A Method to Determine the Magnitude of Deep-focus Earthquakes In and Near Japan

In this paper, a method to determine the magnitude of deep-focus earthquakes in and near Japan from the observation data of Japan Meteorological Agency is proposed.The relation between the maximum amplitude of earthquake motion (mainly S waves) at a certain epicentral distance and the depth of the earthquake origins is approximately expressed by log10A=C-ΣCn(H/R)n where A is the amplitude, R is the radius of the earth, H is the depth of the origin, C=M-C0 (M means the magnitude), and each Cn is a certain constant.From the above equation, the magnitude is determined by M=log10A+K where K=C0+ΣCn(H/R)n.For the sake of convenience, the Ks for several distances and depths are given in a table.