Japan Meteorological Agency magnitude scale

Not to be confused with Japan Meteorological Agency seismic intensity scale.

The Japan Meteorological Agency magnitude scale (Japanese: 気象庁マグニチュード) is a seismic magnitude scale set by the Japan Meteorological Agency.^[1]

Overview

In Japan, for shallow (depth < 60 km) earthquakes within 600 km, the Japan Meteorological Agency (JMA) calculates^[2] 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; they agree "rather well"^[3] with the seismic moment magnitude M_w  in the range of 4.5 to 7.5,^[4] but underestimate larger magnitudes.