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

STUDY OF HISTORICAL EARTHQUAKES IN JAPAN (2)Tatsuo UsarniFaculty of EngineeringShinshu University, Nagano, JapanABSTRACTIn Japan, a project on historical earthquakes (i.e., the collection andpublication of old materials describing historical earthquakes) is acceleratedrecently, The purpose of this article is to introduce the project andsome of the scientific works based on these materials and to show thathistorical documents can aid modern scientific studies, such as seismotectonicsand long-range prediction of large earthquakes.We define “historical earthquake” as before 1873. Studies on historicalearthquakes carried out before 1970 are summarized in Section 1. Thesestudies begin with collection and publication of historical materials relatingto old earthquakes. The first and second phases of the project areintroduced in Section 2, and the status of the third phase being carriedout by the present author and collaborators is given in Section 4.Among studies based on these historical materials, the following threetopics were carried out by the present author:(1) Change of seismicity of destructive earthquakes in Japan is documentedin Section 3. Materials for destructive earthquakes are more reliableand more uniform than for non-destructive earthquakes.(2) The 1858 Omati earthquake is studied employing recently collectedmaterials (Section 5). Other historical earthquakes occurring in valleysconnecting Itoigawa-MatumoteIida-Toyokawa cities are also considered.It is shown that the damaged area of each earthquake contacts each other,covering valleys with almost no gaps.(3) The 1793 Kansei earthquake is studied in Section 5. Comparison withrecent earthquakes suggests that the Kansei event is quite similar to the1896 off-Sanriku event of reverse type. Comparison of this result withother large earthquakes off the Sanriku coast of Japan, provides a clue forthe occurrence time of the next off-Sanriku earthquake of reverse type.1. IntroductionAlthough this is the second paper of the same title, the introductory parts of thefirst paper (Usami, 1979) are reproduced. In this article, we consider earthquakeswhich took place in and near Japan, that is, Hokkaido including the southern Kurile,Nonshu, Shikoku, Kyushu and Ryukyu Islands (Figure 1). In this article, the word“historical” refers to the time period before 1873. The year 1873 was chosen as theyear of division for the following reasons:(1) In this year, instrumental observations of earthquakes started.(2) At the end of this year, the Gregorian calendar replaced the Japanese lunarcalendar. On 9 November of the fifth year of the Meiji era, 1 January 1873, theGregorian calendar was first put into general use.Historical Seismogramsand Earthquakes of the World2 76Copyright 0 I 9RX by Academic Prers, Inc.All rights of reproduction in any form reserved.