Theoretical Analysis of Joint Friction

摩擦实验，即施加剪切力使正常平面岩石表面之间产生滑动，被设计用来模拟在自然断层上观察到的位移。在解释实验结果时出现的一个困难是尺度问题：样品的大小以厘米为单位测量，而自然断层的长度和深度都有许多公里；自然过程和实验室过程在时间尺度上的差异也同样巨大。沃尔什正在研究如何通过建立理论模型来模拟实验观察到的行为，从而弥合由时间和长度尺度的差异造成的差距。他现在正在研究粗糙的弹性表面之间的滑动，在微观尺度上，由库仑摩擦对抗的滑动发生在凹凸不平的接触处。这种分析可以立即应用于实验室的滑动实验，是地震断层分析的基础，其中实验室样品的“粗糙度”相当于断层界面正应力和剪切应力场的非均质性。这项研究可以通过引入更复杂的摩擦行为来进行修改，比如目前正在几个实验室进行研究的速率-状态模型。

Friction experiments, where the applied shear force required to produce slip between normally planar rock surfaces, are designed to simulate displacement observed on natural faults. One difficulty that arises in the interpretation of experimental results is the problem of scale: the size of the samples is measured in centimeters, whereas natural faults are many kilometers in length and depth; and the disparity in the scales of time that are characteristic of natural and laboratory processes is as great. Walsh is studying ways to bridge the gap caused by the disparity in time and length scales by developing theoretical models which simulate behavior observed experimentally. He is now studying slip between rough elastic surfaces where slip, opposed by Coulomb friction, occurs on the microscale at the contacts between asperities. This analysis, which has immediate application to sliding experiments in the laboratory, is the basis for the analysis of earthquake faulting, where 'roughness' of lab samples is equivalent to heterogeneity in the normal stress and shear stress fields at the fault interface. The study can be modified by introducing more complicated frictional behavior, such as the rate-state model, now being studied in several laboratories.