Magnetotelluric Investigation of the Salton Trough

An NSF-funded (EAR-2243695) collaboration between Pieter Share (Oregon State), Samer Naif (Georgia Tech), Jared Peacock (USGS), 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, and the geothermal and lithium resource potential of the area.

By the end of 2025 we had carried out two land field campaigns to collect MT data in 2024 (green) and 2025 (purple). In early 2026 we collected data in the Salton Sea using marine instruments (blue). During the Sea data collection we added a few more land sites in key locations (yellow). 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 squares), and have digitized the PACE data collected 1990/91 by Phoenix for San Diego State University (teal).

In the tradition of the ocean cruises that we carry out, below is a field blog of our activities, most recent at the top (i.e. read from the bottom if you are new to this page).

26th January 2026. Australia Day! We continue to be blessed with good weather. Here you can see the float of a deployed instrument to the right of the bend in the davit. Jake is preparing the next instrument for deployment.

We will need to include the Salton Sea in our inversion models, so we collect CTD (conductivity-temperature-depth) data with a little probe that we built, lowered to the seabed while it sends data up to a logging box. The water is about twice as conductive as seawater.

22nd January 2026. We are collecting two days of data on the sea-bottom instruments, in order to extend the MT responses to long periods (1,000 seconds or longer). In the off-days between sea deployments, the field team is collecting bonus land MT sites. Here they are installing a site on the coast of the Salton Sea (a few years ago this would have been underwater).

19th January 2026. After many months of preparation, boat repair, planning, and coordinating with the Salton Sea Species Conservation Habitat program, the "marine" part of the project is now underway.

The RV Cahuilla loaded up with 4 lake-bottom instruments and ready to launch.

The launch. A very muddy boat ramp. They forgot the toilet.

It floats!

March-October 2025. We used the 2025 land campaign as an 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.