The ground motion excited by the Olyutorskii earthquake of April 20, 2006 and by its aftershocks based on digital recordings

Abstract

We studied broadband digital records of the M W = 7.6 Olyutorskii earthquake of April 20, 2006 and its aftershocks at local and regional distances. We have made a detailed analysis of data on peak ground motion velocities and accelerations due to aftershocks based on records of two digital seismic stations, Tilichiki (TLC) and Kamenskoe (KAM). The first step in this analysis was to find the station correction for soil effects at TLC station using coda spectra. The correction was applied to the data to convert them to the reference bedrock beneath the Kamenskoe station. The second step involved multiple linear regression to derive average relationshis of peak amplitude to local magnitude ML and distance R for the Koryak Upland conditions. The data scatter about the average relationshis is comparatively low (0.22–0.25 log units). The acceleration amplitudes for M L = 5, R = 25 km are lower by factors of 2–3 compared with those for eastern Kamchatka, the western US, or Japan. A likely cause of this anomaly could be lower stress drops for the aftershocks.