摘要
2015年4月15日15时39分,内蒙古自治区阿拉善左旗(39.78°N,106.34°E)发生M_S5.8级地震,震源深度为10km.本文通过收集中国地震科学台阵探测——喜马拉雅Ⅱ期布设在南北地震带北段的34个流动台站连续观测数据,首先以中国地震局台网中心目录给出的138个地震事件作为模板,采用匹配定位方法(Match&Locate)对阿拉善左旗M_S5.8地震前后(2015年1月1日至2015年7月31日)小震进行了检测和识别,检测后给出的地震事件高达1688个,相比于台网地震目录的地震事件数目增加了10倍多.然后利用双差层析成像方法(tomoDD)对研究区域内阿拉善M_S5.8地震前后(2015-01-01—2015-07-31)1级以上的地震序列进行重定位,重定位后的结果显示:主震震中为39.8023°N、106.4388°E,震源深度为20.597km,余震序列展布优势方向为NEE方向,且在深度方向呈近垂直分布,结合野外地质调查结果和震源机制解分析,认为该次地震事件为一次走滑型事件,其发震断裂可能是一条近E-W向的隐伏断层.
On April.15,2015,aM_S5.8 earthquake with a depth of～10 km shook the Alxa,Inner Mongolia Autonomous Region.In this paper,138 events from the China Earthquake Networks Center(CENC)standard catalog are used as templates for scanning through sevenmonth continuous waveform data(Jan.1,2015—July.31,2015)recorded at 34 stations by using the Match and Locate(M&L)technology.We totally detect 1688 events by using the CENC catalog templates which are ten times more events than listed in the CENC catalog.We then relocate the detected events by applying the double difference tomography(tomoDD)technique.Our relocation results show that the mainshock is located at 39.8023°N,106.4388°E with a focal depth of 20.597 km.The spatial distribution of aftershocks demonstrates a NEEstrike and the depth distribution shows a near-vertical plane.Combining with geological investigation and focal mechanism anlaysis,we suggest that the mainshock is a strike-slip event and the seismogenic fault is likely to be a nearly E-W striking blind fault.