SGER Proposal: Field Survey of the Marquesas Islands

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This action is for partial support of a field survey of the Marquesas Islands to identify evidence of the April 1, 1946 Aleutian tsunami, such as possible watermarks from the tsunami when it impacted the Marquesas. During a recent survey of a tsunami in the island of Fatu Hiva, large rocks were discovered that had reportedly moved inland in 1946 at about the time of the Aleutian tsunami, some as much as 300m. The objective of this joint US/France expedition is to document these findings, take measurements, and investigate other anecdotal reports of similar tsunami rocks in other islands in the Marquesas, and assess the local impact of the April 1, 1946. tsunami This work is very timely, as the exact generation mechanism of the April 1, 1946 Aleutian tsunami remains controversial -- it is often speculated that there was coseismic tsunami generation due to a massive landslide. The existing hydrodynamic inundation data from Hawaii are not sufficient to perform meaningful hydrodynamic inversion to identify the likely source mechanism. Discovering if a landslide was involved in the Aleutian tsunami is quite important now, as inundation maps for Hawaii are currently being re-evaluated, and inundation maps for the Pacific states of the US mainland are being developed for the first time. Tsunamis from the Aleutians are a concern that needs to be carefully reassessed, particularly in view of the landslide potential. The findings may also help re-evaluate the work in progress on landslide generation of tsunamis, which since the PNG event has helped refocus global tsunami hazard mitigation efforts.