地震 第2輯
Online ISSN : 1883-9029
Print ISSN : 0037-1114
ISSN-L : 0037-1114
論説
石灯籠の破損から歴史地震の強震動の特徴を推定することは可能か?
——長野善光寺における検討——
加藤 護日岡 惇
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ジャーナル フリー

2016 年 69 巻 p. 23-30

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Strong seismic ground motions often make stone lanterns in temples and shrines collapse and suffer damages, and the stone lanterns tend to collapse in the direction of strong shaking in recent cases. In historic Japanese documents, descriptions of collapsed stone lanterns as results of strong earthquakes appear frequently, and are used in estimating and mapping the seismic intensity. In this report, we examine whether it is possible to further retrieve the characteristics of historic ground motions from the ages and damages of old stone lanterns at Zenkoji Temple, Nagano. We assume that severely damaged stone lanterns would be removed from the site after the earthquakes and be newly rebuilt thereafter, and this will distort the age distribution of stone lanterns. Less severely damaged lanterns would be rebuilt with the damaged parts, and the damages of stone lanterns could be the records of historical strong seismic ground motions at the site. If the directions of the damages caused by collapses are maintained, these could be used to estimate the direction of collapses, or of strong motion. Scarcity of the stone lanterns which were built before 1710s at Zenkoji Temple as well as the sudden increase of repairs and rebuilts in the mid 19th century are likely the results of strong earthquakes and resultant damages at Zenkoji Temple. Ratios between numbers of the damaged and undamaged stone lanterns do not correlate with the time series of historic earthquakes in Nagano. Damages of the stone lanterns are more often found in the rear of the stone lanterns, and we could not find that damages are concentrated into a particular cardinal direction. Stone lanterns at this site are likely to be so maintained that the damaged parts are rotated into the direction which makes the major damages less visible. On the contrary to the findings of the previously published report, we conclude that it is impossible to estimate the direction of historic strong motion from the statistics of damages of stone lanterns at Zenkoji Temple.

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© 2016 公益社団法人 日本地震学会
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