Trapped in travertine: Physical and chemical signature of paleoseismicity in hot spring deposits on active faults of the Central Nevada Seismic Belt

为了了解地震的危害，科学家们调查了过去地震的记录，以此作为限制未来地震可能发生的规模和发生频率的一种手段。在历史记录有限或大而不频繁事件的地区，证据是古代地表破裂的地质影响。但并不是所有的地震都会产生这些裂缝，它们也不是总是完好地保存在地质中。这项提议的工作旨在通过探索与活跃断层上的温泉有关的矿物的数量和化学组成中保存的地震记录，扩大地震历史的地质工具包。由于断层可能是温泉水的管道，而且地震改变了断层的内部结构，研究人员希望看到过去地震前后沉积的温泉矿物的差异。该地区位于内华达州中部一个有大地震历史的地区，包含许多温泉矿床，以及其他记录地震和地下水历史的地质特征，使其成为测试地震与温泉矿床变化之间关系的理想场所。这项研究的结果将为温泉和其他热液系统的生命周期提供重要的新见解，并直接影响美国西部地震活跃地区的地震风险。如果这项工作表明温泉矿物记录了过去的地震，那么温泉矿物可以用来了解美国其他地方和世界各地的地震危险。除了该项目的科学目标之外，它还将为重要的STEM学科的荣誉本科生的培训和研究工作做出贡献，它将支持早期职业女性研究人员的博士后培训，从而扩大代表性不足的群体在地球科学领域的参与。它将与IRIS（地震学联合研究机构）和GeoFORCE教育推广计划一起提供教育推广活动和在线学习材料的开发。热液系统是活跃构造和岩浆活动中的暂态特征，代表了渗透率、热量和流体的短暂共存。它们对影响当地水文的许多因素的内部和外部扰动都很敏感。本研究将探索几个温泉石灰华矿床的流量、成分和温度的千年尺度变化，以探索气候和地震强迫对热液系统的影响。方法包括：1)通过野外填图、浅层（~10米）岩心、主微量元素分析、稳定同位素、放射性成因分析和团块同位素分析，构建物理、化学和同位素石灰华地层；2)地质年代学，以限制春季沉积物中保存的物理和化学变化的时间。该研究地点位于内华达地震带北部的Buena Vista和Dixie山谷，拥有多处石灰华矿床，从晚更新世到全新世湖泊水位波动的详细古水文记录，以及晚更新世到历史大地震（m6至m7）的可靠记录，使其成为评估多时空尺度热液排放影响机制的理想场所。本研究得到的钙华矿床的地层、化学和热史将为断层流体在多个时间尺度上的流动生命周期提供重要的新见解，从同震破裂和震间密封到区域水文变化的影响。这些沉积中保存的水文记录中的地震事件的化学证据将增加对独立于离散地表变形的区域地震风险的理解，并将代表一种识别古地震事件的新方法。这对美国西部历史活跃地区的地震复发间隔有直接影响，对热液活动和地震活动与人口中心重合的各种全球环境的地震危险性评估有更广泛的影响。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

In order to understand earthquake hazard, scientists investigate the record of past earthquakes to as a means to constrain the possible size of future earthquakes and how often they might recur. In regions with limited historical records or large, infrequent events, the evidence is held in the geologic effects of ancient ground-surface ruptures. But not all earthquakes produce these ruptures nor are they always well preserved in the geology. The proposed work seeks to expand the geologic tool kit for earthquake history by exploring the record of earthquakes preserved in the amount and chemical make-up of minerals related to hot springs along active faults. Because faults can be conduits for hot-spring waters, and because earthquakes change the internal structure of faults, researchers expect to see differences in hot-spring minerals deposited before and after past earthquakes. The field sites, located in a region of central Nevada with a history of large earthquakes, contain many hot-spring mineral deposits, along with other geological features that record earthquake and ground water history, making it an ideal place to test the relationship between earthquakes and changes in hot-spring mineral deposits. Results from this study will provide important new insights into the lifecycle of hot springs and other hydrothermal systems and have direct bearing on earthquake risk in a seismically active part of the western United States. If this work shows that hot-spring minerals record past earthquakes, hot-spring minerals could be used for understanding earthquake hazard in other places of the United States and around the world. In addition to the scientific objectives of the project, it will also contribute to the training and research efforts of honors undergraduate students in an important STEM discipline, it will support postdoctoral training for an early career female researcher thus broadening participation of underrepresented groups in the earth sciences, and it will provide for educational outreach activities and development of online learning materials in conjunction with IRIS (Incorporated Research Institutions for Seismology) and the educational outreach program GeoFORCE. Hydrothermal systems are transient features in active tectonic and magmatic regimes, representing the ephemeral co-location of permeability, heat, and fluid. They are sensitive to both internal and external perturbations from the many factors influencing local hydrology. The proposed work will explore millennial-scale variability in discharge, composition and temperature at several hot-spring travertine deposits to explore the impact of climate and seismic forcing on hydrothermal systems. The approach includes: 1) construction of physical, chemical, and isotopic travertine stratigraphy from field mapping, shallow (~10 meter) core, major and trace element analyses, and stable, radiogenic, and clumped-isotope analyses; and 2) geochronology to constrain the time of physical and chemical changes preserved in the spring deposits. The field sites, located in Buena Vista and Dixie valleys in the northern Central Nevada Seismic Belt, contain multiple travertine deposits, detailed paleohydrologic records from Late Pleistocene to Holocene lake level fluctuations, and a robust record of large (M 6 to M 7) Late Pleistocene to historic earthquakes, making it an ideal place to evaluate the mechanisms influencing hydrothermal discharge across multiple spatial and temporal scales. The stratigraphic, chemical, and thermal histories of travertine deposits resulting from this study will provide important new insights into the life cycle of fluid flow from faults across multiple time scales, from co-seismic rupture and interseismic sealing to the influence of regional hydrologic changes. Chemical evidence for seismic events in the hydrologic record preserved in these deposits would add to the understanding of regional seismic risk independent of discrete surface deformation and would represent a new approach for identifying paleoseismic events. This has direct bearing on seismic recurrence intervals in an historically active region of the western United States and broader implications for seismic hazard assessments in a variety of global settings, where hydrothermal activity and seismicity coincide with population centers.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.