PETER J. SMITH
Department of Earth Sciences
Milton Keynes, U.K.
Silt layers in lake sediments up to 2,300 years old have been interpreted as the result of earthquakes that caused landslides on tributary streams and the resuspension of sediment. If this view is valid, the recurrence interval of large earthquakes in eastern North America must have been very variable--120 years between 300 B.C. and 800 A.D., and 75 years from 1500 A.D. to the present. The prospect of estimating seismic risk on the basis of recurrence intervals thus looks remote.
R. Doig, "2300 yr history of seismicity from silting events in Lake Tadoussac, Charlevoix, Quebec," Geology, 18, 820-3, September 1990. (McGill University, Montreal)
Analysis of earthquake catalogs from 1727 to 1982, seismograph network results, and paleoseismic data shows that the probability of a large earthquake occurring in the central/eastern U.S. during the next 30 years is 0.4 to...