Séminaire ISTerre

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Maximizing the value of geologic data in seismic hazard assessment

mercredi 31 janvier 2024 - 10h00

Nicolas Harrichhausen - Séminaire post-doc
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Fault source models are integral to seismic hazard assessments, enabling the inclusion of geological data to refine earthquake locations and frequency predictions. Utilizing fault geometry (location, depth, orientation) and slip rates, these models estimate earthquake occurrence rates for specific faults. Geological inputs thus directly influence earthquake rates and the computed hazard in seismic models. Crucially, fault source models incorporate geological data, which provides insights into earthquake magnitudes and frequencies before the era of instrumental monitoring, less than 100 years ago. The inclusion of geological data in probabilistic seismic hazard analysis (PSHA) is acknowledged as important. However, the variable spatial and temporal scales over which slip-rate observations are made is often not fully considered. For example, paleoseismic studies focusing on a single fault strand may overlook off-fault deformation or slip on parallel strands to the fault core. Conversely, rates derived from the entire fault zone, often more than 1 km wide, might include more off-fault deformation, resulting in higher slip rates. I will present my prior research on the Pallatanga-Puna fault zone, demonstrating that using different slip rates leads to significantly varied earthquake rates for the same fault system. This study shows that geodetic and geomorphic slip rates, measured across the fault zone's entire width, produce earthquake rates aligning closely with those from the seismic catalog surrounding the fault zone. This suggests that slip rates including off-fault deformation (the damage zone) better represent the seismogenic potential of a fault. I will then present a research proposal to test these results on fault systems with different kinematics. Additionally, since the width of the damage zone seems important for determining slip rates, I aim to explore how orientations of inherited structures may control off-fault deformation widths. My broad objective is to better constrain the uncertainty of geological data in fault source models, enhancing their effectiveness in seismic hazard assessments.

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Equipe organisatrice : Organisation labo

Amphithéâtre Killian, Maison des Géosciences, 38400 Saint Martin d'Hères