Historical Seismograms - Evidence from the AD 2000 Izu Islands ...

1. IntroductionCatalogue of Chinese Earthquakes (M 2 6.5) 113Since the publication of a comprehensive catalogue of worldwide earthquakes byGutenberg and Richter (1954), Gutenberg (1956), Richter (1958), Duda (1965),RothC (1969), and others have made supplements and revisions. As the instrumentcharacteristics, the magnitude scale and the measurement methods are different,there is no unified standard for the magnitudes given in various catalogues, and evenfor different earthquakes in the same catalogue. Difficulties were encountered in theinvestigation of seismicity, earthquake prediction and hazard analysis based on suchdata, and incorrect conclusions were sometimes obtained. For example, using thecatalogues given in Seismicity of the Earth and Associated Phenomena (Gutenbergand Richter, 1954) and Great Earthquakes 1896-1903 (Gutenberg, 1956), it was concludedthat from 1896 to 1906 the average annual energy release from earthquakesall over the world was about three times the average value for the years 1907 to1955. Through careful study, Kanamori and Abe (1979) pointed out that this wasdue to the underestimation of the effective magnification for the undamped Milneseismograph in the recording of great earthquakes. When proper corrections weremade (in some cases as large as 0.6 magnitude units), the abnormally high annualenergy release simply did not exist.Since the 1970s, seismologists began work on the unification of the earthquakemagnitude scale. In order to compile a catalogue of global earthquake activity witha uniform magnitude scale defined by Gutenberg and Richter (G-R scale), Gellerand Kanamori (1977), and Abe and Kanamori (1979) investigated in detail themagnitude scale used in Seismicity of the Earth and Associated Phenomena. Abeand Kanamori (1980) also studied the magnitudes of large shallow earthquakes from1953 to 1977. Abe (1981) recalculated the magnitudes of large shallow earthquakesfrom 1904 to 1980 with a uniform magnitude scale. Later, Abe and Noguchi (1983a)redetermined the magnitudes of large shallow shocks from 1898 to 1917 by correctingthe magnification of undamped Milne and Omori seismographs. Thereafter,by re-evaluation of the quality of surface-wave magnitudes of shallow earthquakesbefore 1912, using the data given in the unpublished worksheets of Gutenberg andRichter (1954), Abe and Noguchi (198313) further revised the average effective gainof the undamped Milne seismographs and redetermined the Ms of large shallowearthquakes in the period 1897 to 1912. Thus, a catalogue of worldwide large shallowearthquakes from 1897 to 1980 was completed with uniform magnitude scale.In 1971, the first edition of Catalogue of Chinese Earthquakes was published bythe Central Seismological Group. Many editions were published successively, withthe catalogues of the State Seismological Bureau (1977), Lee et al. (1978), and Gu(1983) used most often. In principle, all these catalogues use the magnitudes given inGutenberg and Richter’s Seismicity of the Earth and Associated Phenomena or theirequivalents as standard (Gu, 1983). Actually, the data source is very complicated,the magnitude scale used is not the same, and detailed study and proper regressionanalysis were not carried out during the compilation. Therefore, the uniformity ofmagnitude in these catalogues is not satisfactory.In compiling the fourth volume of the Compilation of Historical Materials of ChineseEarthquakes (Xie et al., 1985-86), we revised the parameters of all earthquakesthat occurred between 1900 and 1948 to prepare a catalogue with a uniform magnitudescale. In this paper, the magnitude scale used and the method of analysisare described, and the results of the revision are discussed.