EAR-PF: Fault-rock trapped-charge and 4He/3He thermochronometry: new paleothermometers to assess scales and rates of fault slip

Margaret Odlum博士被授予NSF博士后奖学金，在Alexis K Ault教授和Tammy Rittenour教授的指导下，在犹他州州立大学（USU）开展研究和专业发展计划。该项目的目标是开发新的方法来识别断层岩中过去的地震。查明古地震活动的证据对于理解地震过程和力学以及建立更完整的断层活动记录非常重要，这些记录共同为地震活动断层系统的危险评估提供信息。地震中的大部分能量以热的形式释放出来，这在断层岩中产生了热和/或化学特征。拟议的研究使用矿物的耦合发光特性和He同位素测温与纹理分析相结合，以访问整个地震滑动速率范围内的地震事件的热记录，以及时间和空间尺度，以告知断层滑动过程。这些方法提供的补充年龄信息将提供一个更连续的变形记录在历史上的地质时间尺度，这是必不可少的了解地震周期在一个特定的故障。这项研究将在犹他州的瓦萨奇和飓风断层上进行。这些是年轻的地震活跃断层，分别与犹他州的两个最大的人口中心沿着瓦萨奇前线和圣乔治地区相邻。这里开发的新方法将为研究人员量化其他断层系统中断层滑动行为的频谱创造途径。Odlum博士的专业发展计划旨在增加STEM劳动力，并吸引犹他州在STEM领域代表性不足的女性参与地震科学研究和岩土工程技能建设。与犹他州地质调查局合作开发的地震危害模块将影响参加新的USU GeoPaths计划的学生，并通过与位于山间地震带和瓦萨奇前线地区的其他大学分享该模块，以及通过USU地球科学网页和GeoMinutes YouTube频道在线，这项研究的目标是开发新的方法来识别、量化和测定岩石记录中地震滑动引起的摩擦热，这些摩擦热是在地震滑动速率的整个范围内（微米/秒到几十米/秒）。在地震中，大部分（约90%）的能量预算都是克服摩擦阻力做功，并以热量的形式消散。断层两侧的温升幅度是滑移速度、材料性质和应变局部化的函数。反过来，对流热影响这些因素，变量之间的相互作用控制了地震周期中的断层强度。瞬时升高的温度赋予断层岩结构和/或地球化学特征。该项目将联合收割机结合石英和长石的捕获电荷分析以及断层表面和下伏寄主岩石的赤铁矿和磷灰石4 He/3 He热年代学来恢复与地震滑动有关的古温度。犹他州地震活跃的瓦萨奇和飓风断层将是应用这种新方法的第一个现场。这两个发震正断层的纹理证据过去同震摩擦热，散装赤铁矿（U-Th）/He的日期，反映热重置或矿化过程中的地震滑动的可行年龄范围内的捕获电荷热年代学（0.5马），并构成地震风险的大人口中心在犹他州。耦合古温度和纹理信息从断层面将告知动态弱化机制在同震滑动和改善流变学变化的理解断层材料，伴随断层热演化和原位地震力学和断层强度在上孕震区。来自捕获电荷和4 He/3 He热年代学的断层滑动的补充时间信息将填补历史、大地测量和古地震（1 - 10，000年）与低温热年代学（100，000 - 1，000，000年）变形记录之间的关键时间数据空白，并直接应用于地震灾害评估。新的热年代学方法提取同震断层温度和变形的时间限制在这里应用可转移到其他断层系统，给研究人员新的工具，以访问记录的断层滑动跨越地震滑动rate.This奖项反映了NSF的法定使命，并已被认为是值得通过评估使用基金会的智力价值和更广泛的影响审查标准的支持。

Dr. Margaret Odlum has been awarded the NSF EAR Postdoctoral Fellowship to carry out research as well as a professional development plan at Utah State University (USU) under the mentorship of Professors Alexis K Ault and Tammy Rittenour. The goal of the project is to develop new approaches to fingerprint past earthquakes in fault rocks. Pinpointing evidence of ancient seismicity is important for understanding earthquake processes and mechanics and building a more complete record of fault activity, which collectively inform hazard assessment in seismically active fault systems. Most of the energy during an earthquake is given off as heat, which imparts a thermal and/or chemical signature in fault rocks. Proposed research uses coupled luminescence properties of minerals and He isotope thermometry integrated with textural analysis to access the thermal record of earthquake events across the full range of seismic slip rates, as well as temporal and spatial scales to inform fault slip processes. Complementary age information provided by these methods will provide a more continuous record of deformation over historical to geological timescales which is essential to understand earthquake cycles in a particular fault. This research will be conducted on the Wasatch and Hurricane faults in Utah. These are young, seismically active faults that are adjacent to Utah’s two largest population centers along the Wasatch Front and in the Saint George region, respectively. New approaches developed here will create pathways for researchers to quantify the spectrum of fault slip behavior in other fault systems. Dr. Odlum’s professional development plan is aimed at growing STEM workforce and engaging women, an underrepresented group in Utah in STEM, in earthquake science research and geotechnical skill-building. A seismic hazards module developed in partnership with the Utah Geological Survey will impact students enrolled in the new USU GeoPaths program, and reach a wider undergraduate community by sharing the module with other universities located in the Intermountain Seismic Zone and Wasatch Front region, as well as online through the USU Geosciences webpage and GeoMinutes YouTube channel, thus extending the reach and impact of this work.The goal of this research is to develop new approaches to identify, quantify, and date frictional heating caused by seismic slip in the rock record across the full range of seismic slip rates (micrometers/sec to tens of meters/sec). Much (~90%) of the energy budget during an earthquake goes into work done overcoming frictional resistance and dissipates as heat. The magnitude of temperature rise across a fault is a function of slip velocity, material properties, and strain localization. Frictional heat, in turn, impacts these factors and the interplay between variables controls fault strength during the seismic cycle. Transient, elevated temperatures impart textural and/or geochemical signatures in fault rocks. This project will combine trapped-charge analysis on quartz and feldspar with hematite and apatite 4He/3He thermochronometry of fault surfaces and underlying host-rock to recover paleotemperatures associated with seismic slip. The seismically active Wasatch and Hurricane faults in Utah will be the first field sites for applying this novel approach. Both seismogenic normal faults have textural evidence of past coseismic frictional-heat, bulk hematite (U-Th)/He dates that reflect thermal resetting or mineralization during earthquake slip within the viable age range for trapped-charge thermochronometry (0.5 Ma), and pose seismic risk to large population centers in Utah. Coupled paleotemperature and textural information from fault surfaces will inform dynamic weakening mechanisms operative during coseismic slip and improve understanding of rheological changes to fault materials that accompany fault thermal evolution and in-situ earthquake mechanics and fault strength in the upper seismogenic zone. Complementary temporal information on fault slip from trapped-charge and 4He/3He thermochronometry will fill a critical temporal data gap between historical, geodetic, and paleo-seismic (1 - 10,000 years) and low-temperature thermochronometric (100,000 - 1,000,000 years) records of deformation, with direct applications to seismic hazards assessment. The new thermochronometric approach to extract coseismic fault temperatures and temporal constraints on deformation applied here is transferable to other fault systems, giving researchers new tools to access the record of fault slip across seismic slip rates.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.