Coda wave attenuation characteristics for Kumaon and Garhwal Himalaya, India

Uttarakhand Himalayas are among one of the most seismically active continental regions of the world. The Himalayan belt in this region is divided into Kumaon and Garhwal Himalaya. The Kumaon Himalayas has not experienced any large earthquake in the recent past; however, this region is frequently visited by small-magnitude earthquakes. The objective of this paper was to determine regional attenuation characteristics from data recorded by local strong motion networks operating in these two regions, using coda waves. Coda wave quality factor estimates for the Kumaon and the Garhwal Himalaya region have been made in high-frequency range using single backscattering model given by Aki and Chouet (J Geophys Res 80: 3322-3342, 1975). Coda waves of 30-s window length, filtered at six different frequency bands, centered at 1.5, 3.0, 6.0, 12.0, 20.0 and 28.0 Hz, have been analyzed using the single backscattering method. The frequency-dependent Q(c)(f) relationship for the Kumaon and Garhwal Himalaya was obtained as Q(c) = (65 +/- 2.4)f((1.07+.04)) and Q(c) = (96 +/- 6.9)f((1.06+.04)), respectively, which indicate a higher attenuating medium in the Kumaon Himalaya as compared to Garhwal Himalaya. The obtained difference of attenuation characteristics in this region is further compared with the rate of decay of peak ground acceleration with respect to magnitude and distance parameters by using regression model of peak ground acceleration obtained from available strong motion data in this region. Present studies clearly indicate that there is good evidence for high rate of attenuation in the Kumaon Himalaya as compared to the Garhwal Himalaya.