Tomographic images of upper mantle velocity structure beneath an overlapping spreading center (OSC) on the East Pacific Rise indicate that this ridge axis discontinuity is underlain by a continuous region of Low P-wave velocities. The anomalous structure can be explained by an approximately 16-kilometer-wide region of high temperatures and melt fractions of a few percent by volume. Our results show that OSCs are not necessarily associated with a discontinuity in melt supply and that both OSC Limbs are supplied with melt from a mantle source Located beneath the OSC. We conclude that tectonic segmentation of the ridge by OSCs is not the direct result of magmatic segmentation at mantle depths.