Tomographic imaging of the 2017 Ms7.0 Jiuzhaigou earthquake source region and its implications on material extrusion in the northeast Tibetan plateau

Abstract

Due to the heavy damages caused by the 2017 Ms 7.0 Jiuzhaigou earthquake that occurred in a complex tectonic environment, investigations on the seismogenic structure and tectonic environment are very important for understanding the geodynamic mechanism and mitigating earthquake hazards in the region. In this work, we present a high-resolution 3-D crustal seismic model for the source region of the Jiuzhaigou earthquake by exploiting the arrival times of aftershocks based on double difference tomography. Our results revealed that zones of Jiuzhaigou's rupture fault and aftershocks predominantly coincide with the high-velocity anomalies that are surrounded by the low-velocity anomalies, from the western territory to the aftershock zone. An area with a high Poisson's ratio ~0.28 is primarily the cradle for most of the aftershocks, and the lithology is interpreted as consisting of mafic and calcium-rich rocks. In the mid-crust, tomographic images exhibit a low-velocity zone in and around the source region. This low-velocity zone originates from the interior of the Tibetan Plateau, extends across the thrust faults (the Longriba fault and the Minjiang fault and the Jiuzhaigou's causative fault) and then finally encounters the strike-slip faults (the Tazang fault and East Kunlun fault). The counter belt of both the Tazang fault and East Kunlun fault features high-velocity anomalies. The mid-crust low anomalous zone is characterized by a high Poisson's ratio and low shear wave velocity, which indicates a weaker crust that easily flows and deforms. Therefore, we propose that this low velocity is a crustal channel flow in the vicinity of seismic sources, which causes the transformation from thrusting to strike-slip motion in the study area.