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

278 Tatsuo Usarni(3) Documents published after 1 January 1873 are more readily available than thosebefore 1873 and are printed in type which is more readable to young Japanese thanthose of historical period.(4) The collection of documents before 1873 is incomplete and many documentshave remained untouched. Old documents were written with carbon ink and brushpen and young Japanese have difficulty in reading them. Reading the old documentsis a hard and time consuniing job and that couldn’t have been done without specialtraining.2. Brief Sketch of Historical Earthquake Studies before 1970During the historical period, when a disastrous earthquake took place, olderearthquakes were usually referred to and listed for comparison. Considering thiskind of work as a study of historical earthquakes, the history of such study canbe traced back to before the 10th century. Although such non-comprehensive listsof big events could not be said to be scientific, the records include basic data formodern scientific study of historical earthquakes. Employing old records, includinglists of earthquakes as stated above, I. Hattori, Esq. made an extensive study onhistorical earthquakes in Japan (Hattori, 1878). This probably was the first workof its kind in Japan. Thirty-four old documents were employed and 149 destructiveearthquakes were found after the 5th century.Naumann (1878) published a paper on Japanese earthquakes and volcanic eruptions.On 22 February 1880, a moderate earthquake took place near Yokohama(A4 = 5.9). Foreign professors who had been invited to teach modern science andtechnology and had lived near Tokyo were intrigued by the event. On 26 April ofthe same year, the Seismological Society of Japan (which is the first seismologicalsociety in the world) was established through the efforts of foreign scholars.John Milne, one of the invited professors, published a study on historical earthquakesin Japan (Milne, 1881). He used sixty-four old records (including thirty-fourused by Hattori) and listed 366 earthquakes.From about this time, short introductions concerning specific historical earthquakeswere published in various kind of bulletins. On 28 October 1891, the Nobiearthquake (M = 8.0) took place in central Japan. Due to the impact of this eventthe Imperial Earthquake Investigation Committee was established on 25 June 1892,in order to make investigations for preventing disasters due to earthquakes. Oneof the eighteen purposes of the Committee set forth at the start was the “investigationof earthquakes in historical ages, namely, the compilation of earthquakehistory.” Tayama was appointed as a part-time member of the Committee on 13July 1893 and was entrusted to execute the compilation of old earthquakes. His firstwork (Tayama, 1899) is a table containing 1,896 earthquakes (including aftershocks)from the years 416 to 1864. The date, locality, magnitude (not instrumental), andreferences are tabulated for the earthquakes. His second work (Tayama, 1904),perhaps his last work on historical earthquakes, consists of two volumes, totalling1,201 pages. They include earthquakes from the years 416 to 1865. This is the firstcomprehensive and scientific work in the field of historical earthquakes and markedan epoch in the history of the study of historical earthquakes in Japan.On 1 September 1923, the great Kanto earthquake (M = 7.9) hit the southernpart of the Kanto district including the Tokyo and Yokohama area. After theevent, on 13 November 1925 the Imperial Earthquake Investigation Committee was