Displacement field visualization of particle beds after slow impacts using diffusing wave spectroscopy.

For low-velocity impacts into granular materials, most of the impact energy is absorbed by the soil and not transferred into the ejected material. That raises the question of how large the volume of material is that is actually affected by the impact, that is, by subsurface material displacement or compaction. Here we use diffusing wave spectroscopy to detect the changes in local soil packing structure before, during, and after an impact has occurred. We clearly identify a (half)-spherical volume where particles are rearranged, with a radius substantially larger than the diameter of the impact crater. We also show that the size of the rearrangement zone follows similar scaling laws as the crater size.