Geoscience Reference
In-Depth Information
•
Community Connections
that educate the public about tsunami safety and prepared-
ness and inform the public about the TWC's role in tsunami warning. Effective commu-
nity connections include partnerships with media and the community that develop
community preparedness and other resilience initiatives (U.S. Indian Ocean Tsunami
Warning System Program, 2007) (community preparedness efforts are discussed in
detail in Chapter 3).
Tsunami Detection
Tsunami detection requires information gathering, data analysis and assessment, and
decision making and communication. Earthquake detection functions required at both the TWCs
are similar and comprise the following basic steps (see Weinstein, 2008; Whitmore et al., 2008):
(1) Seismic data analysis systems automatically and rapidly evaluate the location, size, and
focal mechanism of an earthquake to determine if it has signiicant potential to trigger
a tsunami. Watchstanders reassess the event by analyzing select seismic data and may
empirically adjust the moment magnitude determination;
(2) Watchstanders determine if the magnitude is above certain thresholds and based on
this analysis, generate and disseminate initial messages (with either a watch, warning,
or information bulletin);
(3) For each signiicant earthquake, watchstanders estimate corresponding tsunami
arrival times and heights for selected critical locations;
(4) Once sea level data are acquired, watchstanders reassess the threat, including scaling
earlier, computed tsunami forecast scenarios to it the sea level observations from the
Deep-ocean Assessment and Reporting of Tsunamis (DART) systems; if needed (e.g., if
sea level data are lacking) watchstanders continue post-processing the seismic data to
reine the threat assessment;
(5) Watchstanders generate and disseminate follow-up informational messages with
the additional detailed information available from sea level and seismic data analysis
(National Oceanic and Atmospheric Administration, 2008a, c);
(6) Watchstanders iterate steps 5 and 6 until an appropriate time interval (based on
the expected tsunami propagation speed and modeled duration of inundation) has
passed and all watches or warnings for the AOR shorelines can be lifted.
The TWCs consider “signiicant” earthquakes as events exceeding certain predetermined
magnitude thresholds, which also depend on the distance offshore. These events automatically
trigger the audio alarm systems of the two TWCs, prompting on-duty watchstanders to initi-
ate a detailed investigation of the earthquake and its potential to trigger tsunamis. Typically,
watchstanders at both TWCs are required to make initial and independent estimates of the
earthquake location and magnitudes within 5 to 15 minutes of the earthquake origin time (Na-
tional Oceanic and Atmospheric Administration, 2008a, c). The location determines which TWC
