Subsurface structure of oblique impact craters

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Impacts of asteroids on planetary surfaces usually occur obliquely with an average impact angle of 45°. The impact vector can be analysed by the uneven distribution of ejecta. On Earth ejecta blankets of meteorite craters are very rare and incompletely preserved, but different degrees of erosion often allow to study the crater floor in detail. The working hypothesis of this proposal is that the crater floor flow field is capable to provide direct evidence for oblique impacts via momentum transfer from projectile to the target. The objective is to determine the impact vector of terrestrial craters from the subsurface crater structure and to infer the structural inventory of oblique impacts. For this purpose a field study is planned at the Spider impact crater in Western Australia, which is believed to have been formed by an oblique impact. In a thorough structural analysis deviations from a radial symmetry of the crater floor structure including a study on shock and damaging in different sectors of the crater will be deduced. A kinematic analysis will be performed to quantify dominant flow trajectories which are relevant for reconstruction of the projectile s vector. The analysis will be linked to 3D numerical modeling of the crater floor flow in an oblique impact scenario, A comparison of the Spider structure with other craters is planned to test if structural elements indicative for oblique impacts can be generally applied and to infer the incidence of impact.