizi fault with recent deformation data of the Heizi reservoir. The result shows that activity characteristics of Heizi fault has changed greatly since 1973 and have experienced four phases. The third phase is characteristics of normal fault, and others characteristic of reverse faults. Constructing the reservoir dam and reservoir sluice has important effect on present activity of the fault, even changed the activity characteristics of faults in some phases. Seismicity has some effect on deformation data and fault activity.展开更多
815 earthquakes recorded by 12 seismic stations of the Zipingpu reservoir seismic network in 2009 were relocated using the double difference algorithm to analyze the seismic activity of the Zipingpu reservoir.Relocati...815 earthquakes recorded by 12 seismic stations of the Zipingpu reservoir seismic network in 2009 were relocated using the double difference algorithm to analyze the seismic activity of the Zipingpu reservoir.Relocation results show that the earthquakes are concentrated relatively in three zones.The distribution characteristics of focal depth are obviously different among different concentration zones.This means earthquakes in different concentration zones may have different causes.Compared to relocation of earthquakes taking place before the Wenchuan earthquake done by other researchers,the seismic concentration zones in the reservoir area shifted obviously after the Wenchuan earthquake.These variations are related to local stress adjustment in the reservoir area and may also be related to the diffusion depth and range of increased pore pressure caused by rock failure in the course of Wenchuan earthquake.展开更多
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.
基金sponsored by the National Key Technology R&D Program (2008BAC38B04),China
文摘In accordance with the requirements of the National Key Technology R＆D Program of the 11th ＂Five-year Plan＂, a densified seismic network consisting of 26 seismic stations was established at the Three Gorges Reservoir area in the section of Hubei Province in March 2009 （21 short-period seismographs, 5 broadband digital seismographs）. From March to December, 2009, a total of 2,995 ML -0. 8 - 2. 9 earthquakes were detected during the trial impounding of the Three Gorges Reservoir （ water level rose from 145 m to 172.8m）. Using the double difference earthquake location algorithm, 2,837 earthquakes were precisely re-located. The results show that the pattern of small local earthquake swarms in the Three Gorges Reservoir area took on a linear distribution or mass-like cluster distribution, the mass-like clusters of events were generally within a distance of 5 km from waterfront, and the linear distribution of the earthquakes could be extended to a distance of 16 km away from the waterfront. In the Hubei section of the Three Gorges Reservoir, earthquakes were mainly concentrated in the northern end of the Xiannvshan and Jiuwanxi faults near the Xiangxihe River, and along the banks of the Yangtze River at the west of Xietan township and the Shenlongxi area on the northern bank in the Badong region, with focal depths less than 10km, and 4km in average. Earthquake frequency in the reservoir region had a positive correlation with reservoir water level fluctuations, indicating that the seismicity belongs to reservoir induced earthquakes. Along the Shenlong River in the reservoir area, earthquakes showed three linear distributions in the northern Badong county, and distributed according to Karst distribution. There are underground rivers in the carbonate strata. When the reservoir was impounded, water permeated into the underground rivers, thus inducing earthquakes. Earthquakes in the areas on the crossriver segment of Xiannvshan fault, the Jiuwanxi fault and at the areas west of Xietan, Shazhen and Xizhen, may be related to the softening of discontinuities, such as the Nukou fault, the Xiannvshan fault, or the bedding joints, which would lead to failure of rock masses, thus, inducing earthquakes. However, convincing conclusions about the triggering mechanism still need further study. Additionally, near the areas south of Wenhua and Yanglin of Zigui county and at Rangkou town east of Badong county, mininginduced earthquakes occurred at the mines nearby, and on the shores of the reservoir are some collapse earthquakes.
文摘Based on other previous researches, we recalculate the micro-displacement along the Heizi fault with recent deformation data of the Heizi reservoir. The result shows that activity characteristics of Heizi fault has changed greatly since 1973 and have experienced four phases. The third phase is characteristics of normal fault, and others characteristic of reverse faults. Constructing the reservoir dam and reservoir sluice has important effect on present activity of the fault, even changed the activity characteristics of faults in some phases. Seismicity has some effect on deformation data and fault activity.
基金funded jointly by National Science& Technology Pillar Program (Grant No. 2008BAC38B0401)special fund for basic scientific research of Institute of Geology,CEA (DF-IGCEA060828)
文摘815 earthquakes recorded by 12 seismic stations of the Zipingpu reservoir seismic network in 2009 were relocated using the double difference algorithm to analyze the seismic activity of the Zipingpu reservoir.Relocation results show that the earthquakes are concentrated relatively in three zones.The distribution characteristics of focal depth are obviously different among different concentration zones.This means earthquakes in different concentration zones may have different causes.Compared to relocation of earthquakes taking place before the Wenchuan earthquake done by other researchers,the seismic concentration zones in the reservoir area shifted obviously after the Wenchuan earthquake.These variations are related to local stress adjustment in the reservoir area and may also be related to the diffusion depth and range of increased pore pressure caused by rock failure in the course of Wenchuan earthquake.
