学会誌「自然災害科学」

アンケート震度算定法の改訂 －高震度領域－

Revision of Algorithm for Seismic Intensity Determination by Questionnaire Survey - In High Intensity Range -

太田 裕*・小山 真紀**・中川 康一***

Yutaka OHTA*, Maki KOYAMA** and Koichi NAKAGAWA***

Abstract

The questionnaire survey for seismic intensity determination has long and widely been used in Japan since its origination in 1972. However, until the 1995 Hyogo-ken Nanbu (Kobe) earthquake there was no chance to examine whether or not the questionnaire survey is valuable for a high intensity range of 6 and 7 on JMA (Japan Meteorological Agency) scale. The intensities determined in use of the existing algorithm were somewhat lower for the Hyogo-ken Nanbu earthquake than those reported by JMA, and this facilitated us a reexamination of the algorithm. In this situation we attempted a sounding for the revision, paying special attention to the following points.

1. To make clear the applicable range on intensity scale for each of question items, so that the contribution of each item for intensity calculation is to be made only within the effective range.

2. Likewise, to analyze the sensitivity of each of the question items for the intensity increment, and to introduce appropriate weights for each of the question items in parallel with the degree of sensitivity.
And, the existing algorithm was revised in consideration of the above analyses.

A comparison of thus obtained intensities with those by JMA ordinal and instrumental scales gave a good agreement. This confirms that the existing questionnaire method, after receiving a little modification of algorithm, is useful enough for a high intensity range of JMA intensity 6 and 7.

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