A New High-resolution Relocation Method And Related Study Of Lushan Earthquake

This thesis includes three parts:(1) we first introduce one new high-resolution earthquake relocation method (named hypoRelocate) and it is application to the aftershocks of Lushan earthquake; (2) then we discuss the foreshock detection of the Lushan earthquake; (3) at last, we present the study of repeating events in aftershocks and try to understand the relationship between the distribution of the aftershocks (larger repeating earthquake clusters and the precisely relocated aftershocks) and finite fault rupture slip distribution.We develop a new method to determine high-resolution earthquake location, utilizing traditional constraints of absolute travel time and differential travel time, and one new constraint of coda cross-correlogram between the events. The relocation is performed by using a simulated annealing method to search for the best-fitting locations and origin times of the events that minimize the total residual of all the above three constraints of the events. HypoRelocate expands the advantage of using differential constraints to better determine high-resolution relative locations between the events by constructing constraint of coda cross-correlograms on inter-event distance, and reduces the dependence of relocation results on the accuracy of the initial catalog by incorporating the absolute time into the joint inversion. The method is applied to relocate the aftershocks of Lushan Earthquake. The comparisons of the relocation results between hypoRelocate and hypoDD indicate that the additional constraints of coda cross-correlogram and absolute travel time place better constraints on relative location between the events and absolute location of the events.We utilize the match and locate method to detect the foreshock of the Lushan earthquake and the result shows that there is no other small seismic signal detected besides the catalog events during the six months before the Lushan earthquake. Although some foreshocks occurred around the epicenter area, there is no convincible seismic activity increase before the mainshock.The analysis of the waveforms of aftershocks reveals that a number of aftershocks are repeating events and they are always small events and locate along the whole fault. The comparison of the precisely relocated aftershock distribution with finite fault slip distribution certificates that most of the aftershocks occur around the primary slip area and the rupture of main fault may trigger seismic acitivities on other faults surrounded.