Collaborative Research: An Experimental Study of the Effects of Off-Fault Damage on Earthquake Rupture Mechanics

研究人员将扩大他们关于断层外破坏对地震破裂传播的影响的实验室研究，从6x6英寸的双折射聚合物板到12x12英寸的大理石板。对于大理石，赖斯等人。(2005)模型预测，裂纹尖端与初始损伤的相互作用应延伸到距断层面约10厘米的距离，而聚合物中的相互作用距离约为1厘米。使用大理石的主要优点是，它具有均匀分布的1毫米颗粒和弱边界，可以被利用来产生均匀的毫米级初始损伤阵列。在大理岩中，较大的损伤区与较小规模的初始损伤的这种组合应该允许观察到靠近裂纹尖端的区域，在那里模型预测应该发生新的损伤和颗粒化。还需要较大的大理石板和从一个边缘成核来防止破裂形成平面外的拉伸机翼裂纹。他们已经构建了一个更大的加载框架，并成功地在这些较大的板块的断层面上成核和传播了II型剪切破裂。还需要更大的板来研究预测的大理岩的更大损伤带。这些数据将使用莱斯等人最近开发的动态滑移脉冲模型进行解释。(2005)。在该模型中，滑移被限制在有限长度的断层面上，当破裂速度接近极限瑞利速度时，这具有将断层外损伤区的宽度限制在有限值的效果。Ashby和Sammis(1990)的细观力学模型将使研究人员能够区分先前存在的裂缝上的库仑滑移和导致局部破坏和断层和角砾岩形成的新损伤的产生。研究人员目前正在与吉姆·赖斯和伊丽莎白·邓普顿合作，将Ashby-Sammis损伤力学转化为一种与弹性-完美塑性模型协同的形式。最终的目标是在现实的非线性介质中模拟自由传播的滑移脉冲，这仍然是一个悬而未决的问题。这里提出的实验室实验将用于指导这样一个模型的发展。

The investigators will extend their laboratory study of the effects of off-fault damage on earthquake rupture propagation from 6x6 inch birefringent polymer plates to 12x12 inch marble plates. For marble, the Rice et al. (2005) model predicts that the interaction of the crack tip with initial damage should extend to distances on the order of 10 cm from the fault plane, in contrast to an interaction distance of about 1 cm in the polymer. The main advantage of using marble is that it has a uniform distribution of 1 mm grains with weak boundaries that can be exploited to produce a uniform millimeter-scale array of initial damage. This combination in marble of a larger damage zone with smaller scale initial damage should allow for the observation of the zone close to the crack tip where models predicts that new damage and granulation should occur.The larger marble plates and nucleation from one edge are also required to keep the rupture from nucleating an out-of-plane tensile wing crack. They have already constructed a larger loading frame and successfully nucleated and propagated mode II shear ruptures on the fault plane in these larger plates. Larger plates are also required to study the larger damage band predicted for marble. The data will be interpreted using the dynamic slip pulse model recently developed by Rice et al. (2005). In this model slip is limited to a finite length of the fault plane, which has the effect of limiting the width of the zone of off-fault damage to a finite value as the rupture speed approaches the limiting Rayleigh speed. The micromechanical model of Ashby and Sammis (1990) will allow the researchers to distinguish between Coulomb slip on preexisting fractures and the generation of new damage, which leads to local failure and the formation of gouge and breccia. The researchers are currently collaborating with Jim Rice and Elizabeth Templeton to cast the Ashby-Sammis damage mechanics into a form that is synergistic with the elastic-perfectly plastic model. The ultimate goal, to model a freely propagating slip pulse in a realistic non-linear medium, remains an unsolved problem. The laboratory experiments proposed here will serve to guide the development of such a model.