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

HISTORICAL SEISMOGRAMS FROM AUSTRALIADavid DenhamBureau of Mineral Resources, Geology and GeophysicsP.O. Boz 378, Canberra City 2601, AustraliaABSTRACTPermanent seismographs were established on the Australian continentshortly after the turn of the century. Milne instruments were set up inPerth (1901), Melbourne (1902), Sydney (1906), and Adelaide (1909) anda Weichert was installed at Riverview (Sydney) in 1909. The magnificationof the early Milne instruments was very low (M 6), however, and itwas not until Milne-Shaw instruments were installed in the 1920’s that auseful network of four stations was established.Most of the seismograms for these four stations are available from the1920’s onward. The records are still stored in their original photographicformat, however, and a significant number of the early seismograms havedeteriorated. Expert conservation will be required if information on theearly seismograms is to be preserved.1. IntroductionThe historical record in Australia goes back only about 200 years. Since Australiawas first settled by Europeans, however, reports of earthquakes and their effects havebeen common. The first reported earthquake was felt at Port Jackson (Sydney) inJune 1788, when “The 22nd of this month (June) we had a slight shock of anearthquake; it did not last more than 2 or 3 seconds. I felt the ground shake underme, and heard a noise that came from the southward, which I at first took for thereport of guns fired at a great distance” (Phillip, 1788).In 1837 the first settlers in South Australia were made aware of the existence ofearthquakes when, “there was a loud rumbling noise that lasted 20 seconds. Theearth shook and trembled. It was an earthquake” (Blackett, 1907). Similarly, inthe early histories of Melbourne (1841; Underwood, 1972) and Perth (1849; McCue,1973) earthquakes were felt. Fortunately, there is no record of anybody being killedby an earthquake in Australia and the total damage to buildings and installationssince 1950 has amounted to a modest 50 million in 1985 dollar values.Although the level of Australian seismicity is comparatively low, the Australiancontinent forms an excellent platform for studies of global seismicity and earthstructure. Active seismic zones range in distance from 5” to 180” from the continent,and the locations of earthquakes in the southwest Pacific and in southeast Asia areconstrained by seismic observations from Australia.2. Early Seismological StationsIn spite of Australia’s global seismological importance, it is somewhat ironic thatthe first seismic instruments were set up there to record local earthquakes. Theseinstruments were constructed in Launceston, Tasmania, by Biggs (1885) to recordthe larger earthquakes from the swarm of over 2,000 events that occurred off theHistorical Seismogramsand Earthquakes of the World45 1 Copyright 3 1988 by Academic Press, Inc.All rights of reproduction in an) form reserved.