Application of time-lapse seismic tomography based on double-difference tomography to reveal P wave velocity changes related to the 2014 Ludian MS6.5 earthquake

Various studies have reported on temporal changes of seismic velocities in the crust before and after earthquake. New time-lapse seismic tomographic scheme based on double-difference tomography could obtain temporal velocity variations of the subsurface medium in different time periods, and it is less affected by different data distribution and quality in different time periods. In this study, we used the absolute and relative arrival data of P-wave recorded by Yunnan regional seismic network to obtain the high precision spatial-temporal distribution of P-wave velocity changes before and after the 2014 Ludian MS6.5 earthquake by using tomoTDD method. The results show that after the Ludian Earthquake, the P-wave velocity in the source area decreased during the coseismic period, but did not drop to the minimum. It dropped to its minimum within 1-4 months after the main shock. Then P-wave velocity began to rise and the source area began to heal. The healing process developed from the shallow layer to the deep layer, and finally, restored to the level before the earthquake. At the same time, we found that the spatial change of P-wave velocity is consistent with the change of aftershock distribution. There is a good consistency between the variation of coseismic coulomb stress and P-wave velocity change. Therefore, we consider that the change of static stress caused by the earthquake is an important reason for the change of P-wave velocity. The dynamic and static stress of the aftershock results in the change of physical properties of medium in the source area, which affects the change of P-wave velocity. © 2021, Science Press. All right reserved.