Did two massive earthquakes in the Holocene induce widespread landsliding and near-surface deformation in part of the Ottawa Valley, Canada?

Recent evidence based on ages of large landslides and the existence of seve rely disturbed terrain in Champlain Sea sediments to the east of Ottawa sug gests that this area mag have been the site of two of the most geologically destructive earthquakes in eastern Canada. The walls of several paleochann els, downcut into sensitive marine clayey silts, are scarred by numerous la rge earthflows of sizes unequaled in historical time. While radiocarbon age s of 15 landslides, as much as 35 km apart, range from ca, 1870 to 5130 yr B.P., the majority of events cluster at ca. 4550 yr B.P. The coincidence of numerous large failures in different paleovalleys, occurring concurrently, long after channel abandonment and at a time of drier climate, suggests th at the widespread landsliding was triggered by a strong earthquake. Close t o the landslide area, areas of very disturbed terrain in a flat erosional p lain show severely deformed bedding and irregular ground subsidence and are attributed to a large earthquake, ca, 7060 yr B.P., that strongly shook a thick sequence of sensitive material filling deep, steep-sided, bedrock bas ins.