Frequency-Dependent Attenuation of<i>P</i>and<i>S</i>Waves In the Kanto Area, Japan, Based On the Coda-Normalization Method

TLDR

The study proposes an extended coda‑normalization method to simultaneously measure P‑ and S‑wave attenuation. The method was applied to 174 local‑earthquake seismograms in the Kanto area, measuring frequency‑dependent P‑ and S‑wave attenuation from 1.5 to 24 Hz. Frequency‑dependent attenuation follows power laws Qs⁻¹ = 0.012 f⁻⁰.⁷³ and Qp⁻¹ = 0.031 f⁻⁰.⁹⁵, with Qp⁻¹/Qs⁻¹ > 1 across the range, similar P‑ and S‑wave attenuation above 1 Hz, and the results imply scattering loss dominates at these frequencies.

Abstract

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.