Study On Seismic Effects Of Sichuan Basinconsidering Structural Inhomogeneity

Considering the lateral inhomogeneity of crustal structure on both sides of Longmen Mountain and the stratification of Quaternary soil layer in Sichuan Basin,a three-dimensional model of Sichuan Basin is established.Based on the spectral element method and parallel computing technology,the seismic response of the basin under the finite fault and point source rupture of the Wenchuan earthquake is simulated.By comparing the distribution of surface velocity peak value(PGV)and its ratio,profile time history and amplification coefficient simulated by different structural models,the influence of structural inhomogeneity on the simulation results of long period earthquake in Sichuan Basin is studied,and the change degree of basin model dimension,focal form and rise time on this influence is discussed.The results showed that:1.When the finite fault obtained by Ji&Hayes inversion is used as the source,the PGV ratio between the uniform crustal model and the inhomogeneous crustal model ranges from0.9 to 1.2,and the area outside the basin between Maoxian-Pingwu-Qingchuan and some areas within the Sichuan Basin are significantly affected,while the influence of non-uniform crust is not obvious in other areas.Compared with the finite fault,the influence degree of the heterogeneous crust under the three-dimensional point source rupture is more prominent,the PGV ratio is between 0.6 and 2.6,and the scope of the affected area inside and outside the basin is larger.Under the point source fracture,the PGV ratio of the two-dimensional basin model is the largest,which can reach more than4.5,and the affected area is concentrated in the basin.In addition,in both 2D and 3D basin models with point source rupture,the influence of the inhomogeneous crust is significantly reduced when the source rise time is prolonged.2.Under the finite fault induced by Ji&Hayes inversion,the velocity peak values and amplification coefficients of the three components in the Sichuan Basin are significantly reduced,and the influence of the Quaternary layer stratification on the earthquake response in the Sichuan Basin is more significant than that of the heterogeneous crust.In addition,records show that the PGV value of Sichuan Basin is in the range of 0.2m/s-0.4m/s,and the simulated PGV value of Sichuan Basin decreases to the range of 0.3m/s-0.6m/s after the stratification of Quaternary soil layers,which makes the model more reliable.Compared with the finite fault source obtained by Ji&Hayes inversion,the ground motion effect of the four models under the USGS source effect is significantly reduced,and the ground motion effect of the Sichuan Basin is relatively underestimated.