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Research about Arkansas, Missouri, Tennessee

Source-linked reports with geographic coverage including Arkansas, Missouri, Tennessee.

3 recordsLinked to original sources
USGS2016

Dense lower crust elevates long-term earthquake rates in the New Madrid seismic zone

Knowledge of the local state of stress is critical in appraising intraplate seismic hazard. Inverting earthquake moment tensors, we demonstrate that principal stress directions in the New Madrid seismic zone (NMSZ) differ significantly from those in the surrounding region. Faults in the NMSZ that are incompatible with slip in the regional stress field are favorably oriented relative to local stress. We jointly analyze seismic velocity, gravity, and topography to develop a 3-D crustal and upper mantle density model, revealing uniquely dense lower crust beneath the NMSZ. Finite element simulations then estimate the stress tensor due to gravitational body forces, which sums with regional stress. The anomalous lower crust both elevates gravity-derived stress at seismogenic depths in the NMSZ and rotates it to interfere more constructively with far-field stress, producing a regionally maximal deviatoric stress coincident with the highest concentration of modern seismicity. Moreover, predicted principal stress directions mirror variations (observed independently in moment tensors) at the NMSZ and across the region.

Arkansas, Missouri, Tennessee↗
USGS1989

The New Madrid earthquakes: An engineering-geologic interpretation of relict liquefaction features

Earthquake-induced sand blows and sand-filled fissures are present in a belt 40 to 60 km. wide that extends from near Charleston, Mo., southward to about 20 km. south of Marked Tree, Ark. This region of earthquake-induced sand blows and other liquefaction-related features is almost exclusively in the St. Francis Basin, an alluvial lowland that typically has a thin (2 to 8 m thick), clay-bearing topstratum underlain by about 30 to 60 m of unconsolidated sand (the substratum). Liquefaction of the substratum sands has made the sand blows. The sand blows and other liquefaction-related features on the ground surface in the St. Francis Basin are almost certainly results of the New Madrid earthquakes of 1811-12. In this report, geologic and engineering properties of the alluvium are used in combination with a map showing the bounds of the liquefaction-related features to locate approximately the epicentral zones for two of the major shocks: the earthquakes of December 16,1811, and February 7,1812. Properties used for the analysis included the Standard Penetration Resistance of the substratum sands, characteristics of the sand's grain size, thickness of the topstratum, and the thickness of the post-Tertiary alluvium. The method of analysis relies largely on the evaluation of the liquefaction potential of the sands. This is done by using the Standard Penetration Test blow counts and by devising a method that uses all possible combinations of liquefaction potential and a realistic relation between attenuation of earthquake accelerations and distance from the epicenter (or more correctly, energy-release center). Two interpreted 1811-12 energy-release centers generally agree well with zones of seismicity defined by modern, small earthquakes. Bounds on accelerations are placed at the limits of sand blows that were generated by the 1811-12 earthquakes in the St. Francis Basin. Conclusions show how the topstratum thickness, sand size of the substratum, and thickness of alluvium affected the distribution of sand blows in the St. Francis Basin.

Arkansas, Missouri, Tennessee↗