Frequency-Dependent Attenuation ofPandSWaves In the Kanto Area, Japan, Based On the Coda-Normalization Method

Abstract

Summary We propose a new method for the simultaneous measurement of P- and S-wave attentuation by extending the conventional coda-normalization method which had been limited to the estimation of S-wave attenuation. Using this method, we measured frequency-dependent attenuation of both P and S waves in the lithosphere beneath the Kanto area, Japan, from seismograms of 174 local earthquakes for the frequency range 1.5 ≤f≤ 24 Hz. the values of Qs−1 and Qp−1 corresponding to peak amplitude decays show strong frequency dependence, and are expressed by using power laws QS−1=0.012f−0.73 and QP−1= 0.031f−0.95, respectively. the ratio QP−1/QS−1 is found to be larger than unity for the whole frequency range. the apparent attenuations of P and S waves with travel distance are almost the same for frequencies higher than 1Hz. Our results differ from the characteristics of low-frequency wave attenuation reported by other studies for frequencies lower than 1 Hz. This frequency dependence and the ratio may suggest that scattering loss due to random heterogeneities in the earth medium plays an important role in seismic-wave attenuation in the lithosphere.