Russell L. Wheeler

The 2014 United States National Seismic Hazard Model

New seismic hazard maps have been developed for the conterminous United States using the latest data, models, and methods available for assessing earthquake hazard. The hazard models incorporate new information on earthquake rupture behavior observed in recent earthquakes; fault studies that use both geologic and geodetic strain rate data; earthquake catalogs through 2012 that include new assessments of locations and magnitudes; earthquake adaptive smoothing models that more fully account for the spatial clustering of earthquakes; and 22 ground motion models, some of which consider more than double the shaking data applied previously. Alternative input models account for larger earthquakes, more complicated ruptures, and more varied ground shaking estimates than assumed in earlier models. The ground motions, for levels applied in building codes, differ from the previous version by less than ±10% over 60% of the country, but can differ by ±50% in localized areas. The models are incorporated in insurance rates, risk assessments, and as input into the U.S. building code provisions for earthquake ground shaking.

A seismotectonic model for the 300-kilometer-long eastern Tennessee seismic zone

Ten years of monitoring microearthquakes with a regional seismic network has revealed the presence of a well-defined, linear zone of seismic activity in eastern Tennessee. This zone produced the second highest release of seismic strain energy in the United States east of the Rocky Mountains during the last decade, when normalized by crustal area. The data indicate that seismicity produced by regional, intraplate stresses is now concentrating near the boundary between relatively strong and weak basement crustal blocks.

Earthquakes and the cratonward limit of Iapetan faulting in eastern North America

The cratonward limit of large normal faults in the passive margin of the Late Proterozoic to early Paleozoic Iapetus Ocean is a fundamental boundary for the assessment of seismic hazards in populous eastern North America. Earthquakes at five localities in the Iapetan margin have been attributed to compressional reactivation of Iapetan normal faults. The northwesternmost locations of known Iapetan faults, both seismic and currently aseismic, lie along a line from Labrador to Alabama. This line coincides approximately with the northwestward transition from a more seismically active continental rim to a generally less active cratonic interior. Thus, the northwestern boundary of Iapetan faults separates two large regions of mostly different seismic hazard.

The Giles County, Virginia, seismic zone

A well-defined seismic zone recently detected in Virginia has an orientation that is not related to the surrounding geologic structures. The orientation of the zone appears to be related to features below the Appalachian overthrust belt. A damaging earthquake that is important in evaluating seismic hazard in the southeastern United States may have occurred in the zone in 1897.

Known and suggested quaternary faulting in the midcontinent United States

Abstract The midcontinent United States between the Appalachian and Rocky Mountains contains 40 known faults or other potentially tectonic features for which published geologic information shows or suggests Quaternary tectonic faulting. We report results of a systematic evaluation of published and other publicly available geologic evidence of Quaternary faulting. These results benefit seismic-hazard assessments by (1) providing some constraints on the recurrence intervals and magnitudes of large, prehistoric earthquakes, and (2) identifying features that warrant additional study. For some features, suggested Quaternary tectonic faulting has been disproved, whereas, for others, the suggested faulting remains questionable. Of the 40 features, nine have clear geologic evidence of Quaternary tectonic faulting associated with prehistoric earthquakes, and another six features have evidence of nontectonic origins. An additional 12 faults, uplifts, or historical seismic zones lack reported paleoseismological evidence of large, Quaternary earthquakes. The remaining 13 features require further paleoseismological study to determine if they have had Quaternary earthquakes that were larger than any known from local historical records; seven of these 13 features are in or near urbanized areas where their study could affect urban hazard estimates. These seven are: (1) the belt of normal faults that rings the Gulf of Mexico from Florida to Texas, (2) the Northeast Ohio seismic zone, (3) the Valmont and (4) Goodpasture faults of Colorado, (5) the Champlain lowlands normal faults of New York State and Vermont, and (6) the Lexington and (7) Kentucky River fault systems of eastern Kentucky.

Seismic Source Characterization for the 2014 Update of the U.S. National Seismic Hazard Model

We present the updated seismic source characterization (SSC) for the 2014 update of the National Seismic Hazard Model (NSHM) for the conterminous United States. Construction of the seismic source models employs the methodology that was developed for the 1996 NSHM but includes new and updated data, data types, source models, and source parameters that reflect the current state of knowledge of earthquake occurrence and state of practice for seismic hazard analyses. We review the SSC parameterization and describe the methods used to estimate earthquake rates, magnitudes, locations, and geometries for all seismic source models, with an emphasis on new source model components. We highlight the effects that two new model components—incorporation of slip rates from combined geodetic-geologic inversions and the incorporation of adaptively smoothed seismicity models—have on probabilistic ground motions, because these sources span multiple regions of the conterminous United States and provide important additional epistemic uncertainty for the 2014 NSHM.

Seismicity and suspect terranes in the southeastern United States

Evaluation of seismic hazard in the eastern United States is hampered by lack of a strong geologic foundation. If suspect terranes exist in the Appalachians, then geologic and mechanical differences between terranes may provide such a foundation. For example, a published map of suggested terranes is consistent with spatial characteristics of southeastern seismicity and with structural models of seismicity in central and southwestern Virginia and in southeastern South Carolina.

Paleoseismic targets, seismic hazard, and urban areas in the Central and Eastern United States

Abstract Published geologic information from the central and eastern United States identifies 83 faults, groups of sand blows, named seismic zones, and other geological features as known or suspected products of Quaternary tectonic faulting. About one fifth of the features are known to contain faulted Quaternary materials or seismically induced liquefaction phenomena, but the origin and associated seismic hazard of most of the other features remain uncertain. Most of the features are in or near large urban areas. The largest cluster of features is in the Boston–Washington urban corridor (2005 estimated population: 50 million). The proximity of most features to populous areas identifies paleoseismic targets with potential to impact urban-hazard estimates.

Evaluating point concentrations on a map: Earthquakes in the Colorado Lineament

A common problem in geology is the objective evaluation of points that are suspected to concentrate nonrandomly in a specified part of a map area. Evaluation can be rigorous with the binomial test, but results often are distorted by prior inspection of the only available group of points. Such distortion can be hard to avoid because concentration may not be suspected until the sample is inspected. Distortion can be evaluated by analyzing overlapping subsamples, mapping independent cells that are significantly overpopulated by points, and arguing that the sample is representative of the population from which it was drawn. Such distortion occurs in evaluation of earthquake hazard. For example, visual inspection of epicenters in the west-central United States suggests that they have been concentrated in the Colorado Lineament for the past century. Results of distortion evaluation support that suggestion: concentration is strongly indicated, although it cannot be evaluated rigorously.

Central US earthquake catalog for hazard maps of Memphis, Tennessee

An updated version of the catalog that was used for the current national probabilistic seismic-hazard maps would suffice for production of large-scale hazard maps of the Memphis urban area. Deaggregation maps provide guidance as to the area that a catalog for calculating Memphis hazard should cover. For the future, the Nuttli and local network catalogs could be examined for earthquakes not presently included in the catalog. Additional work on aftershock removal might reduce hazard uncertainty. Graphs of decadal and annual earthquake rates suggest completeness at and above magnitude 3 for the last three or four decades. Any additional work on completeness should consider the effects of rapid, local population changes during the Nations westward expansion.