Estimation of Lg-coda Q value for the Northern Indian Ocean region based on spectral analysis

Attenuation of ground motion amplitudes with distance is recognised as a significant issue by researchers. Of particular interest is the attenuation or propagation of seismic waves from long distant sources. Regions like Sri Lanka have experienced tremors from events as far as 1500 km. However a comprehensive study of the region with respect to the propagation or attenuation of seismic waves has been generally lacking. With the availability of new archival data of 65 events recorded at Pallekelle Broadband station, the authors have estimated Lg-coda Q values for the Northern Indian Oceanic region surrounding Sri Lanka. Multiple linear regression analysis of recorded data yields a relatively higher Q value which is comparable to similar older crustal regions such as Western Australia and Central Europe. Source spectra for recorded events have also been accounted by correcting the observed amplitude for geometric and anelastic attenuation. This results in typical stress drop values of about 100 bars which is consistent with Brune's source spectra. Based on the estimated values, stochastic modelling of a recent 8.6 Mw event experienced in the region has been undertaken. Initial results are promising. Further analysis would establish reliable attenuation behaviour around the region