Is Ries crater typical for its size? An analysis based upon old and new geophysical data and numerical modeling
K. Wünnemann, J.V. Morgan, H. Jödicke, 2005. "Is Ries crater typical for its size? An analysis based upon old and new geophysical data and numerical modeling", Large Meteorite Impacts III, Thomas Kenkmann, Friedrich Hörz, Alex Deutsch
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Considering the Ries crater as an example for middle-sized complex impact structures on Earth, we use geophysical data to examine the structure underneath the crater and simulate the formation process by numerical modeling. In contrast to previous investigations, we show by reanalyzing seismic refraction profiles that some clues for structural uplift exist beneath the crater in a range of at least 1 km. We propose that the average P-wave velocity inside the crater is lower than outside the crater from the surface to ∼2.2 km depth, but that below this level, the velocity increases beneath the center, presumably due to uplifted basement rocks. In addition, we utilized magnetotelluric depth sounding to investigate the deep electrical structure beneath the crater. Two-dimensional inversion models of the data show anomalously high conductivity beneath the crater. Our best model features a zone of presumably brine-filled fractures in open pore space to a depth of ∼2 km. Furthermore, our numerical modeling results for the crater formation are consistent with surface and subsurface observations in the vicinity of the crater. In order to explain the structural differences between similarly sized craters and Ries, we investigate the sensitivity of crater shape and subsurface structure to varying target compositions. We show that for a reasonable range of constitutive material and acoustic fluidization parameters the model calculations produce a large variety of different crater shapes, even for the same amount of impact energy. In contrast to the conventional estimate of crater diameters, our results suggest that Ries crater is comparable in size with the Bosumtwi and Zhamanshin crater. Despite their apparent lack of similarity at first look, Ries and Bosumtwi are closely matched in terms of transient crater size (inner ring), aspect ratio, and structural elements, and we conclude that they both represent typical complex crater structures of the terrestrial impact record for their size range.