The electrical structures of the upper mantle beneath the East Pacific Rise (EPR) at 17˚S and 15˚45'S are imaged by inverting seafloor magnetotelluric data obtained during the Mantle ELectromagnetic and Tomography (MELT) experiment. In most inversions of the data in the 17˚S array, a vertically aligned sheet-like conductor at the ridge crest is especially prominent in the vertical conductivity. Its presence suggests that the melt is more highly concentrated and connected in the vertical direction immediately beneath the rise axis. On the other hand, the model shows no evidence for a conductive region immediately beneath the ridge at 15˚45'S, in contrast to the model obtained beneath the ridge at 17˚S. This result indicates either that the melting process is episodic and currently at a nadir or that melt at 15˚45'S is poorly interconnected.
