No abstract

Discrepancies arise among magnitudes as derived from local earthquake data (M L ), body waves (M B ) and surface waves (M S)This paper is in continuation of previous investigations Richter 1942, 1956].The earthquake magnitude has statistical and other uses independent of the relation between magnitude and energy. Indeed, it is possible that there is no complete one-to-one correlation between magnitude and energy for large and complex tectonic events. Even so, a mean or representative relation is a legitimate object of inquiry. In attempting to refine the magnitude-energy relation it was found [Gutenberg and Richter 1956] that three imperfectly consistent magnitude scales had been in use:M L determined from records of local earthquakes according to the original definition [Richter 1935]; M S from the amplitudes of surface waves for shallow teleseisms, [Gutenberg and Richter 1936;Gutenberg 1945a]; m B from the amplitude/period ratio of body waves for teleseisms, shallow and deep-focus [Gutenberg 1945b[Gutenberg , 1945c.The two latter were originally adjusted to coincide near M = 7, but were later found to diverge linearly so that The revision is based on a large body of data. Magnitudes have been derived by the senior author, from surface waves and from body waves separately, for a selection of better recorded large shallow earthquakes as listed by Gutenberg and Richter [1954]. Those for which there was suspicion of depth in excess of the normal (believed to be about 25 km) were rejected. Values of m B were plotted against those of M S , and (1) derived from the plot. The values a = 0.37, b = 6.76 are comparable with those found by Bath [1955] as follows:At Pasadena, a weighted mean is taken between m B as found directly from body waves, and m S , the corresponding value derived from M S by applying the relation (1), or still better from tables and charts set up to give m S directly from surface wave data. This weighted mean is designated the unified magnitude denoted by m.In Figure 1 residuals m B -m S on the basis a = 0.37, b = 6.76 are plotted against m, using amplitude and period data from all available station bulletins,

This supersedes Paper 1 (Gutenberg and Richter, 1942). Additional data are presented. Revisions involving intensity and acceleration are minor. The equation log a = I/3 − 1/2 is retained. The magnitude-energy relation is revised as follows: (20) log ⁡ E = 9.4 + 2.14 M − 0.054 M 2 A numerical equivalent, for M from 1 to 8.6, is (21) log ⁡ E = 9.1 + 1.75 M + log ⁡ ( 9 − M ) Equation (20) is based on (7) log ⁡ ( A 0 / T 0 ) = − 0.76 + 0.91 M − 0.027 M 2 applying at an assumed point epicenter. Eq. (7) is derived empirically from readings of torsion seismometers and USCGS accelerographs. Amplitudes at the USCGS locations have been divided by an average factor of 2 1/2 to compensate for difference in ground; previously this correction was neglected, and log E was overestimated by 0.8. The terms M2 are due partly to the response of the torsion seismometers as affected by increase of ground period with M, partly to the use of surface waves to determine M. If MS results from surface waves, MB from body waves, approximately (27) M S − M B = 0.4 ( M S − 7 ) It appears that MB corresponds more closely to the magnitude scale determined for local earthquakes. A complete revision of the magnitude scale, with appropriate tables and charts, is in preparation. This will probably be based on A/T rather than amplitudes.

Finally, in the geographical discussion, a limited use has been made of macroseismic and historical data. Sieberg (1932a) has been consulted throughout. Isobaths on the regional maps and terminology of oceano graphic features are based on Vaughan, et al. (1940). DEEP-FOCUS EARTHQUAKES This section revises and extends the results reported by Gutenberg andRichter in two previous papers (1938; 1939), to which the reader is referred for sources of the material used and for discussion of methods. In addi tion, recent deep shocks in the Japanese area have been checked against a list by Wadati (1939) for the years 1934-1938. New determinations of deep-focus earthquakes are given in Tables 1 and 2. All epicenters of deep-focus shocks now known to the authors are plotted in Figure l .2 They are also plotted, together with normalshocks, on the regional maps (Figs. 3-14).The general characteristics of the distribution of deep shocks are as described in earlier papers. A few individual shocks call for special comment. No. 3 p is in a new location near Barbados.No. 81 M is the first shock with depth in excess of 300 kilometers to be located in the New Hebrides area.Nos. 133 g and 133 i constitute an important southern extension of the line of inter mediate shocks on Luzon.2Maps used in this paper were drafted by Mr, John M. Nordquist. The world maps, Figures 1 and 2, are of his own design. The purpose was to construct a map which would present all the principal seismic areas and belts without excessive distortion or interruption. These world maps are not on any projection in the restricted sense; the meridians are drawn as circles, and divided proportionately into arcs through the ends of which the parallels are drawn.

Summary