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

摘要对实验断裂带的应力变化与孔隙压力变化关系进行系统研究。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引发地震活动性具有重要意义。本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以及在什么条件下对地震发生起力学作用。地质观测表明，地震断裂发生在地壳流体存在的情况下。然而，在地震活动性、地震成核和触发地震活动性的模型中很少考虑流体行为。人们通常认为，地震滑移过程中剪切引起的剪胀会降低孔隙压力，使滑移趋于稳定，阻止地震发生。然而，最近的实验室观察表明，对于位于厚断裂带内的滑动，断裂带随应力变化的弹性扩张或压实具有相反的意义，大大超过剪切引起的剪胀。因此，关于孔隙流体压力在震源力学中的作用的一般假设需要重新审视。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，没有对断裂带的孔隙弹性特性进行实验室测量，也没有在适合地震断层的显著差应力下对无断层（乡村）岩石进行孔隙弹性测量。因此我们将进行两个系列的实验；第一种方法用于测量靠近破坏应力的断裂带的孔隙弹性特性，第二种方法用于确定和比较厚断层泥粘滑过程中剪切诱发剪胀（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.