Abstract Variations in elastic wave velocity and amplitude prior to failure have been documented in laboratory experiments as well as in a limited number of crustal earthquakes. These variations have generally been attributed to fault zone healing, changes in crack density, or pore fluid effects modulated dilatation or fault slip. However, the relationships between amplitude and velocity variations during the seismic cycle, and the underlying mechanisms of precursors to failure remain poorly understood. Here, we perform frictional shear experiments and measure the evolution of elastic wave velocity and amplitude throughout the laboratory seismic cycle. We find that elastic amplitudes and velocities undergo clear preseismic variations prior to fault failure. While preseismic amplitude reduction occurs early in the interseismic period, wave speed reduces later, just prior to failure. We perform a complementary set of stress oscillation experiments to quantify the response of seismic amplitudes and velocities to variations in the stress tensor. Taken together, our results indicate that preseismic amplitude variations are primarily controlled by fault slip rate and acceleration. On the other hand, elastic velocity responds to a combination of fault preslip which reduces seismic wavespeed and increasing stress in the wallrock, which increases wavespeed. Our data show that precursory changes in seismic wave speed may be more common than previously thought because they are masked by changes in wallrock stress. These results underscore the importance of continuous and long-term time-lapse monitoring of crustal faults for seismic hazard assessment and potential precursors to failure.

中文翻译：

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预滑和偏应力之间的竞争调节实验室地震的前兆

摘要 在实验室实验以及有限数量的地壳地震中，已经记录了破坏前弹性波速度和振幅的变化。这些变化通常归因于断层带愈合、裂缝密度的变化或孔隙流体效应调制的膨胀或断层滑动。然而，在地震周期中振幅和速度变化之间的关系以及破坏前兆的潜在机制仍然知之甚少。在这里，我们进行摩擦剪切实验并测量整个实验室地震周期中弹性波速度和振幅的演变。我们发现弹性振幅和速度在断层破坏之前经历了明显的地震前变化。虽然震前振幅降低发生在震间期的早期，波速稍后会降低，就在失败之前。我们进行了一组互补的应力振荡实验，以量化地震振幅和速度对应力张量变化的响应。总之，我们的结果表明震前振幅变化主要受断层滑动率和加速度控制。另一方面，弹性速度响应断层预滑移降低地震波速和增加围岩应力的组合，从而增加波速。我们的数据表明，地震波速度的前兆变化可能比以前认为的更常见，因为它们被围岩应力的变化所掩盖。这些结果强调了对地壳断层进行连续和长期延时监测对于地震危险性评估和潜在故障前兆的重要性。