Coseismic deformation of the 2007 Chuetsu-oki earthquake derived from PALSAR/InSAR and its fault model

The 2007 Chuetsu-oki earthquake (M(j) 6.8) occurred offshore of Niigata Prefecture, northeast Japan, on 16 July 2007. 1 applied PALSAR/InSAR to detect coseismic deformation associated with the earthquake. The interferogram generated from descending data revealed a slant-range shortening exceeding 20 cm in the coastal area of Kashiwazaki adjacent to the epicenter and a maximum slant range extension of approximately 15 cm southeast of the slant-range shortening pattern. The interferogram generated from descending data is consistent with GPS displacements, but the non-crustal deformation component was large in the interferogram generated from ascending data. Based on a fault plane dipping to the southeast, a fault-slip distribution was estimated from the descending interferogram and GPS displacements. The largest fault-slip was located in the southwestern deeper part of the mainshock hypocenter. In the northern part of the focal region, the fault-slip was dominant at depths of 5-15 km, but it Was limited to shallower depths in the Southern part of the focal region. Such fault-slip distribution is consistent with the aftershock distribution. This consistency Supports the assumption that the fault rupture in the mainshock has primarily occurred in the nodal plane dipping to the southeast.