The Japan Meteorological Agency magnitude scale () is a
seismic magnitude scale set by 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 ...
.
Overview
In Japan, for shallow (depth < 60 km) earthquakes within 600 km, the Japanese Meteorological Agency calculates a magnitude labeled MJMA, M
JMA, or M
J. (These should not be confused with moment magnitudes JMA calculates, which are labeled M
w(JMA) or M
(JMA), nor with the
Shindo intensity scale.) JMA magnitudes are based (as typical with local scales) on the maximum amplitude of the
ground motion
Ground motion is the movement of the earth's surface from earthquakes or explosions. Ground motion is produced by seismic waves that are generated by sudden slip on a fault or sudden pressure at the explosive source and travel through the earth a ...
; they agree "rather well" with the seismic moment magnitude in the range of 4.5 to 7.5,
[See also figure 3.70 in NMSOP-2.] but underestimate larger magnitudes.
Notes
Sources
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*. Also availabl
here(sections renumbered).
{{Seismology-stub
Seismic magnitude scales
Japan Meteorological Agency