S-WAVE ATTENUATION IN THE MARMARA REGION, NORTHWESTERN TURKEY

The frequency-dependent attenuation of shear waves in the crust is est imated by using two different methods based on the rate of time decay of coda-wave amplitude, Q(c)(-1), and the rate of decay of the S-wave to coda wave amplitude ratio with distance, Q(s)(-1). The epicentral d istances of selected earthquakes range between 20 and 110 km and magni tudes are around 3. The quality factors, Q(c), are calculated at frequ encies of 1.5, 3., 6., 12., and 24. Hz and lapse times of 40, 50, 60, and 70 s. Estimated Q(c) values show a dependence on frequency and lap se time. We observed the similarity in the frequency dependency of Q(c )=(41+/-1.07)f(1.8+/-0.03) and Q(s)=(50+/-1.7)f(1.09+/-0.05) for a lap se time of 50 s indicating that the attenuation mechanism for coda wav es is similar to that of the direct S waves.