A viscoelastic model of interseismic strain concentration in Niigata-Kobe Tectonic Zone of central Japan

Abstract

The high strain rates of the Niigata-Kobe Tectonic Zone (NKTZ) of central Japan have been simulated using a viscoelastic finite element model of great interplate earthquake cycles that includes the subducting Pacific plate and lateral changes in crustal structure beneath NKTZ. As a result of long-term loading at trenches, the elastic crust over a viscoelastic mantle can transfer stress or strain rate not only as an average of geological time scales, but also during an interplate earthquake cycle. Thus, if the earthquake cycle is several times longer than the relaxation time of the viscoelastic system, deformation of an inland area far from trenches responds to the cycles of interplate earthquakes, and the crust deforms like an elastic sheet during the later stage of an earthquake cycle, allowing efficient transmission of stress during this period. Therefore, in the case of long interplate earthquake cycle, the NKTZ crustal structure with small thickness and rigidity enhances local interseismic strain concentration there. The “plate coupling ratio” (0.4∼0.5) between Pacific and Amurian plates and local crustal heterogeneity beneath the high strain rate zone explain the large strain rate belt if the earthquake cycle offshore Kanto is enough long.