热增压与膨胀强化在实验室破裂中的竞争

中文摘要 AI 辅助

在流体饱和断层中，热增压（TP）被预测会诱发快速弱化，而膨胀强化（DS）则可通过孔隙空间膨胀来抵消这一过程。然而，关于它们之间竞争的实验约束仍然有限。在此，我们利用三轴粘滑实验，在有效围压30-60 MPa下，对饱和、锯切、热开裂的韦斯特利花岗岩进行直接断层上和断层外的孔隙压力（Pp）测量，来研究这些过程。结果显示，随着剪切应变的增加，破裂系统性地从同震Pp上升（TP型）转变为Pp下降（DS型），并伴随快-慢-快的滑动序列，滑动速度差异可达三个数量级。一个不排水、绝热的TP模型重现了早期快速事件中测得的Pp上升演化，并表明剪切带逐渐增宽降低了TP效率。随着滑动持续，累积塑性孔隙度的增加反映了DS主导序列中膨胀的增强。微观结构观察揭示了断层泥的发育和近断层损伤带，为这种结构演化提供了独立证据。这种演化改变了断层刚度，并解释了观察到的滑动行为转变。尽管Pp响应相反，TP型和DS型事件的断裂能随滑动呈相似比例缩放，表明破裂能量学具有可比性。总体而言，本研究提供了TP-DS转变的直接实验证据，表明TP控制早期弱化，但随着剪切带增宽和近断层损伤，膨胀逐渐增强，TP作用减弱。这些结果强调，断层结构及其演化在控制自然断层破裂动力学中起着关键作用。

英文摘要

In fluid-saturated faults, thermal pressurization (TP) is predicted to induce rapid weakening, whereas dilatant strengthening (DS) can counteract this process through pore-space expansion. However, experimental constraints on their competition remain limited. Here, we investigate these processes using triaxial stick-slip experiments with direct on- and off-fault pore pressure (Pp) measurements on saturated, saw-cut, thermally cracked Westerly granite under effective confining pressures of 30-60 MPa. Results reveal a systematic rupture transition from co- seismic Pp rise (TP-type) to Pp drop (DS-type) with increasing shear strain, accompanied by a fast-slow-fast slip sequence, with slip velocities differing by up to three orders of magnitude. An undrained, adiabatic TP model reproduces the measured Pp rise evolution during early-stage fast events and indicates progressive shear zone widening that reduces TP efficiency. With continued slip, increasing cumulative plastic porosity reflects enhanced dilatancy during DS-dominated sequences. Microstructural observations reveal gouge development and a near- fault damage zone, providing independent evidence for this structural evolution. This evolution modifies fault stiffness and explains the observed transition in slip behavior. Despite contrasting Pp responses, fracture energy scales similarly with slip for both TP- and DS-type events, suggesting comparable rupture energetics. Overall, this study provides direct experimental evidence of TP-DS transitions, demonstrating that TP governs early-stage weakening but diminishes as dilatancy progressively strengthens with shear zone widening and near-fault damage. These results highlight that fault structure and its evolution plays a key role in controlling rupture dynamics in natural faults.

发表机构

• Laboratoire de Géologie, École Normale Supérieure/CNRS UMR 8538, PSL University（巴黎文理研究大学）
• Université Savoie Mont Blanc, Université Grenoble Alpes, CNRS, IRD, Université Gustave Eiffel（萨瓦勃朗峰大学）

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