Pn Velocity Variation beneath China Continent and Deep Structure Background for Strong Earthquake Preparation

Abstract

AbstractBased on a previous work of the authors, with abundant supplementary data this study has redone the Pn travel time tomography of China continental region. The supplemented Pn arrival time observations are from Annual Bulletin of Chinese Earthquakes for 1997 and 1998, Korean (DPRK) seismological reports and bulletins of Chinese provincial seismic networks. The amount of collected Pn arrival time data reaches up to 140000, from which we have picked 99440 Pn rays from 8043 earthquakes recorded at 581 stations for the tomography. Spatial resolution reaches to 3° ×3°. This paper has made a comparison study between Pn velocity lateral variation and delineation of the active tectonic blocks of China continent. The result shows that there is a close relation between Pn velocity lateral variation and delineation of the first‐order block regions. Roughly demarcated by 105°E, positive velocity anomaly regions dominate in western part of China continent, with the highest positive anomaly in Xiyu block region and secondary positive anomaly in Qinghai‐Xizang Plateau region, while the Yunnan‐Burma block region exceptionally shows negative anomaly. Negative velocity anomaly regions are mainly seen in the eastern part, with the lowest negative anomaly in North China block region and secondary low anomaly in Northeastern Asia block region. The mean fast Pn velocity direction in upper mantle of western block regions is generally in NWW‐SEE, while in eastern block regions it is about in NNW‐SSE, roughly coinciding with dominant direction of tensional tectonic principal stress therein. Rather significant correlation between Pn velocity lateral variation and location of strong earthquakes can also be seen. Most MS ≥7.0 earthquakes took place in the crust above the low Pn velocity anomaly region, with a few occurring in the transition zone between high and low Pn velocity, or in the relative low velocity zone between two high velocity regions.