RISK OF LARGE, TSUNAMI-INDUCING FAILURES ON THE SCOTIAN MARGIN

The 1929 Grand Banks earthquake produced a significant tsunami which impacted the south coast of Newfoundland, resulting in 27 deaths. Regional geophysical and sampling surveys of the Scotian margin reveal that seabed failures have occurred in multiple drainage systems, are likely earthquake triggered and, by analogy with the 1929 event, are likely to cause a serious tsunami. A widespread failure on the central Scotian Slope recognised from debris flow deposits and erosional unconformities is dated in several cores at 7 ka. No other significant Holocene failures have been recognised, suggesting that in any one segment of the slope the recurrence interval of large earthquakes is on the order of 10 000 years. Common large failures occurred during the late glacial period between 20 and 10 ka and appear to have a recurrence interval on the order of 2000 years. Although clearly climate related, it is uncertain whether late glacial failures are most influenced by ice-load induced seismicity, high sedimentation rates, or melting of gas hydrate. At present the risk of a local large tsunami appears to be low based on the occurrence of only two large failure events during the last 7 ka.