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

152 Tokuji UtsuThe first version of the new catalog was published in 1979 (Utsu, 1979), to whichsome corrections and additions were made in 1982 (Utsu, 1982a). The revisedcatalog is reproduced in Table 1 in a simplified form. In the original form, theaccuracy of epicenter and magnitude determination is indicated by using variousnotations, but these are neglected in Table 1 to save space. The last column ofTable 1 (headed D) gives the degree of damage as judged by the following criteria:0 - No damage.1 - Slight damage (cracks on walls and ground).2 - Light damage (broken houses, road, etc.).3 - 2-19 persons killed or 2-999 houses totally destroyed.4 - 20-199 persons killed.5 - 200-1999 persons killed.6 - 2000-19,999 persons killed.7 - 20,000 or more persons killed.x - Damage inseparable from that caused by the previous earthquake.In compiling the new catalog, I intended to include all earthquakes of M 2 6which were felt in Japan and all earthquakes which caused damage in Japan."Japan" means the present territory of Japan. Table 1 contains 534 felt earthquakesof M > 6 and 178 damaging earthquakes of which 63 have magnitudesbelow 6.0. In addition, if unfelt earthquakes are found in the area enclosed by thesolid lines in Figure 2 (hereafter called region A), they are included in the catalog.Only two earthquakes are in this category. In total, Table 1 lists 599 earthquakes.3. Seismicity of Japan for the Past 100 YearsIt is easy to compile a similar catalog for the years from 1926 to the present,since the hypocenters and magnitudes of earthquakes which occurred from 1926through 1960 were redetermined by the JMA (JMA, 1982). The focal parametersof earthquakes in and after 1961 have been published in monthly bulletins of JMA.By using the catalogs of JMA, Gutenberg and Richter (1954), ISS, ISC, etc., I haveextended the present catalog to the end of 1984. Thus the extended catalog coversjust 100 years from 1885 through 1984. A total of 1812 earthquakes are listed inthis catalog. Table 2 lists the number of earthquakes classified according to thedamage rating.Figures 2 and 3 show the distribution of seismicity for the past 100 years in spaceand time, respectively. Data on deep earthquakes (h 2 100 km) before 1900 are notplotted because of insufficiency of the data.Figure 4 shows the magnitude-frequency relation for shallow earthquakes. Fourformulas representing the relation have been fitted to the data using the maximumlikelihood method (Utsu, 1984). The straight line G indicates the well-knownGutenberg-Richter formula (b = 0.94). The three curves U, L, and M indicate thefollowing formulas :log n = a - bM + log (c - M )In N = A - B exp (a M)log N = A + log (c - M )Utsu (1971)Lomnitz-Adler and Lomnitz (1979)equivalent to MakjaniC (1980)