Shear-wave Velocities of the post-paleozoic sediments across the upper Mississippi embayment

A P-And S-wave velocity model of the post-Paleozoic sediments has been developed across the Upper Mississippi Embayment between the latitudes of 3514°N and 35Y2°N. The model was constructed by P-wave soundings and reversed SH-wave refraction/reflection profiles acquired at 5-km intervals along the corridor. The results from these data were integrated with previously acquired P-And SH-wave velocity estimates, P-wave CDP reflection profiles, P-wave sonic logs, travel-Time differences between earthquake-generated Sand Sp waves, and top-of-bedrock elevation from nearby drillholes. A three-layered S-wave velocity model is proposed from this data set. The uppermost layer, which is not discussed in this paper (see Street et al., 2001), varies from a few tens of meters thick near the edges of the embayment to as much as 190 m thick near the center of the study area; the S-wave velocities of these unlithified to poorly lithified sediments are highly variable (typically ranging between 150 and 600 m/s) and site-dependent. The second layer in the S-wave velocity model extends from the base of the near- 1. Corresponding author. surface layer to the acoustical top of the Cretaceous sediments, which is ,..650m below sea level near the center of the study area. The lateral S-wave velocity variance of this layer is defined in three segments: Near the western edge ofthe study area in northeastern Arkansas the velocity varies between 650 and 700 m/s; the central study area ranges between 795 and 840 m/s; and near the eastern edge of the study area in western Tennessee it ranges between 500 and 550 tnl s. The Swave velocities of the third layer, the Cretaceous section, vary between 725 and 775 m/s at the edges of the study area but between 1,010 and 1,060 mls near the center.