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

206 G. E. Fiedler B.Origin time Epicenter Depth MS References(GMT) Lat. (ON) Lon. (OW) (kin)11.4 66.1911 llm 00s 11.0 66.0 (8.4)*9h 1lm 49s 10.9 66.8 50 7.49h 10m 35s 7.6911 Ilm 00s (7.5)9h 10m 47s9h 10m 57s8.1#7.7#Ceriteno Grau (1940)Richter (1958) - ISCFiedler (1961)Kew record (this paper)Mauritius record (this paper)Trinidad data (this paper)Trinidad data & RichterKanarriori and Abe (1979)Abe arid Noguclii (1983)The average Ms without, the * entry is 7.66zt0.24. The average Ms without the* and i+ entries is 7.55 zt 0.11.Summarizing and forming mean values, we obtain the following final focal datafor the 1900 earthquake: Origin time H = 09h 10m 50s GMT or 05h 10m 50sHLV; Epicenter Lat. 10.9' N, Long. 66.3' W, focal depth about 50 km; MagnitudeMs = 7.6, mb = 7.1.4. ConclusionThese preliiiiiiiary results show that historical seismograms are needed for studyingliistorical earthquakes, especially for determining magnitudes and energy releaseswhich are important for seismic risk studies. In the specific case of this largeVenezuelan earthquake, a possible repetition may cause much more loss of life andof property damage than in the years 1900 and 1967. To help such studies, a feworiginal or reconstructed historical seismographs should be operating at observatorieswhere historical seismograms of such instruments still exist in order to comparerecent earthquakes with historical events.ACKNOWLEDGMENTSI am indebted to hlr. I. Duiiputli, Meteorological Services, Vacoas, Mauritius,arid to Dr. P. W. Burton, Institute of Geological Sciences, Edinburgh for copies ofthe Milne seismograms of the Caracas earthquake; to Mr. W. Person and his staffat USGS, Golden, CO for trying to get an epicenter location, and to the reviewersof coniments arid suggestions of the manuscript.REFERENCESAbe, K. and S. Noguchi (1983). Revision of magnitudes of large shallow earthquakes,1878-1912, Phys. Earth Planet. Interiors, 33, 1-11.Anonymous (1900). Meteorological observations made at the R.A. Observatory Mauritius(1900). Plate I1 & Table I, page LV, Mauritius.Anonymous (1900). Circular No. 9, Brit. Assoc. Science.Anonymous (1908). Seismograph records, Bull. Dept. Agriculture, VIII, 64-67, Governm.Print. Office, Trinidad.