Collaborative Research: Magnetotelluric Investigation of the Salton Trough

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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.