Dependence of coda attenuation on frequency and lapse time in central Greece

The dependence of coda attenuationQ _c on frequency and lapse time was studied. Data from small local earthquakes, recorded at three stations (VMR, VSI and VFI) of the VOLNET network operating in central Greece, were used.Q _c was estimated by applying the single scattering model to bandpass-filtered seismograms, over a frequency range of 1 to 12 Hz. Analysis was performed every 10 s until the end on overlapping time windows.Q _c is found to depend on frequencyf in Hz according to a power law,Q _c =Q ₀ f ⁿ . ObservedQ ₀ ranges from 30 to 100 and the powern ranges from 0.90 to 0.70.Q ₀ increases andn decreases with lapse time increasing. A strong dependence ofQ _c on lapse time was also found. In the frequency range of 1 to 8 Hz and at a short lapse time,Q _c values were found to be similar for all three stations. On the other hand, at the longest analyzed time window (50 s), the estimatedQ _c values show a discrepancy which is more obvious at a higher frequency band. The scattering coefficient around the central station VSI is found to range from 0.029 to 0.0041 km^–1.Q _c from the single scattering model andQ _s from the amplitude ratio of directS to coda waves for the VSI station are similar. We believe dependence of coda attenuationQ _c on frequency and lapse time is caused by a combination of geotectonic features and depth variation asQ _s .