Study On Slip And Stress Variation Of Longmen Shan To Xiaojiang Fault

The generation and occurrence of earthquakes are the process of accumulation and release of energy.The accumulation of energy is closely related to the active faults movement and the activity of faults is an important indicator of stress state of earthquake faults,as well as a significant parameter of the driving mechanism of earthquakes.The release of energy is the process of fault rupture,which can cause the change of regional stress field and coulomb stress change is one of the important factors affecting seismic activity.Therefore,in-depth study of faults motion characteristics such as the faults slip rates,the coupling fractions of earthquake faults and recognizing the slipping of earthquake fault rupture and stress changed which caused by eartquakes are important to study the seismic activity,the seismic hazard and the seismogenic mechanism of the earthquake fault.This paper first studies the movement characteristics of Longmen Shan to Xiaojiang fault.Sichuan-Yunnan and its surrounding areas are divided into nine active blocks according to the main active faults.Firstly,the slip rate,locking depth and slip deficit are investigated based on the block-dislocation model and GPS velocities of three different periods.Consequently,according to the theory of elastic dislocation,the temporal and spatial characteristics of stress near faults are investigated and the accumulative rate and surface density of seismic moment of the LongmenshanXiaojiang fault are calculated based on Crust1.0 crustal layering model.Then,the source rupture process of Wenchuan earthquake and Lushan earthquake and the change of Coulomb stress are calculated.In order to obtain the static slip distribution models of the Wenchuan earthquake and Lushan earthquake,we inverse the source rupture process of the Wenchuan earthquake in 2008 on May 12 and April 20,2013 Lushan earthquake by collecting broadband digital seismic wave data from the IRIS(Incorporated Research Institutionsfor Seismology),intercepting far-field body wave data and doing bandpass filter.Consequently,the static Coulomb stress change on the Anninghe-Zemuhe-Xiaojiang fault caused by Wenchuan earthquake and Lushan earthquak is calculated.Finally,the seismic risk of the Longmenshan-Xiaojiang fault is evaluated according to the slip rate,the coupling fraction,the slip dificit rate,the cumulative rate of seismic moment,the spatiotemporal variation of the stress near the faults and the static Coulomb stress change,which provide reference for the analysis of the earthquake prediction.The result show that after the Wenchuan earthquake,the northward middle of the Longmenshan fault is unlocked in a large area and the slip rate increases which accelerates the accumulation rate of stress and strain in the southern section of the Longmenshan fault.Lushan earthquake is located in the region where static Coulomb stress caused by the Wenchuan earthqauke increase.We conclude that Wenchuan earthquake accelerates the occurrence of Lushan earthquake.After the Lushan earthquake,the southern section of the Longmenshan fault is not fully unlocked and the energy is not released completely.This section is the region which still needs to be concerned in future.The directions of principal stress axes near the Anninghe-ZemuheXiaojiang fault are well consistent.In addition,by the impact of the Wenchuan earthquake and Lushan earthquake,the current locking depth and coupling fraction of the Anninghe-Zemuhe-Xiaojiang fault become higher.The whole Anninghe fault,the middle and southern section of Zemuhe fault and the northern section of Xiaojiang fault,are the areas that should be focused on in future.The southern section of the Xiaojiang fault tends to be completely locked and the future development trend of the section is worth following.