Abstract
The Niigataken Chuetsu-oki earthquake in 2007 occurred west of Kashiwazaki in Niigata Prefecture, central Japan on July 16, 2007. We present an overview of crustal deformation and fault models associated with the earthquake estimated from geodetic measurements including GPS, interferometric SAR (InSAR), and leveling. Although it is difficult to determine which plane in two conjugate planes of the focal solution ruptured solely from the observed geodetic data, the data can be explained by slip on a southeast-dipping main-fault suggested by the aftershock distribution. A combination of the southeast-dipping main-fault and a northwest-dipping subfault gives a reasonable explanation of supplemental relation of the coseismic slip and the aftershocks. The Chuetsu-oki earthquake manifests that the present density of the GEONET stations is not enough to select a ruptured plane from two nodal ones for an inland earthquake with a magnitude of 7 and less. InSAR reveals not only a large deformation near the source area of the earthquake but also a local uplift along the anticline axis of an active fold, 15 km east of the earthquake epicenter. This narrow zone of uplift suggests the episodic growth of active folds, which is triggered by a coseismic stress change. The leveling data for about 110 years suggest the uplift have continued with a rate of 2-4 mm/yr for ~40 years. These geodetic data show that the growth rate of active folds temporally changes in short timescale. We propose that understanding of aseismic deformation including active folds is important to assess the earthquake potential in the Niigata-Kobe Tectonic Zone.
