由地壳速度结构判断郯庐断裂带江苏段未来大震位置

用多震相地震走时成像法反演郯庐断裂带鲁苏皖段及邻区三维地壳速度结构。一些地区如郯庐断裂带临沭到定远及以东地区在中地壳的20~25km出现低速层,一些地区莫霍面埋深有变化。浅层速度结构的分段与断裂活动的分段相一致,表明新沂到泗洪是活动断裂的闭锁段。对比1668年山东郯城8级地震区和研究区的深部速度结构,结合与郯庐带相交的断裂、地震活动、活动断裂的闭锁段、中地壳低速层及莫霍面深度变化,综合判断郯庐断裂带江苏段未来可能发生大震的地区为33.4°~34.1°N,118.2°~118.8°E,重点是宿迁、沭阳、泗阳和泗洪。震级估计可达8级。

Location of Future Large Earthquakes in Jiangsu Segment of Tanlu Fault Zone Based on the Crustal Velocity Structure

The Tancheng-Lujiang Fault Zone (simplified as the Tanlu Fault Zone) is the biggest in east China. In 1668, an M8 earthquake occurred along this fault zone in Tancheng, Shandong Province, China. Seismologists are focusing on the most likely location of the next major earthquake along this fault, particularly in the areas near Shandong and Jiangsu provinces. The multiphase travel time inversion (MUTI) algorithm was developed to invert the three-dimensional crust velocity structure of the Shandong-Jiangsu segment of the Tanu Fault Zone and its adjacent area (30°~37° N, 113°~122° E). The crust can be divided into three layers, the upper (10~15 km thick), the middle (10~15 km thick) and the lower (10~12 km thick). The segmentation of the shallow velocity structure is consistent with that of fault activity, and indicates that the area from Xinyi to Sihong comprises the active fault block section. There is a low velocity layer at a depth of 20~25 km in the Tanlu Fault Zone from Linshu to Dingyuan and its eastern area. A low velocity layer can also be found in the middle crust of the source region of the 1668 Tancheng earthquake. In this study, we present the variation of Moho depths in Suqian, Siyang, Shuyang, and Tancheng. The Wuxi-Suqian fault, the Hongze-Goudun fault, and the Jiashan-Xiangshui fault all intersect with the Tanlu Fault Zone, and the intersection area of these faults may be dangerous. By comparing the depth velocity structure features of the Jiangsu segment along the Tanlu fault zone with the source area of the 1668 Tancheng M8 earthquake, combined with data regarding seismic activity, the active fault block, the low velocity layer in the middle crust, the depth variations of the Moho, and the fault intersections, the area of next large earthquake can be estimated for the Jiangsu segment of the Tanlu fault zone. The most likely position is 33.4°~34.1° N and 118.2°~118.8° E, in Suqian, Shuyang, Siyang and Sihong in particular. The estimated maximum magnitude is 8.