Estimate of the path-averaged Q value for S-wave at low frequencies

Abstract

 We propose a new method to estimate the path-averaged Q_S-value at low-frequencies (<0.5 Hz). In this method, we measure the decay rate of the observed S-wave spectral amplitudes against the travel times; the spectral amplitudes are corrected for effects of the S-wave radiation pattern and site amplification due to the deep sedimentary layers. The corrections are done by using the theoretical S-wave spectral amplitudes calculated assuming the perfect elastic body and the appropriate source and site amplification models; the result of this method depends on accuracy of the source and site amplification models. We examine validity of this method and effects of inappropriate source and site amplification models on an estimate of the Q_S-value. Finally, we apply this method to estimate the Q_S-value within the back-arc side mantle wedge beneath Kyushu islands. The estimated Q_S-value is about 50 in the frequency range of 0.2 to 0.3 Hz.