1992–2002: Perspective on a Decade of Post-Tsunami Surveys

We present a discussion of the field surveys conducted in the wake of fifteen locally devastating tsunamis in the period 1992–2002. The goal of these surveys has been to gather homogeneous databases of run-up and inundation, for the purpose of documenting precisely the penetration of the waves along the affected beaches. In turn, these can be used as datasets to be matched by numerical simulations of the generation of the tsunamis, their propagation and interaction with the beaches. These surveys hav e provided new insight into some complex phenomena, such as the existence of a leading depression in an N_wave, the importance of beach topography on the local enhancement of run-up, the contribution of underwater landslides to tsunami hazard, and the value of an educated population in terms of the mitigation of human losses. We review a simple and robust algorithm allowing the discrimination between tsunamis generated by dislocations and landslides, based on the aspect ratio of the distribution of run-up on a nearby beach, and the comparison of maximum run-up to the seismic slip involved in the parent earthquake. Some of the techniques developed in these recent post-tsunami surveys can be extended to events dating back a few decades through the interview of elderly witnesses and the surveying of remanent watermarks. When applied to the case of the 1946 Aleutian tsunami, the resulting data require both a large dislocative source to explain the far-field tsunami, and a coeval underwater landslide to account for the near-field run-up values which reached 42 meters at the site of the Scotch Cap light-house.