MULTI-SCALE SPACE AND TIME VARIATIONS OF EARTHQUAKE OCCURRENCES

We show results of an ongoing project that aims to provide a better understanding of the space and time variation of seismic activity in Western Europe.

Within plates, assessment of earthquake hazards relies mainly on the assumption that past earthquakes delineate areas where future seismicity will occur (Kafka, 2007). The “cellular seismology” used to test this assessment has only been tested on relatively short time spans earthquake catalogues. We applied this method on the Belgian catalogue (from 1985 to present-day). This catalogue has low magnitude completeness (M> 2) and results seem to confirm this assumption.

What about longer time scale? We compiled a long time span earthquake catalogue (from 1247 to present-day) to apply this method on Western Europe seismicity. Primary results show divergence with the short time scale ones. The paleoseismicity model (Ebel, Bonjer, & Oncescu, 2000) assumes that actual seismicity indicates past large earthquakes. It describes a long time span behavior of intraplate seismicity. Fundamentally both models are not incompatible. They might just be the expression of two different time scale structures. This might be underlined by multifractals analysis. Multifractals characteristics of the temporal distribution of earthquake might indicate different scaling regimes bringing evidence of the complexity and randomness of the earthquake occurrences process.

The different methods have been applied to both catalogues and results are compared in order to estimate the cover time scale ranges.