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

The dependence of coda attenuation Q(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 frequency f in Hz according to a power law, Q(c) = Q(0)f(n). Observed Q(0), ranges from 30 to 100 and the power n ranges From 0.90 to 0.70. Q(0) increases and n decreases with lapse time increasing. A strong dependence of Q(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 (50s), the estimated Q(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 and Q(s) from the amplitude ratio of direct S to coda waves for the VSI station are similar. We believe dependence of coda attenuation Q(c) on frequency and lapse time is caused by a combination of geotectonic features and depth variation as Q(s).