Abstract Classical rock mechanics predicts that normal faults should form at 60–65°, rotating to 30–40° before locking, so widespread slip at around 20° is considered paradoxical. Furthermore, the dip distribution of normal fault earthquakes has a distinct, unexplained peak at ~45°. For both problems, some combination of low friction, high fluid pressures, stress rotation and efficiency of low-angle slip have been suggested but provide at best a partial solution. A simple quantitative model for normal fault rotation (iterating between slip on faults and distributed strain) predicts that faults spend more time at lower angles. Combining this result with Mohr-Coulomb analysis of the range where seismogenic normal faults should lock up predicts the dip distribution of seismogenic normal faults and matches both the range and 45° peak observed for normal fault earthquakes. As even the lowest dips of normal fault ruptures fall within the limits of fault reactivation, slip on seismogenic low-angle normal faults is not paradoxical. A new Mohr-Griffith solution to the limits of fault reactivation extends the analysis into the top few km, where low-angle slip is best constrained by field observations, and shows that low cohesion normal faults can remain active at

中文翻译：

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正断层旋转与摩擦闭锁：正断层地震倾角分布的解释及低角度正断层悖论的破解

摘要 经典岩石力学预测正断层应在 60-65°形成，在锁定前旋转至 30-40°，因此在 20°左右的广泛滑动被认为是矛盾的。此外，正断层地震的倾角分布在~45°有一个明显的、无法解释的峰值。对于这两个问题，已经提出了低摩擦、高流体压力、应力旋转和低角滑移效率的某种组合，但充其量只能提供部分解决方案。正常断层旋转的简单定量模型（在断层滑动和分布应变之间迭代）预测断层在较低角度花费更多时间。将此结果与发震正断层应该锁定的范围的莫尔-库仑分析相结合，预测了发震正断层的倾角分布，并与正断层地震观测到的范围和 45° 峰值相匹配。由于即使是正断层破裂的最低倾角也在断层重新激活的范围内，在地震发生的低角度正断层上滑动并不是矛盾的。断层再激活限制的新 Mohr-Griffith 解决方案将分析扩展到前几公里，在那里低角度滑移最受现场观测的约束，并表明低凝聚力正断层可以在