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Data for Quaternary faults, liquefaction features, and possible tectonic features in the Central and Eastern United States, east of the Rocky Mountain Front

July 1, 2000

The USGS is currently leading an effort to compile published geological information on
Quaternary faults, folds, and earthquake-induced liquefaction in order to develop an internally
consistent database on the locations, ages, and activity rates of major earthquake-related features
throughout the United States. This report is the compilation for such features in the
Central and Eastern United States (CEUS), which for the purposes of the compilation, is
defined as the region extending from the Rocky Mountain Front eastward to the Atlantic
seaboard. A key objective of this national compilation is to provide a comprehensive database
of Quaternary features that might generate strong ground motion and therefore, should be considered
in assessing the seismic hazard throughout the country. In addition to printed versions
of regional and individual state compilations, the database will be available on the World-Wide
Web, where it will be readily available to everyone. The primary purpose of these compilations
and the derivative database is to provide a comprehensive, uniform source of geological information
that can by used to complement the other types of data that are used in seismic-hazard
assessments.
Within our CEUS study area, which encompasses more than 60 percent of the continuous U.S.,
we summarize the geological information on 69 features that are categorized into four classes
(Class A, B, C, and D) based on what is known about the feature's Quaternary activity. The
CEUS contains only 13 features of tectonic origin for which there is convincing evidence of
Quaternary activity (Class A features). Of the remaining 56 features, 11 require further study in
order to confidently define their potential as possible sources of earthquake-induced ground
motion (Class B), whereas the remaining features either lack convincing geologic evidence of
Quaternary tectonic faulting or have been studied carefully enough to determine that they do not
pose a significant seismic hazard (Classes C and D).
The correlation between historical seismicity and Quaternary faults and liquefaction features
in the CEUS is generally poor, which probably reflects the long return times between successive
movements on individual structures. Some Quaternary faults and liquefaction features
are located in aseismic areas or where historical seismicity is sparse. These relations indicate
that the record of historical seismicity does not identify all potential seismic sources in the
CEUS. Furthermore, geological studies of some currently aseismic faults have shown that the
faults have generated strong earthquakes in the geologically recent past. Thus, the combination
of geological information and seismological data can provide better insight into potential
earthquake sources and thereby, contribute to better, more comprehensive seismic-hazard
assessments.

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