Forsyth, D.W., D.S. Scheirer, S.C. Webb, L.M. Dorman, J.A. Orcutt, A.J. Harding, D.K. Blackman, J. Phipps Morgan, R.S. Detrick, Y. Shen, C.J. Wolfe, J.P. Canales, D.R. Toomey, A.F. Sheehan, S.C. Solomon and W.S.D. Wilcock, Imaging the deep structure beneath a mid-ocean ridge: The MELT experiment, Science, 280, 1215-1218, 1998[PDF]
The Mantle Electromagnetic and Tomography (MELT ) Experiment was designed to distinguish between competing models of magma generation beneath mid-ocean ridges. Seismological observations demonstrate that basaltic melt is present beneath the East Pacific Rise spreading center in a broad region several hundred kilometers across and extending to depths greater than 100 kilometers, not just in a narrow region of high melt concentration beneath the spreading center, as predicted by some models. The structure of the ridge system is strongly asymmetric: mantle densities and seismic velocities are lower and seismic anisotropy is stronger to the west of the rise axis.