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| Titel |
The East Aegean Sea strong earthquake sequence of October-November 2005: lessons learned for earthquake prediction from foreshocks |
| VerfasserIn |
G. A. Papadopoulos, I. Latoussakis, E. Daskalaki, G. Diakogianni, A. Fokaefs, M. Kolligri, K. Liadopoulou, K. Orfanogiannaki, A. Pirentis |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1561-8633
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| Digitales Dokument |
URL |
| Erschienen |
In: Natural Hazards and Earth System Science ; 6, no. 6 ; Nr. 6, no. 6 (2006-10-11), S.895-901 |
| Datensatznummer |
250003801
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| Publikation (Nr.) |
 copernicus.org/nhess-6-895-2006.pdf |
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| Zusammenfassung |
| The seismic sequence of October–November 2005 in the Samos area, East Aegean
Sea, was studied with the aim to show how it is possible to establish
criteria for (a) the rapid recognition of both the ongoing foreshock
activity and the mainshock, and (b) the rapid discrimination between the
foreshock and aftershock phases of activity. It has been shown that before
the mainshock of 20 October 2005, foreshock activity is not recognizable in the
standard earthquake catalogue. However, a detailed examination of the
records in the SMG station, which is the closest to the activated area,
revealed that hundreds of small shocks not listed in the standard catalogue
were recorded in the time interval from 12 October 2005 up to 21 November 2005. The
production of reliable relations between seismic signal duration and
duration magnitude for earthquakes included in the standard catalogue, made
it possible to use signal durations in SMG records and to determine duration
magnitudes for 2054 small shocks not included in the standard catalogue. In
this way a new catalogue with magnitude determination for 3027 events was
obtained while the standard catalogue contains 1025 events. At least 55 of
them occurred from 12 October 2005 up to the occurrence of the two strong
foreshocks of 17 October 2005. This implies that foreshock activity developed a
few days before the strong shocks of 17 October 2005 but it escaped recognition
by the routine procedure of seismic analysis. The onset of the foreshock
phase of activity is recognizable by the significant increase of the mean
seismicity rate which increased exponentially with time. According to the
least-squares approach the b-value of the magnitude-frequency relation dropped
significantly during the foreshock activity with respect to the b-value
prevailing in the declustered background seismicity. However, the maximum
likelihood approach does not indicate such a drop of b. The b-value found for
the aftershocks that followed the strong shock of 20 October 2005 is
significantly higher than in foreshocks. The significant
aftershock-foreshock difference in b-value is valid not only if the entire
aftershock sequence is considered but also if only the segment of
aftershocks that occurred within the first 24-h or the first 48-h
after the mainshock of 20 October 2005 are taken into account. This difference
in b-value should be examined further in other foreshock-aftershock sequences
because it could be used as a diagnostic of the mainshock occurrence within
a few hours after its generation. |
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