Attenuation of coda waves on frequency and lapse time in Izmir and Western Anatolia using local earthquakes

Abstract

This study investigated frequency dependent attenuation of seismic waves from earthquakes in Izmir and its surroundings. Earthquakes with a magnitude of M ≥ 2.3, recorded by the local seismic network in the region between 2008–2023, were used. The network of 26 accelerometers is predominantly deployed near the gulf to monitor tectonic features characterized by high seismic activity. The attenuation properties related to seismic wave propagation were evaluated by applying Coda Q analysis. Attenuation in coda waves is due to wave propagation between the inelastic medium and discontinuities or scattering of heterogeneities. The frequency dependence of the seismic quality factor for the coda wave was determined using Q₀ multiplied by fⁿ. Various center frequencies (1,2,4,8,16) were selected to calculate the coda wave quality factor, and bandpass filtering was applied. The CODAQ algorithm in the SEISAN software (Havskov et al. 2020) was used in the study. It was observed that elevated Q values in the study area are associated with geologically stable zones, whereas lower Q₀ values reflect areas of heightened seismic activity. The complex tectonic regime of Izmir and its surrounding areas aligns with the low Q₀ values, suggesting significant heterogeneity in the crust. We found the result Q_c = 61,9. f^0,9 with investigating the Q change examined using different lapse times (20 s,30 s and 40 s) and geometrical spreading (0.5 and 1) parameters.