2010年玉树M_S 7.1级震区上地壳三维P波速度层析成像

3-D P wave velocity tomography of the upper crustal in the Yu shu M_S 7.1 earthquake region

综合利用震后应急流动台阵和青海台网部分固定台站观测数据,采用多震相走时层析成像方法,对玉树震区地壳三维速度结构和玉树MS7.1级地震余震震源位置参数进行了联合反演,获得了研究区上地壳三维速度结构图像和余震序列重新定位结果.结果显示:玉树MS7.1级地震余震整体沿北西向玉树-甘孜断裂呈条带状分布,长约120km;以隆宝镇为界,呈现两段不同的分布特征;震区上地壳速度分布存在横向非均匀性;沉积层厚约6～7km,壳内存在厚约为7～8km的低速层;地震多发生于低速层上方即高、低速过渡区域,区内多条断裂走向与高低速过渡带一致.

The 3-D velocity tomography image and accurate relocation of Yushu Ms 7. 1 earthquake aftershocks is obtained by combined inversion using the method ＂Multiphase Traveltime Inversion＂ from the integrated travel time data recorded at the the earthquake emergency response stations and the digital seismic monitoring network of Qinghai province. The results show that the epicenters of aftershocks spread along Ganzi-Yushu fault extending NW to SE with the length about 120 km and present two different characteristics with the town of Longbao for boundary. There exists lateral inhomogeneity of velocity in the crust, and the thickness of sediment layer is 6-7 km, the thickness of lower velocity layer is 7-8 krn. The earthquakes occurred more often above lower velocity layer where speed transit from high to low, and the spread of faults correspond to the transitional zone.