Geoscience Reference
In-Depth Information
Tsunami risk assessments are challenging due to (1) the paucity of information about the
frequency, sources, and characteristics of past tsunamis, (2) the complex and interdependent
nature of coastal communities in larger economic or sociopolitical systems, (3) the poorly
deined mix of near-ield and far-ield tsunami hazards that coastal communities face, and
(4) the uncertainty of potential impacts of future events. Although societal risk from tsunamis
is challenging to assess, it is critical information for the development and prioritization or risk-
reduction efforts, such as education, preparedness planning, warning-system development,
mitigation planning, and response strategies.
An effective risk characterization should be undertaken with local decision makers in
mind and should be directed toward informing speciic choices of public oficials and affected
individuals (National Research Council, 1996a). When developing the analysis for decision tools
(e.g., inundation maps, vulnerability assessments, evacuation maps), scientists need to en-
gage and deliberate with decision makers to assess their information needs and create useful
decision tools (e.g., Fischhoff et al., 1978; National Research Council, 1996a, 2007; Gregory and
Wellman, 2001; Bostrom et al., 2008; Renn, 2008). Risk analysis involves the systematic collection
and interpretation of quantitative or qualitative data to better understand hazards and vulner-
able communities (National Research Council, 1996a). Risk deliberation is any communicative
process in which technical experts, public oficials, and affected parties collectively consider
risk issues to ensure that decision-relevant knowledge and diverse perspectives are included in
any risk reduction process (National Research Council, 1996a).
There is no single method to properly characterize all aspects of risk from tsunamis; differ-
ent techniques are needed to address different aspects (e.g., demographic sensitivity, structural
fragility, inancial exposure) and their potential risk-reducing adjustments (e.g., education pro-
grams, structural mitigation, insurance). However, best practices suggest including assessments
of possible exposure sources and pathways (including geospatially speciic susceptibilities to
tsunamis), potential consequences, the effects of feasible risk reduction options, and the prob-
abilities and uncertainties of exposures and ensuing effects. Probabilistic assessment can be a
tool to provide a basis for cost-beneit analysis and design considerations for tsunami mitiga-
tion efforts (e.g., design criteria of an evacuation structure) and a transparent basis for prioritiz-
ing resources. Geographic information system (GIS)-based analyses of socioeconomic exposure
to tsunamis are useful for identifying demographic sensitivities within a community that could
impact evacuations. Assessments of adaptive capacity and resilience can identify educational
needs and pre-event preparedness levels.
The level of sophistication, accuracy, resolution, and format required for assessing societal
risk to tsunamis will depend on the intended use of the information. For example, education
efforts designed to raise hazard awareness, such as teaching people to recognize natural cues,
may only require oral histories from tsunami survivors (Dudley, 1999) or coarse delineations of
run-ups from past events (Theilen-Willige, 2006) to indicate tsunami-prone areas (see Box 2.1
for deinitions). By contrast, evacuation planning usually requires computer modeling of
various tsunami evacuation scenarios (Katada et al., 2006; Yeh et al., 2009). Urban planning or
detailed assessments of economic impacts require even higher resolution calculations (Borrero
et al., 2005).
