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

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.