新潟－神戸ひずみ集中帯を横断する測地観測による越後平野周辺の地殻変動

Abstract

We examined GEONET GPS data to clarify the contemporary deformation in and around the Echigo plain, Niigata prefecture where located in the Niigata-Kobe tectonic zone and the deformation zone of the eastern margin of the Japan Sea. Compressional strain in a direction of ESE-WNW is concentrated in a narrow zone where strain rate is about 0.2ppm/yr along the coast of the Japan Sea. This strain concentration zone which is about 25km wide accommodates more than 5mm/yr of compression and geographically corresponds to the Echigo plain. The zone significantly subsided whereas surrounding regions was uplifted. These characteristics of the deformation are concordant with that measured by conventional geodetic surveys spanned more than several decades. The strain rate observed by GPS does not change significantly during more than a decade in the strain concentration zone except for coseismic periods, which is contrast with a large temporal change of a strain rate in the eastern region affected by a subduction of the Pacific plate. We proposed a simple model to explain the characteristics of the deformation. The model consists of stable sliding on a deep part of reverse faults which are extended to the east and west rims of the Echigo plain. Fault geometry penetrating the crust and calculation with gravitational viscoelastic asthenosphere is essential to reproduce the observed subsidence in the strain concentration zone.