Location of the Dongyuan M_S4.8 earthquake sequence of Guangdong and 3D P-wave velocity structure in and around source region

In this paper, we determined the location of Dongyuan M_S4.8 earthquake sequence on 16 February 2012 and velocity structure of the source region using a simultaneous inversion method. On this basis we relocated the earthquake sequence using the double-difference location algorithm. The results show that the Dongyuan M_S4.8 earthquake fits a unilateral fracture model, and ruptured down and westward, with a rupture area of 3 km×5 km. A high velocity zone (HVZ) is at the depth of 712 km, with the velocity 6.2 km/s. The source rupture started from the top of the HVZ, where the velocity shows a large gradient. The ruptured area cuts across HVZ. All aftershocks are not beyond the lower bound, at 16 km, of low velocity zone, which is located below the HVZ. Such a structure of high velocity alternating with low velocity is propitious for strain energy accumulation and release. So Dongyuan region has a crust structure favourable to moderate earthquake occurrence.