Geoscience Reference
In-Depth Information
To date, no structures have been built in the United States speciically to serve as vertical
evacuation sites for tsunamis. In communities with high-rise buildings in low-lying areas (e.g.,
Honolulu, Los Angeles), vertical evacuation into existing buildings to avoid inundation from far-
ield tsunamis is promoted by local emergency managers. In communities threatened by near-
ield tsunamis, oficials should examine the structural integrity of buildings that may be used
for vertical evacuation. Earthquakes that precede the tsunami may make certain building types
(e.g., unreinforced masonry) unsafe for entry or for tsunami refuge and the subsequent tsunami
waves may overtop or destroy wood-based buildings that survive the initial earthquake.
Strong ground motions, ground failure, and land subsidence from earthquakes that pre-
cede near-ield tsunamis may also damage key egress routes, bridges, and critical facilities in
coastal communities, thereby putting additional constraints on an individual's ability to evacu-
ate a tsunami-prone area. Communities in Alaska, the Paciic Northwest, and Puerto Rico are
likely to experience several minutes of strong ground motions with tsunami inundation arriv-
ing only minutes later. An initial large earthquake would likely result in damage to critical infra-
structure in the evacuation zone (e.g., roads, bridges) and create barriers for individuals trying
to evacuate from an imminent tsunami (e.g., toppled power lines, building debris in roads,
etc.). Initial observations of the Chilean earthquake in February 2010 indicate this was the
case in many coastal communities. In addition, critical facilities, such as emergency manage-
ment ofices, police stations, and ire stations, could be destroyed by the original earthquake or
blocked by earthquake-related debris, possibly leaving emergency responders unable to man-
age local evacuations. Radio and television stations and the towers that transmit their signals
could also be damaged, thereby limiting the dissemination of warning or all-clear messages.
The number of critical facilities in tsunami-prone areas has been documented in several studies
(e.g., Charland and Priest, 1995; Lewis, 2007; Wood, 2007) and hazard mitigation plans (e.g., State
of Hawaii Multi-Hazard Mitigation Plan). However, these efforts are simple inventories that do
not delve into evacuation and response consequences of earthquake-damaged infrastructure
and facilities or whether there are redundant facilities and access routes.
Conclusion:
Although many communities in the United States are threatened by a
tsunami that originates from a source at close or intermediate distance, few evacuation
studies have been conducted to evaluate the ability of at-risk individuals to reach higher
ground before tsunami waves arrive. A related problem is that there have been no studies
to assess the potential impact of local earthquakes that generate near-ield tsunamis on
egress routes, supporting infrastructure (e.g., bridges), or facilities considered critical in
response efforts. Without such information, emergency managers are not able to identify
where targeted outreach is needed and where potential vertical evacuation structures
(e.g., buildings, engineered berms) may be warranted.
Recommendation:
For all communities with close or intermediate proximity (i.e., arrival
times ranging from minutes to about an hour) to a potential tsunami source, the NTHMP
should conduct evacuation modeling studies to assess the likelihood of successful
horizontal evacuations. These studies should include the potential impacts of preceding
