Assessment of Tsunami Hazard to the U.S. East Coast Using Relationships Between Submarine Landslides and Earthquakes

Submarine landslides along the continental slope of the U.S. Atlantic margin are potential sources for tsunamis along the U.S. East coast. The magnitude of potential tsunamis depends on the volume and location of the landslides, and tsunami frequency depends on their recurrence interval. However, the size and recurrence interval of submarine landslides along the U.S. Atlantic margin is poorly known. Well-studied landslide-generated tsunamis in other parts of the world have been shown to be associated with earthquakes. Because the size distribution and recurrence interval of earthquakes is generally better known than those for submarine landslides, we propose here to estimate the size and recurrence interval of submarine landslides from the size and recurrence interval of earthquakes in the near vicinity of the said landslides. To do so, we calculate maximum expected landslide size for a given earthquake magnitude, use recurrence interval of earthquakes to estimate recurrence interval of landslide, and assume a threshold landslide size that can generate a destructive tsunami. The maximum expected landslide size for a given earthquake magnitude is calculated in 3 ways: by slope stability analysis for catastrophic slope failure on the Atlantic continental margin, by using land-based compilation of maximum observed distance from earthquake to liquefaction, and by using land-based compilation of maximum observed area of earthquake-induced landslides. The results from all three methods compare well with the slope failure observations of the M7.2, 1929 Grand Banks earthquake, and suggest that the largest expected earthquake in the eastern U.S. must be located offshore and within 100 km of the continental slope to induce a catastrophic slope failure. A minimum triggering earthquake magnitude of 5.5 is suggested for a sufficiently large submarine failure to generate a devastating tsunami and only if the epicenter is located within the continental slope.