coda attenuation analysis of zagreb area, croatia
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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. - PowerPoint PPT PresentationTRANSCRIPT
Coda attenuation analysis of Zagreb area, Croatia
Iva Dasović, Marijan Herak and Davorka HerakAndrija Mohorovičić Geophysical Institute
Department of Geophysics, Faculty of ScienceUniversity of Zagreb
Supported by
The Foundation of the Croatian Academy of Sciences and Arts
Stations and earthquakes
PTJ: 2004-2010, 70 earthquakesZAG: 2001-2010, 71 earthquakes
Δ < 120 km, ML ≥ 2.0, h < 30 km
The single backscattering model
o The coda-Q method (Aki and Chouet, 1975)
fQtfm
ctfStfA
–2
–e,
EnvelopeSource function
Propagation term, m=2 for body waves
Attenuation
tfQf
)f(Slntt,fAlnc
–
n
c ff
QfQ
00)(
Linear regression
Q0 = Qc(f = f0 = 1 Hz)
flnnQlnQln c 0 Linear regression
Procedure
tWL = time window length (30 s)
tL = lapse time → shifted
windowstS = S-wave travel time
fl (Hz) f (Hz) fu (Hz)
1 1.5 2
2 3 4
4 6 8
6 9 12
8 12 16
12 18 24
16 24 32
Band-pass filters [fl,fu] and central frequencies f
Das
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Q0 and n in coastal Croatia (the External Dinarides)
Dasović et al. (accepted for publication in Stud. Geophys. Geod.)
Q0 and n depend on tL – different referent frequency f0?
Dasović et al. (accepted for publication in Stud. Geophys. Geod.)
lnPGA475 vs. Q0 → 11 stations: coastal region + Zagreb area
tL (s) R (km) ρ p
40 76 -0.80 95%
50 95 -0.92 95%
60 114 -0.86 95%
70 133 -0.82 95%
80 152 -0.49 85%
ρ = correlation coefficient
p = statistically significant confidence level
PGA475 = peak ground acceleration for the return period of 475 yr at the
station site
R = radius equivalent to tL for average vs = 3.8 km/s