Providing a wealth of geophysical and geological data, the 2011 Tohoku-oki tsunami offered a rare opportunity to advance research on tsunami sedimentology. In this chapter, six key findings, presented in the form of lessons learned, are identified based on a review of recent studies on the 2011 Tohoku-oki tsunami and other relevant literature:
1. limitations posed when using marine materials as evidence for tsunami inundation;
2. the larger extent and lower preservation potential associated with offshore tsunami deposits;
3. possible false dating of paleotsunami events due to tsunami-induced erosion;
4. uncertainty associated with tsunami inundation distances deduced from deposit extent;
5. spatial variability in deposit thickness and its relation to flow depth;
6. challenges associated with estimating the size and extent of earthquakes based on tsunami deposits.
In response to the extensive loss of life and property caused by the Tohoku-oki tsunami, as well as the fact that geological precursor evidence has not been effectively used in disaster management programs, the importance of tsunami deposit research has gained significant attention with the expectation that it will provide reliable information on the recurrence interval and size of devastating tsunamis. An improved understanding of the provenance, depositional processes, spatial distribution, and tsunami deposit variability will enhance our ability to identify, date, and quantify paleotsunamis.