Séminaire ISTerre

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Unravelling active faults in areas of low crustal deformation rates: a multidisciplinary approach in the perialpine environment

jeudi 26 novembre 2020 - 14h00

Stefano Fabbri - University of Bern
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In intraplate environments with low crustal deformation rates, current probabilistic seismic hazard assessments are primarily based on historically documented and instrumentally recorded earthquakes in Switzerland, especially since documentations on active faults are sparse. In recent years, considerable efforts have been undertaken to overcome the limited time span of historically documented and instrumentally recorded earthquakes in the Alps by the investigation of secondary evidence in the form of earthquake-triggered subaquatic mass movements and their related turbidites in lake sediments. However, only few successful identifications of primary evidence (on- fault) have been reported. Their identification is absolutely vital to minimize uncertainties associated with the calculated recurrence time of strong earthquakes. Free of erosional effects, lacustrine environments have the yet not thoroughly explored potential to record and archive on-fault evidence. Therefore, we will first look into existing off-fault paleoseismic evidence in Switzerland and then present two active fault structures which we unraveled by the combination of multichannel and single channel reflection seismic data, swath bathymetry and on- shore ground-penetrating radar and geological data acquisition. Our recent findings in Lake Thun (Switzerland) and Lake Constance (Austria, Germany, Switzerland) show that active faults in environments with low crustal deformation rates along the Alps do exist, but multidisciplinary approaches are needed to unravel them what makes it extremely costly and time consuming. We will also quickly glimpse at the hazard of delta collapses and its tsunamigenic potential that is to- date poorly understood, but also poses a potential high risk to communities living close to shorelines. Locally focused 4D-bathymetric survey strategies and cost-efficient single-channel airgun seismic data might qualify for a more systematic widespread screening of the perialpine environment to identify hazards created by delta collapses and active fault structures, respectively, and incorporate the findings into current probabilistic seismic hazard models.

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Equipe organisatrice : Cycle sismique et déformations transitoires

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