固体地球物理学术报告通知-胡岩

It is well known that great subduction zone earthquakes produce coseismic and postseismic deformation that can be detected thousands of kilometers from the rupture area. However, fully understanding of the deformation processes at different temporal and spatial scales has yet to be improved. In this work, we have studied the postseismic deformation of the 2011 Mw9.0 Tohoku and 1964 Mw9.2 Alaska earthquakes. We have developed three-dimensional viscoelastic finite element model in Earth that includes the elastic continental plate and subduction slab, viscoelastic mantle wedge, viscoelastic oceanic asthenosphere and upper mantle. The viscoelastic relaxation of the rheological units is represented by the bi-viscous Burgers rheology. The Kelvin transient viscosity is assumed to be one order of magnitude lower than that of the Maxwell steady- state viscosity. Afterslip of the megathrust is simulated through a 2-km thick shear zone attached to the fault. Our optimized model well reproduces the present GPS velocities following both Tohoku and Alaska earthquakes. Our model has determined the Maxwell viscosity of the mantle wedge to be 3x10^19 Pa s near the trench and about one order of magnitude higher in inland areas farther from the 600 km depth contour of the subduction slab. Afterslip takes place immediately after the earthquakes and decays rapidly with time (mostly within the first five years after the earthquake).