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

402 S. Miyamuraberg (1956), Gutenberg and Richter (1954), Rothd (1969), and Duda (1965) areconsidered as standard catalogs for the periods of 1896-1903, 1904-1952, 1953-1965,and 1897-1964, respectively. Recent contributions by Abe and Kanamori (1979),Abe (1981), Abe and Noguchi (1983a, b) and Abe (1984) provide revised catalogs.Nevertheless, many ambiguous cases still remain. For example, Christoskov(1983) gives M = 7.83 for the April 4, 1904 Strumska, Bulgaria earthquake asthe most important event for the seismic risk analysis of that country. Gutenbergand Richter (1954) [hereafter GR] gave MGR = 7.5 and Abe and Noguchi (1983a,b) [hereafter ANand AN’] gave Ms = 7.3 and 7.1 respectively, while Duda (1956)[hereafter DU] did not list it as event of magnitude greater than 7. Abe (personalcommunication, 1984) informed me that MGR was based only on Ms = 7.3at Osaka (undamped seismograph record) and mB(P) = 7.4 and mB(S) = 7.6 atGottingen (A = 13’), which were not reliable. ANand AN’ used undamped Milneseismograph records at 12 stations with revised calibration and seems to be morereliable. Because I do not know how Christoskov (1983) computed his magnitude,I cannot give a definite answer.GR was considered ‘practically complete” for the a-class (M 2 7.75) and b-class (M 2 7.0) shallow earthquakes in 1904-1952 and 1918-1952, respectively,and “probably almost complete” for the large intermediate and deep earthquakes(M 2 7.0, h 2 70 km) in 1918-1952. However, Miyamura (1978) suggested thepossibility of finding earthquakes with magnitudes around 7 that are not listed inGR.RU added 105 earthquakes to GR for 1905-1917 and prepared a catalog ofA4 2 7.0 earthquakes for 1897-1964. Many shocks MCR 2 7 in GR [e.g. April 4,1904 (Region 30, No. 610), MGR = 7.5; December 26, 1936 (Region 12, No. 190),MGR = 7f], however, are omitted in DU.Abe (1981) [hereafter A ] prepared a revised magnitude catalog of earthquakesfor 19041980. The revision was based on Gutenberg’s worksheets, but no effortwas made to add earthquakes not included in GR. AN and AN’ revised the data inA, adding many earthquakes prior to 1917. Ms in AN and AN’ are mostly smallerthan MDU (magnitude in DU), in particular, Ms for 37 out of 105 earthquakesadded to GR by DU are less than 6.8, and are not shown in AN and AN’. However,11 events are MDV 2 7.5 as listed in Table 1. Because I do not have the backgrounddata of DU and AN/AN’, I cannot say which are better.Epicenters given in GR and DU for some earthquakes are very different. Epicentersgiven in A and AN/AN’ follow those of GR. Relocation of some doubtfulearthquakes appears to be necessary.In selecting the earthquakes for the filming project, special attention should begiven to include those earthquakes having doubtful location and magnitude (seeTable 1, remarks 1 and 2; and Table 3, events with *).2.2. WDC-A Catalog for the Filming ProjectIn the first report of the Historical Seismogram Filming Project, Meyers and Lee(1979) presented 3 lists of earthquakes to be used as a guide for the project. Theselists include large worldwide events for the periods 1897-1899 and 1900-1962, andsignificant earthquakes in the United States and neighboring areas for 1887-1962.The lists are included in the second and third reports (Glover, 1980; and Glover