Lapse time dependence of coda wave attenuation in Central West Turkey

• Coda wave attenuation characteristics in Central West Turkey were examined.
• Strong frequency and lapse time dependencies of attenuation were observed.
• The highest n values were obtained for the Izmir-Ankara-Erzincan suture zone.
• Results for subregion IV manifest increasing content of partial melt at depths.
• Higher attenuation and n values were obtained for long hypocentral distances.

The attenuation of coda waves has been inferred for Central West Turkey, which is characterized by a very complex tectonic evolution. The selected dataset is composed of 440 waveforms from 228 local earthquakes with a magnitude range of 2.9–4.9. The coda quality factor (Qc) was estimated for five central frequencies (fc = 1.5, 3, 5, 7, 10 Hz) and eight lapse times (tL, ranging from 25 to 60 s), based on the assumption of single isotropic scattering model. Estimated Qc values were strongly dependent on frequency and lapse time. The frequency dependence of Qc values for each lapse time was inferred from Qc(f) = Q0fn relationships. Q0 values change between 32.7 and 82.1, while n values changes between 0.91 and 0.79 for the lapse times of 25 and 60 s, respectively. The obtained low Q0 values show that the Central West Turkey region is characterized by a high seismic attenuation, in general. The whole region was divided into four subregions to examine spatial differences of attenuation characteristics. Obtained 1/Q0 and n values versus the lapse time for each subregion implies the tectonic complexity of the region. Lapse time dependencies of attenuation and n values were also examined for subdatasets from two different ranges of event depth (h < 10 km and h ≥ 10 km) and distance (r < 40 km and r ≥ 40 km). High attenuation and its high frequency dependence for long distances manifest the elevation of isotherms and increasing heterogeneity with depth. This could be associated with the extensional intra-continental plate setting, forming regional tectonics in the back-arc area.