Simultaneous Inversion of Geodetic and Strong Motion Data for the Source-Process of the Hyogo-ken Nanbu, Japan, Earthquake.

Abstract

We analyze strong ground motions and geodetic data simultaneously with the multiple time-window method in order to infer the source process and the fault geometry of the Hyogo-ken Nanbu earthquake . Considering aftershock distribution and geodetic data, we assume two faults with a step-over near the hypocenter and different strike angles: a northeastern fault (Fault #1) and a southwestern fault (Fault #2) . We divide Fault #1 further into two parts with different dip angles. Large slip occurred at the deeper part (below 8 km) of Fault #1. The rupture propagated smoothly along this area, but decelerated near the boundary of the above-mentioned two parts of Fault #1. We therefore believe that the boundary is a geometric barrier. Large slip occurred over the entire area of Fault #2. The rupture at the shallower part of the fault was of long duration . The seismic moment is estimated to be 2.9×1019Nm. The geodetic data clearly suggest that Faults #1 and #2 have a step-over at a shallower part beneath northern Awaji Island. We also consider other fault configurations . When not dividing Fault #1, some of the geodetic data cannot be explained. We invert the data, assuming the one-fault model whose shallower part bends to the northwest at the southwestern side, and this model explains the data as well as the previous one. In this sense, we cannot deny that the two faults connect at a deeper part . Comparing our results with previous inversion results, we found that two characters of main-shock faulting relate to the magnitude of the largest aftershocks: fault segmentation and slip distribution along the dip direction . This suggests that a detailed investigation of the source process of a main shock is useful for predicting the magnitude of the largest aftershock.