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Earthquake-Tsunami Coupling

In order to realistically simulate and understand the tsunami behavior following an undersea earthquake, the complex interaction of ocean bottom displacement and wave generation needs to be studied. In order to achieve this, the crust deformation and water wave model need to be coupled dynamically.

ASCETE will go beyond current approaches to the coupling problem by developing a 3D earthquake rupture model for simulating the entire faulting process coupled to the hydrodynamic model of tsunami generation and propagation in a computationally efficient way. The coupled rupture process can be roughly divided into three different time-frames, which are characterized by different time scales and coupling scenarios:

  • Faulting occurs within seconds or a few minutes and the resulting ocean bottom displacement acts as input for the simulation of tsunami generation (uni-directional coupling);
  • faulting and strong surface waves induce motion in the water column generating sea-surface displacement with hydrostatic pressure changes that might influence stress and rupture behavior (bidirectional coupling);
  • sea-surface disturbances induce a gravity wave (tsunami) that propagates for hours, when all seismic contributions have already finished and only 3D near-fault hydrodynamic effects act as initial and boundary conditions on 2D tsunami wave propagation (uni-directional coupling).

Due to the three different models involved, the different numerical characteristics (3D vs. 2D; adaptive meshing; adaptive time steps and DG order) and the different time-scales, a partitioned approach to couple and optimize existing solvers towards a combined earthquake-tsunami simulation will be adopted.

First conceptual model of earthquake- tsunami coupling

Based on the dynamic rupture simulation of the 2011 Tohoku earthquake we have developed the first conceptual model of earthquake-tsunami coupling (see figure below). For this purpose we have used the spatio-temporal evolution of the seafloor displacement generated by the dynamic rupture model as input for the tsunami simulations. Our preliminary results show that the tsunami waves reach the coast of Japan about 25-30 minutes after the earthquake. A next step in this study is to investigate the role of the slip reactivation and the surface Rayleigh waves generated by the dynamic rupture on the tsunami generation.

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