利用双差成像方法反演青藏高原东北缘及其邻区地壳速度结构

Crustal velocity structure beneath the northeastern Tibetan plateau and adjacent regions derived from double difference tomography

利用区域尺度双差层析成像方法,使用2009年1月至2017年2月的近震资料,对青藏高原东北缘及其邻区内记录到的地震事件进行震源位置和三维速度结构的联合反演.重新定位后震源空间位置得到明显改善,浅层的地震波速与地形和沉积层厚度对应较好,研究区地震主要发生在河西走廊过渡带的低泊松比区域.本文将研究区分为五个区域并分别对其层析成像结果进行了讨论,结果显示研究区不同地块之间地壳结构变化明显,地壳物质整体呈酸性,青藏高原东北缘地壳增厚可能主要发生在中下地壳.

We applied the double difference tomography method to relocate seismic events and invert crustal velocity structure of the northeastern Tibetan plateau using seismic data from January 2009 to Febrary 2017. The spatial distribution of the events is improved greatly after relocation. Tomography results show that velocity structure at shallow depth coincides well with topography and sedimentary thickness. Earthquakes mainly occur in the Hexi Corridor transition zone after relocation, which is a relatively low Poisson＇s ratio zone between the Alxa block and Qilian orogen. The research area is divided into five parts, which are discussed separately to show the lateral variation of velocity structure. Our results indicate an overall acid crust beneath the northeastern Tibetan plateau and crustal thickening in this region mainly occurs in the mid-lower crust.