Modeling of co- and post-seismic surface deformation and gravity changes of M_W6.9 Yushu, Qinghai, earthquake

Based on the elastic dislocation theory, multilayered crustal model, and rupture model obtained by seismic waveform inversion, we calculated the co- and post-seismic surface deformation and gravity changes caused by the Yushu M_W6.9 earthquake occurred on April 14, 2010. The observed GPS velocity field and gravity field in Yushu areas are disturbed by the co- and post-seismic effects induced by Yushu earthquake, thus the theoretical co- and post-seismic deformation and gravity changes will provide important modification for the background tectonic movement of Yushu and surrounding regions. The time relaxation results show that the influences of Yushu earthquake on Yushu and surrounding areas will last as long as 30 to 50 years. The maximum horizontal displacement, vertical uplift and settlement are about 1.96, 0.27 and 0.16 m, respectively, the maximal positive and negative value of gravity changes are 8.892×10^-7 m.s^-2 and -4.861ׁ10^-7 m.s^-2, respectively. Significant spatial variations can be found on the co- and post-seismic effects: The co-seismic effect mainly concentrates in the region near the rupture fault, while viscoelastic relaxation mostly acts on the far field. Therefore, when using the geodetic data to research tectonic motion, we should not only consider the effect of co-seismic caused by earthquake, but also pay attention to the effect of viscoelastic relaxation.