Statistical Spectral Model of Earthquakes in the Eastern Tohoku District

a 20- × 20-km region in Sendai. In our previous tudy, we defined aPliocene layer, whose S-wave velocity Vs is greater than 500 m/sec and whose N value of the stan-dard penetration test is greater than 50, as engineering bedrock in Sendai and cal-culated 304 engineering bedrock waves (hypocentral distance X = 15 to 300 km) by removing the site response between the engineering bedrock and the surface. As the second stage of our study toward a quantitative prediction of strong ground motions of horizontal components, we propose here a statistical spectral model of the engineering bedrock waves by introducing the site response between the pre-Tertiary bedrock (Vs ~ 3000 m/sec) and the engineering bedrock (Vs ~ 500 to 700 m/sec) and a frequency-dependent Q into Boore's spectral model. We separate the site response between the pre-Tertiary bedrock and the engineering bedrock, an at-tenuation function, and source spectra from the engineering bedrock spectra by as-suming an co- 2 model with the seismic moment M0 from the Harvard CMT solution estimated for earthquakes of M s> = 5.3. Initial values of comer frequency f0 are determined based on a previous empirical M 0- f0 relationship in this district. Usin