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

472 J. RafaCl Goberna, S. J.S.1 SeismogramsOn account of the station being dismantled at the end of 1940, the instrumentsbeing transferred to a new site, and the new place being prepared, the installation ofthe seismographs was delayed until April 1942, when the new photographic verticalcomponent began operation. Therefore, no seismic records exist for these two years.The operation of the Benioff seismograph was somewhat irregular during the yearbecause it was difficult to get photographic paper during the war. For some monthsthe paper available was only 23.5 cm in width, which did not last the 24 hours, andtherefore, some seismic events were missed. This condition lasted for several months,and even at the end of 1942, it was impossible to get any kind of photographic paper.The problem was solved by March, 1943.The Wiechert seismograph was reinstalled on July of 1943 and its normal operationcontinued until the end of this period. Its recording paper was quite thin,but the seismograms are well preserved. The smoke coating was at times too thickso that the seismograms are difficult to read or copy. Often the time marks weremissing, but the seismogram readings can be made from the photographic records;the clock used was the same for both instruments. The time correction was automaticallymarked on the seismogram by radio signals received from the Annapolisstation (U.S.A.) or from Panama.Since July 1947, the records of the horizontal Sprengnether seismograph are alsopreserved, and therefore, the amount of the photographic records was greatly increased.During the early years the drum was kept running at the rate of 1 mm/secand at 5 mm of spacing between the lines. In this way the photographic paper didnot last for 24 hours, and sometimes seismic events were missed. This problem wasnot solved until 1950, when the rotation speed of the recorder was changed to 0.5mm/sec, but the vertical component was kept running at 1 mm/sec.The amount of seismograms for this period is not exactly known as yet, butfrom the time period and the daily papers used, a minimum of records can becalculated. The minimum amount of photographic records may be about 15,000,and the amount of smoked records may be about 6,000.3.2. AnalysisDuring this second period, the analysis of the seismograms were made every day,and the data of all seismic events were published in the Institute Seismic Bulletinsand sent to several other institutions, some of which usually published them in theirseismic bulletins or used them for determining the parameters of the seismic events.Thus, they were published in the Mensuel Bulletin of the B.C.I.S. and in I.S.S. since1943. The first seismic data published by the Instituto Geofisico were those of Juneand July 1942, and after a few months of interruption they resumed publication onApril 1943, until the end of this period.4. 0 ther Colombian StationsWhen the seismic station of Bogotd became well established and its permanentoperation secured, its Director tried to find funds for establishing some other seismicstations so that with their data one could determine the parameters of Colombianearthquakes. Two trading and financial institutions, the National Federation of