Accelerating Moment Release prior to large earthquakes in Central Greece |
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Quarta-feira, 14 Dezembro 2005 | por
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Accelerating Moment Release prior to large earthquakes in Central Greece. Raphael Gardin Bolseiro BIC do projecto CGE/UE "Fonte Sísmica e Previsão de Movimentos Fortes em Portugal"
Data: Quarta-feira 14 de Dezembro de 2005 Hora: 14h30 Local: Colégio L.A. Verney, Anfiteatro I RESUMO
Accelerating Moment Release (AMR) is the increase of seismic activity exhibited inside a region that surrounds a seismogenic fault before the occurence of the main shock. Observations of AMR prior to large earthquakes have been reported since the 60s, but the physical reason for this phenomenon remained unexplained for a couple of decades. The particular shape of the region is linked with the local stess field, and the Stress Accumulation Model has already shown positive results in justifying the spatio-temporal distribution of seismicity in the vicinity of large strike-slip and reverse fault earthquakes.
In this work, we extend this model to normal fault configurations. Normal faults earthquakes occur in extensional regimes, and are knowned to produce fewer large earthquakes. Nevertheless, the very simple geometry of the stess field in such configurations allows us to constraint mechanical parameters with a good accuracy, with the aim of designing a more general model for the monitoring of seismic activity. A very complete catalogue of seismicity is used to search for AMR prior to the 5 large (M>6) normal fault earthquakes that struck Greece since 1980. The results are discussed in order to look for persistent patterns in the characteristics of the distribution of foreshocks. The issues discussed in this study are linked with the possibility of defining a regional stress field, the existence of vertical and lateral heterogeneities of the upper and middle crust, seismicity induced by fluids, quantification of earthquake activity, or the inclusion of seismogenic faults in the large scale tectonics of the region.
Although initially formulated in the hope to find a means of "predicting" earthquakes, the AMR models are now more modestly used to examine past seismicity with a "post-prediction" stategy, in order to give insights on particular problems of tectonics and earthquakes physics.
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