Synthetic aperture radar interferogram of the 1995 Kobe earthquake and its geodetic inversion

Crustal deformation from the Mw=6.9 January 17 (JST), 1995, Kobe, Japan earthquake was detected by synthetic aperture radar interferometry (SAR). More than four fringes with ellipsoidal shape were observed surrounding the Nojima fault on northern Awaji island suggesting a shortening in the range of more than 11.75 x 4 cm on the east side of this fault. The SAR sensor shows ellipsoidal fringes with an uplift zone in the Rokko mountain range and sharp subsidence around the Kobe area. In addition to SAR interferometry, leveling and GPS surveys were conducted by the Geographical Survey Institute of Japan (GSI). The permanent GPS observation sites of the GSI monitored ground displacements from this earthquake with daily updates. Based on these geodetic data, we estimated the faulting mechanism of the earthquake. The analytical procedure was an iterative linearized least squares method. A multi-fault system consisting of six subfaults was constructed. The locations of the estimated model faults were close to those of the active faults in this area, running from the Nojima fault on Awaji island to the Rokko faults in the Kobe area with a change in strike angle near the Ohtsuki fault in the Kobe area. The slip vectors of the Nojima fault on Awaji island had a large component of reverse dip-slip of about 2 m and strike slip of about 2 m. In the Kobe area, the amount of slip ranged from 0.3 to 1.2 m and was small compared with the slip on the Nojima fault. The results of these slip vectors agreed well with the results of other seismic, geodetic, and field studies.