Japan Meteorological Agency seismic intensity scale Japan Meteorological Agency seismic intensity scale The Japan Meteorological Agency seismic intensity scale is a seismic scale used in Japan to measure the intensity of earthquakes. It is measured in units of . Unlike magnitude measures such as the moment magnitude scale (Mw), and the earlier Richter magnitude scale, which attempt to describe the energy released by the earthquake, the JMA scale describes the degree of shaking at various points on the Earth's surface, and is analogous to the Mercalli intensity scale. The intensity of an earthquake is not totally determined by its magnitude, but varies with event's depth, and
Richter magnitude scale used by astronomers. Second, he wanted a magnitude of zero to be around the limit of human perceptibility. Third, he specified the Wood-Anderson seismograph as the standard instrument for producing seismograms. Magnitude was then defined as "the logarithm of the maximum trace amplitude, expressed in microns", measured at a distance of 100 km. The scale was calibrated by defining a magnitude 3 shock as one that produces (at a distance of 100 km) a maximum amplitude of 1 micron (1 µm, or 0.001 millimeters) on a seismogram recorded by a Wood-Anderson torsion seismograph. Finally, Richter calculated a table of distance