Site Response Impacts of the Memphis Sand Layer within the Mississippi Embayment

Shear wave velocity ( VS) profiles to depths of approximately 200 m were developed from active-source surface wave velocity measurements in the Mississippi Embayment region of the Central United States. Soil deposits in this region are hundreds of meters thick, but are poorly characterized at depths below 60 m. Measurements were performed at five locations in Arkansas and Tennessee with a maximum distance between sites of approximately 130 km. The median VS profile calculated from the five profiles is in good agreement with a generic reference VS profile for the Mississippi Embayment that has been used in recent site response studies. The near-surface VS profiles at the five sites were remarkably consistent with average shear wave velocities in the top 30 m ( VS30), varying by less than 10%. Increasing variability between the VS profiles was observed at greater depths. The variability between VS profiles was shown to be correlated with changes in lithology at two of the sites where nearby lithologic information was available.

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Modeling Site Response in the Paducah, Kentucky Area

Earthquake Spectra ◽

10.1193/1.1585787 ◽

1994 ◽

Vol 10 (3) ◽

pp. 519-538 ◽

Cited By ~ 13

Author(s):

J. B. Harris ◽

R. L. Street ◽

J. D. Kiefer ◽

D. L. Allen ◽

Z. M. Wang

Keyword(s):

Land Use Planning ◽

Seismic Data ◽

Site Response ◽

Seismic Refraction ◽

Strong Motion ◽

Response Analysis ◽

Mississippi Embayment ◽

Reflection Data ◽

Upper Mississippi Embayment ◽

Central United States

Site conditions at 37 locations in Paducah, Kentucky, and the surrounding area were modeled using seismic refraction and reflection data to determine site response to a suite of Canadian strong-motion records and a hypothetical central United States earthquake. The seismic data, integrated with local borehole information, indicated that depths to bedrock range from less than 300 to more than 500 ft. The site-response analysis shows that the study area can be subdivided into three zones and the highest spectral amplifications are associated with thick alluvial and lake-bed deposits. The magnitude of spectral ratios ranges from less than five to more than 20 times, and dynamic site periods range from 0.7 to 1.5 sec. Although this study relates directly to the Paducah area, the methods and types of data collected are applicable for other Upper Mississippi Embayment communities for land-use planning and the design of critical structures.

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Ground Motion Site Amplification Factors for Sites Located within the Mississippi Embayment with Consideration of Deep Soil Deposits

Earthquake Spectra ◽

10.1193/091712eqs291m ◽

2015 ◽

Vol 31 (2) ◽

pp. 699-722 ◽

Cited By ~ 8

Author(s):

Mojtaba Malekmohammadi ◽

Shahram Pezeshk

Keyword(s):

Ground Motion ◽

Site Response ◽

Site Amplification ◽

Sediment Depth ◽

Deep Soil ◽

Mississippi Embayment ◽

Soil Response ◽

Amplification Factors ◽

Nonlinear Site Response ◽

Soil Deposits

In this study, site amplification factors for the deep soil deposits of the Mississippi embayment are computed using a nonlinear site response analysis program first to develop a model for nonlinear soil response for possible use by ground motion developers and second to address site amplification estimation. The effects of geology, sediment depth, and average shear wave velocity at the upper 30 m of soil ranging 180–800 m/s, as well as the effect of peak ground acceleration at the bedrock on nonlinear ground motion amplification for the upper embayment, are investigated. The site response computations cover various site conditions, sediment depth of 70–750 m, and peak acceleration of input rock motions of 0.01–0.90 g. The amplification (or de-amplification) at various frequencies implied by the sediment depth is greater than that implied just by site classification of the top 30 m of soil.

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