The role of pore-fluid pressure on fault behavior at the base of the seismogenic zone

为了描述孕震区底部的地震破裂、变形局部化、应力和流变特性，我们将对富含石英的岩石进行实验研究。该项目的重点是孔隙流体的力学作用，以及流体-岩石系统的力学性质如何响应温度和应变率的变化。我们的研究将通过集中于长期构造和地震过程之间的联系，为理解地震灾害的演变提供新的相关数据。我们正在寻找一个相对未被研究的领域，这一领域可能是应用地球物理数据来限制限制地震破裂深度范围的大范围断裂带过程的关键。在实验条件下，微裂纹和粘性流动之间的动力学竞争与地球我们对这些脆性和韧性过程之间的竞争的初步分析表明，断裂和滑动摩擦的有效压力定律在脆塑性转变（BPT）附近不应该像在浅层条件下那样有效。实验将在低孔隙度石英岩和砂岩上进行，温度为700- 1100 ℃，应变速率为10-3/s至5 × 10 -7/s，压力为100 MPa至1 GPa。我们的研究结果将直接关系到了解许多关键的科学问题，有关地震活动和板块边界断层的流变行为。例如（1）断层的长期强度主要取决于孔隙流体压力，因此研究了断层的长期强度实际上是由摩擦性质而不是韧性蠕变控制的地方。以及断层强度在地震周期中是如何演变的？仍然是一个关键问题。(2)流体的存在下（导致低有效应力），和附近的断层滑动稳定性过渡和摩擦性能？完全有效？有效压力定律在几乎所有产生非火山地震的模型中都被引用。然而，在这些条件下，晶体塑性过程和孔隙流体压力之间的相互作用没有得到很好的约束。(3)了解地震滑动过程中断层阻力的演化和地震断层的最大深度的一个关键初始条件是地震孕育带底部在地震间歇期的应力状态和应变局部化规模。

To characterize earthquake rupture, localization of deformation, stress and rheology at the base of the seismogenic zone we will conduct an experimental study on quartz-rich rocks. The project is focused on the mechanical role of pore fluids and how the mechanical properties of fluid-rock systems respond to variations in temperature and strain rate. Our study will provide new data relevant for understanding the evolution of seismic hazards, by concentrating on the links between long-term tectonic and earthquake processes. We are pursuing a relatively unstudied area that may turn out to be critical for applying geophysical data to constrain a wide range of fault zone processes that limit the depth extent of earthquake rupture.The role of fluids on the processes responsible for the brittle-plastic transition in quartz-rich rocks has not been explored at experimental conditions where the kinetic competition between microcracking and viscous flow is similar to that expected in the Earth. Our initial analysis of this competition between these brittle and ductile processes suggests that the effective pressure law for fracture and sliding friction should not work as efficiently near the brittle-plastic transition (BPT) as it does at shallow conditions. Experiments will be conducted on low porosity quartzite and sandstone at T = 700-1100oC, strain rates from 10-3/s to 5x10-7/s, and P = 100 MPa to 1 GPa. The results of our study will be directly relevant for understanding many critical scientific problems related to seismicity and the rheological behavior of plate-boundary faults. For example (1) The long term strength of faults depends critically on pore-fluid pressure, thus investigating where the long-term strength faults is actually controlled by frictional properties rather than ductile creep ? and how fault strength evolves during the seismic cycle ? remains a key problem. (2) The presence of fluids (resulting in low effective stresses), and frictional properties near the fault slip stability transition and a ?fully effective?, effective pressure law are invoked in almost all models for the generation of non-volcanic tremor. However, the interactions between crystal plastic processes and pore-fluid pressure are not well constrained at these conditions. (3) A key initial condition to understanding the evolution of fault resistance during seismic slip and the maximum depth of seismic faulting is the stress state and scale of strain localization at the base of the seismogenic zone during interseismic periods.