The 3D QP model of the China Seismic Experimental Site (CSES-Q1.0) and its tectonic implications

Abstract

The Chuan–Dian (Sichuan–Yunnan) region is located in the southeastern part of the geologically complex and seismically active Tibetan Plateau. Since 2008, the Chuan–Dian region has experienced several major earthquakes, including the Wenchuan MS 8.0, Lushan MS 7.0, and Jiuzhaigou MS 7.0 earthquakes, making it one of the areas with the most severe earthquake disasters. The China Seismic Experimental Site (CSES) under construction in this area will deepen the understanding of the preparation for and generation of earthquakes and the disaster mechanisms, which can further enhance the defense capability against earthquake risks. To build a world-class seismic experimental field, it is necessary to establish high-precision medium structure models. Currently, several institutions have established high-resolution three-dimensional (3D) velocity models in the CSES, but there is still a lack of high-resolution 3D attenuation (∝1/Q) structure models. Using the local seismic tomography method, we obtain the highest-resolution 3D QP model in the CSES to date. Combining the existing velocity models in the CSES with other geophysical and geochemical observations by predecessors, this study shows that the QP value anomalies along large fault zones and some basin areas are low, reflecting the high degree of medium fragmentation in these areas with thick sedimentary layers or rich in fluids. The high-attenuation anomaly of the upper crust dipping westward in the Tengchong volcanic area characterizes the possible upward flow of deep-seated magma from west to east. This study also reveals that most earthquakes above magnitude 6 occurred in low-attenuation zones or the boundary areas of high- to low-attenuation anomalies. The source areas of the 2008 Wenchuan MS 8.0 earthquake and the 2013 Lushan MS 7.0 earthquake were separated by a low-attenuation area, and there is still a risk of major earthquakes in the future. The 3D attenuation model constructed in this study will provide a high-resolution reference model for seismological and earthquake disaster research in the CSES.