Collaborative Research: Developing a Link between Dynamic Friction and Fracture Mechanics Models of Earthquake Rupture using a New Dynamic Double-direct Shear Apparatus

合作研究：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: 1215669
• 负责人: WIlliam Griffith
• 金额: $ 15.96万
• 依托单位: University of Akron
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-07-15 至 2013-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1215669&HistoricalAwards=false
• 关键词: Collaborative; Research; 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，相似的岩石在不同的法向应力和/或滑移速度状态下可能会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弱化行为不能简单地通过缩放练习来完成，法向应力和/或滑移速度的相对较小的变化可能导致滑移的变化一个数量级的弱化距离。 受这些观察的启发，研究人员建议使用两种主要方法来推进我们对地震断层摩擦本构行为的理解：（1）通过协同组合分裂霍普金森压力棒和用于研究完整和粒状地质材料动摩擦的双直剪摩擦装置； (2) 开发一种方法来测试从动态破裂模型中的动态摩擦实验中提取的参数的有效性。 该提案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，包括典型断层破裂事件期间滑移和滑移速度对断层强度的影响。迄今为止，还没有实验室实验将大位移、高滑移率和正应力结合起来，以表征自然断层界面处的动态地震滑移。这些失败意味着地震动态滑移过程中可能发生的过程尚未经过实验探索。这里提出的新实验配置是对工程中常规使用的成熟实验程序的修改，用于研究工程材料的高应变率行为（分裂霍普金森压力棒）和土工材料的准静摩擦研究（双直剪装置）有可能提供与地震物理直接相关的滑移速度和法向应力范围内的摩擦数据。此外，我们提出的工作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着的结果，将促进对相关条件下地震破裂期间动摩擦的理解，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的动态破裂模型的预测来进一步约束推断的摩擦本构模型实验室破裂实验的行为。拟议的研究将从几个方面促进我们对地震的理解。为了构建地震过程的理论模型，我们必须了解地震期间断层上的摩擦阻力如何变化。特别是，我们建议研究的弱化机制对地震期间应力下降的幅度以及因此对强烈地面震动的幅度具有深远的影响。断层强度随位移和破裂速度变化的方式，以及随着破裂尖端后面滑移速度降低而发生愈合的速率，可以控制破裂传播的模式，即作为裂纹或脉冲。因此，了解动态摩擦不仅对于与预测强烈地面运动及其造成的损害相关的实际问题很重要，而且对于回答受到广泛关注的重大科学问题也很重要，例如。圣安地列斯断层/热流悖论的强度，这个问题最终导致了圣安地列斯断层深度观测站（SAFOD）项目。 拟议的项目还通过让来自两个相邻机构的教师和研究生参与，为跨学科研究和教育互动提供了令人兴奋的机会。两所大学都强烈鼓励本科生参与前沿教师研究，这将发生在拟议的工作中：出色地。该项目还将特别关注招募代表性不足的少数族裔学生。研究成果的传播是通过会议演讲和相关同行评审期刊上的出版物来计划的。研究人员还将利用互联网和大众媒体的信息传播来提高人们对拟议研究在减轻地震灾害方面的潜在影响的认识。