Velocity structure of the Northern Mississippi embayment sediments, part I: Teleseismic P-wave spectral ratios analysis


The Mississippi Embayment overlies the New Madrid seismic zone in the central United States and consists of a thick succession of unconsolidated sediments that covers the Paleozoic basement rock. The high-velocity contrast at the basement– sediment interface and the near-vertical ray paths of teleseismic P-waves generate very large P to S conversions on the radial component and large P reverberations on the vertical component. This characteristic of P-wave propagation is used to study P- and S-wave resonance in the sedimentary layer. Horizontal-to-vertical (H/V) and vertical-to-horizontal (V/H) power spectral ratios are calculated for a time window around the teleseismic P-wave arrivals at broadband stations of the USArray Transportable Array, Northern Embayment Lithosphere Experiment, and the New Madrid Cooperative Seismic Network in the embayment. Using a map of sediment thickness, we developed models for average P- and S-wave velocity-versus-sediment thickness. The resulting shear-wave velocity model matches very well with the model obtained from an H/Vambient noise study in the region. The shear-wave velocity model shows low velocity near the edges of the embayment with average velocities increasing with increasing sediment thickness, consistent with increased sediment compaction. Fundamental resonance frequency for S waves ranges from 0.2 to 0.4 Hz for the embayment sediments.

Publication Title

Bulletin of the Seismological Society of America