A two-dimensional finite element model was constructed along a cross section almost perpendicular to the Nagamachi-Rifu Fault Zone, in order to clarify the stress accumulation process on an intraplate earthquake fault. We explain the surface deformations observed by the dense GPS network and leveling surveys using models with heterogeneities in the crust. These heterogeneities are identified from various geophysical surveys in the region. We found that the observed surface deformations cannot be explained by a model having a weak zone in the upper crust, but can be explained by models having a weak zone in the lower crust. Models having an aseismic fault or fault zone in the lower crust can reproduce the spatial pattern of the observed deformations, but amplitudes predicted by these models are smaller than those observed. The weak zone in the lower crust probably plays an important role in the stress accumulation process on the Nagamachi-Rifu fault zone.
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