ESTIMATES OF REGIONAL AND LOCAL STRONG MOTIONS DURING THE GREAT 1923 KANTO, JAPAN, EARTHQUAKE (MS-8.2) - PART 1 - SOURCE ESTIMATION OF A CALIBRATION EVENT AND MODELING OF WAVE-PROPAGATION PATHS

This article is the first of a pair of articles that estimate regional and local strong motions from the 1923 Kanto, Japan, earthquake. This Ms 8.2 earthquake caused the most devastating damage in the metropoli tan area in Tokyo history. In this article, we first calibrate wave pr opagation path effects with a moderate-sized modern event. This event, the Odawara earthquake of 5 August 1990 (M 5.1), is the first earthqu ake larger than M 5 in the last 60 years near the hypocenter of the 19 23 Kanto earthquake. We estimate the source parameters based on a grid -search technique using body-waveform data bandpass filtered from 1 to 10 sec at four local stations, because accurate source parameters are critical for calibrating the propagation effects. We find that the Od awara earthquake had a depth of 15.3 km, a dip of 35 degrees, a rake o f 40 degrees, a strike of 215 degrees, a seismic moment of 3.3 x 10(23 ) dyne-cm, a source duration of 0.65 sec, and a stress drop of 170 bar s. Next, we investigate the effects of the propagation paths to the lo cal and regional stations where seismograms of the 1923 Kanto earthqua ke were recorded, by comparing recorded waveforms with synthetic seism ograms built with the calibration event. Path-specific flat-layered ve locity models are estimated along travel paths from the event to stati ons Hongo (epicentral distance R = 82 km) in Tokyo, Gifu (R = 213 km), and Sendai (R = 374 km) using forward modeling. In constructing the v elocity model for the Gifu station, we use STS-1 broadband seismograms recorded at the nearby Inuyama station. Consequently, at periods grea ter than 3 sec, the velocity models for stations Hongo and Gifu can su ccessfully reproduce both body waves and direct surface waves, and the velocity model for Sendai station can explain the predominant direct surface waves. In the companion article (Sate et al., 1998), these vel ocity models are used to examine the adequacy of the variable-slip rup ture models of the 1923 Kanto earthquake (Wald and Somerville, 1995; T akeo and Kanamori, 1992) to explain recorded seismograms and also to s imulate strong motions from that event.