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

为了确定在哪里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，以及它们的加速程度。每次地震发生，我们都会通过地面运动的测量和震源的模拟来对地震问题有更多的了解。除了来自地震的信息外，我们还可以通过实验室测量和建模来更好地了解地震源，以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，最大的空白之一是在快速同震滑动过程中断层上的剪切阻力如何变化，以及这意味着应力降和近断层加速的大小。在我们拟议的工作计划中，我们将继续研究岩石和模拟材料中的动态摩擦，以更好地了解热致滑移减弱过程及其对地震的影响，重点研究粗糙面交界处的闪热/熔融，以及当正应力快速变化时的断裂带流变响应。我们将采用平板碰撞压力剪切和修正的扭转Kolsky杆实验构型。这些实验技术是由CWRU的实验室开发的，我们已经在SCEC资助的初步实验研究中展示了这些技术，以提供与地震物理相关的滑动速度和正常应力范围内的摩擦数据。除了在研究同震滑移率下的动态摩擦外，这些实验构型还允许产生瞬变，包括法向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。这些研究将在室内和高于室内测试温度的情况下进行。这一建议的学术价值得到了加强，因为它解决了地震物理学中的一些突出问题，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。我们建议的更广泛的方面得到了加强，注意到我们建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。我们将获得对创建真实的地震过程模型至关重要的数据。此外，拟议的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职员工--CWRU凯斯工程学院的Vikas Prakash和布朗大学地质科学系的David Goldsby。拟议的研究计划将涉及CWRU的一名博士后和本科生。这些学生将获得宝贵和独特的跨学科接触地震物理的各个方面，并将受益于不同领域的培训，如断层力学、断裂力学、应力波传播、实验诊断技术和分析建模。CWRU现有的设备代表了高速摩擦测试的最先进水平，从而为参与测试的学生提供了一个独特的实验环境。该大学强烈鼓励本科生参与尖端的教师研究，这也将发生在拟议的工作中。还将特别注意为该项目招收代表人数不足的少数族裔学生。通过在相关同行评议期刊上发表会议报告和出版物，计划传播研究成果。地震物理和断层力学领域的课题无疑将进入系级研讨会系列。私人投资促进机构亦会利用互联网和大众传媒传播资讯，以提高公众对拟议研究在减轻地震危险方面的潜在影响的认识。这一资源将向大学和K-12年级的学生以及普通公众开放。

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.