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

该应用程序的重点是通过在各种冲击能量下进行复杂的成坑实验，在石灰石目标中形成坑。此外，我们还考虑了具有流变分层的混合层目标对撞击成坑过程的影响，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：（一）对弹坑形态进行严格分析;（二）回收的喷出物的喷出特性和变形;（三）对弹坑次表面目标的损害进行系统评价。瞬态和最终弹坑的弹坑体积的确定，以及弹坑效率，使我们能够比较影响弹坑在CaCO 3为主的目标与混合层的目标和那些在SiO2为主的，在MEMIN I的调查主题。该项目包括对目标材料进行详细的撞击前岩相学和机械表征。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。在冲击实验过程中开发的裂缝将通过详细的微观结构和表面分析获得的围压释放技术进行比较，以深入了解断裂机制。我们对实验产生的陨石坑的精确形态和结构分析将为石灰石和混合目标陨石坑提供全面的数据库。有了这些数据，目前的撞击坑的比例律将得到改进，并为改进材料模型和数值计算提供重要的输入数据。在德国直径为3.8公里的Steinheim陨石坑进行的实地活动中，对放大的实验结果进行了测试和验证。这一项目产生了实地调查的结构地质方面，将与提议八详述的地球物理数据合并。由于我们的团队在第一次申请期间获得的经验，该提案的实现是可能的。我们进行了24次撞击坑实验，研究孔隙率，孔隙水，和撞击能量对成坑过程的影响。我们发现，更高程度的水饱和度的目标产生的总喷出物质量的增加（高达400%相对于干目标），更高的喷出物速度，和更陡峭的喷出物锥角。形态测量数据表明，弹坑的深度/直径比与射弹/目标密度比和孔隙率密切相关，在低密度目标中的撞击形成更深的弹坑。在其他撞击条件保持不变的情况下，饱和抵消了孔隙的影响，并增加了弹坑的体积。在一定速度范围内的干砂岩实验的火山口体积缩放与数值模拟的火山口的第一个结果是一致的。

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.