Q ANISOTROPY IN THE REGION OF GARHWAL HIMALAYA

Abstract

Empirical relations have been found out to describe the decay in amplitude with distance of s-waves in the region of Garhwal Himalaya. These functions results from the analysis of spectral amplitudes of three component digital records from 19 local earthquakes obtained from 12-station seismological network deployed in the Garhwal lesser Himalaya. The events lie in a magnitude range from ML 2 to ML 4.5, epicentral distance 5 km to 120 km and focal depth from 5 km to 50 km. To determine the variations of the quality factor Q in the direction of wave propagation (Q anisotropy), independent estimates have been made of the attenuation of SV- and SH-waves using vertically polarized and transversely polarized components, respectively. Frequency analyzed (1-12 Hz) and in the whole distance range, the frequency dependence of Q can be approximated as Qh = for the SH-wave and Q = 81.5 f °95 for the SV-waves. The small difference between SH and SV spectral decay, suggests that Q anisotropy is negligible. However, In the distance range of 5-50 km, Q tends to be significantly greater than Qh at frequency > 8 Hz. So in this distance range we observed Q anisotropy in the studied region. The dependence of Q value with frequency in this range is Qh = 110 f°94 for SH- wave and Q = 134 f' ° for SV-waves.