Depth variations of P-wave azimuthal anisotropy beneath Mainland China.

Wei Wei,Dapeng Zhao,Jiandong Xu,Yaolin Shi,Bengang Zhou

doi:10.1038/srep29614

Abstract

A high-resolution model of P-wave anisotropic tomography beneath Mainland China and surrounding regions is determined using a large number of arrival-time data recorded by the China seismic network, the International Seismological Centre (ISC) and temporary seismic arrays deployed on the Tibetan Plateau. Our results provide important new insights into the subducted Indian plate and mantle dynamics in East Asia. Our tomographic images show that the northern limit of the subducting Indian plate has reached the Jinsha River suture in eastern Tibet. A striking variation of P-wave azimuthal anisotropy is revealed in the Indian lithosphere: the fast velocity direction (FVD) is NE-SW beneath the Indian continent, whereas the FVD is arc parallel beneath the Himalaya and Tibetan Plateau, which may reflect re-orientation of minerals due to lithospheric extension, in response to the India-Eurasia collision. There are multiple anisotropic layers with variable FVDs in some parts of the Tibetan Plateau, which may be the cause of the dominant null splitting measurements in these regions. A circular pattern of FVDs is revealed around the Philippine Sea slab beneath SE China, which reflects asthenospheric strain caused by toroidal mantle flow around the edge of the subducting slab.

Highlights

Mainland China and adjacent regions are surrounded by convergent zones of the Indian, Eurasian, Pacific, Philippine Sea and North American plates (Fig. 1), which are characterized by intense ground deformations[1,2] and widespread seismic and volcanic activities
We present a new model of P-wave anisotropic tomography, which has a high enough resolution in both the lithosphere and asthenosphere, providing new insight into the mantle structure and dynamics of Mainland China
In central Tibet, low-velocity anomalies are prominent at depths of 60–200 km, which is consistent with previous tomographic images[12,13,14,15], possibly reflecting significant variations of rock composition and temperature in the uppermost mantle beneath the southern and central Tibetan Plateau

Summary

Introduction

Mainland China and adjacent regions are surrounded by convergent zones of the Indian, Eurasian, Pacific, Philippine Sea and North American plates (Fig. 1), which are characterized by intense ground deformations[1,2] and widespread seismic and volcanic activities. By using the seismic data recorded by these stations as well as temporary seismic arrays deployed on the Tibetan plateau, high-resolution P and S wave velocity tomographic images beneath Mainland China have been obtained[11,12,13,14,15] These results provide important insights into the structure of the subducting Indian, Pacific and Philippine Sea slabs, and the origin of active intraplate volcanism[10]. We present a new model of P-wave anisotropic tomography, which has a high enough resolution in both the lithosphere and asthenosphere, providing new insight into the mantle structure and dynamics of Mainland China. Detailed resolution tests for our tomographic model are made and discussed in Supplementary Information (see Supplementary Figures S1–S6 online)

Methods

Results

Conclusion