S-wave envelope broadening characteristics of microearthquakes in the Canary Islands

摘要

This study analyzes the S-wave envelope broadening characteristics of 290 earthquakes recorded by 14 stations of the Spanish National Seismograph Network in the Canary Islands region. The S-wave peak delay time (t_p) and envelope duration (t_q) parameters are evaluated phenomenologically to infer the strength of velocity inhomogeneities of the medium along each seismic ray path. Crustal (0 ≤ h ≤ 18 km) and upper mantle (18 < h ≤ 80 km) events are analyzed separately. Results in the frequency range 1 to 12 Hz for hypocentral distances from 30 to 600 km show that both t_p and t_q increase according to a power of hypocentral distance and they are independent of frequency. The spatial distribution of the peak delay time reveals weak strength of heterogeneity in most of the region at shallow depths. Relatively strong inhomogeneous zones are generated under the island of Tenerife and Gran Canaria at depths of 11-22 km.