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So far, no comprehensive risk assessments have been undertaken that could guide the set-
ting of priorities at the state or national level. Existing risk assessments are uneven and are typi-
cally isolated efforts for speciic sites (e.g., González et al., 2006). The only national assessment
to date is an evaluation of tsunami hazards, based on the written historical records available
at the NOAA/National Geophysical Data Center (NGDC) (Dunbar and Weaver, 2008) with the
rationale being that “the state of geologic knowledge [of tsunami sources] does not permit the
calculation of meaningful probabilities of occurrence.”
Although hazard researchers may be uncomfortable with the lack of information about
occurrence, probabilistic risk assessment can be an indicator for the relevance and import of
existing evidence, despite the uncertainties. Probabilistic risk assessment for nuclear power
plants and for earthquakes show how risk assessments can be constructed for rare, high-
consequence events in order to inform planning efforts and designs (e.g., McGuire and Becker,
2004; McGuire, 2008). Where data are sparse, expert judgment can be used to qualify the avail-
able data appropriately. For example, tsunami planning has been so far based on worst-case
scenarios, with inconsistent choices made about speciic scenarios and little understanding
of consequences or expected losses. Where extremely rare, high-consequence events are the
worst case, communities that are much more likely to see smaller yet damaging tsunamis may
not be prioritized for funding. Such tradeoffs deserve to be explicitly considered and can be
incorporated into quantitative and qualitative risk assessments using expert judgment in a
deliberative process (National Research Council, 1996a).
Conclusion: The United States lacks a national tsunami risk assessment that characterizes
the hazards posed by tsunamis, inventories the populations and social assets threatened
by tsunamis, measures the preparedness and ability of individuals and communities for
successful tsunami evacuations, and forecasts expected losses. This information is needed
to help spur and prioritize investments in preparedness, education, detection, and warning
efforts and for developing long-term strategic planning at the local, state, and federal level.
Recommendation: NOAA and its NTHMP partners, in collaboration with researchers in
social and physical sciences, should complete an initial national assessment of tsunami
risk in the near term to guide prioritization of program elements. The national tsunami
risk assessment should (1) incorporate the best possible relevant science (social and
behavioral science, geography, economics, engineering, oceanography, and geophysics)
and (2) include broad stakeholder and scientiic participation to ensure that efforts are
responsive to the needs of at-risk communities and decision makers.
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