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

Documenting New Zealand Earthquakes 237and wave velocities, they did not match the timing accuracies it was possible toobtain from the records, and limited the value of the revisions. With some difficulty,the positions of all stations that have operated in New Zealand have now beenestablished to a second of arc. Once the actual position of the instrument wasknown, reference to large-scale Lands and Survey Department maps yielded accuratecoordinates. The operators of several stations that had been closed for many yearswere found to have died, but it proved possible to find children or other membersof the family who could remember where the instruments had stood, and couldin some cases even describe them in sufficient detail to establish the orientation ofhorizontal components. Seismologists in any doubt whether the coordinates of theirstations are accurately known in terms of a uniform survey are urged to attend tothe matter without delay.4. Major EventsThe dangers that can arise from concentrating the study of past earthquakesupon the events that are known or believed to be major have already been stressed.Nevertheless, closer study of particular events is not only historically valuable initself, but the necessary preliminary to such projects as the “Descriptive Catalogue”and the revised “Seismological Reports”. Neither is intended to contain exhaustiveaccounts of individual earthquakes, but abstracts of incompletely assessed materialare of small worth.There are few connected accounts of New Zealand earthquakes in the pre-instrumentalperiod, and the farther our work takes us into the past, the less systematicwe find the collection of data to have been. The sources are nevertheless voluminous,and the Observatory files contain information about quite recent earthquakes thathas never been correlated and assessed.During the years of depression and the second World War, and for some timeafterwards, the resources of the Observatory did not allow the staff to travel exceptfor instrument maintenance, but a great deal of information about the largerearthquakes was collected and filed. At this period New Zealand was well servedby local newspapers, whose reporters provided detailed accounts of the effects theyobserved, and recorded verbatim their interviews with people affected. The Observatoryalso elicited reports from police and postal officials, Ministry of Worksengineers, harbour authorities, and other informed people in the epicentral area.Even now witnesses can be found, and building repairs made at the time preserveevidence of damage. Detailed assessment of this material forms a substantial partof the work of revision for the ‘Seismological Reports”.The problems are well exemplified in my work on the Marlborough earthquakesof 1848 (Eiby, 1980), the magnitude 8 Wairarapa earthquake of 1855, and twotsunami-generating shocks in 1946 (Eiby, 1982a, 1982b). The existence of a freshlookingfault scarp, and the belief that an elderly lady interviewed by a noted fieldgeologist at the end of last century had been an eye-witness of the breakage ledgeologists to believe that the 1848 earthquakes had been centered in the AwatereValley, and Richter (1957) devotes a lengthy section of his well-known book to the“Awatere Earthquake”. Historical records established that the lady did not reachthe valley until more than five years later, and that the valley was uninhabited atthe time of the earthquake. Non-technical documents included clear descriptionsof fresh breakage on a parallel fault in the Wairau Valley thirty kilometres to the