The Seismicity's Study Around The Seismic Gap Between The Wenchuan And Lushan Earthquakes

A dense seismic array deployed around the seismic gap between the Wenchuan and Lushan earthquakes provided a continuous recording from December 2016 to April 2018 to study seismicity,understand the spatiotemporal distribution characteristics of sources and analyze seismic risk.An earthquake catalogue consisting of 2227 earthquakes with complete magnitude of Mc=0 was obtained after manually picking P and S arrivals,locating and calculating local magnitudes.The complete catalogue carried abundant information about the spatiotemporal distribution of seismicity and earthquake hazard risk.Relocated using hypo DD,focal depths of all earthquakes range from 5 to 20 km,which is consistent with the seismogenic depth of Longmenshan fault zone.Most of events occurred in the source region of the Wenchuan and Lushan earthquakes,and the characteristics of depth expansion is similar to that of early aftershocks.At the same time,the eastward movement of the Tibetan plateau is blocked by Baoxing and Pengguan complexes,forming frequent seismic activities in the northwest side of two complexes.Relocation results clearly delineated a ?30 km long and ?20 km wide seismicity-silent zone on Wenchuan-Maoxian and Yingxiu-Beichuan fault.The seismicity deficit zone is coupled with the low-velocity zone related to partial melting.This phenomenon indicates that the heating effect of the partial melting at the lower crust is a main reason for the abnormally low seismicity.Anticorrelation between seismicity and monthly precipitation variation rate is also observed during the monitoring period,which means earthquake rates is modulated modestly by the seasonal precipitation in the study region.A comprehensive analysis with the 3D velocity model,historical strong earthquakes and b-value suggests the possibility of future earthquake risk along the middle part of Pengguan fault and neighboring blind faults to the east of seismic gap.