Rock stress interpretations from Mt. Torigata (Japan) based on calcite strain gauge and differential strain curve analysis

In order to interpret stress history at the Torigata Limestone Mine (Japan), calcite strain gauge (CSG) and differential strain curve analyses (DSCA) were performed. The maximum principal shortening direction determined by CSG and DSCA is oriented to the NW–SE. However, the published values for the maximum principal directions from these two methods are different from the NW–SE-directed maximum principal compression direction determined by the overcoring method. Accordingly, the directions of in-situ rock stress calculated by DSCA are considered to reflect the paleostress directions. The results by DSCA reflect the direction of pre-existing cracks developed in Torigata limesone, not microcracks induced due to stress relief. This is probably due to shallow depths of sample collection, where stared elastic strains are immeasurable using the DSCA method. Considering the stress fields found in this study area, the maximum principal direction of the paleostress is consistent with the fracture system near the study area and the late Mesozoic and Paleogene movement of the Philippine Sea plate.