Characterizing Temporal and Spatial Variability in Groundwater Helium-Carbon Relationships at Seismically-Active Regions of California

表征加利福尼亚地震活跃地区地下水氦-碳关系的时空变化

• 批准号: 1014236
• 负责人: David Hilton
• 金额: $ 28.88万
• 依托单位: University of California-San Diego Scripps Inst of Oceanography
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-09-01 至 2016-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1014236&HistoricalAwards=false
• 关键词: Characterizing; Temporal; Spatial; Variability; Groundwater

Project AbstractThis project will target naturally-occurring groundwater to define both spatial and temporal variability in He-CO2 characteristics at three seismically active regions of California. The three regions are the San Jacinto Fault (SJF), and the San Andreas Fault (SAF) - both in Central California (Hollister-Parkfield) and southern California (Coachella Valley). The areal extent of He-CO2 variations in the three regions will be mapped paying particular attention to localities close to known fault traces. The new instrument previously developed in this lab (SPARTAH) will be deployed at sites with a strong mantle volatile input (as recorded by the primordial isotope 3He). SPARTAH can provide a high-resolution temporal record (hours-to-days) of He-CO2 variations over extended periods (months-to-years).The following hypotheses, central to understanding the relationship between dissolved volatiles, such as He and CO2, and the occurrence of seismicity in California, will be addressed: 1. Faults are the principal conduits to the surface for mantle-derived volatiles. Observed 3He/4He will be used to determine whether the faults act as high permeability pathways between the deep crust/uppermost mantle and the surface and, if so, to model their fluxes. In turn, this will allow evaluation of whether or not variations in fluxes correlate with regions of intense microseismicity (SJF), virtually no seismicity (southern SAF) and frequent-to-infrequent earthquakes (Hollister-Parkfield). 2. CO2 is the major volatile phase leading to super hydrostatic pressure at depth. Coupled CO2/3He and d13C variations will be used to resolve CO2 into mantle and crustal components. Major areas of mantle CO2 leakage will be determined and realistic estimates of permeability at depth will be derived. 3. Temporal variability characterizes the volatile record and is related to the occurrence of seismic activity. To date, there is little or no record of temporal variations in volatile fluxes in seismically-active regions. This deficiency will be addressed through deployment of the SPARTAH instrument which will enable targeting sections of the temporal record when there is (a) seismic activity - to gauge the response (if any) of the He and CO2 (isotopes and relative abundances), and (b) no evidence of any (major) seismic disturbance. These parts of the He-CO2 background record are essential to establish the temporal baseline value. The temporal record of He-CO2 variations will be compared with the occurrence of nonvolcanic tremor - associated with slip on the SAF - which occurs in bursts ranging in frequency from every few days to months. SPARAH is designed to sample groundwater at high pumping rates/pressures continuously so such events can be captured. This project will liaise with the NSF-funded Center for Ocean Science Education Excellence - California (COSEE CA) to develop a plan to extend the impact of the research beyond the bounds of academia. COSEE CA and Scripps have developed a multi-faceted collaboration with the San Diego Unified School District to support their new, district-wide, high school Earth Sciences program. A key element of this collaboration is partnering to provide a combination of on-going professional development for district Earth Science teachers, many of whom are teaching outside their area of expertise, and robust connections to current research in Earth and Ocean sciences at Scripps. The project will sponsor a 1-day workshop for 15 teachers in support of the Scripps/SDUSD collaboration that combines presentation of basic information on California seismicity and local plate tectonics with a focused look at project results on assessing the relationship between earthquakes and geochemical signals in groundwater.

本项目将以天然地下水为研究对象，确定加州三个地震活跃区He-CO2特征的时空变化。这三个地区分别是圣哈辛托断层（SJF）和圣安德烈亚斯断层（SAF），它们都位于加州中部（霍利斯特-帕克菲尔德）和南加州（科切拉谷）。将绘制这三个地区He-CO2变化的面积范围，特别注意靠近已知断层迹线的地方。该实验室先前开发的新仪器（SPARTAH）将部署在具有强地幔挥发性输入（由原始同位素3He记录）的地点。SPARTAH可以提供长时间（月到年）内He-CO2变化的高分辨率时间记录（小时到天）。以下假设对于理解溶解挥发物（如He和CO2）与加利福尼亚地震活动之间的关系至关重要：断层是地幔源挥发物向地表输送的主要管道。观测到的3He/4He将用于确定断层是否作为地壳深部/上地幔与地表之间的高渗透率通道，如果是，则对其通量进行建模。反过来，这将允许评估通量的变化是否与强烈微震活动（SJF）、几乎没有地震活动（南部SAF）和频繁到不频繁地震（Hollister-Parkfield）的区域相关。2. 二氧化碳是导致深海超静水压力的主要挥发相。CO2/ 3he和d13C的耦合变化将用于将CO2分解为地幔和地壳组分。将确定地幔二氧化碳泄漏的主要区域，并得出深度渗透率的实际估计。3. 时间变率是挥发性记录的特征，与地震活动的发生有关。迄今为止，很少或没有记录地震活跃地区挥发性通量的时间变化。这一缺陷将通过SPARTAH仪器的部署来解决，该仪器将能够在存在(a)地震活动的情况下定位时间记录的部分，以测量He和CO2（同位素和相对丰度）的响应（如果有的话），以及(b)没有任何（主要）地震干扰的证据。He-CO2背景记录的这些部分对于确定时间基线值至关重要。He-CO2变化的时间记录将与非火山性震颤的发生进行比较。非火山性震颤与SAF上的滑动有关，其发生频率从几天到几个月不等。SPARAH的设计目的是在高泵率/压力下连续取样地下水，以便捕获此类事件。该项目将与美国国家科学基金会资助的加州海洋科学教育卓越中心（COSEE CA）联系，制定一项计划，将研究的影响扩展到学术界之外。COSEE CA和Scripps已经与圣地亚哥联合学区开展了多方面的合作，以支持他们新的、全区范围的高中地球科学项目。此次合作的一个关键因素是为地区地球科学教师提供持续的专业发展，其中许多人在他们的专业领域之外教学，并与斯克里普斯目前的地球和海洋科学研究建立牢固的联系。该项目将为15名教师举办为期1天的研讨会，以支持Scripps/SDUSD的合作，该研讨会将介绍加州地震活动和当地板块构造的基本信息，并重点关注评估地震与地下水地球化学信号之间关系的项目结果。