Collaborative Research: Magnetotelluric Investigation of the Salton Trough

索尔顿海槽是一个低洼的干旱区，环绕并包括南加州的索尔顿海，构造复杂，在这里所有三种板块边缘类型，变形，发散和收敛，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、岩石的组成、来自深度和高地壳温度的流体在形成该地区地震和火山灾害中的作用。研究人员将在陆地上和索尔顿海内部使用一种地球物理工具，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，即岩石和材料导电的情况。然后，这些信息将被转化为深度超过100公里的岩石成分、这些深度的流体路径和浓度、地表断层和火山目标、温度变化、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。除了为当地地震和火山灾害提供信息外，更广泛的影响将包括在实地活动期间对两名研究生、一名博士后学者和当地高中生的教育，以及在构造活动与目前正在该地区勘探的关键矿物（如锂）的潜力和普遍程度之间建立联系。索尔顿海槽是所有三种板块构造边缘类型合流的典型例子，它结合了被局部初裂（发散）打断的南部圣安德烈亚斯断层系统（SSAF，变换），并与法拉隆板块俯冲（收敛）的残余半岛山脉相毗邻。所有这些系统都形成了一个复杂的结构和应变，富含水流体和熔体的地区，并在该地区沿严重应变的SSAF发生破坏性地震和火山活动的可能性中发挥了关键作用。研究小组将通过部署多尺度（相距100米至10公里的地点）和两栖（包括索尔顿海）大地电磁阵列，并从地表提取电导率信息到最上层的软流层，对这个构造复杂的地区进行成像和信息。在最大的尺度上（10公里），这些信息将解决岩石圈尺度结构的变化、岩石圈-软流圈边界和俯冲法拉龙板块的脱水问题。中期部署的重点将是地壳和上地幔的组成、流体的分配、部分熔融和由此推断的应变，以及这些性质从转化区到早期裂陷区的演变。在最精细的尺度上（站距1公里），成像的电导率将有助于突出断裂带的孔隙度、流体含量和产状，以及它们在爬行（例如SSAF）和锁定断层链之间的区别。这些多尺度估计，结合现有的地球科学知识，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。

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.