Frequency-dependent attenuation of P and S waves in northeast India

Abstract

We have analysed 202 seismograms recorded at 10 seismic stations in the northeast (NE) India region to infer the frequency-dependent attenuation characteristics of both P and S waves, in the frequency range from 1.5 to 24 Hz and in the distance range from 30 to 100 km. We used extended coda-normalization method to determine the attenuation of P wave (Q−1P) and S wave (Q−1S). The results show that both P and S waves undergo a strong attenuation along ray paths. The values of Q−1P and Q−1S, corresponding to spectral amplitude decays, show strong frequency dependence and are expressed as Q−1P = (0.035 ± 0.014)f−(0.96±0.01) and Q−1S = (0.014 ± 0.006)f−(0.94±0.03), respectively, in 1.5–24 Hz. The ratio Q−1P/Q−1S is found to be larger than unity for the whole frequency range. The high frequency dependence of both P- and S waves indicate the highest attenuation among the world at lower frequencies.