The weight ring does help transform the energy to vertical motion but the intent is to have as much of this energy in the form of vertical motion reach all the way to the end of the core tube so it can liquefy the sediment immediately adjacent to the inside and outside of the tube. This liquefaction is what allows the tube to slide seemingly effortless into the sediment. What happens it with even a fairly small amount of water in the sediment, the vibration moves the particles just enough that the water can act as a lubricant between the particles of sediment. This lubrication is what makes the sediment act as a liquid and move just enough so the tube can slide into the bottom and the sediment can slide into the core tube. The liquefaction inside the tube is why the VibeCore can get so much more sediment into the tube than if you just forced the tube into the bottom. Just forcing the tube into the bottom and you are lucky to get 60% of what you penetrate into the bottom actually inside the tube. With the Vibecore we the on average better than 90% in the tube of what the tube goes into.
Now as to how far this disturbed layer goes in and out radially from the tube wall. My research so far shows it is 3 to 4 times the grain size of the sediment. This will vary some as the water content is increased or decreased but this seems to be a good estimate. This means that with 50 um grain size, which is large for silt and much larger than clay, the disturbed layer is about 1.5 mm to 2 mm thick. I will include a picture taken from a clear VibeCore tube that was driven into sediment. You can see a small uplift of the sediment right at the wall of the tube and completely undisturbed sediment in the rest of the tube. This was taken from a slight slope on the bottom. The top of this material was easily disturbed. When we shook the tube a little by hand the sediment clouded up the water quickly, but this was not the case during collection because the vibration was at a very high rate and the displacement was small.
If the grain size was larger the disturbed layer would be greater.