Deformation And Stress Characteristics In Longmenshan Fault Zone

With its burstiness and impossible accurate prediction,earthquake disasters mayhave great effect on human life,among them,the Wenchuan earthquake in 2008caused huge losses of life and property to Chinese people.One of the greatest progress in Seismology in 20th century is that we have discovered that earthquake take place in fault.With the development of space technology,GPS technology can accurately obtain the earth's crust deformation information,combined with the geological and geophysical data,we can search for the natural law of earthquake gestation and occurrence and development,thus maximumly reduce the damage of the earthquake.Longmenshan fault has a complex geological structure,the geologic activity here is not stable.In this paper,the Longmenshan fault zone is taken as the research area,and the Wenzhou earthquake coseismic GPS observation data is used to simulate the velocity field zoning of this area.The mean moment tensor technique is used to analyze the stress and strain characteristics of the Longmenshan fault crustal.In combination with the fault slip distribution model constructed,coulomb 3.3 software^[1,2]was used to analyze the Coulomb stress triggered by the Wenchuan earthquake and its effect on surrounding fault activity.The main work and achievements of the paper are as follows:?1?Multi-surface function model,power function model,and least squares configuration model are used to partition the velocity field of the studied area,and the results of the above three models are compared and analyzed.The conclusion is that the multi-surface function model The best fitting effect.?2?Using the Tam technique^[3]?mean moment tensor technique?combined with the focal mechanism solution of the aftershocks of the Wenchuan earthquake to study the stress field characteristics of the study area,and compare it with the results of the stress field calculation using the multi-surface function.The distribution characteristics of the Longmenshan fault stress field obtained by the mean moment tensor technique have certain reliability.The stress field results show that the Wenchuan earthquake is an earthquake that is dominated by thrust and has a small amount of right-lateral strike-slip components.Its main pressure P axis orientation is NWW,which is consistent with the orientation of the stress field of the Longmenshan structural belt.?3?Through the RPS algorithm^[4]?global optimization based on the particle swarm algorithm?to invert the slip velocity of the Longmenshan fault,using the slip velocity model and the USGS sliding distribution model^[5]to calculate the above two on the basis of the coulomb 3.3software.The Coulomb stress triggered by the different fault models on the fault plane and the optimal rupture surface of the fault is determined.Through comparative analysis of the calculated results,the sliding velocity model can be used to calculate the Coulomb stress triggered by the Wenchuan earthquake.Based on this,the slip model was used to calculate the Coulomb stress triggered by the specified fault plane and the optimal rupture plane at different depths.The results showed that the number of aftershocks distributed in the Coulomb stress increase area was 15 km at a depth of 15 km.At most,they accounted for 63%and 85%of the number of aftershocks studied.?4?By analyzing the Coulomb stress changes of active faults around the Wenchuan Earthquake,the coseismic Coulomb stress change triggered by the Wenchuan earthquake is significant in the local area,which is in the vicinity of the northwest section of the Xianshuihe fault and the south part of the Minjiang fault.The Pengxian-Quxian fault and the Beichuan-Yingxiu fault have a certain stress loading and the mean stress changes are?0.125 bar,0.75 bar,0.05 bar,and0.1 bar?,which also reduces the Fubian River fault and Hanan.The accumulation of Coulomb stress on the southern section of the Qingshan fault and the Xianshuihe fault reduced the probability of occurrence of these faults.From the results of the Coulomb stress change of the seismogenic fault in the Lushan earthquake in 2017,we can see that the Wenchuan earthquake has a certain triggering effect on the Lushan earthquake.