Figure 3. Graph of BO azimuths (red dots), DITF azimuths (blue dots), and stratigraphy column against measured depth (m MD) for boreholes at the central HSM. Mean BO azimuths and the standard deviation for individual borehole are plotted in black and dashed grey lines respectively. Bi-directional rose diagram of breakout orientations for each borehole is shown below BO panels.
4.2 Southern HSM
A total of 1517 BOs with a combined length of 520 m are identified from borehole image logs in boreholes Ngapaeruru-1, Rauni-2, Titihaoa-1, Tawatawa-1, Te Mai-2, and Orui-1A boreholes (Figure 4; data set 1). For borehole stress data with a WSM quality ranking of B-C (Ngapaeruru-1, Tawatawa-1, and Ranui-2) we observe an Shmin orientation of 016°/196° ± 21° (NNE-SSW) from which we infer an SHmax orientation of 106°/286° (WNW- ESE) (Figure 4). BOs in boreholes Ngapaeruru-1, Tawatawa-1, Te Mai-2, and the shallow (<1130 m MD) interval of Ranui-2 show a consistent WNW-ESE SHmax orientation (Figure 4), whereas BOs measured in boreholes Titihaoa-1, the deeper (>1130 m MD) imaged interval of Ranui-2, and Orui-1A provide dominantly NW-SE SHmax orientations (Figure 4). Our reanalysis of BOs from borehole Ranui-2 suggest a 51° clockwise SHmaxorientation rotation from E-W (094°/274° ± 17°) in the shallower imaged depth interval (842-1130 m MD) to NW-SE (145°/325° ± 16°) in the deeper imaged interval (1130-1422 m MD) (Table 2) that was first reported by Griffin (2019).
Table 2. Stress Indicators From Analysis of Borehole Image Logs in the Southern HSM, New Zealand.