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结果显示，沿着构造板块边界的大断层沿着有规律地滑动，其速度比地震慢，但比构造板块快。这些中等速率的滑动事件通过它们在断层的邻近段上引起地震或控制未来地震的可能性来影响地震灾害。虽然这些滑动事件的原因仍然存在争议，但它们在填充岩石孔隙的流体被认为处于非常高的压力的区域中被一致地观察到。受先前和初步实验室观察的启发，随着孔隙流体压力的增加，断层变得更慢，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学的影响。这项研究的目的是提供输入到模型的区域地震灾害，包括沿着圣安德烈亚斯断层和卡斯卡迪亚，在这些滑动事件已被观察到。这项研究支持了一个早期职业研究人员的实验室的发展，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。这项研究量化了一个实验观察，这是不能用现有的断层模型来解释的，并给出了断层带流体压力升高的大量证据，对缓慢滑动的原因和特征有直接的影响。特别是，以前的实验观察表明，滑动弱化距离和断裂能的断层流体压力增加。流体压力稳定的物理模型，通过一个过程被称为硬化剂硬化不能预测这种影响的大小或明显的单调下降，随着流体压力的增加，故障率。这项工作的目的是（1）确定导致稳定的过程和（2）开发本构关系，包括流体压力的影响，然后可以纳入模型的断层。为此，研究人员和一名研究生正在使用实验岩石变形来量化断层的滑动弱化距离和断裂能，作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NSF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.