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

~ RelationsThe Standardization of Seismological Data 435Rejection of the poorof tinifiedResearch intoRedetermination ofmagnitude andRegional character i s ti cs ofthe seismic activity,between earthquakeoccurrence and polar motionof the earth, etc.Publish the dataFigure 2. Block diagram for the standardization of seismological data.2.1. Filming the SeismogramsSeismograms to be filmed were restricted to records from significant earthquakesgreater than or equal to magnitude 6.0, which had occurred in and near Japanbetween 1902 and 1970; and to records from large earthquakes, which had occurredelsewhere in the world and were listed in "Rika Nenpyo" (1975, 1981). The totalnumber of seismograms to be filmed was about 3,000.The size of the recording paper of the C W and N-S components of the Omoriseismographs is 350 x 750 mm. All three components of the Nasu seismograph arerecorded on the same seismogram, which is 450 x 750 mm in size. The seismictrace on the recording paper is 0.05 mm in width. The reading accuracy limits are0.1 sec in time and 0.1 mm in amplitude. Therefore, it is necessary to maintainthe sharpness of the trace in the photographing procedure. We compared 35-mmand 70-mm film copies, and found that 70-mm film reproduces more accurately andcovers the wide range of contrast on the smoked paper better. The width of thetraces after enlarging the film to its original size was 0.23 mm and 0.08 mm for the35-mm and 70-mm film, respectively. Also, the 70-mm film is kept in separate filmholders, which allows seismograms to be retrieved easily. Because of these factors,70-mm film is considered to be more suitable for filming our seismograms.