Uncertainties on Fault Parameters and Seismotectonic Source Zones for Site-Specific PSHA in Southeastern France

Date: 4/24/2019

Time: 06:00 PM

Room: Grand Ballroom

The quantification of uncertainties is crucial to correctly assess a seismic hazard for safety purposes. Among other sources of uncertainties, the ones associated with the seismic sources are still considerable and are likely to remain high for many more years. Indeed, French instrumental and historical catalog durations are short compared to the return period of significant earthquakes and progress in resolving the French fault activity is limited due to low seismicity and deformation rates.

We present a site-specific PSHA study focused on Southeastern France, where debates are still open with divergent opinions and where strong efforts are devoted to the characterization of faults and seismic activity. We explore the variability of the computed hazard curves at different frequencies in order to depict the current diversity of seismotectonic zone models and fault models. We use the FCAT-17 catalog, which incorporates the instrumental catalog (SiHex) and the historical catalog (SisFrance) converted in Mw. We compare several source zone models to take into account different interpretations existing among specialists, especially the CEA zoning integrating recent neotectonic indices. We also investigate extreme plausible fault models based on information given in the French Active Fault Database (BDFA) including some geodetic data.

PSHA computation is performed using OpenQuake and implemented assuming three main hypotheses: (1) zoning with diffuse seismicity, (2) faulting with characteristic earthquakes and (3) faulting with seismicity following a Gutenberg-Richter law. Logic trees enable to take into account epistemic uncertainties on input source parameters and on suitable GMPEs for the French seismotectonic context. Sensitivity tests show that uncertainties on the fault parameters are the dominant factor controlling the variability of the seismic hazard level at various time scales, greater than epistemic uncertainties due to GMPEs and zonings. Finally, this study opens discussions towards alternative models of seismicity generation in intra-continental regions.

Presenting Author: Clara Duverger

Authors