engleski

CODA ATTENUATION IN THE CROATIAN COASTAL REGION (EXTERNAL DINARIDES)

The tectonics of the coastal region of Croatia are driven by the convergent motion of the Adriatic microplate and the Dinarides. The greater Adriatic area is geologically and tectonically considered to be one of the most complicated regions in Europe. The seismicity of the area varies from low and moderate (in the NW and central parts) to high in the SE. In the past decade the Croatian seismological network was enlarged and modernised by addition of several digital broadband stations. This enabled formation of high quality local earthquake seismograms dataset. In order to determine seismic attenuation in the coastal region of Croatia, we analysed attenuation of coda waves for nine seismic stations. The coda quality factor Qc was estimated using the single backscattering model for up to seven central frequencies (f = 1.5, 3, 6, 9, 12, 18 and 24 Hz). To explore the lapse-time dependence of Qc, its values were estimated for a series of 30 s sliding time-windows. Observed Qc displays pronounced frequency dependence according to Qc = Q0 fn, as well as considerable spatial variability. In addition, both Q0 and n exhibit notable lapse-time dependence. In general Q0 increases with the lapse-time (indicating decrease of attenuation with the depth), whereas n decreases. The results also indicate a correlation of observed attenuation with the seismotectonic activity – the areas of high activity are characterized by lower Q0 and higher values of n, than seismically less active regions.

coda waves; seismicity; quality factor

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