Resolving Three-dimensional Impacts on Understanding Cascadian Subduction Zone Conductivity and Fluid Structures

The Magnetotelluric Observations of Cascadia using a Huge Array (MOCHA) experiment provides amphibious data useful for imaging subducted fluids from trench to mantle wedge corner. A type of seismic activity known as Episodic Tremor and Slip is thought to play a key role in regional seismic activity along the Cascadian Subduction Zone, potentially influencing future mega thrust earthquakes. Through magnetotelluric imaging providing 3-D electrical conductivity maps of the Cascadia subduction zone we have discovered correlation between possible fluid concentrations and Episodic Tremor and Slip. In using MOD3DEM, a finite difference inversion package, we encountered problems inverting sea floor stations due to the strong, nearby conductivity gradients and stations exhibiting out of quadrant phase anomalies. We introduce improved interpolation schemes that more accurately track EM fields across large conductivity gradients at cell boundaries, with an eye to enhancing the accuracy of the simulated responses and, thus, inversion results. With a future aim of inverting the stations exhibiting these phase anomalies, we use forward models to determine what geologically feasible structures could produce the observed anomalous behavior