ABSTRACT Understanding the in-situ stress field in the subsurface provides insights on the tectonic processes and seismic hazards of a basin. This paper presents observations and interpretations of present day maximum horizontal stress (SHmax) orientation from well Ranui-2 located in the onshore southern East Coast Basin. Fractures identified in the Ranui-2 image log have been divided into distinct subsets based on fracture orientation. These subsets correspond in a general sense, to changes in lithology in the well, which are associated with changes in formations. Analysis of the image log shows the present day SHmax in the borehole has two primary stress directions, W–E and NW–SE, and most of the fractures strike NE–SW. The change in SHmax occurs at a depth of circa. 1130 m measured depth (918 m true vertical depth subsea), below the depth at which the borehole changes from vertical to ≥10° deviation. When these data are compared to the regional stress field obtained using other stress indicators such as earthquake focal mechanisms, the results are consistent with each other. This study shows that shallow subsurface indications of present-day SHmax in southeastern North Island reflect SHmax orientations from deeper within the subsurface.

中文翻译：

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根据钻孔图像测井确定的地下 SHMAX，新西兰东海岸盆地南部陆上

摘要 了解地下的原位应力场可以深入了解盆地的构造过程和地震灾害。本文介绍了位于东海岸盆地南部陆上的 Ranui-2 井对当今最大水平应力 (SHmax) 方向的观察和解释。Ranui-2 图像日志中确定的裂缝已根据裂缝方向分为不同的子集。这些子集在一般意义上对应于井中岩性的变化，这与地层的变化有关。图像测井分析表明，目前钻孔中的 SHmax 有两个主要应力方向，W-E 和 NW-SE，大部分裂缝走向 NE-SW。SHmax 的变化发生在大约 100 米的深度处。1130 m 测量深度（918 m 真正的海底垂直深度），低于钻孔从垂直变为≥10°偏差的深度。当这些数据与使用地震震源机制等其他应力指标获得的区域应力场进行比较时，结果相互一致。这项研究表明，北岛东南部现代 SHmax 的浅层地下迹象反映了地下深处的 SHmax 方向。