Spatial variation of body wave attenuation in Garhwal-Kumaun Himalaya region, India

Abstract

We have investigated the spatial variation of body wave attenuation in Garhwal-Kumaun Himalaya region from the datasets of 465 well located earthquakes, recorded at 52 broadband stations between 2017 and 2020. The body wave attenuation parameters $Q_P$ and $Q_S$ were estimated at each station by applying the extended coda normalization method for five different central frequencies ranging from 1.5 to 18 Hz. Strong frequency-dependent body wave attenuation was observed at each station over the whole region. Also, we found a significant variation of $Q_P$ and $Q_S$ from north to south which is consistent with geotectonic diversity beneath the study region. We have also made separate estimations of frequency-dependent relations for Garhwal and Kumaun Himalaya region in order to investigate the lateral variation in attenuation characteristics, and obtained the frequency-dependent relations as follows: $Q_P=\left(30\pm 3\right)f^{\left(1.05\pm 0.05\right)}$, $Q_S=\left(143\pm 20\right)f^{\left(0.88\pm 0.07\right)}$ for the Garhwal Himalaya region and $Q_P=\left(31\pm 1\right)f^{\left(1.09\pm 0.02\right)}$, $Q_S=\left(121\pm 11\right)f^{\left(1.00\pm 0.04\right)}$ for the Kuamun Himalaya region. Obtained $Q$ values indicate strong body wave attenuation for both the region with no significant lateral variation. It may suggest the presence of crustal level folding, faulting, aqueous fluids, and metamorphic fluids below both the regions. Also, the ratios of $Q_S$/$Q_P$ are high ($>1$) for the entire analyzed frequency range, suggesting a significant level of heterogeneity and tectonic complexities in the crust of the study region.