ESTIMATION OF QUALITY FACTOR OF CODA WAVES FOR THE DELHI REGION

Abstract

Seismograms of 19 earthquakes which have occurred in and around Delhi region during 2007 to 2014 and recorded at different stations have been analyzed to study the seismic coda wave attenuation characteristics in this region. In the present study, local earthquake events with depths less than 75 km and magnitude range between 3.3 and 5.1 is used to study coda Q, i.e. Q, using the single isotropic backscaltering model proposed by Aki. Q values are estimated at 6 central frequencies 1, 2, 4, 8, 12 and 16 Hz using several starting lapse-times of 40. 50 60 and 70 sec., and coda window-lengths of 25, 30, 35 and 40 sec. In the considered frequency range, Q lit the frequency dependent power-law Q. = QOP. The frequency dependent power law for 40 sec lapse time with 25 sec coda window length is QC = 86.83 f° and for 70 sec lapse time with 40 sec coda window length is Qe = 168.44 f°96. The Q (Qc at 1 Hz) estimates vary from about 87 for a 40 sec lapse time and 25 sec window length, to about 168 for a 70 sec lapse time and 40 sec window length combination. The exponent of the frequency dependence law n ranges from 0.96 to 1 .05, which correlates well with the values obtained in other seismically and tectonically active and heterogeneous regions of the world. It is observed for the study region that Q values increases both with respect to lapse time and frequency or attenuation decreases as quality factor is inversely proportional to attenuation. The low Q values or high attenuation at lower frequencies and high Q values or low attenuation at higher frequency may indicate that the heterogeneity decreases with increasing depth, in the study region.