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-field tsunami that arrives minutes after an earthquake to a far-field 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-field 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 sufficiently reliable for the purposes of detecting likely tsunami-producing earthquakes. However, because the majority of the seismic stations are not operated 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 concerns 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-time2 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 finds 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 significantly 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 significant gaps in the sea level observation network that had left many U.S. coastal communities subject to uncertain 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-

2

The report generally uses the term near-real-time rather than real-time. Near-real-time data are returned by geophysical instruments after a variety of intermediary processes including filling 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, fiber optics, or network switches). Real-time data can generally be achieved only with very special sampling and transmission protocols.



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