Fig. 3
From: Spatial heterogeneities in tectonic stress in Kyushu, Japan and their relation to a major shear zone
a Principal direction of the stress tensor at the grid points. Two of the eigen directions of the stress tensor close to the horizontal plane are plotted. The blue and red segments are the directions of σ 1 and σ 3, respectively, and the green segment shows the moderate principal stress direction of σ 2. The black segment indicates the stress condition with σ 2 ≈ σ 1 from the obtained stress ratio. Gray circles denote the hypocenters in this area. b Stress ratios ϕ’ = (σ Hmax − σ Hmin)/(σ v − σ Hmin) at the grid points. Blue, green, and red circles denote stress ratio ranges ϕ’ > 1.05, 1.05–0.95, and <0.95, respectively; their radii are proportional to the ratio. The outer and inner circles of the estimated value indicate the 95 % confidence range