Faulting under high confinement: Experimental investigation and model development

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。深层地震是所有地震中规模最大、破坏力最强的地震之一，自20世纪20年代被发现以来，它一直是一个悖论。随着深度的增加，围压和温度的共同增加抑制了摩擦滑动，摩擦滑动是浅层地震的主要地震机制，在深度超过几十公里的断裂面上，但地震发生在深度接近700公里的地方。高约束条件下的脆性剪切破坏也发生在岩石和冰的撞击坑中，并且限制了高约束条件下岩石+冰混合物的稳态流动应力，因此可能对某些卫星和行星的热力学演化提供重要的约束。该项目包括新的实验和模型，旨在阐明在高约束下局部脆性压缩破坏的基本物理机制。初步实验表明，随着约束的增加，脆性失效模式发生转变，高约束的断裂似乎不受摩擦控制。它们似乎也与其他已建立的断裂机制无关，包括ⅰ型裂裂、脱水脆化或相变。他们的工作假设是，起作用的是一种完全不同的断裂机制，称为塑性断裂——一种由绝热加热辅助的非摩擦剪切不稳定性。被过去成功地使用冰作为岩石模型材料所鼓舞？冰参与了转换断层的发现，以及我们自己发现的似乎是中等约束脆性破坏的普遍机制。由于其与岩石和矿物行为的显著相似性，该项目包括一个为期三年的三轴压缩实验项目，以确定约束、晶粒尺寸和应变对终端破坏应力和破坏模式的影响（如果有的话），并注意微观结构细节，如使用视觉显微镜、冷阶段SEM电子背散射成像和冷室微ct断层扫描观察到的。研究人员试图揭示故障的物理原理，然后开发塑性断层启动的定量模型，该模型仅依赖于独立的可测量参数。这些模型是关于地球物理过程中某一特定破坏过程可能作用的任何结论的先决条件。这项拟议中的工作还将通过高级荣誉论文和达特茅斯？美国科学领域的女性（WISP）实习项目。参与该项目的学生将通过达特茅斯的学习促进中心和教育推广项目参与专业发展机会，包括地区高中的JuniorScience caf<s:1>，由蒙特舍科学博物馆赞助的冰屋建造项目，以及达特茅斯的nsf资助的极地研究igert项目，包括交流极地科学和极地研究的伦理和政策影响的课程。以及与格陵兰社区开展教育外展活动。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Deep earthquakes, some of which are among the largest and most damaging of allearthquakes, have been a paradox since their discovery in the 1920s. The combined increase ofconfining pressure and temperature with depth inhibits frictional sliding, the principal earthquakemechanism for shallow earthquakes, along fault planes beyond depths of a few tens ofkilometers, yet earthquakes occur to depths approaching 700 km. Brittle-like shear failure underhigh-confinement also occurs with impact cratering in both rock and ice and limits the steadystate flow stress of highly confined rock+ice mixtures and thus the may provide importantconstraints on the thermomechanical evolution of certain moons and planets. This projectincludes new experiments and modeling aimed at elucidating the fundamental physicalmechanism(s) that underlie localized brittle compressive failure under high confinement.Preliminary experiments demonstrate a transition in brittle-like failure mode with increasingconfinement and that the high confinement faults appear not to be friction controlled. Nor dothey appear to be related to other well established faulting mechanisms, including mode IIcracking, dehydration embrittlement, or phase transformations. Their working hypothesis is thatat play is a fundamentally different faulting mechanism called plastic faulting -- a non-frictionalshear instability aided by adiabatic heating.Spirited by past success in using ice as a model material for rock?ice was involved in thediscovery of transformational faulting and our own discovery of what appears to be a universalmechanism of moderate-confinement brittle failure?and encouraged by its marked similarity tothe behavior of rocks and minerals, this project consists of a three-year program of triaxialcompression experiments to determine the effects, if any, of confinement, grain size and strainrate on both the terminal failure stress and the failure mode, with attention to microstructuraldetail, as observed using visual microscopy, cold stage SEM electron backscatter imaging, andcold room enabled micro-CT tomography. The researchers seek to reveal thephysics of failure, and then to develop quantitative models of plastic fault initiation that only relyon independently measurable parameters. Such models are prerequisites for any conclusionsconcerning the possible role of a particular failure process in geophysical processes.The proposed work also will contribute to Dartmouth's long tradition of involving undergraduates in research, through senior honors thesesand through the Dartmouth?s Women In Science (WISP) internship program. Students involvedin this project will participate in professional development opportunities through Dartmouth'sCenter for the Advancement of Learning and in educational outreach programs, including JuniorScience Cafés in regional high schools, Igloo Build programs sponsored by the MontshireMuseum of Science, and those supported through Dartmouth's NSF-funded Polar StudiesIGERT program, including courses on communicating polar science and the ethics and policyimplications of polar research, and educational outreach activities with communities inGreenland.