We present the results of mantle P velocity and attenuation tomography from the combined KRISP 1985 and KRISP 1990 teleseismic data sets. We incorporate the results from the KRISP 1990 refraction survey to remove crustal effects from the teleseismic data and thereby better image the lithospheric and asthenospheric structure in the mantle beneath the rift. We find a broad 6% low-velocity anomaly that extends beyond the limits of the rift, as defined by its bounding faults, and superimposed on this a narrower 6% low-velocity zone that is confined to the rift zone. The latter anomaly has a total contrast of 12% compared to nearby unrifted cratonic lithosphere The broad structure persists at all depths to 165 km, and is aligned with the rift, while the narrower structure varies with depth and does not extend along the entire length of the rift covered by our array. The attenuation signal is noisier than the travel time signal, but shows the greatest attenuation beneath the rift and at the southern and northern ends of our array.