This is a collaborative project to image details of convergent margin segmentation and the distribution of fluids associated with the subducting slab using combined onshore and offshore magnetotelluric (MT) data in Oregon and Washington. This data will allow us to image the electrical conductivity of the crust and upper mantle of the subduction system in 3D to map the distribution of fluids, constraining both the fluid input to the system from offshore and the distribution of fluids released from the down-going slab, including along the transitional zone where episodic tremor and slip (ETS) occurs.