Abstract: Based on data collected from a temporary seismic network,in addition to some nearby permanent stations,we investigate velocity structure and seismicity in Rongchang gas field,where significant injection-induced seismicity has been identified. First,we use receiver functions from distant earthquakes to invert for detailed 1-D velocity structures beneath typical stations. Then,we use the double-difference hypocenter location method to relocate earthquakes of the 2010 M_L5.1 earthquake sequence occurring at the region. The relocated hypocenters show that the 2010 M_L 5.1 earthquake sequence was distributed in a small area surrounding major injection wells and clustered mostly along pre-existing faults. Major earthquakes show a focal depth less than 5km with a dominant depth of～2km,a depth of major reservoirs and injection wells. We thus conclude that the 2010 M_L 5.1 earthquake sequence might be induced by deep well injection of unwanted water at a depth～3km in Rongchang gas field.

Key words: induced earthquake, receiver function, double difference location, Rongchang

摘要： 根据重庆市地震台网和流动地震台网记录到的天然地震资料,利用接收函数反演得到荣昌地区的精细一维速度结构。在此基础上用双差定位法对2010年9月10日重庆荣昌M_L5.1地震序列进行了精定位。结果表明,地震定位精度得到极大提高,震中分布与区域地质构造的关系更加清晰。多数地震集中在主要断层附近并呈条带状分布,震源深度集中在2km附近,与主要储藏层及注水井深度吻合,初步认为该地震序列为注水活动所诱发的构造地震活动。文中获得的精准的速度结构及地震空间分布对于进一步深入研究震区深部地质构造特征、注水诱发地震的机理等具有重要意义。

关键词: 诱发地震, 速度结构, 接收函数反演, 双差定位, 荣昌