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

DOCUMENTING NEW ZEALAND EARTHQUAKESG. A. EabySeismological ObservatoryP.O. Box 1320, Wellington, New ZealandABSTRACTThe record of even large earthquakes in New Zealand is likely to beseriously incomplete until organized colonization began in 1840, but accountsof over 300 earlier shocks exist. Colonists soon recognized thepractical importance of earthquakes, and in 1868 the reporting of feltearthquakes was included in the duties of an organized network of climatologicalobservers. This reporting still continues in a greatly expanded way.The archives of the Seismological Observatory, Wellington, contain seismogramsdating from 1900, but the earliest instruments were more effectivein recording teleseisms than in recording local shocks. The presentnetwork of short-period instruments was started in 1930, and stored seismogramsnow cover about 140 square metres of floor-space.Several earthquake catalogues have been prepared, the most comprehensivebeing a list of 24,000 shocks stored on magnetic tape. Fully referencedhistorical material forms the basis of a “Descriptive Catalogue”of which two sections, up to the year 1854, axe published. A great deal oflater information exists in manuscript, but is incomplete.Origins and magnitudes based upon instrumental data recorded before1964 are being recalculated using improved knowledge of crustal structure,wave velocities, and propagation characteristics, and are being publishedtogether with the associated felt reports and other comment. Severalmonographs dealing with the more important events revealed by thesestudies have appeared.1. IntroductionNew Zealand has an earthquake of magnitude 7 or more about once a decade(Figure 1). The shocks have been widely distributed, and only one has resulted inmore than a score of deaths. Nevertheless, some eighty per cent of the population(which totals a little over three million) is urban, and recognizes that the evaluationof seismic risk is a practical problem of some urgency.In comparison with the countries of Europe and the ancient civilizations of Asiaour history is brief, but we are fortunate in the detail and completeness of ourseismic record. Until about 1000 A.D., when the first Polynesian voyagers arrived,the country was completely without human inhabitants; and although Maori oraltradition records an important earthquake in about 1460, it is not until 1773, whenCaptain Furneaux of the “Adventure”, James Cook’s companion on his secondvoyage, experienced a moderate shock in the Marlborough Sounds, that we have awritten description giving the date, place, and time of a New Zealand earthquake.During the next three quarters of a century, the explorers were joined by sealersand whalers, and mission stations and trading-posts appeared. Unfortunately, mostof them were in the far north, the least seismic part of the country, but the letters,Historical Seismogramsand Earthquakes of the World232 Copyright 0 I YXH by Academic Press, Inc.All rights of reproduction in any form reserved.