Location Of Small Seismic Essence In Aba Area And Its Active Structural Significance

The seismic activity is closely related to the active structure,and the small seismic activity contains abundant structural information.The trend and tendency of active faults can be inferred from the distribution of small seismic events in plane and depth,which is usually used as an important means to identify hidden faults and active faults,and is of great significance to the study of active structures.The study area is located in the northwest of Sichuan Province,where the Chuanqing block(Bayangkala block)is an active zone of neotectonic activity in the eastern edge of the Qinghai-Tibet Plateau,with strong seismicity.In recent years,frequent earthquakes in the region,through the study of regional seismic events can better understand the seismic geological environment and active fault distribution,properties,hazards and other aspects,help to provide scientific basis for urban spatial planning and urban disaster prevention and mitigation work.However,the uncertainty of conventional seismic location often causes many tectonic information to be ignored,which seriously limits the application of these important basic data in seismic activity analysis,active structure and so on.In order to obtain more accurate location data of small earthquake essence,we use multi-step locating method to carry out seismic positioning of the studied area.The results show that the multi-stage positioning method can not only eliminate the dependence of the relative positioning method on the positioning accuracy of the main event position,but also effectively reduce the influence of the wrong speed structure.Using the data of Sichuan seismic station network,the 3118 earthquakes with M_L1.6 magnitude and above recorded from January 2008 to June 2019 were repositioned in the range km(100-103.2°E、31.3-34.5°E)with Aba County as the center radius.According to the result of repositioning,the relationship between seismicity and surface active structure in Aba area and the revealed structural significance are analyzed.After precise positioning,the focal location accuracy is obviously improved,and the epicenter distribution is consistent with the linear distribution of seismic fault zones.The results show that the earthquakes in the study area are mainly concentrated in the south of Aba County,and the Xianshuihe fault zone in the south of the study area,Songgang-Fubian River fault zone is the most concentrated.There are differences in the depth distribution characteristics of small seismic sources in different seismic zones.By summing up the distribution of seismic events around each fault zone,it is found that the Xianshuihe fault zone has the difference of north-south structure,the Maqin-Maqu section of the East Kunlun fault zone has seismic empty area,the earthquake risk is strong,and the Aba fault zone has seismic activity corresponding to the surface active structure,which is consistent with the results of field geological survey.