Collaborative Research: Magnetotelluric Investigation of the Salton Trough

合作研究：索尔顿海槽的大地电磁调查

• 批准号: 2243695
• 负责人: Steven Constable
• 金额: $ 31.75万
• 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: 2023
• 资助国家: 美国
• 起止时间: 2023-07-01 至 2026-06-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2243695&HistoricalAwards=false
• 关键词: Collaborative; Research; Magnetotelluric; Investigation; Salton

The Salton Trough, a low-lying arid region surrounding and including the Salton Sea in Southern California, is tectonically complex, where all three plate margin types, transform, divergent and convergent, come together. This project addresses key questions in the region, including the location of the active plate margin, the composition of the rocks, the role do fluids sourced from great depth and high crustal temperatures in shaping earthquake and volcanic hazards in the area. The researchers will employ a geophysical tool, both on-land and within the Salton Sea, that is capable of recording tiny fluctuations in the Earth’s natural electromagnetic field and extract from these data estimates of subsurface electrical conductivities, i.e., how well the rocks and materials conduct electric currents. This information will then be translated to rock composition to depths greater than 100 km, fluid pathways and concentrations from these depths to mapped surface faults and volcanic targets, temperature variations, and fault dimensions and geometries, all with the aim of better defining the Salton Trough’s unique tectonic architecture. In addition to informing local seismic and volcanic hazards, broader impacts will include the education of two graduate students, a postdoctoral scholar, and local high schoolers during field campaigns as well as building connections between tectonic activity and the potential and prevalence of critical minerals (e.g., lithium) being explored in this area at present.The Salton Trough is an exemplary case of the confluence of all three plate tectonic margin types, combining the southern San Andreas fault system (SSAF, transform) interrupted by localized incipient rifting (divergent) and abutted to the west by the Peninsular Ranges, a remnant of Farallon slab subduction (convergent). All these systems contribute to a region of complex structure and strain, rich in aqueous fluids and melts, and play key roles in the potential for destructive earthquakes along the critically strained SSAF and volcanic activity in the area. The research team will image and inform this tectonically complex region by deploying multi-scale (sites 100s m to 10s km apart) and amphibious (including the Salton Sea) magnetotelluric arrays and extracting electrical conductivity information from the surface into the uppermost asthenosphere. At the largest scale (10 km) this information will address questions on variations in lithospheric-scale fabric, the lithosphere-asthenosphere boundary and dehydration of the subducted Farallon slab. The focus of the mid-scale deployments will be crustal and uppermost mantle composition, the partitioning of fluids, partial melt, and by inference strain, and the evolution of these properties from transform to incipient rifting areas. At the finest scales (stations 1 km apart), the imaged conductivities will help highlight fault zone porosity, fluid content and attitudes and how these differ between creeping (e.g., SSAF) and locked fault strands. These multi-scale estimates, combined with existing geoscientific knowledge, will provide a more holistic understanding of local tectonics and its related geohazards.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.

索尔顿海槽是一个低洼干旱地区，环绕并包括南加州索尔顿海，其构造复杂，所有三种板块边缘类型（变换、发散和汇聚）都聚集在一起。该项目解决了该地区的关键问题，包括活动板块边缘的位置、岩石的成分、来自大深度和高地壳温度的流体在该地区地震和火山灾害中的作用。研究人员将在陆地和索尔顿海内使用地球物理工具，该工具能够记录地球自然电磁场的微小波动，并从这些数据中提取地下电导率的估计值，即岩石和材料传导电流的能力。然后，这些信息将被转化为深度超过 100 公里的岩石成分、从这些深度到绘制的地表断层和火山目标的流体路径和浓度、温度变化以及断层尺寸和几何形状，所有这些都是为了更好地定义索尔顿海槽独特的构造结构。除了告知当地地震和火山灾害外，更广泛的影响还包括在实地考察期间对两名研究生、一名博士后学者和当地高中生进行教育，以及在构造活动与目前该地区正在勘探的关键矿物（例如锂）的潜力和盛行之间建立联系。索尔顿海槽是所有三种板块构造边缘类型汇合的典范，结合了 南部的圣安德烈亚斯断层系统（SSAF，变换）被局部初期裂谷（发散）打断，西面毗邻半岛山脉，这是法拉隆板片俯冲的残余部分（会聚）。所有这些系统都形成了一个结构和应变复杂、富含水性流体和熔体的区域，并在该地区沿临界应变 SSAF 和火山活动发生破坏性地震的可能性中发挥着关键作用。研究小组将通过部署多尺度（站点相距 100 米至 10 公里）和两栖（包括索尔顿海）大地电磁阵列，并从地表提取到最上层软流圈的电导率信息，对这一构造复杂的区域进行成像和信息通报。在最大尺度（10公里）上，这些信息将解决有关岩石圈尺度结构的变化、岩石圈-软流圈边界以及俯冲法拉隆板片脱水的问题。中期部署的重点将是地壳和最上地幔的组成、流体的分配、部分熔融和推断应变，以及这些特性从转变到早期裂谷区域的演变。在最精细的尺度（站点相距 1 公里）下，成像电导率将有助于突出断层带孔隙度、流体含量和产状，以及蠕动断层带（例如 SSAF）和锁定断层带之间的差异。这些多尺度估计与现有的地球科学知识相结合，将提供对当地构造及其相关地质灾害的更全面的了解。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。