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Abstract

Magnetotelluric (MT) and seismic methods provide information about the conductivity and velocity structure of the subsurface on similar scales and resolutions. The independent electrical and seismic tomograms can be combined, using a classification approach, to map lithologic, tectonic, and hydrologic boundaries. The method employed is independent of theoretical/empirical relations linking electrical and seismic parameters, and based solely on the statistical correlation of physical property models in parameter space. Regions of high correlation (classes) can in turn be examined in the spatial domain. The spatial distribution of these clusters, and the boundaries between them, provide structural information not always evident from the individual models. The method is applied to coincident seismic velocity and electrical resistivity models from two active transform margins. Along the San Andreas Fault, classification studies reveal the strong lithological contrast across the fault, suggesting it is sub-vertical in the upper crust throughout central California. A possible hydrologic boundary is further identified to the northeast of the fault. Classification studies along the Dead Sea Transform reflect the dominant lithologies surrounding the fault, and suggest the fault is again vertical in the upper crust, but offset to the east of the surface trace. There are indications that the basement is uplifted by $sim 2$ km east of the fault. These results suggest a quantitative, joint interpretation of MT and seismic data can greatly improve our ability to delineate lithologic, tectonic, and hydrologic boundaries, thus overcoming some of the resolution limitations inherent to the MT and seismic methods.