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Title:: Seismic Wave Velocity Ratio under Water Body of Reservoir during Reservoir-induced Earthquakes

Author(s):: HU Xian-ming; XIE Rong-hua; HAN Jin; SUN Yi; (Earthquake Administration of Sichuan Province, Chengdu 610041, Sichuan, China)

Keywords:: earthquake prediction; reservoir-induced earthquake; vP /v_S ratio anomaly; Sichuan

摘要:: 以大桥水库M_S4.6诱发地震和紫坪铺水库M_L2.5诱发震群为例,研究了穿过水体下方的地震波的波速比在地震前后的变化。由彝海子台记录的穿过大桥水库水体下方的地震波所计算的波速比,在蓄水后4.6级主震前存在高值异常,反映库水对波速比有影响; 由八角台记录的穿过紫坪铺水库水体下方的地震波所计算的波速比显示,在2006年8月28日后一时段库区东北部出现微小的波速比高值异常,结果于2006年10月至2007年2月在八角台附近的汶川水磨发生了2.5级水库诱发震群。因此认为,根据穿过水库水体下方的地震波射线计算的单台波速比,能够反映地震孕育过程中震源及周围地区介质特性的改变,可作为监测水库地震的一种手段。

Abstract:: Taking the Daqiao reservoir-induced earthquake(M_S4.6)and Zipingpu reservoir-induced earthquake swarm(the maximum M_L2.5)for example, we studied the change of seismic wave velocity ratio before and after the earthquakes using the data of seismic ray that passed through the medium under water body. Based on the Yihaizi station's records(the seismic ray passed through the medium under the water body of the Daqiao reservoir), the velocity ratio showed high-value anomaly after the reservoir impounding and before the earthquake occurring, which reflects the influence of impounding on velocity ratio. Based on the Bajiao station's records(the seismic ray passed through the medium under the water body of the Zipingpu reservoir), the velocity ratio also showed high-value anomaly during a period of time after Aug. 28, 2006; and an M_L2.5 earthquake swarm occurred about the Bajiao station in the following months. So, the wave velocity ratio computed by using the data of seismic ray that passed through the medium under the water body of reservoir, can reflect the change of the medium characteristics in and around an epicenter during a seismogenic process, and can be as a way to reservoir-induced earthquake prediction.