Abstract

A case study of determining orientations of three dimensional in-situ stresses by anelastic strain recovery (ASR) method using drill core samples was carried out in six scientific drilling sites in Shikoku Island and Kii Peninsular, Japan near Nankai Subduction Zone where M8 class great earthquakes repeat. Anelastic strain of a specimen in nine directions, including six independent directions, was measured after its in-situ stress was released. Values of acquired anelastic strains were more than several ten microstrains being dependent on lithology of the specimens. As a preliminary result, the stress orientations which showed that the stress regimes in this area are not uniform were reported.

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