Collaborative Research: Generation Mechanisms for Near- and Far-Field Tsunamis

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This action is to support a collaborative research project to study the generation and propagation of tsunamis in both the near and far fields, as generated by earthquakes or underwater landslides. The principal goal is to define features ("observables") that can be used to discriminate between an earthquake or a landslide as the origin of a tsunami.In the near field, hydrodynamic simulations are used to examine the influence of various source parameters on the expected maximum runup on a nearby beach, and on the lateral distribution along the beach. The strategy is to identify combinations of observables that would be largely invariant for one type of source, and thus could serve as source discriminants. In addition, this approach will be applied to the existing databases collected during the post- tsunami surveys conducted in the past decade, in order to determine in detail the source mechanisms that controlled the amplitude and extent of devastation. This research will result in a better understanding of the association between source parameters (for both types of sources) and the resulting runup at nearby beaches, and will improve the models used in estimating and mitigating the impact of future tsunamis on a regional scale.In the far field, the project considers the frequency dispersion and its effect on the evolution of tsunami waveshapes under a variety of source scenarios, again including both earthquakes and landslides. Comparing simulations performed with dispersive and non-dispersive codes should identify those source conditions that may enhance the effect of dispersion in the far field, and generalize to a full two-dimensional ocean earlier results obtained for one-dimensional propagation. The influence of source type on directivity will be addressed systematically. This is well understood for earthquake sources, but remains debatable for landslides. This research will establish the possible contribution of landslide sources to tsunami hazard in the far field, and clarify the question of the suitability of various approximations in hydrodynamic theories under a number of source scenarios. The results will be applied to the case of the 1946 Aleutian earthquake, which inflicted the greatest devastation by a tsunami on the United States in the past 100 years, but whose exact generating mechanism is still elusive. A number of historical tsunamis will also be studies, for which no exact description of source mechanism is available.The research will significantly improve the capability to predict inundation and runup during future tsunamis, and thus for mitigation of their effects. The principal investigators will continue their tradition of graduate and undergraduate student involvement in all aspects of the research, and active interaction with the news media. They will also compile and permanently archive the large dataset of videotaped interviews obtained during previous tsunami field surveys.