Investigating pressure magnitudes at depth for oblique impacts into layered targets: Applications to terrestrial impacts in sedimentary targets

The positive identification of the Rock Elm impact structure (Wisconsin, USA) and the Upheaval Dome (Utah, USA) as impact craters was complicated by a lack of distinctive shock features in the record. Low‐impedance surface layers over high‐impedance bedrock affect energy coupling and shock effects in the substrate; in both cases, removal of surface sediments erased most of the original impact structures, thereby making identification of the impact origin difficult. In this study, a combination of laboratory and 3‐D numerical experiments reveals the underlying processes controlling subsurface deformation and demonstrates that a low‐impedance layer can reduce expression of peak shock pressures left in the rock record, as at the Rock Elm and the Upheaval Dome impact sites. 3‐D CTH models of the Rock Elm impact structure predict that peak shock pressures should fall below the hugoniot elastic limit of quartz in the basement rocks, yet still induce permanent deformation. The model predicts peak pressures around 5–10 GPa, levels consistent with field observations of shocked quartz from both Rock Elm and the Upheaval Dome. Consequently, other impact sites exhibiting minimal shock features might be explained.     

利用卫星图像分析南京信息工程大学校园变化特征

本文主要目的是利用卫星图像资料分析南京信息工程大学（Nanjing University of Information Science and Technology,NUIST）建校之初至今校园的变化特征.共分析了1964年11月至1970年12月之间的5幅无云的美国侦察卫星图像（1995年解密）,地理配准后图像的位置精度为4.8至7.8 m,图像中的建筑物、道路和水体都清晰可见.通过对比这些黑白的侦察卫星图像与2006—2018年的Google Earth彩色图像,发现现在校园面积远远大于旧校园;旧图像里中苑老操场跑道长度为298 m,2006年Google Earth图像中为406.5 m,操场中心点向东移动了9 m,向南移动了47 m.侦察卫星图像和Google Earth图像都是以统一坐标系做地理位置校正,相关图像见附件.