MSK Intensity Scale as Compared with JMA Intensity Scale

Abstract

In order to examine the MSK seismic intensity scale as to its suitability to a country like Japan,106 stations under JMA (Japan Meteorological Agency) observed perceptible earthquakes by the MSK and JMA scales in the same time during four years from 1967 to 1970. Questionaire cards were made for the report of the observation of phenomenal items to determine the MSK intensity whose final determination was done by the authors. The reported shocks were divided into two categories, small shock and large one. Then they were investigated statistically in comparison with the JMA one. It was made clear that the JMA scale is adequate to the lower grades of intensity (1-3 in JMA), but it is rather rough to apply to the higher grades, whereas MSK scale is suitable to the higher grades and not adequate to the lower ones. The formula to estimate the MSK intensity corresponding to the JMA one of lower grade as high as 3 is obtained as M=1.5J+1.5, where M is the MSK intensity and J the JMA one. In the case of a large earthquake the relation between the two scales is approximately given by M=1.5J+0.75 for MSK 5-8. Each scale has its merits and defects and it is advisable to employ both of them by JMA using the JMA scale for urgent report and the MSK one for minute investigation in field work in the case of a large earthquake.