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

THE STATUS, IMPORTANCE, AND USE OFHISTORICAL SEISMOGRAMS IN SWEDENOta KulhdnekSeismological DepartmentUppsala University, Uppsala, SwedenThe birth of observational seismology in Sweden dates back to the beginning ofthe 20th century, to be more specific, to October 1904, when a Wiechert-type instrument(1000 kg, horizontal pendulum) was installed in the Observatory Park incentral Uppsala. This seismograph, the first in the country, has been in continuousoperation since that time, with practically unchanged characteristics during theentire period of more than eight decades. Amplitude characteristics of the instrument’stwo horizontal components are shown in Figure 1. At this writing, almost60,000 Wiechert records have been produced, all stored in archives at the SeismologicalDepartment, in Uppsala. Uppsala Wiechert seismograms were systematicallyanalyzed from October 1904 to December 1955 (except for the time from June 1905to June 1906). All collected relevant information is listed in annual SeismologicalBulletins from Uppsala. The Bulletins provide the date, phase identification andcorresponding arrival times. For large events, periods and amplitudes, epicentraldistances, focal regions and often even brief commentaries are also given. Onlyexceptionally (more recent events), information on focal depth and first-motion polarityis included. Uppsala Wiechert records constitute one of the most extensive,complete, homogeneous and well documented seismogram series available, this inrespect to the long operation time, practically unchanged instrumental constantsand regular daily record readings. This and similar series are invaluable for studyingearthquake history of various regions and for comparative investigations of largehistorical earthquakes.Several other seismograph stations operated temporarily in Sweden at the beginningof this century. In 1906, an 80 kg horizontal Wiechert seismograph wasdeployed at Vassijaure in northern Sweden. In 1915, the apparatus was moved toAbisko where its operation ceased on July 12, 1951. The Abisko station was alsoequipped with a three-component Galitzin system having a photographic recordingvia mirror galvanometers. During the period 1917-1953, a Wiechert seismograph,similar to that installed at Uppsala, was in operation in Lund in southern Sweden.Station name, seismometer used, recording type and time of operation of historicalSwedish seismograph stations are given in Table 1. The station locations are shownin Figure 2. As follows from the table, during the period 1917-1951, there were threeseismograph stations operating in Sweden, covering the country relatively well inthe N-S direction. All records are now stored in Uppsala. However, whereas theUppsala records were continuously analyzed, seismograms from Vassijaure/Abiskoand Lund were not.Considerable efforts had been spent to establish a convenient seismogram storagesystem in Uppsala. After many years of improvisation, all records are now depositedin the Seismological Department’s building in a permanent archive facility; they areaccessible within minutes for inspection and/or further processing.In spite of the vast and continuous instrumental modernization taking place atthe Uppsala station since the early 1950’s, the veteran Wiechert pendulum is stillHistorical Seismogramsand Earthquakes of the World64Copyright @> 1988 by Academic Press, Inc.All rights of reproduction in any form reserved.