This week was insanely busy for me as I worked on a grant proposal with my CosmoQuest Moon Mappers colleagues. For the proposal, we are looking at very high resolution images from the NASA Lunar Reconnaissance Orbiter Narrow Angle Camera (LROC NAC). What always strikes me as so interesting is the strange kinds of surfaces we see on the Moon at these very high resolutions.
Each impact into the lunar surface creates a mini-moonquake. Calculations from the 1970's (by scientists Pete Schultz and Don Gault) show that each impact-induced moonquake shakes the surrounding regolith to a distance that is several times farther than the resulting crater. Looking at the number of craters that are visible on the lunar surface, it is clear that there's a whole lot of shaking going on!
Over time, this shaking works to modify craters; toppling their rims, filling in their centres, and eventually obliterating the craters completely. The various stages of this process can be clearly seen in high resolution images of the Moon.
Also, because moonquakes affect regolith more than solid rock, this kind of process will be more prevalent in areas where the regolith is thicker. This is usually found in older areas, since they have had more time to build up a thick layer of rubble from lots of different impacts. So, when I see this kind of "taffy-like" texture, I know I am looking at highly degraded craters in an old, thick regolith layer.
Explore this taffy-like texture for yourself at the ACT-REACT QuickMap online LROC image atlas tool. (A simple guide for using the ACT-REACT QuickMap can be found here).
Schultz and Gault, Seismically induced modification of lunar surface features, Proceedings of the 6th Lunar Science Conference, 2845-2862, 1975.