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| | Abstract | | We have been developing new analysis for estimating crustal stress orientation at shallow depth using the long-term trends observed by a multi-component borehole strainmeter. The long-term trends can be interpreted as the relaxation process of stress disturbance caused by a borehole drilled in stressed rock mass. On the base of this model, the differences of long-term deformations in different orientations are due to an anisotropic stress field so that a borehole is compressed in the direction of maximum horizontal stress. We analyzed long-term strain data observed at 14 sites, southwestern Japan nearby the Nankai Trough, for several years. Time-varying principal stress orientations were estimated throughout the entire observed period. The obtained stress orientations at 13 sites are nearly constant in time within a standard deviation of about 10 degrees. We compared the orientations from the present analysis with the results estimated by the hydraulic fracturing and borehole breakout at the same borehole, suggesting that this analysis has a potential to provide a crustal stress orientation with the different principle than before. |
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