Cross-scale model of seismic cycles of great subduction earthquakes
Subduction is substantially multi-scale process where the stresses are built by long-term tectonic motions, modified by sudden jerky deformations during earthquakes, and then restored by following multiple relaxation processes. In collaboration with RU 4, we develop a cross-scale thermomechanical models aimed to simulate the subduction process from ca. 1 minute (earthquake) to million years’ time scale. It generates spontaneous earthquake sequences and recreates the deformation process as observed naturally during the seismic cycle and multiple seismic cycles. A surprising prediction of the model is that the viscosity in the mantle wedge drops by more than 3 orders of magnitude during great earthquakes with magnitude above 9. As a result, the postseismic transient deformation after just an hour or day is controlled by visco-elastic relaxation in a several hundred km wide mantle wedge and not by the afterslip localized at the fault as it is currently believed. The model also demonstrates that there is no contradiction between extremely low mechanical coupling at the subduction megathrust in South Chile inferred from long-term geodynamic models and appearance of the largest earthquakes, like the Great Chile 1960 Earthquake.
See more in Sobolev and Muldashev (2017)