Study On The Coulomb Stress Evolution And Stress Interaction Amont Strong Earthquakes Along Altyn Fault

Coulomb stress change is an effective way to study earthquake stress trigger and fault stress state change.The change of coulomb stress on the fault plane of the subsequent earthquake caused by the previous earthquake has a direct impact on the spatiotemporal distribution of subsequent earthquakes.Therefore,studying the seismic coulomb stress accumulation in the fault zone has important scientific significance for the long-term seismic risk study in this region.Altyn fault zone is located in the northwestern margin of the Qinghai-Tibet Plateau,is a giant fault zone with multiple fault sections,which is the most frequent area of strong earthquake activity in China.At present,the elapsed time of the earthquake with magnitude 7 or above in the Altyn fault zone has approached or exceeded the recurrence period of the historical earthquake and has the danger of strong earthquakes.In this paper,the Altyn fault zone and its neighboring areas are used as research areas.The Maxwell's stratified viscoelastic model is used to study the mutual triggering relationship between several strong earthquakes in the adjacent area of the Altyn fault zone and the evolution of the cumulative coulomb stress change over time from 1900 to 2020 in the Altyn fault zone by PSGRN/PSCMP program.The research results show that:1.When considering the coseismic dislocation effect only,the Gulang earthquake,the Changma earthquake and the Shandan earthquake occurred in the coulomb stress loading region in the five subsequent earthquakes,only considering the post-earthquake viscoelastic relaxation effect,the five subsequent earthquakes in the Gulang earthquake,the Shandan earthquake and the Gonghe earthquake occurred in the Coulomb stress loading region.At the same time,considering the coseismic dislocation and the post-earthquake viscoelastic relaxation effect,the Gulang earthquake,the Changma earthquake,the Shandan earthquake and the Gonghe earthquake occurred in the coulomb stress loading region in the five subsequent earthquakes.It shows that the coseismic dislocation and the post-earthquake viscoelastic relaxation have different effects on subsequent earthquakes,comprehensive considering the coseismic and post-earthquake effects caused by strong earthquakes on the coulomb stress on the fault,the triggering effect between strong earthquakes can be more accurately simulated.2.Considering the coseismic and post-earthquake effects,the study found that the Gulang earthquake was triggered by the coseismic and post-earthquake effects of the Haiyuan earthquake;the Changma earthquake was mainly caused by the long-term tectonic stress loading of the Altyn fault;the Shandan earthquake was mainly caused by the coseismic and post-earthquake effects of the 1927 Gulang earthquake;the Gonghe earthquake was mainly caused by the viscoelastic effect of the 1937 Dulan earthquake.3.At the same time,the coulomb stress evolution of the Altyn fault zone was calculated by considering the three effects of coseismic,postseismic and interseismic tectonic loading.It was found that all the two strong earthquakes on the fault zone all occurred in the coulomb stress loading region and the long-term structural loading of the fault zone is the main reason of earthquake triggering.Affected by the Changma earthquake and the long-term loading of the interseismic structure,the cumulative stress of the Wuzunxiaoer section and the 4th south section of Shulehe is higher in the entire rupture section of the Altyn fault.In particular,the maximum cumulative coulomb stress of the 4th south section of Shulehe is 2.58 Mpa,and the strong earthquake of the 7 grade or above is more dangerous,and needs to be focused.