Post-Seismic Crustal Deformation Associated with the 1995 Hyogo-ken Nanbu Earthquake Derived from GPS Observation. Preliminary Analysis of Trimble Data

Within 1 to 4 days following the 1995 Hyogo-ken Nanbu earthquake (M 7.2) that occurred on January 17, 1995, the Japanese University Consortium for GPS Research deployed more than 30 GPS receivers in the hypocentral area to investigate post-seismic activity. Of these stations, we analyzed data from 8 sites that were placed near the hypocentral area; six in Kobe and two in Awaji. Two methods of analysis were employed: 1) change of absolute geocentric coordinates were estimated by assuming Usuda global site, which is about 300 km northeast of the hypocentral area, as fixed, 2) analyses for short baselines were conducted within the hypocentral area using the automatic processing technique. Results suggest that 1) rapid displacements toward the southeast of more than 4cm/year were found at all of the analyzed sites, which might be part of a post-seismic deformation process, 2) largest of which was found at Rokko Farm site, at which displacement amounted to about 3 cm until the end of February, though its cause were not specified, and 3) local straining seems to be taking place at both Kobe and Awaji areas.