Joint inversion of near- and far-field waveforms and geodetic data for the rupture process of the 1995 Kobe earthquake

The geodetic data, strong-motion waveforms, and far-field waveforms from the 1995 Robe earthquake (M-JMA 7.2) were inverted to determine the rupture process. The geodetic data, including the horizontal displacements measured at 43 stations and the vertical displacements measured at 61 stations, were provided by the Geographical Survey Institute of Japan and the Japanese University Consortium for GPS Research. We assumed two fault planes, one each Awaji Island and Kobe, with different strike directions and dip angles, and which were consistent with the active fault map and the aftershock distribution. We first inverted the geodetic data alone to determine the heterogeneous distribution of slip on the assumed faults. Second, the strong-motion records provided by the Japan Meteorological Agency, the Committee of Earthquake Observation and Research in the Kansai Area, and the Robe City government were inverted to obtain the temporal variation of slip. Third, the displacement waveforms of far-field P- and SH-waves were analyzed. Finally, we performed a triple joint inversion to determine the source model most suitable for explaining all the data sets. The solution of the joint inversion expressed very strong ground motions, which well simulated the ones observed in Kobe at frequencies lower than 1 Hz. Concentrated slips are recovered in the shallow northeastern portion of the Nojima fault on Awaji Island and beneath the Strait of Akashi between Awaji and Kobe. Using the geodetic data, we also examined the possibility of another hidden fault beneath the extremely damaged area in Kobe, but matching of the data was not improved by the introduction of this fault.