Assessing attenuation characteristics prevailing in a seismic prone area of North Eastern Region, India

Abstract

Microearthquake spectra from the Kopili region, one of the seismic prone areas of northeast India, are examined to observe the effect of attenuation on these spectra. The spectral ratio method is utilized in order to estimate Q values for both P and S waves in the subsurface layer wherein the ratio of spectral amplitudes at lower and higher frequencies are taken into consideration for six stations at varying epicentral distances. Average values of Q p and Q s are computed to be ∼481 36 and 966 98, respectively. Q s/Q p having a value greater than 1 is contemplated in major parts of Kopili and the neighboring area, which can be ascribed to underlying sediment deposits. The estimates of attenuation parameters are well substantiated by site geology. The values obtained in this study are in good conformity with the worldwide average. The estimates will help in seismic hazard estimation of this seismically active area.