MAGNETOTELLURICS IN WESTERN US: NEW CHALLENGES AND PERSPECTIVES FROM EarthScope MT TRANSPORTABLE ARRAY

In the past six years, EarthScope MT (EMscope) transportable array has covered much of western United States, extending from the US-Canadian border in the North, to Northern California, Nevada and Utah in the South on a quasi-regular grid with 70 km nominal resolution. After 2011, the focus of EMscope moves to the mid-continent rift.

In western US, the data cover the Cascadia subduction zone and the Cascade Volcanic Arc, as well as the Snake River Plain and Yellowstone magmatic system. Sensitivity of MT data to partial melt and water content make it possible to image these targets with three-dimensional magnetotelluric inversion. In conjunction with seismic and petrological constraints, this provides a new perspective at the lithospheric structure in this tectonically and magmatically active area.

The large station spacing and unprecedented spatial extent of the array present their own challenges, notably in imaging and compensating for the near-surface structures. We summarize the results obtained to date with EarthScope MT, and show that magnetotelluric inversion images the slab and the Cascade Volcanic Arc in a geophysically consistent manner that complements the seismic results. As an example of what can be achieved with EarthScope MT data, we discuss the implications of these models on the multi-disciplinary understanding of Snake River Plain magmatism.