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

A CATALOG OF LARGE EARTHQUAKESAND DAMAGING EARTHQUAKES IN JAPAN1. The Old CatalogFOR THE YEARS 1885-1925Tokuji UtsuEarthquake Research InstituteUniversity of Tokyo, Tokyo 113, Japan(M 2 6)In 1885, the Central Meteorological Observatory (CMO) in Tokyo began to collectmacroseismic and instrumental data on earthquakes throughout Japan. Sincethen, the CMO successively published the bulletins containing the occurrence times,locations of epicenters, and radii of shaken areas of moderate to large earthquakesin Japan. The catalog of Japanese earthquakes compiled by the CMO (1952) liststhe occurrence times, epicenters, radii of felt areas of earthquakes between 1885 and1950 taken from the previous bulletins of CMO, together with the magnitudes givenby Kawasumi in 1952. The epicenters, focal depths, and magnitudes of earthquakeswhich occurred after 1926 were redetermined by the Japan Meteorological Agency(JMA - the successor of CMO) in 1958 and 1982 (JMA, 1958, 1982), but no revisionwas made for earthquakes before 1925.The old CMO catalog is inaccurate in several respects. No consideration wasgiven to the depth of focus. Most deep earthquakes which occurred before the discoveryof the deep earthquake were mislocated by up to 1000 km. Magnitudes wereconsiderably overestimated for many earthquakes especially those which occurredbefore 1913. Some fairly large earthquakes are missing in the list. In view of thesesituations, I undertook a compilation of a new catalog of Japanese earthquakes forthe years 1885-1925.2. Compilation of a New CatalogMost of the data collected by the CMO before September 1, 1923 were lost in thefire caused by the great Kanto earthquake on that date. To prepare a new catalog,we had to re-collect the old data. Data on some large earthquakes are found in theCMO bulletins and some seismological papers. Most of the written data-files storedin the JMA stations were microfilmed about 20 years ago. The Geophysical Instituteof the University of Tokyo stores voluminous written data-sheets collected frommany CMO stations before 1925, some of which are unavailable at the reportingstations and the main office of JMA now. Some data can be obtained only atindividual JMA stations.During this work, some old seismograms were examined by myself. Many seismogramswere missing or stored in bad condition. It was often difficult to accessrequired seismograms quickly, even if they were preserved in the storeroom of ast ation.Time-keeping in seismic observation during the period 1885-1925 was not sufficientlyaccurate for the determination of hypocenters from arrival times of P-waves.S-P times could be used in the later stage of the period. In the earlier stage,few S-P times were available, and the epicenters were estimated by the use ofthe distribution of seismic intensities. I constructed isoseismal maps of about 2000Historical Seismogramsand Earthquakes of the World150Copyright (? 1988 by Academic Press, Inc.All rights of reproduction in any form reserved.