古い地層中にみられる液状化現象

概要

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Soft-sediment deformation with liquefation phenomena occured in strata is categorized into post-, meta- and syn-depositional ones by the criterion of formation phase of stratum. The post-depostional deformation is caused by gravitational force during sedimentation (e.g. deep seated slumping) or by tectonics tress. The recognition of those genesis should be examined in association with all other structural and sedimentological information (e.g. tectonic folds, paleocurrents). In the lower part of the Eocene (?) Otonashigawa Group, the sandstone dikes, which are a kind of products of liquefaction, were intruded in relation with tectonic folding. From the examination of this condition by porosity-burial depth relation, the sand liquefaction even in the sediments deeply buried could occur under excess pore-fluid pressure (pore-pressure ratio; more than 0.75) which kept the sediments unconsolidated. Such a liquefaction due to tectonic deformatiom in ancient strata might usually take place even at deep burial depth in active margin such as the Japanese Islands, through along geologic time.
日本地質学会の論文