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Générateur stochastique de séismes en contexte de sismicité faible à modérée : des données à l'aléa. Cas de la France métropolitaine

Abstract : French mainland seismicity is considered as low to moderate due to its remoteness from tectonic plate boundaries. A first consequence is that the origins of its seismicity are harder to understand than in active regions close to tectonic plate boundaries. Another consequence is the lack of available data (earthquakes recorded but also strain rates, active faults...). These two observation make difficult to estimate seismic hazard in low-to-moderate seismic areas. The proposed approach is to generate synthetic earthquakes by combining observation and theoretical knowledge on the seismicity of the studied territory. This generator is based on a three-step scheme: (i) the temporal draw of main shocks, (ii) their spatial draw conditioned by magnitude and finally (iii) the generation of aftershocks they produce. The temporal step needs a recurrence rate. Past seismicity of the whole studied area is analysed thanks to the non-parametric inter event time method in order to obtain this wished recurrence rate. Computing the recurrence rate at the whole territory scale allows to keep the maximum quantity of data, reduce the return periods and so estimate main shock frequencies directly form observed data for each magnitude. An implementation has been developed to overcome the accuracy fall of the inter event time method observed when data are sparse. The spatial step needs a regionalization and a spatial density representing seismicity. The regionalization allows maximum magnitude limitation in space: each region is characterized by an allowed maximal magnitude. Location of a synthetic earthquake with a given magnitude is drawn in the spatial density only within regions that allow this magnitude. Aftershocks are generated around main shocks thanks to the Bath law and the proportion – magnitude distribution of aftershocks. The seismic hazard produced by each of the generated earthquakes (main shocks and aftershocks) is computed thanks to a set of weighted Ground-Motion Prediction Equations. The weights are obtained as function of magnitude and distance thanks to The European ground-motion database RESORCE. Finally, from direct observation of the seismic hazard produced by synthetic earthquakes over one million years, annual probabilities of exceedance can be calculated with ease.
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Submitted on : Friday, November 5, 2021 - 2:49:16 PM
Last modification on : Saturday, November 6, 2021 - 4:21:09 AM

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  • HAL Id : tel-03417067, version 1

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Corentin Gouache. Générateur stochastique de séismes en contexte de sismicité faible à modérée : des données à l'aléa. Cas de la France métropolitaine. Géophysique [physics.geo-ph]. Université de Lorraine, 2021. Français. ⟨NNT : 2021LORR0136⟩. ⟨tel-03417067⟩

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