Structure of the upper mantle under the EPR from waveform inversion of regional events.

Waveform inversions of seismograms recorded at the Mantle Electromagnetic and Tomography (MELT) Experiment ocean bottom seismometer array from regional events with paths following the East Pacific Rise (EPR) require that low shear velocities (<3.7 km/s) extend to depths of more than 100 km below the rise axis. Velocities increase with average crustal age along ray paths. The reconciliation of Love and Rayleigh wave data requires that shear flow has aligned melt pockets or olivine crystals, creating an anisotropic uppermost mantle.