Crater structure and excavation: the effect of lithology and target layering on crater formation in experimental and natural impact craters

这项应用通过在不同撞击能量下进行复杂的陨石坑实验，重点研究石灰石目标中的陨石坑形成。此外，我们还考虑了具有流变性层结的混合层靶对冲击成坑过程的影响，并完成了孔隙度和含水饱和度的参数研究。撞击后调查包括(1)对陨石坑形态的严格分析，(2)回收的抛射物的抛射特征和变形，以及(3)对陨石坑亚表面的目标损伤进行系统评估。对瞬时和最终陨石坑的陨石坑体积以及陨石坑效率的测定，使我们能够比较以碳酸钙为主的混合层目标和以二氧化硅为主的目标中的撞击陨石量，这些都是第一次调查的主题。本项目包括目标材料撞击前的详细岩相学和力学特征。研究了不同加载速率下目标岩石的强度特性和破坏时的断裂特征。通过详细的微观结构和表面分析，将冲击试验中形成的断口与围压释放技术获得的断口进行比较，以深入了解断裂机理。我们对实验产生的陨石坑进行了准确的形态测量和结构分析，这将为石灰岩和混合目标陨石坑提供一个全面的数据库。有了这些数据，现有的撞击坑刻度定律将得到改进，并为材料模型的改进和数值计算提供重要的输入数据。放大的实验结果在德国直径3.8公里的施泰因海姆陨石坑的野外活动中得到了测试和验证。该项目产生了现场调查的结构地质方面，将与提案VIII中详细介绍的地球物理数据合并。由于我们的团队在第一个申请期内获得了经验，因此实现这一提案是可能的。我们进行了24次冲击成坑实验，研究了孔隙率、孔隙水和冲击能量对成坑过程的影响。我们发现，目标的水饱和度越高，喷射物的总质量就越大(相对于干目标高达400%)，喷射物速度更高，喷射物锥角更陡峭。形态测量数据表明，弹坑的深度/直径比与弹丸/目标密度比和孔隙率密切相关，低密度目标的撞击形成了更深的弹坑。当其他撞击条件保持不变时，饱和度抵消了孔隙率的影响，并增加了陨石坑的体积。在干燥砂岩中的实验在一定速度范围内的陨石坑体积标度与数值模拟的陨石坑的初步结果很好地吻合。

This application focuses on crater formation in limestone targets through the performance of sophisticated cratering experiments at various impact energies. Moreover, we consider the effects of mixed-layer targets with a rheological stratification on impact cratering processes and finalize the parameter study on porosity and water saturation. Post-impact investigations comprise (i) rigorous analysis of crater morphologies, (ii) ejection characteristics and deformation of recovered ejecta, and (iii) the systematic evaluation of target damaging in the crater’s sub-surface. The determination of crater volumes of transient and final craters, as well as crater efficiencies, allows us to compare impact cratering in CaCO3-dominated targets with mixed-layer targets and those in SiO2-dominated that were the subject of investigation in MEMIN I. This project includes a detailed pre-impact petrographic and mechanical characterization of the target material. The strength properties of the target rocks and fracture characteristics at failure are investigated for various loading rates. Fractures developed during the impact experiments will be compared with those obtained by the confining pressure release technique by means of a detailed microstructure and surface analysis to gain insights into the fracture mechanisms. Our accurate morphometric and structural analysis of the experimentally produced craters will yield a thorough data base for limestone and mixed-target craters. With these data at hand, current scaling laws for impact cratering will be refined and provide important input data for the improvement of material models and numerical computation. The up-scaled experimental results are tested and validated in a field campaign at the 3.8 km diameter Steinheim crater, Germany. This project yields the structural geology aspects of the field survey that will be merged with the geophysical data detailed in proposal VIII. The realisation of this proposal is possible due to the experience our team has gained during the first application period. We conducted 24 impact cratering experiments to study the effects of porosity, pore water, and impact energy on the cratering process. We found that a higher degree of water saturation of the target yields an increase of total ejecta mass (up to 400% with respect to dry targets), higher ejecta velocity, and a steeper ejecta cone angles. Morphometric data showed that the depth/diameter ratio of the craters strongly correlates with projectile/target density ratios and porosity, with impacts in low density targets forming deeper craters. Saturation counteracts the effect of porosity and increases crater volumes when other impact conditions are kept the same. Crater volume scaling of experiments in dry sandstone over a range of velocities is in good agreement with first results of numerically modeled craters.