Present-day tectonic stress state was investigated in three deep boreholes located in the eastern segment of the Polish Outer Carpathians (POC). Significant rotations of the maximum horizontal stress (SH) were observed in these boreholes, located at the hinge of the anticlines in the upper part of the nappes. For the deepest borehole, D-1 (5.5 km depth), 1D geomechanical modelling was performed to determine the stress gradient profiles. An optimal solution of the model, validated by numerous compressional and extensional failures (breakouts and drilling-induced fractures, respectively) of the borehole wall, was obtained for variable elastic horizontal strain. The strain varies stepwise across the Main Thrust Fault (MTF) and linearly within its walls. The dominance of a strike-slip faulting stress regime was determined for the Carpathian nappes, with contributions from thrust faulting above the MTF and normal faulting below the MTF. A critical stress state for reactivation of preferentially oriented pre-existing faults and fractures was inferred for the competent strata. A consistent interpretation of the variations in stress orientation and magnitude, suggests a contemporary refolding of the anticline at a shallower structural level, enhanced by the reactivation of the MTF and a lack of reactivation of the Carpathian Bottom Thrust. Integration of these results with measurements from previous studies in the eastern segment of the POC indicates a different regional orientation of SH in the autochthonous basement (N-S) and in the nappes (NE-SW). These results indicate a thin-skinned compressive reactivation of the upper part of the accretionary wedge, with the lower part of the nappes remaining passive, or locally prone to minor strike-slip or normal faulting. These results contradict the hypothesis of a contemporaneous extensional collapse of the POC.

中文翻译：

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喀尔巴阡山脉构造活跃吗？：外喀尔巴阡山脉深井的地质力学研究（波兰）


在位于波兰外喀尔巴阡山脉 （POC） 东段的三个深井中研究了当今的构造应力状态。在这些钻孔中观察到最大水平应力 （SH） 的显着旋转，位于衬垫上部背斜的铰链处。对于最深的钻孔 D-1（5.5 公里深），进行了 1D 地质力学建模以确定应力梯度剖面。对于可变弹性水平应变，获得了模型的最佳解决方案，并通过钻孔壁的大量压缩和拉伸破坏（分别为突破和钻孔诱发的裂缝）进行了验证。应变在主逆冲断层 （MTF） 上逐步变化，并在其壁内线性变化。确定了喀尔巴阡松片走滑断层应力状态的优势，其贡献来自 MTF 上方的逆冲断层和 MTF 以下的正常断层。为有能力的地层推断出优先定向的预先存在的断层和裂缝重新激活的临界应力状态。对应力方向和大小变化的一致解释表明，背斜在较浅的结构水平上是当代的重新折叠，MTF 的重新激活和喀尔巴阡底部推力的缺乏重新激活增强了这种高度。将这些结果与 POC 东部先前研究的测量结果相结合，表明 SH 在原生基底 （N-S） 和尿布 （NE-SW） 中的区域方向不同。这些结果表明，增生楔的上部出现薄皮压缩再激活，而 napes 的下部保持被动状态，或局部容易出现轻微的走滑或正常断层。 这些结果与 POC 同时期伸展性塌陷的假设相矛盾。