Geoscience Reference
In-Depth Information
Tsunami Detection and
Forecasting
SUMMARY
An incoming tsunami may be anticipated in many ways, from direct human recognition
of cues such as earthquake shaking or an initial recession of the sea, to technological warn-
ings based on environmental sensors and data processing. This chapter reviews and evaluates
the technological detection and forecasting capabilities of the U.S. tsunami warning centers
(TWCs) paying speciic attention to the infrastructure of the earth and ocean observation
networks and to the data processing and tsunami modeling that occur at the TWCs. The next
chapter discusses the centers' operations, their human resources, and the infrastructure for
their warning functions.
The initial decisions by the TWCs to issue an initial tsunami advisory, watch, or warning
after an earthquake are based on analyses of data from a global seismic detection network,
in conjunction with the historical record of tsunami production, if any, at the different seismic
zones (see Weinstein, 2008; Whitmore et al., 2008 for greater detail on the steps taken).
Although adequate for most medium-sized earthquakes, in the case of very large earthquakes
or tsunami earthquakes
1
the initial seismological assessment can underestimate the earth-
quake magnitude and lead to errors in assessing the tsunami potential (Appendix G). Far from
the tsunami source, data from sea level networks provide the only rapid means to verify the ex-
istence of a tsunami and to calibrate numerical models that forecast the subsequent evolution
of the tsunami. Near the source, a tsunami can come ashore before its existence is detected by
the sparse sea level observation network.
Two separate U.S. TWCs monitor seismic activity and sea levels in order to detect tsunamis
and warn of their presence. Based on their own data analysis, the TWCs independently decide
whether to issue alerts to the emergency managers in their respective and complementary
areas of responsibility (AORs). The TWCs must not only provide timely warnings of destructive
tsunamis, but also must obviate needless evacuations that can cost money and even lives. An
ideal warning would provide emergency managers with the necessary information to call for
an evacuation in a timely fashion at any particular location in the projected tsunami path. The
ideal product would also be clearly worded so that the general public easily understands the
threat and who is affected by the threat. This information includes predictions of the time of
arrival of the ocean waves, the duration of the occurrence of damaging waves, when the larg-
1
An earthquake that produces an unusually large tsunami relative to the earthquake's magnitude (Kanamori, 1972).
