Potential of Radar Imaging and Sounding Methods in Mapping Heavily Eroded Impact Craters: Mapping Some Structural Elements of the Hico

Shuttle Radar Topography Mission (SRTM) and Ground Penetrating Radar (GPR) data collected over an area north of the town of Hico, central Texas, have been used to map disturbances in the surface topography and subsurface stratigraphy. The Radar topography results confirm the presence of multiple rings suggestive of an impact crater. Correlation between the orbital SRTM and on-the-ground GPR field data are affected by different biases related to variations in terrain and vegetation cover. Nevertheless, the correspondence of the two data sets supports the earlier conclusions that a complex, multiple ring impact structure is reflected in the topography of this area. The SRTM data reveal three previously unrecognized rings; with the outermost ring some 5-6 km in diameter. The crater appears to be significantly larger than the size (2.5 km diameter) previously inferred on the basis of aerial images [1, 2]. In addition, the GPR data suggest the presence of subsurface faulting that spatially coincides with the two inner rings of the crater. This suggests that the topographic rings are structurally controlled by faulting. Introduction: The Hico crater is located N 32.03 and W 98.33, 3 km North of the town of Hico, Central Texas, and some 90 km southwest of Fort Worth. A structurally disturbed area of 3 km diameter bounded by a ring, a graben and includes a stratigraphically uplifted core, approximately 1 km in diameter. These structures in an otherwise flat-laying, undisturbed sequence of Cretaceous sediments and the discovery of shatter cones identify this disturbance as an impact crater. The age of the structure is unknown, other then post-Cretaceous. It was also not known previously whether the structurally disturbed zone, manifested predominantly by folding rather than faulting, defines the crater in its entirety or whether the actual crater diameter is somewhat larger, possibly as large as 9 km [1], [2]. Aerial images of the Hico crater (see figure 1, bottom), suggests that the crater size is around 2.5 km. Erosion and vegetation have changed significantly the surface topography making very difficult to map the original global shape of the crater. Efficient subsurface prospections were required in order to accomplish this task and get more precise information about the crater form and dimensions as key information to any further studies. Radar surface and subsurface mapping: Radar sounding and imaging techniques are able to probe the subsurface down from few tenths of centimeter to several meters depending on the frequency, the ground geometry (slop and surface roughness) and dielectric properties [3].