Abstract
In determining the instrumental magnitude of an earthquake we often experience that magnitudes determined for the same earthquake at different stations differs considerably from one another.
In the present paper, the discrepancies which are caused by the mechanism of an earthquake occurrence are investigated in the case when the magnitudes are determined by amplitudes of surface waves at each station.
We investigated in particular, the seismograms of the earthquake which occurred off the coast of Boso Peninsula, Japan, Nov. 25, 1958, recorded at 29 stations in various azimuths, and computed the energies of Rayleigh waves corresponding to the respective stations. The discrepancy which happened in magnitudes deduced from the energies are discussed.
The results obtained are as follows:
1) The relation between the energy of Rayleigh waves and the azimuth is expressed by formula (3) or figure (1).
2) The maximum discrepancy of magnitudes owing to the difference in azimuth is about 0.7 in magnitude scale.
