Beginning in 2021, annual magnetotelluric (MT) surveys have been collected at The Geysers geothermal field in northern California in hopes of measuring temporal changes within the steam field. These repeat surveys are compared to a baseline survey collected in 2017 as well as using 2021 as a baseline for 2022 and 2023 surveys. The 2017 survey was spatially limited to the northwest Geysers and was extended to include more of the geothermal field in the repeat surveys. Temporal variations in the MT transfer functions are observed to be spatially coherent and compartmentalized possibly related to injection of fluids. Three-dimensional inversion of the MT data using previous years as apriori models indicates the general trend is that the steam reservoir has become more resistive over time, on the order of 10 percent, suggesting more steam in the field. A few pockets within the steam field have become more electrically conductive over time and are collocated with injection wells, suggesting either more fluid content in those zones, less steam, or more saline fluids. Changes between 2021-2022-2023 are minor relative to changes between 2017 and the later surveys indicating observable changes in the electrical resistivity of the steam field occur over a long period of time, and only if permanent stations were installed could transient changes be observed.

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