Experimental Investigation of Mechanisms for High Pore Fluid Pressure Associated Slow Faulting

各俯冲带的缓慢滑动为研究大地震间大断裂的状态提供了新的契机。俯冲带中的高孔隙流体压力通常在发生慢滑事件的地区被检测到，但人们并不清楚这种高孔隙压力实际上是如何与慢滑联系在一起的。这个项目通过对岩石变形的实验室实验，探索流体和缓慢滑动机制之间的这种联系。该项目将使用一种新的成像技术--动态显微层析成像，当岩石样品被压到破碎点时，它可以帮助对岩石样品的内部进行成像。这些实验可以在不同的孔压水平和不同的变速下进行，以探索导致断层从快速滑动到稳定慢滑的条件范围。最近的实验研究表明，高孔隙流体压力既可以稳定完整岩石中的断层传播，又可以减缓存在断层的岩石中的摩擦滑动。不排水条件下的膨胀剂硬化被认为是这些观察到的稳定效果的原因。初步实验数据表明，在名义排水条件下，高孔隙流体压力也会阻碍断层的生长。该项目是一套系统的裂缝和摩擦实验，以了解升高的孔隙流体压力在稳定断层和摩擦滑动方面的作用。其目的是1)利用动态显微层析成像技术来表征显微组织的实时演化。这将导致对渗透率、孔隙度和孔隙形状的时空分布的定量评估，从而更好地约束脆性破坏过程中的排水条件；2)阐明膨胀剂硬化在沿先前存在的断层从粘滑事件向慢滑事件的转变中的作用。研究人员将使用不同的断层泥材料来产生不同的排水条件，并研究高孔隙流体压力和慢滑行为之间的力学联系；3)确定与缓慢断层作用相关的断层几何形状和断层外损害的诊断特征。这项研究的结果将有助于更好地了解不同的不稳定性和导致它们的机械过程。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。

Slow slip at various subduction zones provides a new opportunity to study the state of megathrust faults in between great earthquakes. Elevated pore fluid pressure in the subduction zone is often detected in regions where slow slip events occur, but it is not well understood how this high pore pressure is actually linked to the slow slip. This project explores this link between fluids and the mechanisms for slow slip through laboratory experiments on how rocks deform. The project will use a new imaging technique, dynamic microtomography, that helps image the interior of a rock sample as it is pressed to the point of failure. These experiments can be conducted at different levels of pore pressure and at different and variable speeds to explore the range of conditions that can lead a fault to move from fast slip to steady slow slip.Recent experimental studies show that high pore fluid pressure can stabilize both fault propagation in intact rocks and decelerates frictional slip in rocks with an existing fault. Dilatant hardening under undrained conditions is thought to be responsible for these observed stabilization effects. Preliminary experimental data show that high pore fluid pressure can also impede fault growth under nominally drained conditions. This project is a systematic set of fracture and friction experiments to understand the role of elevated pore fluid pressure on stabilizing faulting and frictional slip. The goal is to 1) characterize the real-time microstructure evolution using dynamic microtomography. This will result in a quantitative assessment of the spatio-temporal distributions of permeability, porosity, and pore shape, thus better constraints of the drainage conditions during brittle failure; 2) elucidate the role of dilatant hardening in the transition from stick-slip events to slow slip events along a pre-existing fault. The researchers will use different gouge materials to produce different drainage conditions and investigate the mechanical link between high pore fluid pressure and slow slip behaviors; 3) identify diagnostic characteristics of fault geometry and off-fault damage associated with slow faulting. The findings of this study will lead to a better understanding of different instabilities and the mechanical processes responsible for them.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.