VARIABLE-SLIP RUPTURE MODEL OF THE GREAT 1923 KANTO, JAPAN, EARTHQUAKE - GEODETIC AND BODY-WAVE-FORM ANALYSIS

The available geodetic and teleseismic data sets for the 1923 Kanto ea rthquake (M(s) = 8.1) have been combined into a joint inversion for bo th temporal and spatial slip variations. We assumed an initial faultin g model to be consistent with the geometry determined by Kanamori (197 1) on the basis of first-motion data, aftershock area, and the amplitu de of surface waves at teleseismic distances and also to enclose the s lipped area estimated by Matsu'ura et al. (1980) from the geodetic dat a employed here. We then inverted for a heterogeneous distribution of slip of the fault plane. The leveling routes and triangulation station s used (consisting of 225 bench marks and 31 triangulation points) are from Matsu'ura et al. (1980). We chose to first determine the overall , static slip distribution by inverting the geodetic data alone. We th en proceeded to gradually increase the importance of the teleseismic d ata, always requiring a good fit to the geodetic leveling and horizont al displacements. In this way, we could provide a constraint on the ov erall static slip characteristics from the geodetic data and provide s tability for the teleseismic inversion, yet determine the degree of sl ip heterogeneity and time history most suitable for matching the wavef orm data and for simulating strong ground motions. Our analysis yields a seismic moment of 7 to 8 x 10(27) dyne-cm (M(w) = 7.8 to 7.9) with a maximum slip of approximately 8 m. The most concentrated slip is in the shallow central and western portion of the fault. The location of the concentrated slip on the fault plane has important consequences fo r the amplitude; duration, and frequency content of the resulting grou nd motions as documented by Takeo and Kanamori (1993).