Abstract
Three-dimensional attenuation structure based on frequency-dependent shear wave quality factor, Q β (f), has been determined for the Kumaon region of the Himalayas. An algorithm based on inversion of strong motion data developed by Joshi (Curr Sci 90:581–585, 2006a) and later modified by Kumar et al. (Pure Appl Geophys, doi: 10.1007/s00024-013-0658-x , 2013) was used for determination of three-dimensional attenuation coefficients. The input of this algorithm is the spectral acceleration of the S phase of the accelerogram and the outcome is the attenuation coefficient and the source acceleration spectra. A dense network monitoring strong ground motion in the Kumaon region of the Uttarakhand Himalayas has been operating since 2006. This network recorded 287 earthquakes up to July, 2013, of which 18 were used for this work. Shear-wave quality-factors were estimated for frequencies of 1.0, 5.0, and 10.0 Hz for two rectangular blocks of surface of dimensions 85 × 55 and 90 × 30 km2 in the Kumaon region of the Himalayas. Both blocks were divided into 25 three-dimensional blocks of uniform thickness with different Q β (f) values. The spatial distribution of frequency-dependent shear-wave quality factors in two different blocks reveal the attenuation properties of the region. The profiles of the contours of shear-wave quality factors observed were comparable with those of major tectonic units present in the region.
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