Magnitudes of large shallow earthquakes from 1904 to 1980

In order to obtain a uniform magnitude catalogue, surface-wave magnitudes M_s and broad-band body-wave magnitudes m_B have been determined for large shallow earthquakes from 1904 to 1980. In making the catalogue homogeneous, the author consistently adheres to the original definitions of M_s and m_B given by Gutenberg (1945) and Gutenberg and Richter (1956). The determinations of M_s and m_B are all based on the amplitude and period data listed in Gutenberg and Richter's unpublished notes, bulletins from stations worldwide, and other basic information. m_B is measured on broad-band instruments in periods of ～8 s. Consistency of the magnitude determinations from these different sources is carefully checked in detail. More than 900 shallow shocks of magnitude 7 and over are catalogued. The meaning of the magnitude scales in various catalogues is examined in terms of M_s and m_B. Most of the magnitudes listed by Gutenberg and Richter (1954) in their “Seismicity of the Earth” are basically M_s for large shocks shallower than 40 km, but are basically m_B for large shocks at depths of 40–60 km. The surface-wave magnitudes given by “Earthquake Data Reports” are higher than M_s by 0.2 unit whether the combined horizontal amplitude or the vertical amplitude is used. m_B and the currently used 1 s body-wave magnitude are measured at different periods and should not be directly compared.