Diffusion of crustal deformation from disturbances arising at plate boundaries—a case of the detachment beneath the Izu Peninsula, central Honshu, Japan—

We carry out numerical simulation of disturbance propagation within a plate floating over a viscous layer based on the 2-dimensional equations of Lehner et al. (1981). We apply the results to the anomalous crustal movements in central Honshu that followed the dike intrusion event between Miyakejima and Kozushima in the mid of 2000. We assume that the anomalous crustal movements represent diffusive transfer of a slip on the detachment beneath the Izu Peninsula, that occurred at the time of the dike intrusion event, over thin viscous layers such as the fault gouge of nearby great interplate earthquakes (Seno, 2005). From the arrival times of the disturbance in the Tokai district, the diffusion coefficient is determined to be 50–150 m²/s, and the viscosity of the fault gouge to be 10¹³–10¹⁵ Pa s. This value of viscosity is significantly smaller than that of the asthenosphere, and would probably be caused by the elevation of pore fluid pressure close to the lithostatic in the rupture zones of nearby great earthquakes. The serpentinized wedge mantle landward of the rupture zones may also constitute part of the thin viscous layers.