Comparative Study On Coulomb Stress Change Of Three Gorges Zigui M4.5 And Jilin Songyuan M5.5 Seismic Sequence

In recent years,the issue of earthquakes induced by human activities such as reservoir water storage and oil and gas resource exploitation has attracted much attention.This paper selects two typical human activity areas of the Three Gorges Reservoir and Jilin Song Oilfield to carry out seismic activity research.M4.5 and M4.7earthquakes occurred in Zigui area of the Three Gorges on March 27 and March 30,2014,respectively.From October 31 to November 23,2013,five earthquakes with M?5 occurred in Songyuan,Jilin.The Zigui and Songyuan study areas are both weak earthquake areas,with reservoir water storage and oilfield exploitation activities respectively.In this paper,the Coulomb stress variation and seismic activity characteristics of the above two seismic swarms are discussed respectively.In order to provide help for the analysis of earthquake risk and the possible mechanism of earthquake occurrence in weak earthquake area.This paper is based on the geological tectonic background and seismicity distribution characteristics of the Three Gorges Reservoir head area and the Songyuan area of Jilin Province.Catalogue data of earthquake sequences recorded by seismic stations in the Three Gorges Zigui M4.5 on March 27,2014 and Songyuan M5.5 in Jilin Province on October 31,2013.Calculate the triggering relationship between the respective main shocks of the two earthquake swarms,and the relationship between the Coulomb stress change results and the aftershock distribution is analyzed.Combining the rate-state(R-S)friction law to analyze the trend of seismic activity,some conclusions are obtained.Calculate the static Coulomb stress change in the source area of the Zigui M4.5earthquake on March 30,2014,Trigger the M4.7 earthquake located in the area of increased Coulomb stress.Calculate the relationship between the different values of the effective friction coefficient and the Coulomb stress change,and discuss the impact of the Three Gorges Reservoir water seepage action on the earthquake.Calculate the seismic activity rate based on the rate-state friction law.The results show that,the stress disturbance caused by the main earthquake causes the seismicity level of Xiannvshan fault zone to be higher than the background seismicity level for a period of time.Seismicity near Jiuwan xi fault zone is slightly less than background seismicity.Calculate the Coulomb stress change of the main shock of the Jilin Songyuan M5.5earthquake swarm in 2013,and the analysis has a triggering effect on the aftershocks.Calculate the seismic activity rate of the Songyuan research area,analyze the seismic activity trend,and compare the fitting results with the actual earthquake distribution.By comparing the static stress triggering effects of the seismic sequences in the two study areas,it is found that there are obvious triggering effects among other earthquakes except the M5.0 earthquake on November 23,2013 in Songyuan.The decrease in the effective friction coefficient causes more aftershocks to be concentrated in the area where the Coulomb stress increases,and the aftershocks are concentrated where the sign of the Coulomb stress changes near the main fault.Both areas have high rates of seismic activity for a period of time after the main earthquake,The seismic frequency in Songyuan area is much lower than that in Three Gorges area.The high frequency period of the earthquake is concentrated within a few months after the main shock.The magnitude of the earthquake in the Three Gorges study area is relatively small.The number of earthquakes is much greater than the number of earthquakes in the Songyuan area.The focal depths of the earthquakes in the two regions are relatively shallow.There is a certain difference from the local tectonic earthquake.Compare the temporal and spatial distribution characteristics of earthquakes in the two study areas,and explore the cause mechanism of earthquakes.Comprehensive studies have shown that the concentration of tectonic stress at the northern end of the Xiannvshan fault and the increase in pore pressure caused by the seepage and diffusion of reservoir water are the main causes of the 2014 M4.5 earthquake swarm.The superimposition of long-term oil and gas production activities and regional faults in the Songyuan area may be the cause of this earthquake swarm.