The epicenter of the 1929 “Grand Banks” earthquake (M_s = 7.2) was on the continental slope above the Laurentian Fan. The zone in which cables broke instantaneously due to the earthquake is characterized by surface slumping up to 100 km from the epicenter as shown by sidescan sonographs and seismic reflection profiles. The uppermost continental slope, however, is almost undisturbed and is underlain by till deposited from grounded ice.

The Eastern Valley of the Laurentian Fan contains surficial gravels molded into large sediment waves, believed to have formed during the passage of the 1929 turbidity current. Sand sheets and...