Geoscience Reference
In-Depth Information
In modern TWS this technology is automized. However, the main physical prin-
ciples of operative tsunami forecasting remain the same. The possibility itself of
warning is based on the propagation velocity of seismic waves being many times
larger than the velocity of a tsunami wave. A warning is announced, when registra-
tion occurs of an underwater earthquake of magnitude exceeding a threshold value.
In Russia, the Far East tsunami service is implemented by seismic stations of
the Geophysical service of the Russian Academy of Sciences and by meteosta-
tions of the Administrations of Hydrometeorological Services (AHMS) subordinate
to the Committee for Hydrometeorology of the Russian Federation. The tsunami
service relies on seismostations of Petropavlovsk-Kamchatskyi and Ust-Kamchatsk
(Kamchatka), Yuzhno-Sakhalinsk (isl. Sakhalin), Severo-Kurilsk (isl. Paramushir),
Kurilsk (isl. Iturup) and Yuzhno-Kurilsk (isl. Kunahsir). The meteostations of
the Kamchatka AHMS and the Sakhalin AHMS, as well as the tsunami centres
of these Administrations are on round-the-clock duty for implementation of oper-
ative tsunami warning service and preparation of routine and/or urgent dispatches
and reports.
A well-developed Tsunami Warning System has been organized in the USA
within the National Oceanic and Atmospheric Administration (NOAA). It includes
several hundreds of seismic and mareographic stations. All these stations, as well as
several large oceanic buoys and sea-floor sensors reporting the ocean level transmit
the information obtained in a real-time mode to the common servers of two cen-
tres: ATWC in Palmer, Alaska and PTWC in Honolulu, Hawaii. The information is
freely available to all Internet users. The tsunami service in Japan, created signifi-
cantly earlier than the others, is subordinate to the Japanese Meteorological Agency
(JMA) and is noted for its very high level of organization.
An important success, achieved in operative tsunami prognosis, consists in
the possibility of rapid (real-time) calculation, with a precision and reliability suffi-
cient for practical purposes, of the arrival time of a wave at a given (protected) point
of the coast. Such a calculation can be performed by applying simple ray theory. To
this end it is only necessary to know the location of the tsunami source and the dis-
tribution of depths in the basin considered. We recall that the tsunami propagation
velocity depends on the ocean depth, c = g H . Data on the bathymetry of the World
Ocean are free for a grid with steps of 1
1 angular minutes, and for many regions
even with a significantly improved spatial resolution.
The situation concerning calculation of a tsunami run-up height at a given point
of the coast is much worse. The calculation precision and speed required for prac-
tical purposes in resolving this problem have not been achieved yet. On the one
hand, this is due to the enormous volume of calculations to be performed in esti-
mating the evolution of a wave starting from its rise at the source up to its run-up to
the shore. On the other hand, in the real-time mode it is impossible to calculate what
has happened at the tsunami source with necessary precision. The time required for
the reliable determination of sea-floor deformations, due to an earthquake, essen-
tially exceeds minutes or even hours available for operative forecasting. In those
cases, when underwater landslides participate in the tsunami generation, operative
resolution of the problem turns out to be practically impossible.
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