The Conrad discontinuity is identified in the U.S. Midcontinent Precambrian crust as a prominent seismic velocity change from about 6.1 to 6.7 km/sec at a depth of between 7.5 and 13.7 km (4.7 and 8.6 mi) in Kansas. There is some discussion, however, as to whether the discontinuity really exists, and if it does, what it represents. It is at this depth that numerous intermediate-depth microearthquakes occur suggesting that these quakes define the discontinuity. Mapping the depth of the microquakes gives a configuration of the discontinuity consistent with the relation of the fault-bounded Midcontinent Rift System to the overall Precambrian basement-rock pattern.