ATTENUATION OF CODA WAVES IN NORTHERN GREECE

The single scattering model has been applied for the estimation of coda Q values for local earthquakes that occurred in northern Greece during the period 1983-1989 and recorded by the telemetered network of the Geophysical Laboratory of the University of Thessaloniki. Coda Q estimations were made for four frequency bands centered at 1.5 Hz, 3.0 Hz, 6.0 Hz and 12.0 Hz and for the lapse time windows 10-20 sec, 15-30 sec, 20-45 sec, 30-60 sec and 50-100 sec. The coda Q values obtained show a clear frequency dependence of the form Q(c) = Q0f(n), while Q0 and n depend on the lapse time window. Q0 was found equal to 33 and n equal to 1.01 for the time window of 10 to 20 sec, while for the other windows Q0 increased from 60 to 129, with n being stable, close to 0.75. This lapse time dependence is interpreted as due to a depth dependent attenuation. The high attenuation and the strong frequency dependence found are characteristic of an area with high seismicity, in agreement with studies in other seismic regions.