Variable-slip rupture models for large earthquakes, obtained by the source inversion of long-period (> 4 sec) seismic waves, are taken into account in a semi-empirical method for simulating broadband (< about 10 sec) strong ground motions. The high-frequency (> 0.25 Hz) source spectrum of the (p,q)-th sub-fault is inferred by the omega-squared model with two circular corner frequencies. The first is Vpq /Dpq, due to the temporal integration of the slip-velocity time function, where Vpq is the maximum slip velocity and Dpq is the final slip. The other is 2ƒÀpq /ƒÉpq, due to the spatial integration of the slip-velocity time function on the sub-fault, where ƒÀpq is the S-wave velocity of the medium and ƒÉpq is the equivalent radius of the sub-fault. Here, Vpq, Dpq, ƒÀpq, and ƒÉpq are specified by the long-period source-inversion results.
The method is applied to the variable-slip rupture model for the 1923 Kanto, Japan, earthquake of MS 8.2 obtained by Wald and Somerville (1995). This earthquake is one of the most important earthquakes for the mitigation of earthquake disaster in the Tokyo metropolitan area; unfortunately, strong motion records for this earthquake were off-scaled in the region of strong shaking and significant damage.
The simulated velocity at Yayoi, Tokyo, shows a good agreement with the Kanto earthquake record observed at Hongo, Tokyo, whose off-scaled parts were restored as well as possible by Yokota et al. (1989). The instrumental JMA seismic intensities of the simulated accelerations at Tokyo JMA and Yokohama JMA are consistent with the observed JMA seismic intensity 6. The instrumental JMA seismic intensities of the simulated accelerations at Tateyama JMA and a soil site in Odawara are also consistent with the JMA seismic intensity 7, estimated from the ratio of collapsed houses (Mononobe, 1925).
The simulated broadband (0.1 to 10 sec) motions will be useful in the mitigation of earthquake disaster in the Tokyo metropolitan area.