Fig. 9

Estimated stress field in the Tohoku District inland area. A, B The estimated stress field using data from January 1, 1997 to March 10, 2011 (before the Tohoku-Oki earthquake) and from March 11, 2011 to December 31, 2019 (after the Tohoku-Oki earthquake), respectively. The number and letter codes in the upper left corners of each square correspond to the subareas identified in Fig. 8. Red, green, and blue circles denote the optimal solution for \({\sigma }_{1}\), \({\sigma }_{2}\), and \({\sigma }_{3}\), respectively. Small pastel red, green, and blue without outlines denote the 95% confidence ranges for \({\sigma }_{1}\), \({\sigma }_{2}\), and \({\sigma }_{3}\), respectively. The black line and gray fan denote the best and the 95% confidence ranges for the \({S}_{Hmax}\) orientation, respectively. \({\upphi }_{{\text{best}}}\) is the optimal value for the stress ratio (\(\phi (={\sigma }_{2}-{\sigma }_{3})/({\sigma }_{1}-{\sigma }_{3})\)) at a 95% confidence range of \(\phi\). \({{\text{N}}}_{{\text{a}}}\)= is the number of focal mechanisms used for each stress inversion in each area