The Mantle ELectromagnetic and Tomography (MELT) experiment was designed to image the melting region beneath a mid-ocean ridge with seismic waves and deep electrical currents.  The ocean bottom siesmometer array is marked on the above figure with white triangles.  This ridge segment on the East Pacific Rise is exceptionally long and spreads ~140mm/yr (close to the global maximum of spreading rates).  This site was chosen largely because it was thought likely to have the simplest, most 2-D upwelling structure on the mid-ocean ridge system.  However, one of the most striking results of the experiment is the pronounced asymmetry about the rise axis in nearly all measured geophysical properties.