Coulomb stress interaction among strong earthquakes around the Bayan Har block since the Manyi earthquake in 1997

Using the crustal structure model and precise earthquake source model,we have calculated the coseismic and viscoelastic postseismic deformation field of the Manyi,Kokoxili, and Wenchuan earthquake.The results show as follows:the source fault of the Kokoxili earthquake has got energy accumulated in the postseismic deformation field of the Manyi earthquake,while the source of the Wenchuan earthquake has not been apparently affected by the Manyi and Kokoxili earthquakes.The postseismic deformation field of all the 3 previous earthquakes has got significant dextral deformation trend across the Yushu fault,which makes it more dangerous.After that,the Coulomb stress changes have been obtained after the projection of the changed stress field.We have found that the Coulomb stress of the Kokoxili earthquake, which was produced by the Manyi earthquake,changed from negative to positive.The Coulomb stress near the source of the Wenchuan earthquake changed negligibly after the Manyi and Kokoxili earthquake.But the Coulomb stress of the initial rupture point of the Yushu earthquake,generated by all the 3 previous earthquakes,has increased about 0.012 MPa,larger than the threshold for earthquake triggering.Finally,we have got the yearly accumulation value via the relationship between the slip rate and the stress accumulation,and calculated the ratio of the influence value and yearly accumulation value.It is shown that the influence degree among the studied strong earthquakes is not large enough,even the largest one is only about 1 year s acceleration on the Yushu fault by the Kokoxili earthquake.To sum up,the influence from distant strong earthquakes is still not obvious even the viscoelastic stress changes have been taken into account.The energy accumulation is the decisive factor of the strong earthquakes successively occurred in a short period on the boundary fault of the same block.