Theoretical and numerical study of seismic tsunami dynamics

Abstract : The impact of tsunamis on mankind is well known. During recent years, several events showed us the disasters they can trigger which reiterate the importance of understanding their dynamics. Due to the lack of in-situ data, the generation is the least known aspect of tsunamis. As a result, simplified models of the source are used for numerical tsunami modeling, as for seismic generation for which the traditional approach neglects several phenomena, among which is the kinematic deformation of the sea floor. This motion canbe characterized by two temporal parameters: the rupture velocity vp and a hydraulic rise time tr. The novelty here, is to investigate both parameters simultaneously and to extend the linear theoretical development to a non-linear numerical study. From these works, a resonance zone is identified for small tr and vp close to the long wave celerity. For these particular values, the waves are amplified beside the sea floor deformation and dispersive effects develop. To illustrate this theory, the 1947 New Zealand tsunami is simulatedwith the Non-Linear Shallow Water and Boussinesq models of Telemac2D. This seismic event corresponds to a tsunami earthquake with slow kinematics of deformation. Four generation models, with different values of vp and tr are compared. The impact of vp on the generated wave amplitudes is strong whereas the influence due to tr is significantly smaller. Additionally, it was found that the expected dispersive effects did not develop during the numerical modeling. Meanwhile, in the scope of the TANDEM project, the validation of the Telemac system is performed through test cases, covering: generation, propagation and run-up of tsunamis. Globally, the models from the Telemac system match the validation data, however we note a reliance on numerical parameters for sensitive cases as the propagation of a solitary wave. Finally, the Non-Linear Shallow Water model of Telemac2D is used to simulate the Tohoku-Oki tsunami that hit Japan in 2011. Thenumerical model succeeds in representing this real event incorporating all the stages of tsunami life, from generation to flooded areas. Some limitations in using the method were found, which one discussed in detail within the present manuscript
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Marine Le Gal. Theoretical and numerical study of seismic tsunami dynamics. Fluids mechanics [physics.class-ph]. Université Paris-Est, 2017. English. ⟨NNT : 2017PESC1008⟩. ⟨tel-01529253⟩

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