Japan
Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...
has a nationwide Tsunami Warning system (). The system usually issues warnings a few minutes after an
Earthquake Early Warning
An earthquake warning system or earthquake early warning system is a system of accelerometers, seismometers, communication, computers, and alarms that is devised for notifying adjoining regions of a substantial earthquake while it is in progress ...
(EEW) is issued, should waves be expected,
usually when a combination of high magnitude, seaward epicenter and vertical
focal mechanism
The focal mechanism of an earthquake describes the deformation in the source region that generates the seismic waves. In the case of a fault-related event it refers to the orientation of the fault plane that slipped and the slip vector and is ...
is observed. The tsunami warning was issued within 3 minutes with the most serious rating on its warning scale during the
2011 Tōhoku earthquake and tsunami
The occurred at 14:46 JST (05:46 UTC) on 11 March. The magnitude 9.0–9.1 (M) undersea megathrust earthquake had an epicenter in the Pacific Ocean, east of the Oshika Peninsula of the Tōhoku region, and lasted approximately six minutes ...
; it was rated as a "major tsunami", being at least 3 m (9.8 ft) high.
An improved system was unveiled on March 7, 2013, following the 2011 disaster to better assess imminent tsunamis.
Overview
When an earthquake occurs, the
Japan Meteorological Agency
The , abbreviated JMA, is an agency of the Ministry of Land, Infrastructure, Transport and Tourism. It is charged with gathering and providing results for the public in Japan that are obtained from data based on daily scientific observation an ...
(JMA) estimates the possibility of tsunami generation from seismic observation data. If disastrous waves are expected in coastal regions, JMA issues a Tsunami Warning/Advisory for each region expected to be affected based on estimated tsunami heights. JMA also issues information on tsunami details such as estimated arrival times and heights.
After an earthquake occurs, JMA issues Tsunami Warnings/Advisories and Tsunami Information bulletins if a tsunami strike is expected. Major Tsunami Warnings are issued in the classification of Emergency Warnings as of 30 August 2013.
Tsunami Warning / Advisory
When an earthquake occurs that could generate a disastrous tsunami in coastal regions of Japan, JMA issues Major Tsunami Warnings, Tsunami Warnings and/or Tsunami Advisories for individual regions based on estimated tsunami heights around three minutes after the quake (or as early as two minutes in some cases
[Earthquakes in and around Japan to which JMA can apply the Earthquake Early Warning technique to promptly and accurately determine the hypocenter and magnitude]).
Immediately after an earthquake occurs, JMA promptly establishes its location, magnitude and the related tsunami risk. However, it takes time to determine the exact scale of earthquakes with a magnitude of 8 or more. In such cases, JMA issues an initial warning based on the predefined maximum magnitude to avoid underestimation.
When such values are used, estimated maximum tsunami heights are expressed in qualitative terms such as "Huge" and "High" in initial warnings rather than as quantitative expressions. Once the exact magnitude is determined, JMA updates the warning with estimated maximum tsunami heights expressed in quantitative terms.
Major Tsunami Warnings are issued in the classification of Emergency Warnings. Detailed information on Emergency Warnings is provided on the
Emergency Warning System article.
See also
*
Emergency Warning System
References
Note
External links
Tsunami Warning / Advisory- JMA
{{CC-notice, by4, cc=CC-BY4.0, url=https://www.jma.go.jp/jma/en/copyright.html
Warning systems
Warning system
Japan Meteorological Agency