Scattering and anelastic attenuation of seismic energy in the vicinity of north anatolian fault zone, eastern Turkey

Erzincan basin, eastern Turkey, is seismically very active pull-apart basin and developed in between the eastern segments of the north anatolian fault zone. A study of the regional and site attenuation of seismic waves of ear thquakes in this area will contribute in predicting earthquake generated gr ound-motion and becomes vital in making decisions for earthquake regulation s and building codes, especially for the cities on the north anatolian faul t zone. In this paper, anelastic and scattering attenuation in Erzincan region is i nvestigated by using of multiple lapse time window (MLTW) method based on t he hypothesis of multiple isotropic scattering with uniform distribution of scatters. It is found that the scattering and intrinsic Q(-1) are almost e qual for 3 Hz and lower frequencies and intrinsic attenuation is dominant o ver scattering attenuation for 6 Hz and higher frequencies. Model fitting w as quite good for almost all frequencies at long distances, more scattered data and observed poor model fitting at low frequencies (1.5 Hz) and short distances (5-15 km) may indicate the complexities in the shallower part of crust in Erzincan. The seismic albedo is 0.52 for 1.5 Hz and 0.32 for 12 Hz . L-e(-1) value increases slightly with frequency as 0.058 for 1.5 Hz and 0 .032 for 12 Hz. The coda Q(c)(-1) determined from the decay rate of coda wa ves is similar to Q(s)(-1) for 1.5 and 3 Hz and it is close to Q(t)(-1) for frequencies higher than 3 Hz. We found that the scattering attenuation is strongly frequency dependent, decreasing proportional to f(1.48) whereas in trinsic Q(i)(-1) is considerably less frequency dependent f(1.1). A decreas e of Q(s)(-1) faster than f(1.0) with increasing frequency implies that the medium may be characterized by a Gaussian rather than exponential auto-cor relation function. (C) 2000 Elsevier Science B.V. All rights reserved.