Collaborative Research: Laboratory Experiments to Understand Dynamic Slip Weakening in Rocks and Analog Materials

为了确定在哪里最好地部署有限的资源来减轻美国的地震损失，我们需要了解地震可能发生的时间和地点以及它们的加速强度。每次地震发生时，我们通过测量地面运动和模拟震源，对地震问题有了更多的了解。除了从地震中获得的信息外，我们还可以通过实验室测量和建模来提高对震源的了解，从而预测未来地震可能发生的情况。在我们对震源过程的理解中，一个巨大的空白是在快速同震滑动期间断层上的剪切阻力是如何变化的，以及这意味着应力下降和断层附近加速度的大小。在我们提出的工作计划中，我们将继续研究岩石和模拟材料的动态摩擦，以更好地理解热诱发滑动减弱过程及其对地震的影响，重点研究粗糙连接处的闪热/融化，以及当正应力快速变化时断裂带的流变响应。我们将采用板冲击压力-剪切和修正扭转科尔斯基杆的实验配置。这些实验技术是我们在CWRU的实验室开发的，我们已经在SCEC资助的试点实验研究中展示了这些技术，以提供与地震物理相关的滑移速度和正应力范围内的摩擦数据。除了在同震滑动率下的动态摩擦研究中有用外，这些实验配置允许产生瞬态，包括正应力和剪切载荷的突然变化，以研究它们对断层强度的影响。这些研究将在室温和高于室温的测试温度下进行。这一建议的知识价值由于它解决了地震物理学中的一些突出问题而得到加强，这些问题包括在典型的断层破裂过程中滑动、滑动速度和正应力变化对断层强度的影响。我们提议的研究将以各种方式直接有助于减少美国地震造成的损失，这加强了我们提议的更广泛方面。我们将获得对建立地震过程的真实模型至关重要的数据。此外，该计划为跨学科研究和教育互动提供了令人兴奋的机会。它涉及来自两所大学的教员？来自CWRU凯斯工程学院的Vikas Prakash和来自布朗大学地质科学系的David Goldsby。拟开展的研究项目将包括一名博士后和一名本科生。这些学生将获得宝贵而独特的跨学科机会，接触到地震物理学的各个方面，并将受益于断层力学、断裂力学、应力波传播、实验诊断技术和分析建模等不同领域的培训。CWRU的现有设备代表了最先进的高速摩擦测试，从而为学生提供了一个独特的实验环境。大学强烈鼓励本科生参与最前沿的教师研究，这也将发生在拟议的工作中。还将特别注意为该项目征聘代表性不足的少数民族学生。研究成果的传播计划通过在相关同行评审期刊上发表会议报告和出版物来进行。地震物理和断层力学领域的主题无疑将进入部门系列研讨会。这些项目还将利用互联网和基于大众媒体的信息传播，提高人们对拟议研究在减轻地震危害方面的潜在影响的认识。该资源将提供给大学水平和K-12学生以及公众。

In order to determine where best to deploy limited resources for mitigating earthquake loss in the US, we need to understand when and where earthquakes may occur and how intense their accelerations can be. Every time an earthquake occurs, we gain more understanding of the earthquake problem through measurements of ground motion and modeling of seismic sources. In addition to information derived from earthquakes, we can also benefit from improved understanding of the seismic source through laboratory measurements and modeling, to anticipate what may occur in future earthquakes. One of the great gaps in our understanding of source processes is how shear resistance varies on a fault during rapid co-seismic slip and what this implies about the magnitudes of stress drops and near-fault accelerations. In our proposed work plan we will continue our studies on dynamic friction in rocks and analog materials to better understanding thermally-induced slip weakening processes and their consequences for earthquakes, focusing on studies of flash heating/melting at asperity junctions, and fault zone rheological response when there is rapid change in normal stress. We will employ the plate-impact pressure-shear and the modified torsion Kolsky bar experimental configurations. These experimental techniques, developed in our laboratory at CWRU, have been shown by us in pilot experimental studies funded by SCEC, to provide friction data in the slip-speed and normal stress range of relevance to earthquake physics. Besides being useful in the study of dynamic friction at coseismic slip rates, these experimental configurations allow transients, including sudden alterations in both normal stress and shear loading, to be produced to investigate their effects on the fault strength. These studies will be carried out at both room and higher than room test temperatures. The intellectual merit of this proposal is strengthened by the fact that it addresses some of the outstanding problems in earthquake-physics, including the influence of slip, slip velocity, and alterations in normal stress on fault strength during a typical fault rupture process. The broader aspects of our proposal are strengthened by noting that our proposed research will contribute directly towards reducing losses due to earthquakes in the US in a variety of ways. We will acquire data that are essential for creating realistic models of the earthquake process. Moreover, the proposed program provides exciting opportunities for interdisciplinary research and educational interactions. It involves faculty from two universities?Vikas Prakash from Case School of Engineering, CWRU, and David Goldsby from the Department of Geological Sciences at Brown University. The proposed research program will involve one post-doctoral student and undergraduate students at CWRU. These students will receive valuable and unique interdisciplinary exposure to various aspects of earthquake physics, and will benefit from training in diverse areas such as fault mechanics, fracture mechanics, stress wave propagation, experimental diagnostic techniques, and analytical modeling. The available facilities at CWRU represent the state-of-the-art in high-speed friction testing thereby offering the students involved a unique experimental environment. The University is strongly encouraging the involvement of undergraduate students in cutting edge faculty research, and this would occur for the proposed work as well. Special attention will also be given to recruitment of underrepresented minority students for the project. Dissemination of research results is planned by conference presentations and publications in relevant peer-reviewed journals. Topics in the area of earthquake physics and fault mechanics will undoubtedly enter the departmental seminar series. The PIs will also employ internet and mass-media-based information dissemination to increase awareness of the potential impact of the proposed research in earthquake hazard mitigation. This resource will be available to university level and K-12 students as well as the general public.