Passage of the EarthScope Transportable Array across the Mississippi Embayment is
providing an opportunity to investigate lithospheric structure associated with active
deformation and an ancient, intracratonic rift. The Mississippi Embayment is a first-order
geological structure of the North American continent with a long and complex geological
history affected by at least two periods of continental breakup. The reason for geologically
recent basin subsidence is enigmatic since subsidence began in Late Cretaceous and
is not linked to a major tectonic episode. In addition, the active New Madrid seismic
zone (NMSZ) is located in the upper crust within the northern Mississippi Embayment.
Lithospheric seismic velocity heterogeneity and anisotropy are likely indicators of
the dynamic processes associated with basin subsidence and earthquake genesis in the
The seismic experiment incorporates stations of the USArray and a portable FlexArray
deployment to provide an overall framework of lithospheric velocity and anisotropy
structure to depths including the upper mantle transition zone. Detailed variations
in deep structure perpendicular and parallel to the embayment axis are imaged using
three dense lines of FlexArray stations that extend within and outside of the Mississippi
Major issues that are addressed include:
- the primary differences in lithospheric structure between the embayment and the surrounding
- the nature of early Cambrian rifting and relationship to pre-existing structure
- the dynamic processes responsible for basin subsidence, and
- the relationship of the NMSZ to large scale lithospheric structure.
This is accomplished through joint interpretation of compressional and shear velocity
tomography, potential fields, transfer/receiver functions, and depth-dependent anisotropy
images generated using traditional and new geophysical techniques.