抄録
Matsushiro Seismological Observatory, Japan Meteorological Agency.
Ih this paper, the author investigated the relation between the maximum perceptible distance, Δ and magnitude, M, by use of data for Matsushiro Swarm Earthquakes and shallow earthquakes occurred in or near Japan.
According to the result derived from present study, this relation was found to depend on the value of magnitude.
Therefore, the following formulae are useful for estimating the magnitude from maximum perceptible epicentral distance, namely, for Matsushiro Swarm Earthquakes and other earthquakes of M<5.5
M=1.5logΔ+1.6
and for greater earthquakes of M>5.5
M=2.6logΔ-0.8
and for the near shock, the hypocentral distance is rather suitable than epicentral distance.
The reason is as follows;
The attenuation of the maximum trace amplitude with epicentral distance by the same characteristic seismograph depends on the value of magnitude, M, i. e. earthquakes of smaller magnitude are subject to higher attenuation with epicentral distance.
