Controls of Pore Fluid Pressure on Fault Slip Weakening and Fracture Energy

在过去的15年里，大地测量学和地震学领域的测量表明，沿构造板块边界的大断层有规律地以比地震慢但比构造板块快的速度滑动。这些中速率滑动事件影响地震的危险性，因为它们有可能在断层的邻近部分引起地震，或控制未来地震的强度。虽然这些滑动事件的原因仍有争议，但在流体填充岩石孔隙的区域，它们被认为处于非常高的压力下，它们一直被观察到。由于之前和初步的实验室观察发现，随着孔隙流体压力的增加，断层会变得更慢、更稳定，莱斯大学的科学家们正在量化流体压力对断层物理的影响。这项研究的目的是为区域地震危险模型提供输入，包括沿着圣安德烈亚斯断层和卡斯卡迪亚，这些滑动事件已经被观察到。这项研究支持了一个早期职业研究人员的实验室发展，以及一名研究生和几名本科生的教育。研究人员和学生将把这项工作纳入自然灾害的讲座和教学活动中。这项研究量化了目前断层模型无法解释的实验观察结果，并且考虑到断层带流体压力升高的大量证据，对慢滑的原因和特征有直接的影响。实验结果表明，断层的滑动弱化距离和断裂能随流体压力的增大而增大。通过膨胀硬化过程实现流体压力稳定的物理模型无法预测这种效应的大小，也无法预测故障率随流体压力增加而明显单调下降的情况。这项工作的目的是：(1)确定导致稳定的过程，(2)建立包括流体压力影响的本构关系，然后将其纳入断层模型。为此，研究者和一名研究生利用实验岩石变形，将断裂的滑动弱化距离和断裂能量化为孔隙流体压力大小和有效应力大小的函数。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

In the past 15 years, measurements from the fields of geodesy and seismology have revealed that large faults along the boundaries of tectonic plates regularly slip at rates slower than earthquakes, but faster than the tectonic plates. These intermediate-rate slip events influence earthquake hazards through their potential to cause an earthquake on an adjacent segment of the fault or to control how big a future earthquake may become. Although the cause of these slip events is still debated, they are consistently observed in regions where the fluids filling pores in the rock are thought to be at very high pressure. Motivated by previous and preliminary laboratory observations that faulting becomes slower and more stable with increasing pore fluid pressure, scientists at Rice University are quantifying the effects of fluid pressure on the physics of faulting. This study is designed to provide inputs into models of regional seismic hazards, including along the San Andreas Fault and in Cascadia, where these slip events have been observed. This research is supporting the development of a laboratory by an early career researcher and the education of one graduate student and several undergraduate students. The researcher and students will incorporate this work into lectures and teaching activities on natural hazards.This research quantifies an experimental observation that is not explained by current models for faulting and, given the abundance of evidence for elevated fluid pressures in fault zones, has direct implications for the cause and characteristics of slow slip. Specifically, previous experimental observations show that the slip weakening distance and fracture energy of faulting increase with fluid pressure. Physical models for fluid pressure stabilization through a process known as dilatant hardening cannot predict the magnitude of this effect or the apparent monotonic decrease in failure rates with increasing fluid pressure. The purpose of this work is to (1) determine the processes that cause stabilization and (2) develop constitutive relations that include the effect of fluid pressure, which can then be incorporated into models of faulting. To this end, researcher and a graduate student are using experimental rock deformation to quantify the slip weakening distance and fracture energy of faulting as a function of pore fluid pressure magnitude and effective stress magnitude.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.