Separation of scattering attenuation and intrinsic absorption in Japan using the multiple lapse time window analysis of full seismogram envelope

Abstract

Two seismic wave attenuation factors, scattering attenuation (Qs−1) and intrinsic absorption (Qi−1), can be determined from estimates of two parameters, the reciprocal of extinction length Le−1 ≡ (Qs−1 + Qi−1) ·ω/v and seismic albedo B0≡ Qs−1 / (Qs−1 + Qi−1), where ω and v are angular frequency and seismic wave velocity, respectively. These parameters are measured using the multiple lapse time window analysis method over frequency bands of 1–2, 2–4, and 4–8 Hz from 16 stations located throughout Japan. In the analysis, time‐integrated seismic wave energy from earthquakes having hypocentral distances less than 120 km and focal depths less than 40 km are compared with simulations of multiple isotropic scattering based on the assumption of spatial uniformity of Qs−1 and Qi−1. The modified coda normalization method is used to correct for sources and site effects, where the spatially non uniform distribution of the coda wave energy is considered. The Le−1 estimates do not have a distinct frequency dependence, but the Be estimates do: 0.2–0.7 for 1–2 Hz and 0.1–0.3 for 4–8 Hz. The results mean that Qs−1 is similar to Qi−1 for 1–2 Hz but is 3–5 times smaller for 4–8 Hz and that the frequency dependence of Qs−1 is larger than Qi−1. Analyses using different components of motion and different window lengths give nearly the same results. Coda attenuation (Qc−1) estimates based on the single scattering approximation are nearly equal to intrinsic absorption Qi−1 rather than to total attenuation (Qs−1 + Qi−1) for Japan.