Although this group has derived excellent 2-D modeling comparisons between observed and calculated magnetotelluric (MT data) from the EMSLAB experiment, there are ample reasons to suspect significant 3-D effects. They are evident in the data and are suspected from the geomorphic - geologic setting, the distribution of geophysical anomalies (particularly gravity and seismicity), and volcanic arc segmentation. The importance of the EMSLAB findings demands the final step of 3-D modeling to confirm or reject the 2-D interpretations which can be totally incorrect. The PI will first complete a 2-D Backus-Gilbert inversion, which has tentatively identified the top of the Juan de Fuca plate at 25-30 km depth beneath the Oregon Coast Range. Secondly, he will realistically evaluate the regional 3-D effects of the Willamette Valley area and of the segmented Juan de Fuca plate. Smaller 3-D effects due to volcanic intrusives and topography near to the land EMSLAB MT sites will also be evaluated.
