Collaborative Proposal: Developing a Link Between Dynamic Friction and Fracture Mechanics Models of Earthquake Rupture using a new Dynamic Double-Direct Shear Apparatus

合作提案：使用新型动态双直剪装置建立地震破裂的动态摩擦和断裂力学模型之间的联系

• 批准号: 1215765
• 负责人: Vikas Prakash
• 金额: $ 30万
• 依托单位: Case Western Reserve University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-07-15 至 2016-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1215765&HistoricalAwards=false
• 关键词: Collaborative; Proposal; Developing; Link; Between

There is broad agreement amongst researchers in the geophysics community that similar rocks may undergo very different weakening processes in different normal stress and/or slip velocity regimes. Consequently, inference of weakening behavior of fault rocks in situ from laboratory experiments at interfacial conditions of relevance to earthquake physics cannot be done simply by scaling exercises, and relatively small changes in normal stress and/or the slip speed can result in changes in the slip weakening distance of an order of magnitude. Motivated by these observations, the investigators propose to advance the current state of our understanding regarding the frictional constitutive behavior of earthquake faults using two principal approaches: (1) implementing a new dynamic shear friction testing apparatus by synergistically combining the split-Hopkinson pressure bar and the double-direct shear friction apparatus to the study of dynamic friction in both intact and granular geo-materials; and (2) developing a methodology for testing the efficacy of parameters extracted from dynamic friction experiments in dynamic rupture models. 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 and slip-velocity on fault strength during a typical fault rupture event. No laboratory experiments to-date combine the large displacement, high slip rates, and normal stresses that are understood to characterize dynamic earthquake slip at natural fault interfaces. These failings mean that processes that may occur during dynamic slip in earthquakes have not been explored experimentally. The new experimental configuration proposed in here, which is a modification of the well-established experimental procedures employed routinely in engineering for investigating high-strain-rate behavior of engineering materials (split Hopkinson pressure bar) and quasi-static friction studies in geo-materials (double-direct shear apparatus), has the potential to provide friction data in the slip-speed and normal stress range of direct relevance to earthquake physics. Furthermore, the two-pronged methodology of our proposed work aims to fundamentally change the way we approach studying the frictional resistance of faults. The first task guarantees significant results that will advance the state of understanding of dynamic friction during earthquake rupture under relevant conditions, whereas the second approach will further constrain the inferred frictional constitutive models by comparing predictions of dynamic rupture models that incorporate lab-derived frictional slip constitutive behavior with laboratory rupture experiments. The proposed research will contribute toward our understanding of earthquakes in several ways. To construct theoretical models of the earthquake process, we must understand how frictional resistance on faults changes during an earthquake. In particular, the weakening mechanism that we propose to study have profound implications for the magnitude of stress-drops during earthquakes and consequently for the magnitude of strong ground shaking. The manner in which fault strength varies with displacement and rupture velocity, as well as the rate at which healing occurs as the slip velocity decreases behind the rupture tip, can control the mode of rupture propagation, i.e. as a crack or a pulse. Thus, understanding dynamic friction is important not only for practical matters related to predicting strong ground motions and resulting damage, but also for answering major scientific questions receiving considerable attention, e.g. the strength of the San Andreas fault/the heat-flow paradox, the question that ultimately is responsible for the San Andreas Fault Observatory at Depth (SAFOD) project. The proposed program also provides exciting opportunities for interdisciplinary research and educational interactions by involving faculty and graduate students from two neighboring institutions.. Both universities are 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. The investigators 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.

地球物理学界的研究人员普遍认为，在不同的正应力和/或滑移速度下，类似的岩石可能经历非常不同的弱化过程。因此，从与地震物理相关的界面条件下的实验室实验推断断层岩石的原位弱化行为不能简单地通过标度练习来完成，而正应力和/或滑动速度的相对较小变化可能导致滑动弱化距离的一个数量级的变化。基于这些观察结果，研究者建议采用两种主要方法来提高我们对地震断层摩擦本构行为的认识现状：(1)将劈裂-霍普金森压杆和双直剪摩擦装置协同结合，实现一种新的动剪切摩擦试验装置，用于研究完整和颗粒状地材料的动摩擦；(2)开发了一种方法来测试动态破裂模型中从动态摩擦实验中提取的参数的有效性。这一建议的理论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，包括在典型的断层破裂事件中滑动和滑动速度对断层强度的影响。到目前为止，还没有实验室实验将大位移、高滑动率和正常应力结合起来，以表征自然断层界面的动态地震滑动。这些缺陷意味着在地震动力滑动过程中可能发生的过程还没有得到实验的探索。本文提出的新实验配置是对工程中用于研究工程材料的高应变率行为（劈裂霍普金森压杆）和土工材料的准静摩擦研究（双直剪装置）的成熟实验程序的修改，有可能提供与地震物理直接相关的滑移速度和正应力范围内的摩擦数据。此外，我们提出的双管齐下的方法旨在从根本上改变我们研究断层摩擦阻力的方式。第一个任务保证了显著的结果，这将促进对相关条件下地震破裂过程中动态摩擦的理解，而第二个方法将通过比较包含实验室推导的摩擦滑移本构行为的动态破裂模型的预测与实验室破裂实验，进一步约束推断的摩擦本构模型。这项提议的研究将在几个方面有助于我们对地震的理解。为了建立地震过程的理论模型，我们必须了解地震时断层上的摩擦阻力是如何变化的。特别是，我们提出研究的减弱机制对地震期间应力降的大小以及因此对强震的大小具有深远的意义。断层强度随位移和破裂速度变化的方式，以及随着滑移速度在破裂尖端后减小而发生愈合的速度，可以控制破裂传播的方式，即裂纹或脉冲。因此，了解动态摩擦不仅对预测强地面运动和由此造成的破坏的实际问题很重要，而且对回答受到相当关注的重大科学问题也很重要，例如圣安德烈亚斯断层的强度/热流悖论，这个问题最终负责圣安德烈亚斯断层深度观测站（SAFOD）项目。该计划还提供了令人兴奋的跨学科研究和教育互动的机会，涉及来自两个邻近机构的教师和研究生。两所大学都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。研究人员还将利用互联网和基于大众媒体的信息传播来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。