The Earthquake Problem in the Eastern United States

Earthquakes in the eastern United States have longer recurrence times, less attenuation of damaging ground motion, and occur in more diffuse source zones than their western counterparts. As a consequence, hazard specification, either by deterministic or probabilistic techniques, is more uncertain in the East. Many of the eastern source zones in historic time have not had the largest earthquake of which they are capable. Two eastern source zones, the St. Lawrence valley of Canada and the New Madrid fault of the central Mississippi valley, produced great earthquakes (magnitude larger than 8). They probably are the only zones in the East which can generate such great earthquakes. A number of other zones, however, can produce major earthquakes which will affect a large number of people, because of the high density of population and the low attenuation of damaging ground motion in the East. All critical facilities should be designed to withstand the maximum expected ground shaking, even though it may have a long recurrence time, of the order of 1000 years.