The heterogeneity of the continental crust: Results from deep crustal seismic reflection profiling using the Vibroseis technique

Abstract

Deep reflection surveys carried out by the Consortium for Continental Reflection Profiling (COCORP) are revealing major structures within the continental crust in a variety of tectonic settings across the U.S. In many cases, these structures bear directly upon such geologic problems as the state of stress during large scale crustal deformations, the migration of magma, and the nature of the crust‐mantle transition zone. COCORP, formed during the U.S. Geodynamics Project and funded by the National Science Foundation, has surveyed eight different localities along lines totalling over 800 km in length. The VIBROSEIS technique has been used in all cases and has proven to be a flexible and effective tool for deep crustal exploration. Among the more significant observations made thus far are: (1) the details of the extensional structure of the Rio Grande Rift; (2) evidence for at least 21 km horizontal and 13 km vertical displacement along the Wind River Thrust, which dips uniformly at about 30 degrees and extends to a depth of at least 25 km; (3) evidence for at least 225 km displacement along a major subhorizontal thrust system beneath the southern Appalachians, in which the Brevard Zone appears to be rooted; and (4) the apparently discontinuous nature of the Moho or crust‐mantle transition zone, which has been observed to some degree at most of the sites studied. Taken together, the results of all surveys analyzed thus far demonstrate a much larger degree of heterogeneity in crustal structure than is indicated by more conventional geophysical techniques for exploration of the basement.

Crust and Lithospheric Structure - Global Crustal Structure

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Seismic Wave Propagation and Scattering in the Heterogeneous Earth : Second Edition

“…Rigorously speaking, lithosphere refers to the solid portion of the earth that overlays the low velocity zone or the asthenosphere, and the thickness varies from place to place depending on the tectonic setting; however, we will use this term loosely for the upper 100 km of the earth that consists of the crust and the uppermost mantle. Surveys using the reflection method, such as those conducted by the Consortium for Continental Reflection Profiling (COCORP) reveal that the Moho is not a simple discontinuity but a transition zone consisting of many segments of small reflectors, and that the crust is heterogeneous on scales of a few kilometers to tens of kilometers (Schilt et al 1979). The characterization of the earth as a random medium is complementary to the classical stratified medium characterization.…”

An investigation of the regional variations and frequency dependence of anelastic attenuation in the mantle under the United States in the 0.5-4 Hz band

“…The recent COCORP studies, for example (Schilt et al 1979), show a large degree of lateral variability of seismic wave velocity in the crust. The velocity inhomogeneities manifest themselves in teleseismic studies as large, azimuthally varying, relative amplitude anomalies for closely spaced sensors.…”