Magnitudes of great shallow earthquakes from 1953 to 1977

Abstract

The surface-wavemagnitudes M s are determined for 30 great shallow earthquakes that occurred during the period from 1953 to 1977. The determination is based on the amplitude and period data from all available station bulletins, and the same procedure as that employed in Gutenberg and Richter's “Seismicity of the Earth” is used. During this period, the Chilean earthquake of 1960 has the largest M s , 8.5. The surface-wave magnitudes listed in “Earthquake Data Reports” are found to be higher than M s on the average. By using the same method as that used by Gutenberg, the broad-band body-wave magnitudes m B are determined for great shallow shocks for the period from 1953 to 1974. m B is based on the amplitudes of P, PP and S waves which are measured on broadband instruments at periods of about 4–20 s. The 1-s body-wave magnitudes listed in “Bulletin of International Seismological Center” and “Earthquake Data Reports” are found to be much smaller than m B on the average. Through the examination of Gutenberg and Richter's original worksheets, the relation between m B and M s is revised to m B = 0.65 M s+ 2.5 which well satisfies the mg and M s data for M s between 5.2 and