Comparison of stress state around the Atera fault, central Japan, estimated using boring core samples and by improved hydraulic fracture tests

An often disputed subject is whether the stress memory of rocks can be reproduced by deformation rate analysis (DRA). Doubt has also been expressed on whether a rock can memorize its stress history. We compared the stress state around the Atera fault system, central Japan, using the hydraulic fracture test (HFT) and DRA at the same boreholes. The quality of the HFT results at these holes, especially that of the magnitude of maximum horizontal compression (S_Hmax), was recently improved by considering the tensile strength of the borehole wall. The S_Hmax azimuth determined by the DRA was about N-S. Although this is inconsistent with the geological presumption, it agrees well with the S_Hmax azimuth estimated by the HFT and the drilling-induced tensile fracture (DITF). The magnitudes of horizontal principal stresses obtained by DRA were generally consistent with the improved HFT results, and the consistency between stress states estimated by the DRA and the HFT indicates the existence of stress memory. Based on our results, we conclude that the DRA can be one option for measuring the stress state of the earth's crust.