Crustal structure in Missouri by seismic-refraction methods

abstract Two reversed seismic-refraction profiles, each about 300 km long, were established in Missouri. One profile was in northern Missouri, oriented east-west. The other was in southern Missouri, oriented in a northeasterly direction across the Ozark uplift. Interpretation of the seismic refraction data indicates that the crust in northern Missouri may be characterized by three major layers. Approximate velocities and depths of these layers are 6.1 km/sec from near the surface to a depth of 8 km, 6.2 km/sec to 20 km, and 6.6 km/sec to 40 km. Upper-mantle velocity is 8.0 km/sec. A westward component of dip is indicated on all these layers such that the crust is a few kilometers thicker along the west portion of the profile than along the east. An alternate interpretation based upon the Herglotz-Wiechert method indicates that the velocity variation in the upper 15 km of the crust is similar to that suggested by Birch for a granitic material. The velocity of 6.6 km/sec in the lower portion of the crust is further supported by interpretation of reflected phases. The seismic data do not require the pressence of a low-velocity channel within the crust. The data from southern Missouri were more difficult to interpret, possibly because of the effect of lateral inhomogeneities within the crust. If a layered crustal model is assumed for this region, then the interpreted crustal structure does not differ greatly from that derived for northern Missouri.)