17:15 〜 18:45
[SSS04-P01] A study of earthquakes in Changning area, SW China by double-difference seismic location and tomography
キーワード：induced earthquakes, velocity structures, seismicity, double-difference tomography method
An earthquake of MS6.0 struck Changning Country in Sichuan Province on 17 June, 2019. It occurred at the southeastern margin of Sichuan Basin. Four aftershocks with magnitude larger than MS5.0 occurred during the following days till to July 4, 2019. Based on the history record, there is no any other earthquakes with magnitude larger than the Changning MS6.0 earthquake in this area. However, a large amount of small earthquakes have been recorded since 2010 in Changning, Gongxian and Junlian area, the frequency and intensity is increasing especially in recent five years. In this study, we use seismic data from January 2015 to December 2023 recorded by Sichuan, Yibin local network and Sichuan-Yunnan national earthquake monitoring and prediction experimental field network to carry out velocity structure inversion and seismic precise location by double-difference (DD) seismic tomography method.
The earthquake relocation results show than the earthquakes are concentrated in Changning-Gongxian and Junlian-Gongxian regions. In Changning-Gongxian region, the distribution of earthquakes presents NE direction with approximate 50 km and NW direction with approximate 10 km, respectively. In Junlian-Gongxian region, the distribution of earthquakes presents uneven intensity, the seismicity in east is dense while in west is sparse. In eastern segment of this region, the earthquakes present NE and SE directions. Meanwhile, the focal depth of relocated earthquakes ranges from 0 km – 15 km, and the mainly concentrated from 2 km – 8 km.
Based on the checkerboard tests, we mainly analyze the P-wave and S-wave velocity structures at different depth within 8 km. Within the study area, both the P-wave velocity and the S-wave velocity structures present significant lateral heterogeneity. The earthquakes are mostly occurred in the transition zone of high and low velocity structure where the medium is relatively fragile or the high-velocity areas where the stress is often concentrated. Comparing the distribution of earthquakes, the result of P-wave velocity and S-wave velocity structures and the geological condition of this study area, the southeastern margin of Sichuan Basin is capable of accumulating a large amount of strain energy and is apt to release stress.
The earthquake relocation results show than the earthquakes are concentrated in Changning-Gongxian and Junlian-Gongxian regions. In Changning-Gongxian region, the distribution of earthquakes presents NE direction with approximate 50 km and NW direction with approximate 10 km, respectively. In Junlian-Gongxian region, the distribution of earthquakes presents uneven intensity, the seismicity in east is dense while in west is sparse. In eastern segment of this region, the earthquakes present NE and SE directions. Meanwhile, the focal depth of relocated earthquakes ranges from 0 km – 15 km, and the mainly concentrated from 2 km – 8 km.
Based on the checkerboard tests, we mainly analyze the P-wave and S-wave velocity structures at different depth within 8 km. Within the study area, both the P-wave velocity and the S-wave velocity structures present significant lateral heterogeneity. The earthquakes are mostly occurred in the transition zone of high and low velocity structure where the medium is relatively fragile or the high-velocity areas where the stress is often concentrated. Comparing the distribution of earthquakes, the result of P-wave velocity and S-wave velocity structures and the geological condition of this study area, the southeastern margin of Sichuan Basin is capable of accumulating a large amount of strain energy and is apt to release stress.