Characteristics of Crustal Structure and Their Relation with Major Earthquakes in Western China

Major and/or great earthquakes frequently occured in western China, where exist many striking seismotectonic zones such as Tian Shan, Altay, Pamir and Kunlun Mountains. This paper analyzes the characteristics of the gravity field in western China, inverts the depth of Moho interface by the Parker-Oldenburg method with gravity data and seismic profiles. Through comparison with the results of seismic tomography inversion, we analyze crustal structure of the study area. The results show that the study area is significantly heterogeneous in crustal structure, with main orogenic belts of high-speed while basins and major depressions of low speed. The orogenic belts in the study area are generally Moho depression areas while the basins are the Moho uplift areas. According to the calculation results and epicenter distribution of the study area, we discuss the correlation between crustal structure and major earthquakes. The earthquakes in this region are closely related to crustal heterogeneity, which mainly happen around the crustal velocity change belts and in the regions with great crustal velocity differences. Under the effect of tectonic stress, these crustal non-uniform areas are prone to major earthquakes, which is one of the tectonic reasons for high seismicity in orogenic belts and near the boundary between basins and mountains in western China.