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的滑动速度通常比地震慢，但比构造板块快。这些中速滑动事件通过其在断层相邻部分引发地震的可能性或控制未来地震可能变得多大来影响地震危险。尽管这些滑移事件的原因仍有争议，但在岩石中填充孔隙的流体被认为处于非常高的压力的地区，它们一直被观察到。由于先前和初步的实验室观察，随着孔隙流体压力的增加，断层作用变得更加缓慢和稳定，赖斯大学的科学家们正在量化流体压力对断层作用物理学的影响。这项研究旨在为区域地震灾害模型提供信息，包括圣安德烈亚斯断层沿线和卡斯卡迪亚，在那里观察到了这些滑动事件。这项研究正在支持一名早期职业研究人员开发一个实验室，并支持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关于自然灾害的讲座和教学活动中。这项研究量化了现有断层模型无法解释的实验观察结果，鉴于断裂带流体压力升高的大量证据，这项研究对缓慢滑动的原因和特征有直接影响。具体地说，以往的实验观测表明，断裂的滑动弱化距离和断裂能随着流体压力的增加而增加。通过一种称为膨胀剂硬化的过程来稳定流体压力的物理模型无法预测这种影响的程度，也无法预测随着流体压力的增加故障率的明显单调下降。这项工作的目的是(1)确定导致稳定的过程和(2)建立包括流体压力影响的本构关系，然后将其纳入断层作用模型。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滑动减弱距离和断裂能作为孔隙流体压力量级和有效应力量级的函数。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.