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

为了了解地震的危险性，科学家们调查了过去地震的记录，以此来限制未来地震的可能规模以及它们可能发生的频率。在历史记录有限的地区，或者大规模的、罕见的事件，证据是古代地表断裂的地质影响。但并不是所有的地震都会产生这种破裂，而且它们在地质学上也并不总是保存得很好。拟议的工作旨在通过探索与活动断层沿着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。由于断层可以成为温泉沃茨的通道，而且地震会改变断层的内部结构，研究人员希望看到过去地震前后沉积的温泉矿物质的差异。这些现场位于内华达州中部一个有大地震历史的地区，含有许多温泉矿床，沿着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质记录了过去的地震，温泉矿物质可以用于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外，它还将有助于培养和研究一个重要的STEM学科的荣誉本科生，它将支持对早期职业女性研究人员的博士后培训，从而扩大地球科学中代表性不足的群体的参与，它将提供教育推广活动，并与IRIS一起开发在线学习材料（合并的地震研究机构）和教育推广计划GeoFORCE。热液系统是活跃构造和岩浆体系中的瞬态特征，代表渗透率、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。拟议的工作将探讨几个温泉水矿床的流量、成分和温度在千年尺度上的变化，以探讨气候和地震对热液系统的影响。该方法包括：1）通过野外测绘、浅（~10米）岩心、主元素和微量元素分析以及稳定、放射成因和聚集同位素分析，构建物理、化学和同位素同位素地层学; 2）地质年代学，以限制保存在春季沉积物中的物理和化学变化的时间。位于内华达州中北方地震带的布埃纳维斯塔和迪克西山谷的现场，包含多个白垩纪沉积物，从晚更新世到全新世湖平面波动的详细古水文记录，以及晚更新世到历史地震的大型（M6至M7）记录，使其成为评估多个空间和时间尺度上影响热液排放的机制的理想场所。从这项研究中产生的地层，化学和热历史的沉积物将提供重要的新的见解，从多个时间尺度的断层流体流动的生命周期，从同震破裂和地震间密封区域水文变化的影响。保存在这些矿床中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，并将代表识别古地震事件的新方法。这直接关系到美国西部历史活跃地区的地震复发间隔，并对各种全球环境中的地震危险性评估产生更广泛的影响，其中热液活动和地震活动与人口中心重合。该奖项反映了NSF的法定使命，并被认为值得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来支持。

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.