ATTENUATION OF CODA WAVES IN THE GARHWAL-HIMALAYA, INDIA

Q(c) estimates have been obtained by analysing coda waves of seven local earthquakes recorded in the Garhwal Himalaya. The earthquakes have their epicentral distances within 100 km, focal depths up to 20 km with 2.4 less-than-or-equal-to M(L) less-than-or-equal-to 4.9. Q(c) values have been computed at central frequencies of 1.5, 3.0, 6.0, 12.0 and 18.0 Hz for different earthquake stations falling in the lapse time window of 30-60 s using a single backscattering model. The mean value of Q(c) shows a dependence on frequency, varying from 206 at 1.5 Hz to 2090 at 18 Hz. The frequency-dependence average Q(c) relationship (Q(c) = Q0f(n)) has been obtained for the region as Q(c) = 126f0.95 which indicates that attenuation at higher frequencies is less pronounced. Q(c) values estimated for the region represent the average attenuation properties for a surface area of about 20 000 km2 in a circular shape with a radius of about 80 km assuming single backscattering.