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

项目摘要该项目将以自然形成的地下水为目标，以确定加州三个地震活动区的He-CO2特征的空间和时间变异性。这三个地区是圣哈辛托断层(SJF)和圣安德烈亚斯断层(SAF)--都位于加利福尼亚州中部(霍利斯特-帕克菲尔德)和南加州(科切拉山谷)。将绘制这三个地区氦-二氧化碳变化的面积范围图，特别注意靠近已知断层痕迹的地点。先前在该实验室开发的新仪器(SPARTAH)将部署在具有强烈地幔挥发性输入的地点(如原始同位素3He所记录的)。SPARTAH可以提供较长时期(月到年)氦-二氧化碳变化的高分辨率时间记录(小时到天)。以下假设是理解溶解挥发物(如氦和二氧化碳)与加州地震活动发生之间关系的核心假设：1.断层是地幔挥发分到达地表的主要通道。观测到的3He/4He将被用来确定断层是否在地壳深部/最上地幔和地表之间充当高渗透性通道，如果是的话，将对它们的通量进行模拟。反过来，这将允许评估通量的变化是否与微震强烈(SJF)、几乎没有地震活动(南部SAF)和频繁到不频繁的地震(Hollister-Parkfield)的区域相关。2.CO2是导致深部超静水压的主要挥发相。CO2/3He和d13C的耦合变化将被用来将CO2分解成地幔和地壳成分。将确定地幔二氧化碳泄漏的主要区域，并得出对深度渗透率的实际估计。3.时间变异性是波动记录的特征，与地震活动的发生有关。到目前为止，地震活动区挥发通量的时间变化很少或根本没有记录。这一不足之处将通过部署SPARTAH仪器加以解决，该仪器将能够在以下情况下针对时间记录的部分进行定位：(A)地震活动--测量氦和二氧化碳(同位素和相对丰度)的响应(如果有的话)，以及(B)没有任何(重大)地震干扰的证据。氦-二氧化碳背景记录的这些部分对于确定时间基准值是必不可少的。氦-二氧化碳变化的时间记录将与非火山地震的发生进行比较-与SAF上的滑动相关-以爆发的频率从每隔几天到几个月不等。Sparah的设计目的是在高抽水率/高压力下连续采样地下水，以便捕获此类事件。该项目将与NSF资助的加州海洋科学教育卓越中心(COSEE CA)联系，以制定一项计划，将研究的影响扩展到学术界之外。COSEE CA和斯克里普斯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计划。这一合作的一个关键因素是合作，为地区地球科学教师提供持续的专业发展，他们中的许多人在其专业领域之外任教，并与斯克里普斯大学目前在地球和海洋科学方面的研究建立牢固的联系。该项目将为15名教师举办一次为期一天的讲习班，以支持斯克里普斯和SDU.S.的合作，该合作结合了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中地球化学信号之间关系的项目结果。

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.