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E.S. Schweig

Publications and source records attributed to E.S. Schweig.

11 recordsLinked to original sources
USGS2006

First USGS urban seismic hazard maps predict the effects of soils

Probabilistic and scenario urban seismic hazard maps have been produced for Memphis, Shelby County, Tennessee covering a six-quadrangle area of the city. The nine probabilistic maps are for peak ground acceleration and 0.2 s and 1.0 s spectral acceleration and for 10%, 5%, and 2% probability of being exceeded in 50 years. Six scenario maps for these three ground motions have also been generated for both an M7.7 and M6.2 on the southwest arm of the New Madrid seismic zone ending at Marked Tree, Arkansas. All maps include the effect of local geology. Relative to the national seismic hazard maps, the effect of the thick sediments beneath Memphis is to decrease 0.2 s probabilistic ground motions by 0-30% and increase 1.0 s probabilistic ground motions by ???100%. Probabilistic peak ground accelerations remain at levels similar to the national maps, although the ground motion gradient across Shelby County is reduced and ground motions are more uniform within the county. The M7.7 scenario maps show ground motions similar to the 5%-in-50-year probabilistic maps. As an effect of local geology, both M7.7 and M6.2 scenario maps show a more uniform seismic ground-motion hazard across Shelby County than scenario maps with constant site conditions (i.e., NEHRP B/C boundary).

Seismological Research Letters↗
USGS2004

Sensitivity analysis of seismic hazard for the northwestern portion of the state of Gujarat, India

We test the sensitivity of seismic hazard to three fault source models for the northwestern portion of Gujarat, India. The models incorporate different characteristic earthquake magnitudes on three faults with individual recurrence intervals of either 800 or 1600 years. These recurrence intervals imply that large earthquakes occur on one of these faults every 266-533 years, similar to the rate of historic large earthquakes in this region during the past two centuries and for earthquakes in intraplate environments like the New Madrid region in the central United States. If one assumes a recurrence interval of 800 years for large earthquakes on each of three local faults, the peak ground accelerations (PGA; horizontal) and 1-Hz spectral acceleration ground motions (5% damping) are greater than 1 g over a broad region for a 2% probability of exceedance in 50 years' hazard level. These probabilistic PGAs at this hazard level are similar to median deterministic ground motions. The PGAs for 10% in 50 years' hazard level are considerably lower, generally ranging between 0.2 g and 0.7 g across northwestern Gujarat. Ground motions calculated from our models that consider fault interevent times of 800 years are considerably higher than other published models even though they imply similar recurrence intervals. These higher ground motions are mainly caused by the application of intraplate attenuation relations, which account for less severe attenuation of seismic waves when compared to the crustal interplate relations used in these previous studies. For sites in Bhuj and Ahmedabad, magnitude (M) 7 3/4 earthquakes contribute most to the PGA and the 0.2- and 1-s spectral acceleration ground motion maps at the two considered hazard levels. ?? 2004 Elsevier B.V. All rights reserved.

Tectonophysics↗
USGS2002

CPT site characterization for seismic hazards in the New Madrid seismic zone

A series of cone penetration tests (CPTs) were conducted in the vicinity of the New Madrid seismic zone in central USA for quantifying seismic hazards, obtaining geotechnical soil properties, and conducting studies at liquefaction sites related to the 1811–1812 and prehistoric New Madrid earthquakes. The seismic piezocone provides four independent measurements for delineating the stratigraphy, liquefaction potential, and site amplification parameters. At the same location, two independent assessments of soil liquefaction susceptibility can be made using both the normalized tip resistance ( q c1N ) and shear wave velocity ( V s1 ). In lieu of traditional deterministic approaches, the CPT data can be processed using probability curves to assess the level and likelihood of future liquefaction occurrence.

Arkansas, Missouri, Tennessee↗
USGS1998

Evidence for large prehistoric earthquakes in the northern New Madrid seismic zone, central United States

We surveyed the area north of New Madrid, Missouri, for prehistoric liquefaction deposits and uncovered two new sites with evidence of pre-1811 earthquakes. At one site, located about 20 km northeast of New Madrid, Missouri, radiocarbon dating indicates that an upper sand blow was probably deposited after A.D. 1510 and a lower sand blow was deposited prior to A.D. 1040. A sand blow at another site about 45 km northeast of New Madrid, Missouri, is dated as likely being deposited between A.D. 55 and A.D. 1620 and represents the northernmost recognized expression of prehistoric liquefaction likely related to the New Madrid seismic zone. This study, taken together with other data, supports the occurrence of at least two earthquakes strong enough to induce liquefaction or faulting before A.D. 1811 and after A.D. 400. One earthquake probably occurred around A.D. 900 and a second earthquake occurred around A.D. 1350. The data are not yet sufficient to estimate the magnitudes of the causative earthquakes for these liquefaction deposits although we conclude that all of the earthquakes are at least moment magnitude M ∼ 6.8, the size of the 1895 Charleston, Missouri, earthquake. A more rigorous estimate of the number and sizes of prehistoric earthquakes in the New Madrid seismic zone awaits evaluation of additional sites.

Arkansas, Illinois, Kentucky, Missouri, Tennessee↗
USGS1996

Recognizing and dating prehistoric liquefaction features: Lessons learned in the New Madrid seismic zone, central United States

The New Madrid seismic zone (NMSZ), which experienced severe liquefaction during the great New Madrid, Missouri, earthquakes of 1811 and 1812 as well as during several prehistoric earthquakes, is a superb laboratory for the study of world-class, earthquake-induced liquefaction features and their use in paleoseismology. In seismically active regions like the NMSZ, frequent large earthquakes can produce a complex record of liquefaction events that is difficult to interpret. Lessons learned studying liquefaction features in the NMSZ may help to unravel the paleoseismic record in other seismically active regions. Soil characteristics of liquefaction features, as well as their structural and stratigraphic relations to Native American occupation horizons and other cultural features, can help to distinguish prehistoric liquefaction features from historic features. In addition, analyses of artifact assemblages and botanical content of cultural horizons can help to narrow the age ranges of liquefaction features. Future research should focus on methods for defining source areas and estimating magnitudes of prehistoric earthquakes from liquefaction features. Also, new methods for dating liquefaction features are needed.

Journal of Geophysical Research B: Solid Earth↗
USGS1996

Sand boils induced by the 1993 Mississippi River flood: Could they one day be misinterpreted as earthquake-induced liquefaction?

In areas that are seismically active but lacking clear surficial faulting, many paleoearthquake studies depend on the interpretation of ancient liquefaction features (sand blows) as indicators of prehistoric seismicity. Sand blows, however, can be mimicked by nonseismic sand boils formed by water seeping beneath levees during floods. We examined sand boils induced by the Mississippi River flood of 1993 in order to compare their characteristics with sand blows of the New Madrid earthquakes of 1811–1812. We found a number of criteria that allow a distinction between the two types of deposits. (1) Earthquake-induced liquefaction deposits are broadly distributed about an epicentral area, whereas flood-induced sand boils are limited to a narrow band along a river's levee. (2) The conduits of most earthquake-induced sand blows are planar dikes, whereas the conduits of flood-induced sand boils are most commonly tubular. (3) Depression of the preearthquake ground surface is usual for sand blows, not for sand boils. (4) Flood-induced sand boils tend to be better sorted and much finer than sand-blow deposits. (5) Source beds for earthquake-induced deposits occur at a wide range of depths, whereas the source bed for sand boils is always near surface. (6) Materials removed from the walls surrounding the vent of a sand blow are seen inside sand blows, but are rarely seen inside sand boils. In general, flood-induced sand boils examined are interpreted to represent a less-energetic genesis than earthquake-induced liquefaction.

Geology↗
USGS1996

The enigma of the New Madrid earthquakes of 1811-1812

Continental North America's greatest earthquake sequence struck on the western frontier of the United States. The frontier was not then California but the valley of the continent's greatest river, the Mississippi, and the sequence was the New Madrid earthquakes of the winter of 1811–1812. Their described impacts on the land and the river were so dramatic as to produce widespread modern disbelief. However, geological, geophysical, and historical research, carried out mostly in the past two decades, has verified much in the historical accounts. The sequence included at least six (possibly nine) events of estimated moment magnitude M ≥ 7 and two of M ≃ 8. The faulting was in the intruded crust of a failed intracontinental rift, beneath the saturated alluvium of the river valley, and its violent shaking resulted in massive and extensive liquefaction. The largest earthquakes ruptured at least six (and possibly more than seven) intersecting fault segments, one of which broke the surface as a thrust fault that disrupted the bed of the Mississippi River in at least 2 (and possibly four) places.

Arkansas, Kentucky, Missouri, Tennessee↗
USGS1994

Reconciling short recurrence intervals with minor deformation in the New Madrid seismic zone

At least three great earthquakes occurred in the New Madrid seismic zone in 1811 and 1812. Estimates of present-day strain rates suggest that such events may have a repeat time of 1000 years or less. Paleoseismological data also indicate that earthquakes large enough to cause soil liquefaction have occurred several times in the past 5000 years. However, pervasive crustal deformation expected from such a high frequency of large earthquakes is not observed. This suggests that the seismic zone is a young feature, possibly as young as several tens of thousands of years old and no more than a few million years old.At least three great earthquakes occurred in the New Madrid seismic zone in 1811 and 1812. Estimates of present-day strain rates suggest that such events may have a repeat time of 1000 years or less. Paleoseismological data also indicate that earthquakes large enough to cause soil liquefaction have occurred several times in the past 5000 years. However, pervasive crustal deformation expected from such a high frequency of large earthquakes is not observed. This suggests that the seismic zone is a young feature, possibly as young as several tens of thousands of years old and no more than a few million years old.

New Madrid seismic zone↗