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

MICROFILMINGHISTORICAL SEISMOGRAMS ATABUYAMA SEISMOLOGICAL OBSERVATORY,KYOTO UNIVERSITYYasuhiro Umeda and Katsuyoshi It0Abuyama Seismological Observatory, Kyoto University944 Nasahara Takatsuki, Osaka 569, Japan1. History of Seismological ObservationsAbuyama Seismological Observatory of the Faculty of Science, Kyoto University,was established in 1930. In the previous year, the experimental seismologicalobservations began with a two-component horizontal Wiechert seismograph. Continuousobservation with a three-component Wiechert seismograph began in 1932.The Wiechert seismograph is an excellent instrument which has a response of relativelylong-period and high-gain. In those days, many good records were obtained.However, for the moderate and large earthquakes occurring in and around Japan,the instrument is unstable because of its complex structure.In 1934, two types of strong-motion seismographs were designed and operated bythe staff of our observatory. One of them is a set of long-period (To = 24 - 27 sec),low-magnification (V = 1.1) two-component horizontal seismographs. The lengthof the pendulum is 1.7 m, and the recording stroke is about 30 cm. This instrumenthas recorded destructive earthquakes occurring near the Abuyama Observatoryand great earthquakes such as the 1960 Chile and the 1964 Alaska earthquakes.The other instrument is a set of short-period (To = 1.4 - 6.0 sec), strong-motion(V = 5 - 15) three-component seismographs. Those two sets of seismographs constitutethe low-gain broad-band seismograph system.Historical seismograms have been obtained mainly using the above three kindsof seismographs. The Wiechert seismograms are recorded daily and saved, but theseismograms of the latter two sets of instruments are saved only when events arerecorded.2. Microfilming in the First StageIn response to the resolutions of the 1982 Tokyo Workshop on Historical Seismograms,we began preliminary work in preparation for microfilming. On one handwe applied for financial support, and on the other hand we arranged our archivedseismograms in chronological order and listed all missing records. In 1984, this microfilmingproject was supported by the Science Research Fund of the Ministry ofEducation of Japan. Because this support will continue until March 1987, we havemade a three-year plan for the microfilming project as shown in Figure 1.In the first fiscal year (from April 1984 to March 1985), 20,346 sheets of Wiechertseismograms were arranged and filmed on 30 rolls of microfilm. An average of 500frames are filmed on one roll 30.5 m long. The total number of frames is 14,196.3. Filming FormatEvery roll of film is kept in a small box. The roll number, the kind of instrument,and the dates of the records are given on the face of this box.Historical Seismogramsand Earthquakes of the World439Copyright 0 198h by Academic Press, Inc.All rights of reproduction in any form reserved.