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

1.本研究厘清了从明日至平安早期(主要是公元672-887年)日本历史最重要的编年史--陆国史料的每日变化。统计描述中日复一日记录现象和事件的汉字字数，作为衡量历史信息量的参数。尽管总信息量和自然现象信息量都呈现出相似的随时间增长的趋势，但它们的数量却随着编年史编者的变化而变化。尤其是公元850年编年史界线上地震记录的急剧增加，预示着编年史编撰方针的变化。因此，根据编年史记录计算的地震频率的变化可能不能反映这一时期的真实地震活动。这项研究还阐明了公元887年至1595年期间京都及其周边地区由政府官员或牧师撰写的历史日记数量的每月变化。在这一时期，由陆国末期引起的公元887年史料的减少是变化最为剧烈的。在上述结果的基础上，本研究重新评估了以前地质和历史记录之间的相关性，并指出了它们存在的问题，即公元878年的Isehara地震、762年的平田美野地震和1331年的富士地震。这项研究还指出了普遍接受的地震活动/火山活动变化观点的问题，如日本9世纪的地震活动高峰和12-15世纪富士火山的休眠。

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.