A method for processing marine electromagnetic signal measurements
includes acquiring magnetotelluric (MT) measurements from below a bottom
of a body of water at a plurality of positions along the water bottom at
substantially the same times at each position. Controlled source
electromagnetic (CSEM) measurements are acquired from below the water
bottom at substantially the same positions at substantially the same time
at each position. The MT measurements and the CSEM measurements are
jointly processed to obtain a model of conductivity distribution in the
formations below the water bottom.