Reevaluation of volcanic and seismic histories in Japanese historical ages based on mapping of blank periods of historical information

1.《立国志》是记述日本明日香时代至平安时代初期（主要是公元672 -887年）历史的重要编年史，本研究阐明了《立国志》史料信息量的日变化。记录日常现象和事件的描述中的汉字字符的数量被统计并作为历史信息量的参数。尽管总信息量和自然现象信息量都呈现出随时间推移而增加的趋势，但它们的数量却随着编修者的变化而变化。特别是公元850年前后，志界地震记载的急剧增加，反映了历代志编纂方针的变化。因此，根据编年史记录计算的地震频率变化可能并不能反映这一时期真实的地震活动。本研究还澄清了公元887 -1595年期间京都及其周边地区的政府官员或牧师撰写的历史日记数量的月度变化。在这一时期，以公元887年因《礼记》的终结而导致的史料减少最为剧烈.在此基础上，对公元878年的伊势原地震、公元762年的飞田美浓信浓地震和公元1331年的富士地震的地质记录与历史记录的相关性进行了重新评价，并指出了存在的问题。本研究还指出了人们普遍接受的地震/火山活动变化观点的问题，例如日本的地震活动高峰在世纪，富士火山在12- 15世纪处于休眠状态。

1. This study clarified daily changes of amount of historical information in Rikkokushi, which are the most important chronicles describing the Japanese history from the Asuka period to the early Heian period (mainly during A.D.672-887). The number of Kanji characters of descriptions, which record phenomena and events day by day, were counted and regarded as a parameter for the amount of historical information. Although both the total information and the information about natural phenomena show similar tendency of increase with time, their amounts varies coincidently with changes of chronicle editors. Particularly, drastic increase of earthquake records at the chronicle boundary in A.D.850 suggests the change of editing policy of the chronicles. Thus, changes in earthquake frequency, which were calculated from the chronicle records, probably do not reflect the real seismicity in this period.2. This study also clarified monthly changes of the number of historical diaries, which were written by government officials or priests in and around Kyoto during A.D.887-1595. In this period, the decrease of historical information in A.D.887, which was caused by the end of the Rikkokushi, is the most drastic change.3. On the basis of the above results, this study reevaluated previous correlations between geological and historical records and pointed out their problems, which are of the A.D.878 Isehara earthquake, 762 Hida-Mino-Shinano earthquake, and 1331 Fuji earthquake. This study also pointed out the problems of commonly accepted views of changes in seismicity/volcanic activity, e.g. a seismicity peak in the 9th century in Japan, and a dormancy of Fuji Volcano during the 12-15th centuries.