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<p>In this study, the influences of initial shear stress ratio <i>c</i> and cyclic shear on the normal stress <i>σ</i><sub>n</sub> oscillation-induced slip behaviors of rough fractures are investigated through a series of laboratory experiments. The experiments were conducted on naturally rough fractures with different initial stress states. A constant shear stress and a sinusoidal <i>σ</i><sub>n</sub> are applied on fractures initially, after which the amplitude Δ<i>σ</i><sub>n</sub> was gradually increased to trigger the slip of fractures. The evolutions of mechanical parameters, released seismic energy, and moment magnitude during the slip process of fractures are analyzed. The results show that as <i>c</i> increases from 0.5 to 0.9, the shear stress <i>τ</i> transits from sinusoidal to chaotic, with the Δ<i>σ</i><sub>n</sub> required for slip initiation decreasing significantly. The fracture with a low <i>c</i> (i.e., <i>c</i> = 0.5) exhibits weak self-instability, and the Δ<i>σ</i><sub>n</sub> required for inducing slip is large, whereas the fracture with a high<i> c</i> (i.e., <i>c</i> = 0.9) displays high self-instability, leading to the occurrence of stick–slip events with high frequency. For the fracture with a moderate <i>c</i> (i.e., <i>c</i> = 0.7), the <i>σ</i><sub>n</sub> oscillation triggers the fewest stick–slip events, but the largest moment magnitude <i>M</i><sub>w</sub>. The total released seismic energy <i>E</i><sub>t</sub> generally increases with <i>c</i>. As <i>c</i> increases from 0.5 to 0.9, the <i>E</i><sub>t</sub> increases from 18.17&#xa0;J to 28.97&#xa0;J during the first shear cycle. With the increase in shear cycle, the frequency of stick–slip events significantly increases. From the third to the fifth shear cycle, the aseismic slip is observed, followed by the consecutive stick–slip stages. As the shear cycle increases from 1 to 5, the <i>E</i><sub>t</sub> decreases by 82.05%, 72.72%, and 63.79% for the fractures with <i>c</i> = 0.5, 0.7, and 0.9, respectively. These findings emphasize the critical roles of <i>c</i> and cyclic shear in modulating fault stability under <i>σ</i><sub>n</sub> oscillations and offer insights for triggering seismicity.</p>

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Role of Initial Stress State on Normal Stress Oscillation-Induced Slip Characteristics of Fractures and Implications for Triggering Seismicity

  • 期刊论文

  • 发表日期：

    2025年10月28日

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  • Xinjie Zhu,
  • Richeng Liu,
  • Wei Qiao,
  • Shuchen Li,
  • Minghui Hu,
  • Zheng Yuan

摘要

In this study, the influences of initial shear stress ratio c and cyclic shear on the normal stress σn oscillation-induced slip behaviors of rough fractures are investigated through a series of laboratory experiments. The experiments were conducted on naturally rough fractures with different initial stress states. A constant shear stress and a sinusoidal σn are applied on fractures initially, after which the amplitude Δσn was gradually increased to trigger the slip of fractures. The evolutions of mechanical parameters, released seismic energy, and moment magnitude during the slip process of fractures are analyzed. The results show that as c increases from 0.5 to 0.9, the shear stress τ transits from sinusoidal to chaotic, with the Δσn required for slip initiation decreasing significantly. The fracture with a low c (i.e., c = 0.5) exhibits weak self-instability, and the Δσn required for inducing slip is large, whereas the fracture with a high c (i.e., c = 0.9) displays high self-instability, leading to the occurrence of stick–slip events with high frequency. For the fracture with a moderate c (i.e., c = 0.7), the σn oscillation triggers the fewest stick–slip events, but the largest moment magnitude Mw. The total released seismic energy Et generally increases with c. As c increases from 0.5 to 0.9, the Et increases from 18.17 J to 28.97 J during the first shear cycle. With the increase in shear cycle, the frequency of stick–slip events significantly increases. From the third to the fifth shear cycle, the aseismic slip is observed, followed by the consecutive stick–slip stages. As the shear cycle increases from 1 to 5, the Et decreases by 82.05%, 72.72%, and 63.79% for the fractures with c = 0.5, 0.7, and 0.9, respectively. These findings emphasize the critical roles of c and cyclic shear in modulating fault stability under σn oscillations and offer insights for triggering seismicity.