A crustal scale seismic refraction experiment was conducted over the Kapuskasing structural zone, northern Ontario, in 1984. The zone cuts obliquely across the east-west structural grain of the Superior Province in the Canadian shield and has been proposed as a cross section of Archean crust exposed by thrust faulting along the Ivanhoe Lake cataclastic zone during early Proterozoic time. Five seismic refraction lines of 360--450 km were shot over the area. There were 18 profile shots and two fan shots with a recorder spacing of 2--5 km. We have modeled the travel times and amplitudes of the data from the profile lines and analyzed reflections from the crust-mantle boundary on the fan shots. We have imaged a low-velocity zone under the Abitibi greenstone belt ranging from 4--5 to 9--12 km depth that is underlain by a highly reflective zone. There is a considerable deepening of the Moho from 40--43 km to 50--53 km under and to the west of the southern end of the Kapukasing structural zone. A high-velocity anomaly of 6.6--6.7 km/s has been imaged in the upper crust down to 20 km depth beneath the Kapuskasing structure with a suggested dip of 15¿¿2¿ to the west. This corresponds well to the proposed location of a granulite zone thrust up from the middle or lower crust in the early Proterozoic. ¿ American Geophysical Union 1989