Lateral variation of body wave attenuation in crust of Bhutan Himalaya

We have studied the spatial variation of body wave (P and S wave) attenuation properties in crust of Bhutan region using small magnitude (2-4 M_L) earthquakes. We have used continuous waveform data of 385 local earthquakes recorded by the GANSSER network operated by Swiss Seismological Service at ETH Zurich. Initially, the attenuation quality factors (Q_p, Q_s) have been estimated using Extended Coda Normalization method for five different frequencies (1.5, 3,6,12,18 Hz) at each station, as well as for two zones (eastern and western Bhutan). Q₀ (Q value at 1 Hz) values are found to vary between 21-102 and 43-191 for P wave and S wave respectively for the whole region. We observe Q_p = (72 ± 6)f^{(0.94 ± 0.06)} and Q_s = (104 ± 6)f^{(1.03 ± 0.05)} for the eastern Bhutan whereas for the western part, Q_p = (28 ± 1)f^{(1.41 ± 0.03)} and Q_s = (90 ± 5)f^{(1.07 ± 0.05)} are found. Overall, frequency dependent coefficient values indicate the strong frequency dependent nature of Bhutan Himalaya. The spatial maps of Q₀ for both waves suggest P-wave attenuates faster in the crust of western Bhutan compared to the eastern part. Paro, located in eastern Bhutan, shows comparatively high attenuation for both P and S waves. Further, azimuthal variation of attenuation properties around each station has been evaluated. The observed results are in good agreement with the tectonic settings of the region. The estimated attenuation properties are well comparable with the tectonically active regions in the world.