Tsunami Warning and Preparedness An Assessment of the U.S. Tsunami Program and the Nation's Preparedness Efforts (2011) / Chapter Skim
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2 Aligning Priorities with Societal Risks from Tsunamis
2 Aligning Priorities with Societal Risks from Tsunamis
Pages 37-72
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From page 37... ...
• Periodic reappraisal of tsunami sources and modeling codes, achieved in part through workshops and peer review. • Greater consistency, across state boundaries, in the methods, criteria, and judgments employed in modeling of tsunami inundation, achieved in part through collaboration among federal and state partners and through external review of inundation maps.
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From page 38... ...
Inundation models determine the areas likely to be flooded by a tsunami and involve numerical computations of tsunami evolution for specific tsunami scenario or consider an ensemble of tsunami scenarios that might affect the map area. Hazard maps depict inundation areas on base maps that typically include contours, imagery, buildings, roads, and/or critical infrastructure and take into account local geologic knowledge.
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From page 39... ...
The rest of the chapter reviews progress in assessing tsunami hazard and tsunami vulnerability. Aspects of perceptions, knowledge, and preparedness levels that influence individual resilience are discussed in the following chapter.
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From page 40... ...
. To this date, NTHMP resources are being allocated on the basis of estimated hazards, without regard for vulnerability (National Tsunami Hazard Mitigation Program, 2009a)
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From page 41... ...
the complex and interdependent nature of coastal communities in larger economic or sociopolitical systems, (3) the poorly defined mix of near-field and far-field tsunami hazards that coastal communities face, and (4)
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From page 42... ...
. 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.
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From page 43... ...
Inundation Modeling Credible tsunami inundation modeling requires three elements: (1) an understanding of the tsunami source that generates the tsunami, usually through estimation of seafloor displacement; (2)
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From page 44... ...
a tsunami hazard map developed for a Cascadia subduction zone earthquake scenario and (B) an evacuation map that includes evacuation zones for a Cascadia-related tsunami (in yellow)
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From page 45... ...
Local tsunami sources caused loss of life in the Virgin Islands in 1867 and in western Puerto Rico in 1918 (O'Loughlin and Lander, 2003)
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From page 46... ...
(A) Global sketch of subduction zones and landslides known or inferred to pose tsunami hazards.
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From page 47... ...
Inundation modeling in Alaska uses historical events (e.g., the 1964 Great Alaskan Tsunami) as well as a set of hypothetical tsunami scenarios unique for each local community for the tsunami sources.
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From page 48... ...
A tsunami hazard assessment based on U.S. written history alone would overlook nearly all the tsunami hazards from earthquakes on the Cascadia subduction zone and the Seattle fault, and from most of the landslides off southern California and the U.S.
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From page 49... ...
Conclusion: Because knowledge about the sizes and the recurrence intervals of tsunami sources are only emerging, improving the understanding of the tsunami sources is critical to producing comprehensive tsunami risk assessment. Currently, no formal procedures for periodic re-evaluation of tsunami risks exist.
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From page 50... ...
Therefore, inundation modeling requires integrated bathymetry data over the entire ocean basin and coastal topographic data. Requirements for horizontal resolution of bathymetric data are not constant and vary depending on depth.
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From page 51... ...
In addition to the source parameters, there is inherent uncertainty in the models and the accuracy of topographic and bathymetric data that precludes the possibility of a completely accurate and precise tsunami inundation model. It is multi-scale because of differ e of differences in the wavelength of tsunamis (on the order of hundreds of kilometers)
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From page 52... ...
Recommendations: To improve tsunami inundation modeling, the NTHMP, through workshops convened with the USGS and academic institutions, should periodically review progress in hydrodynamic models, including peer-reviews of modeling codes and discussions on how to better incorporate variations in coastal bathymetry, topography, vegetation, and buildings into inundation models.
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From page 53... ...
Despite an increase in demand for tsunami hazard maps in the wake of the 2004 Indian Ocean tsunami, federal support to undertake mapping efforts did not increase and, in contrast, some states actually received fewer financial resources thereafter (Figure 2.3)
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From page 54... ...
. Under the recently adopted NTHMP strategic plan (National Tsunami Hazard Mitigation Program, 2009a)
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From page 55... ...
enhanced by 3 to 10 m DEMs on shore HI Report and maps of Evacuation maps from Initial 725 of 1,500 km of coastlines tsunami inundation 1-D modeling for state completed with 1-D modeling; completed; Updating 28 Credible worst-case scenarios used; communities with 2-D 2-D numerical modeling of five major modeling; Oahu modeling/ trans-Pacific tsunamis during the past inundation mapping century under way; Validation with complete and Hawaii historical run-up records; Identified in progress; Expected 10 locations of the current evacuation completion Dec 2009 maps that may need modification OR Report, maps, GIS Detailed hazard maps for Distinguish between a tsunami caused projects 10 communities completed; by an undersea earthquake near the Tsunami evacuation zone Oregon coast (local tsunami) and an maps for 23 communities undersea earthquake far away from completed the coast (distant tsunami)
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From page 56... ...
shores, because nearby sources pose the greater tsunami hazard, provide the least amount of time for at-risk individuals to react and evacuate, and details of slip distribution on a fault plane, or of the orientation of a landslide block, tend to have their greatest effects on tsunami heights nearby. In addition to tsunami sources, several different numerical codes are being used by NTHMP members, including MOST, Cornell Multi-grid Coupled Tsunami Model (COMCOT)
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From page 57... ...
as well as a set of hypothetical Center, tsunami scenarios unique for each local community are used for the University of tsunami sources. Alaskan inundation modeling is challenging because Alaska of large tidal fluctuations (more than 7 m in some localities)
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From page 58... ...
Lastly, states also vary in their approach to postprocessing of the inundation modeling output. Similar to tsunami source determinations, inundation model outputs and the numerical codes that produced them have not been universally peer-reviewed or subject to quality control standards.
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From page 59... ...
This approach may also alleviate strains on state budgets and the lack of financial resources, which were cited by many NTHMP members as one of the key challenges to making progress in producing the next generation of inundation maps. This approach follows language in the 2006 Tsunami Warning and Education Act, which calls for the NOAA Tsunami Program to provide "tsunami inundation models and maps for use in increasing the preparedness of communities" (Section 4(b)
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From page 60... ...
To eliminate these unnecessary and costly differences in inundation modeling approaches, the committee recommends that inundation modeling be conducted consistently across state lines and be executed through a cooperative partnership among NOAA, the USGS, and NTHMP members, and not by the individual NTHMP members as is the current practice. The committee proposes the following strategy: • irst, NOAA could take a lead to organize a workshop to establish community F hydrodynamic models used for tsunami inundation modeling: one set for co-seismic tsunami sources and another set for landslide tsunami sources.
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From page 61... ...
Throughout the task of inundation modeling, the committee emphasizes that NTHMP members would continue to be responsible for producing hazard maps that reflect local conditions and needs. Evacuation Maps Evacuation maps depict areas that may need to be evacuated in the event of a tsunami and are designed to be understood and used by at-risk individuals and by local emergency managers in their evacuation-planning efforts.
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From page 62... ...
As outlined in its strategic plan (National Tsunami Hazard Mitigation Program, 2009a) , the NTHMP plans to inventory all tsunami evacuation maps by 2010 and to thereafter increase the number of maps annually by 10 percent.
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From page 63... ...
Evacuation maps in Oregon, Washington, California, and Puerto Rico use yellow to denote tsunami evacuation zones, while in Hawaii the static maps found online denote the hazard zones as gray and the maps in phone books in red. Variations also exist among tsunami evacuation maps with regard to accompanying text on the map products that explains how to use the map and to prepare for future tsunamis (Table 2.5)
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From page 64... ...
was active, but led to the static PDFs of evacuation maps for the island. b For the static evacuation maps in Hawaii and in Puerto Rico, no accompanying documentation was included in the map or could be found.
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From page 65... ...
To improve public access to evacuation maps, the NTHMP should develop a national, online repository for tsunami evacuation maps and host a consistent online mapping application for all tsunami evacuation zones across the United States. The NTHMP should annually update the inventory of evacuation maps relative to the number of at-risk communities.
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From page 66... ...
As the tsunami research community increases its efforts into assessments of population exposure and other elements of vulnerability assessment, it would benefit from leveraging ongoing efforts for other hazards in the various agencies. Individual and community vulnerability to tsunami hazards are dynamic processes that require monitoring due to changing coastal populations, risk perceptions, and use of tsunamiprone areas.
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From page 67... ...
. The committee found that by 2010, reports attempting to inventory the number and types of people in tsunami hazard zones in coastal communities have been completed for the tsunami-prone areas of Hawaii (Wood et al., 2007)
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From page 68... ...
Some state plans estimate the number of individuals in tsunami hazard zones of each county, some simply list the communities with populations with tsunami risk, and some only discuss general tsunami-related population issues. Many plans, however, did include detailed information on financial, structural, and critical facility exposure, suggesting that plans are written to help document potential long-term economic impacts and not preparedness issues to save lives.
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From page 69... ...
coastal communities that are threatened by tsunamis reaching shores in an hour or less. Such modeling efforts have been used to study the influence of congestion due to crowds and road bottlenecks on the ability of individuals to evacuate tsunami hazard zones (e.g., Lammel et al., 2008)
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From page 70... ...
Strong ground motions, ground failure, and land subsidence from earthquakes that precede near-field tsunamis may also damage key egress routes, bridges, and critical facilities in coastal communities, thereby putting additional constraints on an individual's ability to evacuate a tsunami-prone area. Communities in Alaska, the Pacific Northwest, and Puerto Rico are likely to experience several minutes of strong ground motions with tsunami inundation arriving only minutes later.
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From page 71... ...
Aligning Priorities with Societal Risks from Tsunamis earthquakes on key egress routes and consideration of any special-needs populations in tsunami-prone areas. In communities where the time required for at-risk individuals to reach higher ground is likely greater than predicted tsunami wave arrival times, the NTHMP should conduct feasibility and effectiveness studies of various vertical evacuation strategies (e.g., buildings, engineered berms)
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