Geoscience Reference
In-Depth Information
Once the TWCs issue warnings, watches, or advisories, it is the responsibility of county
emergency management and/or public-safety agencies to issue their own messages to indi-
viduals in tsunami-prone areas (except in the case of near-ield tsunamis where evacuations
will be spontaneous and local agencies will have to react to, and instead of lead, the evacua-
tions). In many cases, after the TWCs issue their messages, county and state agencies discuss
the situation and potential strategies with the TWCs through teleconferences. Following these
conversations, individual jurisdictions will then make their own decisions regarding whether
to evacuate tsunami-prone areas or not. Pre-event tsunami education of local public-safety
oficers is important because their knowledge of tsunami threats, the vulnerability of local
populations, and the time and logistics required to evacuate these populations all play a factor
in the evacuation decision making process.
Disparities in knowledge and risk tolerance at the local level can lead to different decisions.
Although the TWCs are releasing information to an entire region (e.g., the Cascadia subduction
zone from northern California to Washington), individual county jurisdictions will decide how
to use this information in their own warning messages sent to people along their coasts. In the
response to the warning messages released during the June 14, 2005, event, there were cases
where adjacent counties in Oregon received the same information from the TWCs and yet
made different decisions. One county called for an evacuation, while the adjacent county did
not. To the public, these disparities in response are inconsistent and create confusion.
Effective Delivery of Warning Messages
Actions taken by the public are inluenced by the warning delivery method because of the
time it takes people to convert pre-warning perceptions of safety into current perceptions of
risk. The frequency of warning-message communications and the increasing number and types
of communication channels are shown to positively impact people's warning response. There
is no one single credible source of information, because various groups attach credibility to
different spokespeople, perceptions of credibility change with time, and credibility and warn-
ing message belief are not identical. Consequently, it is vital to create diverse sources of public
warnings, an effort that requires pre-event emergency planning and agreement from many
partners to disseminate the same warning message long before an event occurs.
Effective dissemination of warnings involves multiple organizations using multiple chan-
nels to frequently deliver the same message. Both TWCs disseminate their messages over
multiple channels, such as the National Warning System (NAWAS), State Warning Systems (e.g.,
Hawaii Warning System (HAWAS), California Warning System (CALWAS)), the Global Telecom-
munications Service (GTS), the NOAA Weather Wire, the Aeronautical Fixed Telecommunica-
tions Network, the military-related Gateguard circuit, emails, faxes and telex, and phone calls
(among others). With two warning centers sending messages over multiple channels, it is most
important that messages be consistent in order to minimize confusion by the public. However,
because the TWCs have different areas of responsibility (AORs), warning messages from the
two centers are designed for different audiences and contain different information (see more
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