Contrast of Rheology of Crust and Mantle near Moho Revealed by Depth Variation of Earthquake Mechanism in Continental China

Abstract

AbstractRheology of continental lithosphere is an important basic issue in geodynamics, but not well resolved yet. There are observational and experimental evidences to support a model of strong mantle ‐ ductile weak lower crust near the Moho; there are also evidences to support a contrast model of weak ductile mantle ‐ strong crust. In this study, we use CMT data of Harvard with corrected focal depth to analyze the depth variation of plunge angle of principal stresses in continental China. It is found that the plunge angles are either nearly horizontal or close to vertical for very shallow earthquakes, while there are great varieties in plunge angle of earthquakes in the middle and lower crust and earthquakes in the mantle. This feature is distinctively different from results of regions with weak ductile lower crust, where at the base of earthquake generation layer, plunge angles of principal stresses are found nearly horizontal or vertical similar to the case of very shallow earthquakes. It may indicate that both kinds of crust‐mantle rheology models exist in China. Therefore, integrated detailed study on regional lithospheric rheology is necessary.