Abstract
The three-dimensional viscoelastic crustal structure beneath Japanese islands was modeled to simulate their crustal deformation by using a finite-element method and applying boundary conditions of the east-west horizontal compression. The result shows that there are relatively narrow zones of high strain rate at shallow depths, whose pattern is similar to that of the Niigata-Kobe tectonic zone revealed by GPS. High strain rates are not necessarily concentrated in regions where the elastic layer is relatively thin, but rather where its thickness changes abruptly.
Highlights
A strong three-dimensional (3D) nonuniformity is likely to exist in the thermal structure of the crust and the upper mantle beneath Japanese islands, where cool oceanic plates are subducting while hot melts are rising from the mantle (Nakajima and Hasegawa, 2009) (Fig. 1)
We used the experimental results of quartz, anorthite, and olivine to model the viscosity for the upper crust, lower crust, and upper mantle, respectively (Table 1)
The strain rate is high on the coast of Niigata in the Sea of Japan and further north, and on the Pacific Ocean coast. This distribution pattern at locations other than the north of northeastern Japan along the Pacific Ocean coast corresponds well with the deformation concentration zone inferred from the GPS data, known as the Niigata-Kobe tectonic zone (NKTZ)
Summary
A strong three-dimensional (3D) nonuniformity is likely to exist in the thermal structure of the crust and the upper mantle beneath Japanese islands, where cool oceanic plates are subducting while hot melts are rising from the mantle (Nakajima and Hasegawa, 2009) (Fig. 1) This nonuniformity is expected to affect the viscoelastic structure and cause deformation of the islands. We conducted numerical simulations of the crustal deformation of Japanese islands, with the ultimate goal of longterm (a few decades) forecasting of inland large earthquakes (Fig. 2) To this end, Cho and Kuwahara (2013) have modeled the thermal structure of the crust and the upper mantle beneath Japanese islands. It may become possible to model, for example, the postseismic crustal deformation after the 2011 Tohoku earthquake
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