Geoscience Reference
In-Depth Information
event is another signiicant factor in understanding societal vulnerability to tsunamis (National
Science and Technology Council, 2005). These resilience factors inluence the ability of an
individual to prepare for future tsunamis and to take self-protective measures when a tsunami
occurs. This sub-section on evacuation potential focuses on assessing the ability of individuals
to evacuate tsunami-prone areas based on physical characteristics of the tsunami hazard zone
(e.g., distance to higher ground, integrity of egress routes, island with no high ground), while the
role of perceptions, knowledge, and preparedness levels in increasing resilience is discussed in
the following chapter on education, preparedness, and evacuation coordination.
Evacuation modeling estimates the amount of time necessary for people to reach safe
havens from various locations in tsunami hazard zones (Post et al., 2008), which is especially
critical for U.S. coastal communities that are threatened by tsunamis reaching shores in an
hour or less. Such modeling efforts have been used to study the inluence of congestion due
to crowds and road bottlenecks on the ability of individuals to evacuate tsunami hazard zones
(e.g., Lammel et al., 2008); the effectiveness of oficial routes in managing the typical number
of people who will need to evacuate (Ismail et al., 2008); the likelihood of casualties (Koshimura
et al., 2006); or the need for vertical evacuation structures (e.g., buildings, engineered berms)
in places where time is not available to reach naturally occurring higher ground (Yeh et al.,
2005; Federal Emergency Management Agency, 2008). Such analysis can answer fundamental
questions that might ultimately determine the survival of people: Under what circumstances is
it most effective to evacuate on foot instead of car due to congestion or earthquake-damaged
infrastructure? Under what circumstances is it best to use vertical evacuation (e.g., tall build-
ings, engineered berms) because ground-based evacuations may not be practical in communi-
ties that must evacuate thousands of people from a large tsunami-prone area?
Although there is basic research focused on tsunami evacuation modeling, the committee
found little applied evacuation modeling research (e.g., Yeh et al., 2009) to examine speciic U.S.
coastal communities that may only have minutes to an hour to evacuate thousands of indi-
viduals from tsunami-prone areas (e.g., Seaside, Oregon; Ocean Shores, Washington). In areas
where ground-based evacuations may not be feasible (due to short times before inundation
and substantial distances to higher ground) and where there are no existing structures or fea-
tures capable of serving as a vertical refuge, workshops are being held in coastal communities
(e.g., Cannon Beach, Oregon, in September, 2009; Long Beach, Washington, in January 2010) to
further discuss the opportunities and constraints of vertical evacuation structures for tsunamis
(e.g., buildings, engineered berms). Although engineering guidelines have been published and
oficials in some coastal communities are expressing interest in new structures (Federal Emer-
gency Management Agency, 2008), the committee found no case studies that delve into the
social and economic aspects of vertical evacuation structures in at-risk communities. In addi-
tion, because there is very limited information about current velocities as the tsunami interacts
with the built environment (and currently no measurements are being taken), it is dificult to
estimate the forces involved with a tsunami low ield and to assess what structures might re-
main intact during a tsunami. Before communities commit signiicant time and funds to these
structures, communities need a careful determination of the feasibility and issues related to
near-ield tsunami evacuations.
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