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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Ambiguities are inherent in seismic refraction traveltime curves based on first arrivals recorded from a multi‐layered medium. Even for reversed profiles, inflections of traveltime curves caused by the onset of arrivals from successively deeper horizons frequently cannot be delineated from those caused by lateral geologic changes. In addition, the secondary arrivals which may represent essential portions of a traveltime curve are not available. Numerous inversions having different geologic implications are possible. Ambiguities may be resolved by using multiple shotpoints for each spread and combining their individual first‐arrival traveltime curves to yield a consistent set of curves for each refracting horizon. A set of rules applies for combining individual traveltime curves based on reversed, split, and offset profile configurations. The combined curves lend themselves to a unique inversion.