The Meteor crater of Arizona is the best-preserved example of a terrestrial meteorite impact crater. Gilbert [1896], an early investigator in concepts of lunar impact cratering, was among the first geologists to study Meteor crater. Gilbert advocated volcanism as the agent responsible for Meteor crater. Barringer [1905], a mining engineer, spent an estimated halfmillion dollars in a vain attempt to find a buried meteorite that would be economical to mine. The Gilbert-Barringer controversy was finally conclusively settled when coesite and stishovite, both high-pressure polymorphs of quartz, were found in crater breccia derived from the Coconino sandstone [Chao et al., 1960]. Coesite and stishovite require formation pressures of more than I00 kbar, far greater than the maximum pressures that can be generated by a volcanic explosion [Roddy, 1968]. Only a hyperVelocity impact could have produced the high pressures required to shock metamorphose the Coconino sandstone.The initial purpose of this study was to investigate subsurface layering within Meteor crater and its surrounding rim by means of conventional seismic refraction methods. This technique requires that the lateral extent of a refracting horizon be large in comparison with its depth. Such conditions do not exist at Meteor crater, particularly for the deeper units within the crater. Seismic reflection was tried with no success. However, a thick sequence of high-velocity limestone beds known to occur at a depth Of approximately 850 m suggested using them as a refractor. The crater was treated as a lowvelocity hole wi. thin a homogeneous layered half space. An interpretative technique was developed that considered arrival time delays caused by the hole on critically refracted waves from both the limestone horizon and the crystalline basement rocks at a depth •f approximately 1100 m. Results compare favorably with the known structure of the crater [Shoemaker, 1963] and provide new data on an extensive fractured zone. GEOLOGIC AND SEISMIC SETTING Meteor crater is on the southern part of the Colorado plateau, in north central Arizona (Figure 1). The crater is bowl Copyright ¸ 1975 by the •merican Geophysical Union. A seismic refraction technique for interpreting the subsurface shape and velocity distribution of an anomalous surface feature such as an impact crater is described. The method requires the existence of a relatively deep refracting horizon and combines data obtained from both standard shallow refraction spreads and distant offset shots by using the deep refractor as a sourc• of initial arrivals. Resul!;s obtained from applying the technique to Meteor crater generally agree with the known structure of the crater deduced by other investigators and provide new data on an extensive fractured zone surrounding the crater. The breccia lens is computed to extend roughly 190 m below the crater floor, about 30 m less than the value deduced from early drilling data. Rocks around the crater are fractured as distant as 90t3 m from the tim crest and to a depth of at...

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The relation of in‐situ compressional‐wave velocities to porosities, determined by seismic refraction for unsaturated near‐surface rocks from different areas in Arizona, New Mexico, and California, is grossly similar to relations determined by other investigators for water‐saturated rock and unconsolidated sediments. The principal difference is that in the porosity range 0.0–0.2, compressional waves travel somewhat more slowly in unsaturated rocks than in water‐saturated rocks, and much more slowly, in the porosity range 0.2–0.8. The function, ϕ=−0.175 ln (α)+1.56, where ϕ is the fractional porosity and α is the compressional‐wave velocity, was obtained as a least squares fit to the experimental data. Bulk densities are reported for all samples; moisture contents are reported in some instances.