Geoscience Reference
In-Depth Information
est wave is expected to arrive, the extent of the inundation and run-up, and the appropriate
time to cancel the warning. Whether a call for evacuation is practicable, and how soon the “all
clear” can be sounded, will depend on many factors, but especially on how soon the tsunami is
expected to arrive and how long the damaging waves will continue to come ashore. Therefore,
the warning system needs to be prepared to respond to a range of scenarios. They range from
a near-ield tsunami that arrives minutes after an earthquake to a far-ield tsunami that arrives
many hours after a triggering, distant earthquake yet lasts for many more hours due to the
waves' scattering and reverberation along their long path to the shore. In the case of the near-
ield tsunami, major challenges remain to provide warnings on such short timescales.
The committee concludes that the global networks that monitor seismic activity and sea
level variations remain essential to the tsunami warning process. The current global seismic
network is adequate and suficiently reliable for the purposes of detecting likely tsunami-
producing earthquakes. However, because the majority of the seismic stations are not oper-
ated by the TWCs, the availability of this critical data stream is vulnerable to changes outside
of the National Oceanic and Atmospheric Administration's (NOAA's) control. The complex
seismic processing algorithms used by the TWCs, given the available seismic data, quickly yield
adequate estimates of earthquake location, depth, and magnitude for the purpose of tsunami
warning, but the methodologies are inexact. Recommendations to address these two con-
cerns fall under the following categories: (1) prioritization and advocacy for seismic stations;
(2) investigation and testing of additional seismic processing algorithms; and (3) adoption of
new technologies.
The tsunami detection and forecasting process requires near-real-time
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observations of
tsunamis from
both
coastal sea level gauges
and
open-ocean sensors (such as provided by the
Deep-ocean Assessment and Reporting of Tsunamis (DART) network). The committee inds that
the upgrades enabled by the enactment of the Tsunami Warning and Education Act (P.L. 109-
424) to both coastal sea level gauges and the DART network have signiicantly improved the
capacity of the TWCs to issue timely and accurate tsunami advisories, watches, and warnings.
Furthermore, these sensors provide researchers with the essential data to test and improve
tsunami generation, propagation, and inundation models after the fact.
The new and upgraded DART and coastal sea level stations have closed signiicant gaps in
the sea level observation network that had left many U.S. coastal communities subject to un-
certain tsunami warnings. Although both sea level gauge networks have already proven their
value for tsunami detection, forecasting, and model development, fundamental issues remain
concerning gaps in coverage, the value of individual components of the network, and the risk
to the warning capability due to coverage gaps, individual component failures, or failures of
groups of components.
Of special concern is the relatively poor survivability of the DART sta-
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The report generally uses the term near-real-time rather than real-time. Near-real-time data are returned by geo-
physical instruments after a variety of intermediary processes including illing a data buffer (e.g., with a length of a second
or more) and transferring data through various switches and routers in the Internet. Normally the resulting latency can
be as little as a second, several seconds, or minutes associated with the Internet connection modality (e.g., satellite, iber
optics, or network switches). Real-time data can generally be achieved only with very special sampling and transmission
protocols.
