The mechanism of postseismic deformation triggered by the 2006-2007 great Kuril earthquakes

摘要

In 2006-2007, a doublet of great earthquakes (M_w > 8) struck in the center of the Kuril subduction zone, a thrust event followed by an extensional event. Our observations of the Kuril GPS Array in 2006-2009 outline a broad zone of postseismic deformation with initial horizontal velocities to 90 mm/a, and postseismic uplift. We show that most of the postseismic signal after the great Kuril doublet is caused by the viscoelastic relaxation of shear stresses in the weak asthenosphere with the best-fitting Maxwell viscosity in the range of (5-10) × 10~(17) Pa s, an order of magnitude smaller than was estimated for several subduction zones. We predict that the postseismic deformation will die out in about a decade after the earthquake doublet. Our results suggest large variations among subduction zones in the asthenospheric viscosity, one of the most important rheological parameters.