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

该应用程序通过在不同冲击能量下进行复杂的陨石坑实验，重点研究石灰岩目标中的陨石坑形成。此外，我们还考虑了具有流变分层的混合层靶体对撞击坑过程的影响，并完成了孔隙度和含水饱和度的参数研究。撞击后的调查包括(i)对陨石坑形态的严格分析，（ii）弹射特征和回收的弹射物的变形，以及（iii）对陨石坑地下目标破坏的系统评估。通过确定瞬态和最终陨石坑的体积以及陨石坑效率，我们可以比较以caco3为主的目标与混合层目标和以sio2为主的目标的陨石坑，这些目标是MEMIN i研究的主题。该项目包括详细的撞击前岩石学和目标材料的力学特性。研究了不同加载速率下靶岩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，将冲击实验中产生的裂缝与围压释放技术得到的裂缝进行比较，以深入了解断裂机制。我们对实验产生的陨石坑进行精确的形态测量和结构分析，将产生一个完整的石灰岩和混合目标陨石坑数据库。有了这些数据，将完善当前的撞击尺度规律，并为改进材料模型和数值计算提供重要的输入数据。放大后的实验结果在直径3.8公里的德国施泰因海姆陨石坑进行了实地测试和验证。这个项目产生了实地调查的构造地质学方面的资料，这些资料将与建议八中详述的地球物理数据合并。由于我们的团队在第一个申请期间获得的经验，这个建议的实现是可能的。我们进行了24次撞击实验，研究孔隙度、孔隙水和撞击能量对撞击过程的影响。我们发现，目标的含水饱和度越高，总喷射质量就会增加（相对于干目标而言，可达400%），喷射速度越快，喷射锥角越陡。形态测量数据显示，弹坑的深度/直径比与弹靶密度比和孔隙率密切相关，低密度目标的撞击形成更深的弹坑。当其他撞击条件保持不变时，饱和度抵消了孔隙度的影响，增加了陨石坑的体积。在一定速度范围内，干砂岩试验的陨石坑体积尺度与数值模拟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.