Estimation of Site Effects and Q Factor Using a Reference Event

The site effects and the quality factor were inverted by applying the spectral ratio technique with the variation of using one of the earthquakes as a reference event instead of a reference site. The spectral ratios were written as logarithmic summations that allowed us to retrieve the absolute site amplification and Q. We tested this inversion scheme by first inverting synthetic data that contained different levels of noise, and then by changing the seismic moment and the corner frequency of the reference event. Finally, we used data from two strong motion networks (K-Net and KiK-Net) that recorded the aftershocks of the 2000 Tottori, Japan, earthquake to estimate the site effects at those sites. Since the KiK-Net stations had instruments located at the surface and at depth, we performed two inversions: one using the surface records and the other using the borehole records. Our results indicate that there is amplification at the borehole sites although it is smaller than the amplification at the surface sites.