Séminaire ISTerre

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Forward Modeling of Nonlinear Wave Propagation in Earth with Co-seismic Wave Speed Changes from source to site

mardi 1er octobre 2024 - 11h00

Zihua Niu - Université de Munich
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The weakening of rocks during the passage of acoustic/elastic waves has been widely observed in laboratory experiments. With the development of long-term continuous monitoring of Earth's subsurface, e.g., using ambient noise interferometry, coseismic drops of wave speeds have also been recorded in the field over the past two decades. However, it is unclear whether the observations in the field and in the laboratory can be attributed to the same physical processes. Vastly different scales and sparsity of high-resolution observations challenge a unified interpretation of laboratory and field observations. We here present progress in physics-based numerical modeling of nonlinear seismic wave propagation. In Niu et al. (2024), we show that a damage model adapted from Lyakhovsky et al. (1997) explains both the softening and the recovering phases of rocks under dynamic perturbations, and compare this adapted model with the damage model of Berjamin et al. (2017). We use the Markov chain Monte Carlo method to explore connections and uncertainties of nonlinear parameters. We now extend SeisSol, a HPC open-source software for wave propagation and dynamic rupture simulations based on Arbitrary high order using Derivatives Discontinuous Galerkin Method, to simulate 3D nonlinear wave propagation and implement both damage models. The implementation enables us to explicitly investigate the co-seismic changes of seismic wave speed accounting for non-linear source, path and site effects . We apply these damage models to the Kathmandu sedimentary basin and study the co-seismic velocity drop after the 2015 Mw7.8 Gorkha earthquake. We also compare effects from simulations with elastic, visco-elastic, elasto-plastic, and damage rheology.

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Equipe organisatrice : Mécanique des failles

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

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