1. Coda attenuation analysis of Zagreb area, Croatia Iva Dasović, Marijan Herak and Davorka Herak Andrija Mohorovičić Geophysical Institute Department of Geophysics, Faculty of Science University of Zagreb Supported by The Foundation of the Croatian Academy of Sciences and Arts

2. Seismicity of Croatia – Croatian Earthquake Catalogue: 373 BC - 2010

3. Stations and earthquakes PTJ: 2004-2010, 70 earthquakes ZAG: 2001-2010, 71 earthquakes Δ < 120 km, M L ≥ 2.0, h < 30 km

4. The single backscattering model o The coda-Q method (Aki and Chouet, 1975) Envelope Source function Propagation term, m=2 for body waves Attenuation Linear regression Q 0 = Q c (f = f 0 = 1 Hz) Linear regression

5. Procedure t WL = time window length (30 s) t L = lapse time → shifted windows t S = S-wave travel time f l (Hz)f (Hz)f u (Hz) 11.52 234 468 6912 8 16 121824 162432 Band-pass filters [f l,f u ] and central frequencies f Dasović et al. (accepted for publication in Stud. Geophys. Geod.)

6. Results: Q c (t L, f) Smoothed values of Q c (t L, f) in contour-graph

7. Q 0 and n depend on t L h = ½ v s t 40 80 120 160 200 240 h (km) 40 80 120 160 200 240 h (km)

8. Q 0 and n in coastal Croatia (the External Dinarides) Dasović et al. (accepted for publication in Stud. Geophys. Geod.)

9. Q 0 and n depend on t L – different referent frequency f 0 ? Dasović et al. (accepted for publication in Stud. Geophys. Geod.)

10. lnPGA 475 vs. Q 0 → 11 stations: coastal region + Zagreb area t L (s)R (km)ρp 4076-0.8095% 5095-0.9295% 60114-0.8695% 70133-0.8295% 80152-0.4985% ρ = correlation coefficient p = statistically significant confidence level PGA 475 = peak ground acceleration for the return period of 475 yr at the station site R = radius equivalent to t L for average v s = 3.8 km/s

11. Conclusions o Q 0 and n indicate highly heterogeneous medium o Coda-Q is lapse time dependent o A marked change of Q 0 and n at about 100 km depth (upper mantle) o Different choice of f 0 might “eliminate” lapse time dependence of Q c o Very convincing correlation between Q 0 and PGA 475 (seismicity)