PALEOSEISMOLOGICAL TARGETS IN THE EASTERN UNITED STATES

We evaluated published geologic information on 31 geologic features in the U.S. Appalachian Mountains and Atlantic Coastal Plain for evidence of Quaternary tectonic faulting. Wheeler and Crone (Eng. Geol., 2001, v. 62, p. 51-78) evaluated similar information for the region between the Appalachian and Rocky Mountains, and we followed their methodology. All the evaluations are part of a Web-served national database on Quaternary faulting (URL http://qfaults.cr.usgs.gov/faults) for use in seismic-hazard assessment and Quaternary studies. The 31 faults, young folds, recognized seismic zones, and fields of shaking-induced liquefaction phenomena in the Appalachians and Coastal Plain fall into four classes. (1) Three of the 31 features can be discounted as having nontectonic origins. (2) Three other features are shaking-induced liquefaction fields that were caused by historical and Holocene tectonic faulting (coastal South Carolina including Charleston, the Central Virginia seismic zone, and the Newbury, Massachusetts area). Within these three features, Charleston, South Carolina, has the highest hazard because of large, frequent, Holocene earthquakes, but Charleston hazard is also highly uncertain because the paleoearthquake locations are poorly constrained. (3) An additional 18 features, most of them faults, have little or no published geologic evidence of Quaternary tectonic faulting that could indicate the likely occurrence of earthquakes larger than those observed historically. However, only three of the 18 features have been studied paleoseismologically: the Belair fault zone (Georgia), the Ramapo fault system (New Jersey, New York), and the South Sebec seismic zone (Maine). (4) Seven other features require additional work, mainly paleoseismological, before they can be assigned to classes (1)-(3). All seven are in or near urban areas: the Moodus seismic zone (east-central Connecticut), Dobbs Ferry fault zone and Mosholu fault (New York City), Lancaster seismic zone and epicenter of the shallow Cacoosing Valley earthquake (southeastern Pennsylvania), Kingston fault (central New Jersey), and Everona fault – Mountain Run fault zone (northeastern Virginia). Additional paleoseismological studies of these features will improve the accuracy and precision of urban-hazard estimates.