Resolution Study of Marine CSEM Imaging of Subduction Zones

Marine controlled source electromagnetic (CSEM) data allow us to image seafloor electrical resistivity from which we can constrain the porosity and fluid content of the subsurface. In subduction zones, CSEM data can be used to constrain geologic structure, hydrogeology and fluid-tectonic processes. The scales of features we are interested in recovering with CSEM data range from large-scale features such as the incoming tectonic plate and subducting slab, to the narrow dipping plate boundary interface where slip occurs, to thin faults that cut the overriding forearc crust and shallow fluid seeps and mounds on the seafloor. Thus electrical structure is expected to vary on scales ranging from scales of meters to tens of kilometers. CSEM data collected by Scripps at the Middle America Trench in 2010 is the first and to-date the only application of the method for studying a subduction zone. The results from this pioneering data set highlight the types of new discoveries that are possible with CSEM data, such as imaging conductive bending faults and a water-rich channel of subducting sediments. In this work we explore the magnitude and scale of 2D resistivity structures that can be resolved with CSEM data through a suite of synthetic inversion studies. We build resistivity models that are representative of various known and hypothesized subduction zone plate boundary structures. We generate synthetic noisy data for these models and invert them using the freely available MARE2DEM inversion code. We compare the recovered models to the original models in order to determine which resistivity structures may be successfully identified using CSEM. We explore the potential effects of receiver spacing, frequency bandwidth and system noise levels on the ability of CSEM to recover these different subduction zone structures.