Collaborative EAGER Research: Mineral reactions during seismic slip and earthquake instability

EAGER 协作研究：地震滑移和地震不稳定期间的矿物反应

• 批准号: 1247951
• 负责人: Harry Green
• 金额: $ 7.06万
• 依托单位: University of California-Riverside
• 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: 2012-08-15 至 2014-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1247951&HistoricalAwards=false
• 关键词: Collaborative; EAGER; Research; Mineral; reactions

Although a great deal is known about the location of earthquakes and their danger to society, our knowledge of the underlying physics of how they nucleate and, especially, the physical processes operating as the slipped area on the fault expands during an earthquake is still poorly understood. Greater knowledge of these processes is necessary to better predict seismic shaking danger and, it is hoped, to one day enable prediction of major earthquakes. This EAGER project will use experimental studies and high-resolution electron microscopy to test a new hypothesis of how the slip on continental earthquakes occurs. Earthquakes are understood to initiate by two distinctly different processes: In the cold, low-pressure, environment of the upper few tens of km within the Earth, earthquakes generally begin by overcoming static friction on pre-existing faults. However, earthquakes also occur continuously to depths approaching 700 km in subducting oceanic lithosphere where the pressure is too high to allow brittle failure. Experiments show that shear failure (faulting) at high pressure requires a mineral reaction that yields a small amount of 'fluid' for their initiation and expansion; the 'fluid' can be either a true fluid (eg. H2O or CO2) or a nanocrystalline solid exhibiting an extremely low viscosity in the solid state. One of the two PIs of this project (Reches) is a leading expert in frictional sliding and the other (Green) is the world leader in high-pressure shear failure. They are joined by two leading experts on the physics of earthquakes of the US Geological Survey (D. Lockner and N. Beeler) at no cost to the project. This EAGER project will test the hypothesis that the process of mineral-reaction-induced shearing instability, the mechanism of faulting at high pressure, can also operate in shallow earthquakes where it is activated by the frictional heating/straining that occurs during initiation of earthquake slip. The team envisions two main ways in which this may occur: (1) Breakdown of clay minerals or carbonates in the fault zone releasing a fluid (water or CO2, respectively) that results in a large drop of the resistance to sliding on the fault; (2) generation of extremely small particles during initiation of sliding that form a nanocrystalline solid that can flow by grain-boundary sliding at seismogenic speeds, as has already been demonstrated for high-pressure faulting. Models of earthquake slip, experiments, and examination of fault zones in the field strongly suggest that shear-heating-induced devolatilization occurs in some earthquakes. The high-pressure experimental observations that such reactions lead to shearing instabilities further suggest that similar processes could enhance shallow earthquakes. Similarly, recent laboratory work in at least two laboratories concludes that powder-lubrication may be a critical part of fault propagation and lubrication. The key question we will test experimentally is whether such shear-heating-induced mineral reactions can lead to rapid drop in friction and/or enhancement of slip under shallow crust conditions. The team will investigate the role of 'fluid'-producing reactions in fault mechanics. They will activate shear-induced devolatilization in laboratory experiments at the University of Oklahoma by high-speed sliding under a range of normal stresses. They then will characterize by high-resolution Scanning and Transmission electron microscopy at UC Riverside the microstructure of gouge and sliding surface produced in these experiments and compare those microstructures with the 'superplastic' fault-filling materials produced in high-pressure faulting experiments. Preliminary results on carbonate that are very encouraging. Broader Impacts: This project brings together scientists and graduate students from two university campuses and a federal government lab for an EAGER project with potentially profound consequences for residents of earthquake-prone areas such as California. If this work demonstrates that devolatilization is directly responsible for friction drop and/or that fault gouges of large earthquakes are weak nanocrystalline solids, they will have opened a door that will lead to greater understanding of faulting and potentially will lead to a better understanding of which parts of which faults in a given area such as California are dangerous and which are not. The students of this project (one at OU and the other at UCR), with the likely addition of undergraduate assistants, will receive training on state-of-the-art instrumentation and will participate in research at the frontier of their science.

尽管人们对地震的位置及其对社会的危害了解很多，但我们对地震如何成核的基本物理学，特别是地震期间断层滑移区域扩大时的物理过程的了解仍然知之甚少。为了更好地预测地震震动危险，有必要更多地了解这些过程，并希望有一天能够预测大地震。这个 EAGER 项目将使用实验研究和高分辨率电子显微镜来测试关于大陆地震滑动如何发生的新假设。 人们认为地震是由两个截然不同的过程引发的：在地球上部几十公里的寒冷、低压环境中，地震通常是通过克服预先存在的断层上的静摩擦力而开始的。然而，在俯冲海洋岩石圈中，地震也会持续发生到深度接近700公里的地方，那里的压力太高，无法发生脆性破坏。实验表明，高压下的剪切破坏（断层）需要发生矿物反应，产生少量“流体”来引发和扩展； “流体”可以是真正的流体（例如H2O或CO2），也可以是在固态下表现出极低粘度的纳米晶体固体。该项目的两位 PI 之一（Reches）是摩擦滑动领域的领先专家，另一位（Green）是高压剪切破坏领域的世界领先专家。美国地质调查局的两位地震物理学顶尖专家（D. Lockner 和 N. Beeler）也加入了他们的行列，项目无需支付任何费用。该 EAGER 项目将测试以下假设：矿物反应引起的剪切不稳定性过程（高压断层机制）也可以在浅层地震中运行，在浅层地震中，它是由地震滑动过程中发生的摩擦加热/应变激活的。研究小组设想了两种主要方式可能会发生这种情况：（1）断层带中粘土矿物或碳酸盐的分解释放出流体（分别为水或二氧化碳），导致断层上的滑动阻力大幅下降； (2) 在滑动开始过程中产生极小的颗粒，形成纳米晶体固体，该固体可以以发震速度通过晶界滑动流动，正如高压断层已经证明的那样。 地震滑移模型、实验和现场断层带检查强烈表明，在某些地震中会发生剪切热引起的脱挥发分。高压实验观察到这种反应导致剪切不稳定性，进一步表明类似的过程可能会增强浅层地震。同样，至少两个实验室最近的实验室工作得出结论，粉末润滑可能是故障传播和润滑的关键部分。我们将通过实验测试的关键问题是，这种剪切加热引起的矿物反应是否会导致浅地壳条件下摩擦力的快速下降和/或滑移的增强。该团队将研究“流体”产生反应在断层力学中的作用。他们将在俄克拉荷马大学的实验室实验中通过在一定范围的法向应力下高速滑动来激活剪切引起的脱挥发分。然后，他们将通过加州大学河滨分校的高分辨率扫描和透射电子显微镜来表征这些实验中产生的凿岩和滑动表面的微观结构，并将这些微观结构与高压断层实验中产生的“超塑性”断层填充材料进行比较。关于碳酸盐的初步结果非常令人鼓舞。更广泛的影响：该项目汇集了来自两个大学校园和一个联邦政府实验室的科学家和研究生，共同开展一个 EAGER 项目，该项目可能会对加利福尼亚州等地震多发地区的居民产生深远的影响。如果这项工作证明脱挥发分直接导致摩擦下降和/或大地震的断层泥是弱纳米晶体固体，那么它们将打开一扇大门，使人们更好地了解断层，并有可能更好地了解特定地区（例如加利福尼亚州）的断层的哪些部分是危险的，哪些部分不是。该项目的学生（一名在俄勒冈大学，另一名在加州大学河滨分校），以及可能增加的本科生助理，将接受最先进仪器的培训，并将参与其科学前沿的研究。