Nonlinear site response from the 2003 and 2005 Miyagi-Oki earthquakes

抄録

We estimate nonlinear site response by comparing site response estimates from the 16 August 2005 Mj=7.2 and 26 May 2003 Mj=7.0 Miyagi-Oki earthquakes with site response estimates from aftershocks of the 2003 event. Site response is solved by a spectral inversion technique to separate source, path, and site components. The constraint motion in the inversion is a regional attenuation model derived from fitting the spectra of data recorded at borehole KiK-net stations in the region and a theoretical source spectrum for each event determined using the same borehole stations. Site response is calculated at the surface of the KiK-net and K-NET stations. In general, the average aftershock site response is larger than for the two mainshocks, especially at a higher frequency. When comparing site response with input ground motion level, the predominant frequency and the site response values tend to decrease as the level of input ground motion increases.