Empirical Spectral Characteristics of the Medium near Strong-Motion Seismic Stations of Kamchatka

Abstract

Abstract—Spectral characteristics of the medium around 23 digital strong-motion seismic stations of Kamchatka region have been studied from local earthquake data relative to a reference bedrock station (Petropavlovsk, PET). Spectra are determined by multiband filtering. In each band peak velocity amplitudes, levels of Fourier S-spectra and mean-square coda amplitudes were compared. Average Fourier spectra were obtained from S-wave energy using Parseval’s equation. The difference in hypocentral distances for pairs of stations was compensated by empirical S-wave attenuation functions. Records of more than 300 events were processed, with M = 5–6 and hypocentral distances mainly 100–600 km. The spectral ratios estimated by the three methods show behavior diversity. Some non-rock stations show expected spectral characteristics at high frequencies. The conditions at other stations can be considered similar to those at PET. Some stations show amplifications of up to 10 times in the 20–30 Hz frequency range. In general, the obtained spectral characteristics within 3–5 Hz are consistent with the expected trends corresponding to known local geology around strong-motion stations.