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

为了描述地震破裂特征，形变、应力和流变学在孕震带底部的局部化，我们将对富石英岩石进行实验研究。该项目的重点是孔隙流体的力学作用，以及流体-岩石系统的力学特性如何响应温度和应变速率的变化。我们的研究将通过关注长期构造和地震过程之间的联系，为了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区域，这个区域可能对应用地球物理数据来限制大范围的断层带过程至关重要，这些断层带过程限制了地震破裂的深度范围。流体在富石英岩石脆性-塑性转变过程中的作用尚未在实验条件下进行探索，在实验条件下，微开裂和粘性流动之间的动力学竞争与地球上的预期相似。我们对这些脆性和延性过程之间竞争的初步分析表明，断裂和滑动摩擦的有效压力律在脆性-塑性转变（BPT）附近不应该像在浅层条件下那样有效。实验将在温度为700-1100℃、应变速率为10-3/s ~ 5 × 10-7/s、P = 100 MPa ~ 1 GPa的低孔隙度石英岩和砂岩上进行。我们的研究结果将直接关系到理解与地震活动性和板块边界断层流变行为有关的许多关键科学问题。例如(1)断层的长期强度主要取决于孔隙流体压力，因此研究断层的长期强度实际上是由摩擦特性而不是延性蠕变控制的。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（导致较低的有效应力），以及断层滑动稳定性过渡和a ？完全有效?，有效压力定律几乎适用于所有非火山性震颤的产生模型。然而，在这些条件下，晶体塑性过程与孔隙流体压力之间的相互作用并没有得到很好的约束。(3)震间期孕震带基底应变局部化的应力状态和规模是了解地震滑动过程中断层阻力演化和地震最大断裂深度的关键初始条件。

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.