摘要
On September 5,2022,a strong MS6.8 earthquake struck the Luding area in the Kangding-Moxi segment of the Xianshuihe fault zone,which is the northern boundary of the Sichuan-Yunnan rhombic block,causing considerable casualties.The Bamei-Kangding segment of the Xianshuihe fault zone,which is located only tens of kilometers away from the Luding earthquake,has hosted frequent moderate to strong earthquakes in history and is a dangerous earthquake-prone zone.Therefore,it is critical to investigate the regional seismogenic environment for strong earthquakes and to evaluate the impact of the Luding earthquake in this area.For this purpose,we deployed a dense seismic array comprising over 200 short-period nodes in this region from July to August,2022 and acquired seismic ambient noise for over 30 days.Using the collected data,we conducted surface wave tomography and obtained a high-resolution 3-D shear wave velocity model for the regional shallow crust down to 8 km in depth.The key findings include:(1)the Bamei-Kangding segment of the Xianshuihe fault zone exhibits widespread stripped lowvelocity anomalies,suggesting shear movements at a relatively high temperature of the Xianshuihe fault zone;the Zheduoshan granitic pluton situated between the Zheduotang and southern Selaha faults shows a distinct low-velocity anomaly,which may be attributed to the localized high-temperature anomaly resulted by a deep magmatic heat source and the recent rapid uplift of the Zheduoshan area;(2)a ten-kilometer-wide high velocity body found below 4 km in depth near the Zhonggu area in the Bamei segment coincides with the seismic gap of moderate to strong earthquakes in this region,suggesting that the high velocity body may act as a seismic barrier;(3)the heterogeneity of the velocity structure along the Bamei-Kangding segment of the Xianshuihe fault zone corresponds to the regional changes in temperature,which reveals the reason for the spatially varying seismogenic potential in this segment;especially,the Selaha and Zheduotang faults which
基金
supported by the National Key Research and Development Project of China(Grant No.2021YFC3000602)
the Special Fund of Key Laboratory of Earthquake Prediction,CEA(Grant No.2021IEF0103).
