Magnetotelluric Investigation of the Salton Trough

An NSF-funded (EAR-2243695) collaboration between Pieter Share (Oregon State), Samer Naif (Georgia Tech), and Steven Constable (Scripps Institution of Oceanography)

The Salton Trough in Southern California represents an unusual confluence of all three plate tectonic margins, combining the southern San Andreas fault system (SSAF, a transform margin) which is interrupted by incipient rifting (the opening of the Gulf of California, a divergent mid-ocean ridge system). These are abutted to the west by the Peninsular Ranges, a remnant of Farallon slab subduction (convergent margin). 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 this tectonically complex region by deploying multi-scale and amphibious (by including the Salton Sea) magnetotelluric (MT) arrays. The MT data provide electrical conductivity information from the surface into the uppermost asthenosphere. At the largest scale 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 the imaged conductivities will help highlight fault zone porosity, fluid content, and how these differ between creeping (e.g., SSAF) and locked fault strands. These multi-scale estimates, combined with existing geoscientific knowledge, will provide an understanding of local tectonics, related geohazards, the geothermal and lithium resource potential of the area.

To date we have carried out two land field campaigns to collect MT data in 2024 (green) and 2025 (purple), and plan to collect data in the Salton Sea using marine instruments in early 2026 (blue). We have also obtained access to heritage data collected in 2004 by Schlumberger for the California Energy Commission, which includes some Salton Sea sites (red crosses), and have digitized the PACE data collected 1990/91 by Phoenix for San Diego State University (teal).

We used the opportunity to introduce a Scripps undergraduate geophysics class to MT field work, and also ran an early career workshop at Scripps on EM methods for North American students, postdocs, and researchers (see Workshop 2005).

Undergraduate students learning to set up an MT site.

Graduate students setting up an MT site.