HR: 1340h
AN: S43B-1071    [Abstracts]
TI: Foreshock activity monitoring on a quasi-real time and earthquake forecasting in Greece
AU: * Papadopoulos, G A
EM: g.papad@gein.noa.gr
AF: Institute of Geodynamics, National Observatory, 1 Lofos Nymfon, Athens, Greece, 11810 Greece
AU: Andreou, A
S43B-1071 AF: Institute of Geodynamics, National Observatory, 1 Lofos Nymfon, Athens, Greece, 11810 Greece
AU: Daskalaki, E
S43B-1071 AF: Institute of Geodynamics, National Observatory, 1 Lofos Nymfon, Athens, Greece, 11810 Greece
AU: Fokaefs, A
S43B-1071 AF: Institute of Geodynamics, National Observatory, 1 Lofos Nymfon, Athens, Greece, 11810 Greece
AU: Orfanogiannaki, K
S43B-1071 AF: Institute of Geodynamics, National Observatory, 1 Lofos Nymfon, Athens, Greece, 11810 Greece
AB: Foreshock sequences are characterized by some common properties of interest for the mainshock prediction: the activity extends up to a few months before mainshock following exponential or power-law increase, and the b-value is lower than in background seismicity. However, foreshocks precede only some mainshocks and not others. In addition, foreshocks should be discriminated from swarm-type activity. Studies indicate that the stronger the crustal heterogeneity the larger the percentage of mainshocks preceded by foreshocks and the longer the duration of each individual foreshock sequence. An interpretation is that material of increased small-scale compositional and/or geometric heterogeneity favours an initial rupture nucleation to be stopped than growing to a large shock. Foreshocks may cause a stress step on nearby nucleation patches that advance the onset time of subsequent shocks originating on patches. Consequently, at long times before instability the slip rates are low, but slip rapidly accelerates as the time of instability approaches. A retrospective investigation in Greece indicated that foreshocks were detected before a percentage of 0.62 strong mainshocks. It seems, however, that the mainshock magnitude does not depend on the duration of the foreshock activity. The highly seismogenic zone of Corinth rift, Central Greece, has been selected as a test site for the identification of foreshock sequence before the mainshock. Seismicity criteria were developed to discriminate between foreshocks and swarms given that swarms are characterized by large b-values, higher number of events per time unit and no exponential increase with time. An algorithm is developed which automatically updates the earthquake catalogue with data produced from the national seismograph system, re-calculates parameters like seismicity rate and b-value and discriminates between foreshock sequences and swarms. The daily application of the procedure since the beginning of 2003 concluded with the identification on real-time of only one swarm during July 2003. No foreshock alarm was indicated and no earthquake of magnitude larger than 5 occurred to date. Very recently the algorithm was modified and a daily foreshock monitoring of the entire territory of Greece started.
DE: 7209 Earthquake dynamics (1242)
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
SC: Seismology [S]
MN: Fall Meeting 2005