Probabilistic Seismic Hazard Assessment In the Upper Rhine Graben, Eastern France

Abstract:

The southern part of the Upper Rhine Graben (URG) straddling the border between eastern France and western Germany, presents a relatively important seismic activity for an intraplate area. A magnitude 5 or greater shakes the URG every 25 years and in 1356 a magnitude greater than 6.5 struck the city of Basel. Several potentially active faults have been identified in the area and documented in the French Active Fault Database (web site in construction). These faults are located along the boundary of the Graben but also in the middle, under heavily populated areas and critical facilities and are capable of producing earthquakes with magnitude 6 and above. Regional models and preliminary geomorphological investigations provided provisional assessment of slip rates for the individual faults (0.1-0.001 mm/a). Two possible geodynamic models are still debated for the URG: one where the most active faults are along the border of the URG and a second one where they are in the middle. This uncertainty on slip rates is explored through a logic-tree, as well as the impact on the seismic hazard estimation of different input key parameters such as the fault geometry, the slip-rate of the faults, the seismicity model associated to the faults (Characteristic / Gutenberg-Richter). We also show the influence of the minimum magnitude considered for modeling the faults in PSHA. PSHA results will be discussed and comparisons between three PSHA codes (CRISIS, OpenQuake and a PSHA-code developed by IRSN) will be presented.