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

Abstract

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 earthquakes in this area will contribute in predicting earthquake generated ground-motion and becomes vital in making decisions for earthquake regulations and building codes, especially for the cities on the north anatolian fault zone. In this paper, anelastic and scattering attenuation in Erzincan region is investigated by using of multiple lapse time window (MLTW) method based on the hypothesis of multiple isotropic scattering with uniform distribution of scatters. It is found that the scattering and intrinsic Q −1 are almost equal for 3 Hz and lower frequencies and intrinsic attenuation is dominant over scattering attenuation for 6 Hz and higher frequencies. Model fitting was 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 waves 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 intrinsic Q i −1 is considerably less frequency dependent f 1.1. A decrease 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-correlation function.