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Title:: Crustal Media Seismic Velocity Changes in Jinzhong Reservoir Area in Fujian by Using Ambient Noise

作者:: 胡淑芳¹; 李军¹; 戴宗辉²; 李强¹; 蓝姝¹; (1.福建省地震局,福建福州 350000; 2.山东省地震局,山东济南 250014)

Author(s):: HU Shufang¹; LI Jun¹; DAI Zonghui²; LI Qiang¹; LAN Shu¹; (1.Fujian Earthquake Agency,Fuzhou 350000,Fujian,China)(2.Shandong Earthquake Agency,Jinan 250014,Shandong,China)

Keywords:: ambient noise; Jinzhong reservoir area; relative wave velocity change; the water level

摘要:: 基于2011年10月—2015年12月福建测震台网金钟库区周边台站的连续波形数据,利用地震背景噪声互相关技术提取台站对间的经验格林函数,分周期(1～2 s,2～4 s和4～8 s)测量每天经验格林函数与参考格林函数的走时偏移,进而计算了库区各台站对之间的相对地震波速变化。结果表明:2～4 s周期内地下介质相对波速变化表现出夏高冬低的年变规律,与库区水位变化及当地降雨量存在明显的正相关性,说明在此周期范围内,水位变化及降雨量对波速变化的影响最大。2013年8—10月,仙游地区接连发生了4次M_L≥4.0地震,其中在2013年9月4日仙游震群最大M_L5.0地震发生后,波速变化出现趋势性下降,幅度约为0.1%,随后波速逐渐恢复,在整个震群活动后期,对库区介质波速的影响不明显。

Abstract:: Based on continuous seismic data of the stations in Fujian Seismic Network in the surrounding area of the Jinzhong Reservoir during Oct.,2011 and Dec.,2015,we extracted the empirical Green's function between station pairs by using seismic ambient noise correlation methods,and measured the travel-time shifts between the empirical Green's function and the reference Green's function periodically(1～2 s,2～4 s and 4～8 s),and then calculated the relative seismic velocity changes between the stations in the reservoir area.The results show that the relative seismic velocity changes for underground medium in the 2～4 s period show the annual variation rule of increases in summer and decreases in winter,which obviously correlated with the change of water level and precipitation in the reservoir area.It shows that the change of water level and precipitation have the greatest influence on the change of seismic velocity in this period.From Aug.,2013 to Oct.,2013,four M_L≥4.0 earthquakes occurred successively in Xianyou area,among which,after the M_L5.0 earthquake on Sep.4,2013,the wave velocity decreased by about 0.1%,and then the wave velocity recovered gradually.At the later stage of the whole earthquake swarm activity,the influence on the seismic velocity of the reservoir medium was not obvious.