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| Titel |
Coda attenuation analysis of Zagreb area, Croatia |
| VerfasserIn |
Iva Dasović, Marijan Herak, Davorka Herak |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250052563
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| Zusammenfassung |
| The area surrounding the Croatian capital Zagreb is characterised by complex faulting system
as a result of compressional tectonic forces. It is situated in the transitional zone between the
Alps, the Pannonian basin and the Dinarides, and exhibits a significant seismic activity. Two
seismic stations (ZAG and PTJ) are set in this area of interest and recordings from these
stations were used in this analysis.
In order to estimate seismic attenuation, we analysed the attenuation of coda waves. Only
earthquakes with the local magnitude greater than 2.0 which occurred within 100 km
from the stations were considered. Coda-Q (Qc) was estimated using the single
backscattering model, applied to seven frequency bands with central frequencies of 1.5, 3,
6, 9, 12, 18 and 24 Hz. Moreover, we also calculated Q0 (Qc = 1 Hz) and n that
describe the frequency dependence according to Qc = Q0fn. Although the single
backscattering model assumes there is no lapse-time dependence of Qc, many studies
have demonstrated the opposite. To explore this kind of dependence of Q0 and n,
we used a series of 30 s long time-windows along the first 50 s of the coda of an
earthquake. Starting at the coda onset at twice the S-wave travel time, the time-window
was shifted by one second at a time. Every estimated Qc is associated with the
lapse-time of the middle of the corresponding time-window and is accordingly
distributed to classes. Both Q0 and n exhibit notable lapse-time dependence. In general
Q0 increases with the lapse-time which indicates decrease of attenuation with the
depth, whereas n decreases almost symmetrically. The values of Q0 suggest that
the area is highly heterogeneous and the values of n suggest significant frequency
dependence of Qc. These estimations are compared to the results for coastal part of
Croatia.
These results will help in determination of seismic moments and quantification of small
and moderate earthquakes occurring in the Zagreb area, as well as in the ongoing studies of
the lithospheric structure.
This work was supported by Croatian Academy of Sciences and Arts. |
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