GNGTS 2013 - Atti del 32° Convegno Nazionale

Where f is the frequency, S s ( f ) is the spectral amplitude of S waves, P ( f , t c ) is the coda- excitation factor and I ( f ) is the instrument response. The code excitation factor P ( f , t c ) represents how the spectral amplitude of coda waves decays with lapse time. After solving mathematically, we get following equation (Aki, 1980): (1) where A s ( f , r ) is the spectral amplitude of the direct P-wave, Q s ( f ) is the quality factor of S wave and V s is the average S-wave velocity. Eq. (1) was first proposed by Aki (1980). Yoshimoto et al. (1993) extended this method for the measurement of Q P by assuming that earthquakes within a small range of magnitude have the same spectral ratio of P- to S-wave radiation within a narrow frequency range f ± Δf for different spectral shapes of P and Swaves (Molnar et al. , 1973; Rautian et al. , 1978). We are writing same symbol as Yoshimoto et al. (1993) used. (2) where A p ( f , r ) is the spectral amplitude of the direct P-wave, Q p ( f ) is the quality factor of P wave and V p is the average P-wave velocity. In our study we used Eqs. (1) and (2). Data. A network of nine strong motion accelerographs of Kinemetrics, USA, have been installed in the Kumaun Himalaya under the major research project sponsored by Department of Science and Technology/MOES, Government of India, in March 2006. Location of the stations are shown in Tab. 1. Fig. 1 – Generalized tectonic sequence for the Lesser Kumaun Himalaya (from Valdiya, 1978). 141 GNGTS 2013 S essione 1.1