Postdoctoral Fellowship: EAR-PF: To roll, flow, or fracture - that is the question: Investigating the mechanisms behind friction and the stability of faults

博士后奖学金：EAR-PF：滚动、流动或断裂 - 这就是问题：研究摩擦和断层稳定性背后的机制

• 批准号: 2305630
• 负责人: Kristina Okamoto
• 金额: $ 18万
• 依托单位: Okamoto, Kristina
• 依托单位国家: 美国
• 项目类别: Fellowship Award
• 财政年份: 2024
• 资助国家: 美国
• 起止时间: 2024-04-01 至 2026-03-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2305630&HistoricalAwards=false
• 关键词: Postdoctoral; Fellowship; EAR; PF; roll

Dr. Kristina Okamoto has been awarded an NSF EAR Postdoctoral Fellowship to conduct research at the University of Minnesota investigating the physics governing the frictional behavior of fault gouge. Fault failure can occur at a range of slip speeds varying from slow creep (cm/year) to fast earthquakes (m/s) and this rate of failure depends on the friction (resistance to sliding) of the fault. Therefore, understanding where and when earthquakes happen requires a frictional model. The predominant model is a set of equations that fit laboratory data called rate and state friction. While these equations have been generally useful, they do not include any underlying physics of the system. Because of this, scientists are unable to extrapolate results to pressure and temperature conditions not directly explored in the lab. Due to experimental constraints, many pressure and temperature conditions relevant to the earth are not attainable. Recently, a new frictional model has been defined, where the frictional state is governed by the permanent deformation of grains during sliding. This permanent deformation is called plastic deformation, and adds shear strength to the system, called backstress. While this model can fit experiments similar to rate and state friction, the effect of backstress on friction has not been investigated systematically in the laboratory. This project will vary the amount of backstress in the starting grains and then perform friction experiments on this material. Preliminary experiments at 550°C and 100 MPa normal stress show that the amount of backstress in the starting grains causes a large change in the amount of shear stress required to slide the material at a steady state. Testing and enhancing this new model will allow for better predictions of the conditions that allow for earthquakes versus slower slip. Outside of this research, Dr. Okamoto will mentor students through the Research Opportunities in Rock Deformation (RORD) REU at UMN and co-supervise an undergraduate research project. Dr. Okamoto will also engage with and aid in ongoing initiatives at UMN that aim to promote diversity and support geoscientists from under-represented groups.This work will further investigate this new model by determining the velocity dependence of materials over a range of pressure and temperature conditions that may span deformation mechanisms such as dilation, fracture, and plastic deformation at grain contacts. At conditions relevant to plasticity, the steady-state friction coefficient as well as the frictional rate-dependence will depend on backstress, but when temperatures and pressures are low, the effect of plasticity will be low, and friction should be a function of dilation rather than backstress. When pressures are high and temperature is low, friction should mostly depend on the ability of the grains to fracture. However, there is a feedback between backstress and fracture that is currently unmapped. Backstress is fundamentally caused by additions of small separations in the crystal lattice called dislocations. The dependence of the ability for grains to fracture on dislocation density will be explored through novel indentation techniques. This will enable a better understanding of how the frictional system at low temperatures and high pressures will behave. Overall, exploring whether friction depends on backstress over a wide parameter range will be fundamental to extrapolating laboratory friction to pressure/temperature conditions not explored in the lab as well as to larger spatial and temporal scales.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

Kristina Okamoto 博士获得了 NSF EAR 博士后奖学金，在明尼苏达大学进行研究，研究控制断层泥的摩擦行为的物理现象，断层破坏可能发生在从缓慢蠕变（厘米/年）到不同的滑移速度范围内。快速地震 (m/s) 的破坏率取决于断层的摩擦力（抗滑动性），因此，了解地震发生的地点和时间需要一个摩擦模型。虽然这些方程通常很有用，但它们不包括系统的任何基础物理学，因此科学家无法将结果推断为实验室中未直接探索的压力和温度条件。由于实验限制，许多与地球相关的压力和温度条件无法实现，最近定义了一种新的摩擦模型，其中摩擦状态由滑动过程中颗粒的永久变形控制。 ，并增加剪切力虽然该模型可以拟合类似于速率和状态摩擦的实验，但实验室中尚未系统地研究反应力对摩擦的影响，然后改变初始颗粒中的反应力大小。在 550°C 和 100 MPa 正应力下对该材料进行摩擦实验表明，起始晶粒中的反应力会导致材料稳定滑动所需的剪切应力发生较大变化。测试和增强这个新模型将能够更好地预测地震与较慢滑动的条件。除了这项研究之外，冈本博士还将通过 UMN 和 co 的岩石变形 (RORD) 研究机会来指导学生。 -监督一个本科生研究项目。冈本博士还将参与并协助UMN正在进行的举措，这些举措旨在促进多样性并支持代表性不足群体的地球科学家。这项工作将通过确定来进一步研究这一新模型。材料在一系列压力和温度条件下的速度依赖性，这些条件可能跨越变形机制，例如晶粒接触处的膨胀、断裂和塑性变形，在与塑性、稳态摩擦系数以及摩擦速率相关的条件下。依赖性取决于背应力，但当温度和压力较低时，塑性的影响会较低，摩擦力应该是膨胀的函数而不是背应力。当压力较高且温度较低时，摩擦力应主要取决于能力。的然而，目前尚未绘制出反应力和断裂之间的反馈，这从根本上说是由晶格中添加的称为位错的小间距引起的，晶粒断裂的能力将取决于位错密度。通过新颖的压痕技术进行探索，这将有助于更好地了解摩擦系统在低温和高压下的表现。总体而言，探索摩擦是否取决于宽参数范围内的背应力将是基础。将实验室摩擦力推断到实验室未探索的压力/温度条件以及更大的空间和时间尺度。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。