最新断層活動時におけるパレオドースゼロイング度の定量的評価 : 微粒子法の初適用 : 野島地表地震断層の場合

概要

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In order to verify whether the paleodose was fully zeroed at the last faulting，we have investigated two samples from the Nojima earthquake surface fault，Awaji island in Japan，which occurred on January17，1995． Tne samples were collected from the fault plane itself and the rest of the same crush zone．Tne scraped widths were less than 1 mm for the former，and less than 7 mm for the latter．Both samples of fine grains（1～8□m diameter）were subjected to the thermoluminescence (TL)measurement using the fine grain method． Tne detectable existence of the natural TL glow in both samples was clearly verified at the last faulting．Tne TL intensities were summed over the plateau region to evaluate the paleodoses using the additive dose method，and the results were compared with each other．As a result，the extent of zeroing was estimated，being 24～32％ by TL intensity or 31～41％ by paleodose． The present results are found to give larger values than those from the conventional samples collected from the lump of a crush zone．Therefore，the fine grain method proposed in this study is thought to be more desirable one for evaluating the realactivity of a fault． Additionally，the estimation of the paleodoses，annual doses and TL ages was applied to the fault gouges for the first time using the fine grain method．