Teleseismic P-wave Velocity Structure and Its Relationship with Seismicity Differences in and around the Ordos Plateau

Abstract:

Seismic tomography is a powerful tool to investigate the interior velocity structures of the earth. Ordos plateau, located in the western portion of the North China craton, is a uniquely stable terrane in Asia. However, Weihe-shanxi graben and Yinchuan-hetao graben systems, around the Ordos plateau, present high-level seismic activities. We deployed a dense seismic array composed of 650 temporal stations in and around the Ordos plateau recently. The seismic array provides a good opportunity to study the deep structure and further look into its relationship with the mechanism of the seismicity differences in these areas. In this study, we applied the tomographic inversion method to determine the 3-D Vp structures of the upper mantle and transition zone beneath the Ordos plateau and the surrounding areas with teleseismic data. We have selected 2252 teleseismic events with high signal-to-noise ratio from 2006 to 2014. P-wave arrival times were extracted using waveform cross-correlation method for each earthquake. Then we calculated the relative residuals as the input data for the teleseismic inversion. The relative travel time residual was calculated from the individual station residual by removing the average residual for each event. Through the detailed deep structure obtained by the teleseismic inversion, we find out that low velocity structures in the upper mantle around the Ordos plateau probably have great influence on the occurrence of the destructive earthquakes around the Ordos plateau. Besides, the upper mantle velocity structure in the southern margin of the Ordos plateau which differs from that in other parts around the Ordos plateau may cause seismicity difference in this area.