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Numerical modeling of submarine landslides and surface water waves which they generate

University of British Columbia

Underwater landslides are a common source of tsunamis in coastal areas. In this thesis, three numerical models are developed to simulate the coupling of submarine landslides and the surface waves which they generate. Three different rheologies of the submarine sediments are considered: a viscous fluid, a Bingham-plastic fluid, and a Coulomb frictional material. Formulations of the dynamics are presented for the slides on a gentle uniform slope reactively coupled with the surface waves which they generate. The governing equations are solved by a finite-difference method. In the first model, the submarine slide is treated as a laminar flow of incompressible viscous fluid. Three major waves are generated: the first wave is a crest which propagates into deeper water, this crest is followed by a trough in the form of a forced wave; the third wave is a small trough which travels shoreward. Two major parameters dominate the interaction between the slide and the waves: the density of sliding material and the depth of water at the slide site. The landslide is treated as an incompressible Bingham-plastic flow in the second model. Because of the yield stress (or plasticity), the slides stop on the slope when the shear stress exerted on the bottom becomes smaller than the yield stress. The Bingham-plastic behavior of the mud significantly reduces the run-out distance and the speed of the slide, and also reduces the magnitude of the surface waves and the water current generated. In the third model, the submarine sediment is treated as a Coulomb frictional material. A frictional material model can well describe the slide of soft sandy sediment, in which the Coulomb friction law applies to the basal friction on the bottom of the slide. It is found that the friction angle between the slide material and the slope has the most significant effect on the slide dynamics and wve generation. The numerical results obtained in this thesis indicate that the rheology of the sediment (i.e., the constitutive relation) dominates the slide dynamics, and hence the surface wave generation. The greater the mobility of the sediment, the greater the amplitudes of the waves generated.

Thesis/Dissertation

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2008-09-17

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http://hdl.handle.net/2429/2118

Oceanography

University of British Columbia

UBCV

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