Geoscience Reference
In-Depth Information
would have been forced to issue a warning at Hawaii, given the magnitude of the earthquake,
with a subsequent costly and time-consuming evacuation of coastal zones. As it was, the
Midway Island record conirmed that the tsunami was not going to signiicantly threaten lives
or property in the main Hawaiian island, and no evacuation order was issued.
After a similar Kuril Island earthquake on October 4, 1994, the lack of direct conirmation of
the existence of a tsunami (including lack of high-resolution sea level data from the temporar-
ily inoperative Midway Island station) resulted in the issuance of a warning that precipitated an
unnecessary evacuation of Hawaii's coastal zones.
Although many gaps exist in the sea level network for rapid tsunami detection, limitations
in U.S. and international resources preclude immediate closure of all gaps, and some of these
gaps are more important than others. A sophisticated analysis is needed to evaluate critical
coverage gaps for coastal sea level gauges to inform the warning decision process. Ideally,
such a study would include an evaluation of a region's tsunami-producing potential, sensitiv-
ity analysis of source location, tsunami travel time, local population density, timing for initial
warning versus evacuation decision process for communities at risk, and warning/evacuation
time gained for additional station coverage. Such an analysis could also determine the rela-
tive importance of each existing coastal sea level gauge to the tsunami warning decision and
evacuation decision processes. Although there is some degree of redundancy in coverage
in the current sea level gauge network, there has been no evaluation of the associated risk
and the vulnerability of the system to failures of single or multiple stations. It is possible that
isolated gauges near historically tsunami-producing seismic zones would be considered highly
important, while individual gauges among a relatively compact group of gauges might be
considered less important (although the need for at least one gauge within the group might
be considered highly important). Such an assessment of the relative importance of existing
gauges could then be the basis of prioritization for maintenance schedules and enhance-
ment opportunities, and for the identiication of critical stations that are not under U.S. control
and may require augmentation with new U.S. gauges as well as operations and maintenance
support.
In order to mitigate the cost of enhancing and maintaining tsunami-useful sea level moni-
toring stations, the U.S. Tsunami Program could continue coordinating with other programs
interested in monitoring sea level variability for other purposes, such as climate variability. Sea
level stations maintained by the NOS, UHSLC, etc., have evolved from their primary missions to
include higher sampling and reporting rates to serve the tsunami community. Coastal stations
with a broad user base have enhanced sustainability.
Reliability of the Coastal Sea Level Gauge Network
International coastal sea level networks vary greatly in station density, transmission rates,
and data quality. Improved near-real-time international sea level data observations are crucial
to proper TWC response for events distant to U.S. territories, and are necessary for the TWCs to
provide advice to their international customers.
