Experimental Study of the Role of Pore Fluid Pressure in Earthquake Nucleation

我们将进行一项系统的研究，以了解实验断裂带的应力变化与孔隙压力变化的关系。了解地震成核过程中孔隙流体压力变化的力学贡献，以及孔隙流体压力变化如何触发地震活动具有重要意义。这项研究的地球物理目的是确定孔隙流体压力变化在多大程度上对地震发生起到力学作用，以及在什么条件下。地质观测表明，地震断裂是在地壳流体存在的情况下发生的。然而，在地震活动、地震成核和触发地震活动的模型中，很少考虑流体行为。通常认为，在地震滑动过程中，剪切引起的剪胀会降低孔压，使滑动趋于稳定，从而抑制地震的发生。然而，最近的实验室观测表明，对于位于厚断层带内的滑动，断裂带随应力变化而发生的弹性扩容或压实与之相反，远远超过了剪切诱导的扩容。因此，关于孔隙流体压力在震源力学中的作用的常见假设需要重新审视。没有在存在孔隙流体的情况下进行粘滑滑动的实验室实验，没有对断裂带的孔弹性性质进行实验室测量，也没有在适合地震断裂作用的显著差异应力下对未断裂的(围岩)进行孔弹性测量。因此，我们将进行两个系列的实验；第一个实验旨在测量破裂应力附近断裂带的孔弹性性质，第二个实验旨在确定和比较厚泥层中粘滑过程中剪切诱导的扩容(非弹性应变)和弹性应变的大小。我们将在实验观测的基础上建立地震断层滑动的本构方程，并将结果外推到地壳条件。

EAR-0230170Terry E. TullisABSTRACT We will conduct a systematic study to understand the relationship between stress change and pore pressure change in experimental fault zones. It is important to understand the mechanical contributions of pore fluid pressure change during earthquake nucleation and how pore fluid pressure change may trigger seismicity. The geophysical purpose of this research is determine to what degree changing pore fluid pressure plays a mechanical role in earthquake occurrence and under what conditions. Geologic observations show that seismic faulting occurs in the presence of crustal fluids. However rarely is fluid behavior accounted for in models of seismicity, earthquake nucleation and triggered seismicity. It is most often assumed that shear induced dilatancy during seismic slip will decrease the pore pressure, tend to stabilize the slip, and discourage earthquake occurrence. However, recent laboratory observations suggest that for slip localized within thick fault zones, elastic dilation or compaction of the fault zone with stress change is of the opposite sense and greatly exceeds shear induced dilatancy. Thus, common assumptions about the role of pore fluid pressure in earthquake source mechanics require renewed scrutiny. No laboratory experiments where stick-slip sliding occurs have been conducted in the presence of pore fluids, no laboratory measurements of the poroelastic properties of fault zones have been made, and no poroelastic measurements have been made on unfaulted (country) rock at the significant differential stresses appropriate for seismic faulting. Therefore we will conduct two series of experiments; the first designed to measure the poroelastic properties of fault zones near the failure stress, the second to determine and compare the magnitudes of shear induced dilatancy (inelastic strain) and elastic strain during stick-slip in thick gouge layers. We will develop constitutive equations for seismic fault slip based on the experimental observations and extrapolate the results to crustal conditions.