Joint analysis of P-traveltimes teleseismic tomography and gravity modelling for Northern Tibet

Abstract

A combined study of delay time tomography analysis and gravity modelling was carried out for a profile across the Northern Tibetan plateau. During the summer and fall of 1993, a seismological array was installed along the Tibetan highway from the Tangula Shan piedmont to the Nan Shan range. A P-wave delay time tomography analysis was conducted, using 1630 P arrival times from 124 earthquakes recorded by more than 6 stations. The resulting velocity model reveals three main crustal units and a low velocity zone in the mantle. The resulting seismic image was used to construct a 2D gravity model, using a linear velocity-density relationship, focusing on the important features of the velocity anomalies. A high coherency is observed between low velocity zones and low density zones. The crust shows a gathering of thick and thin, low and high velocity blocks. This crustal structure is similar to the crustal structure known for southern Tibet. It is well correlated with the tectonic map and reveals that the main sutures visible at the surface have a lithospheric prolongation. The very low velocity anomaly (−5% maximum) of the model is located between the Jinsha suture and the Kunlun fault, with its top at 200 km depth. The size and the amplitude of this deep velocity anomaly suggest a mantle plume.