A Probabilistic Methodology For Seismic Hazard Assessment In France
Abstract
We have developed a methodology to assess accelerations expected to be exceeded on a given site for different return periods, taking site effects into account. The analysis is based on a seismotectonic zoning of France, that consists of areas of diffuse seismic- ity characterised by a frequency/magnitude distribution. In the south-eastern France, active faults can be included as potential sources and are assumed to follow the char- acteristic earthquake model. An attenuation law adapted to the french context could be estimated thanks to the recent installation of high-sensitive digital accelerographs and seismographs in France. This law for peak ground acceleration on bed rock has been derived from earthquakes with local magnitudes between 2.5 and 5.6 recorded in near field. Local geological conditions are known to affect significantly ground motion. To account for these site effetcs, a simplified approach is adopted : first step consists in a classification of sedimentary formations from the 1/1000000 geological map, and sec- ond step consists in affecting a mean amplification factor for each. For this study cov- ering the whole french territorry, we integrate site effects into a standard probabilistic seismic hazard analysis. Maps of peak horizontal accelerations expected for differ- ent return periods in the country are shown. A comparison with accelerations of the last thousand years inferred from macroseismic intensities (SISFRANCE catalogue) shows a good agreement with peak ground acceleration expected for one thousand years return period. The variability of ground motion is integrated in the computation of mean frequency of exceedance of acceleration and its effects on the hazard map is shown. The possibility of including in the model the occurrence of scenari such as paleo-earthquake to improve long term hazard assessment in south-eastern France is discussed.
- Publication:
-
EGS General Assembly Conference Abstracts
- Pub Date:
- 2002
- Bibcode:
- 2002EGSGA..27.5397M