Well I can't check myself so going completely of my memory, after WB grabbed BB by the neck he punched or slammed him(?) and were there tremor/explosion like effects that implied quake to me.
There was no punch, WB formed the sphere with the hand that has helding BB's neck. The ground broke after that, but it wasn't the widespread island-sized damage WB usually does. It wasn't that different from the destruction other haki users did after timeskip.
I'm sorry but I just remember that scene as being completely unambiguous.
Search it out (in the manga), please. It's not so unambiguous.
Wait, I just remembered that Croc would use only his hand to turn stuff into sand, so this could be a similar case with BB?
Could be, but in CHapter 441 BB describes his ability and says to Ace that being in contact with his body is enough to rob a DF user of its powers.
Also, in Chapter 441, Whitebeard is able to hit Ace despite not holding him in his hand (BB gives him a backhand punch to the neck).
I remember we being confused back in Marineford when WB seemed to use his abilities despite directly touching BB. We all just assumed BB needed to use his hand, but now, with haki being expanded, I started re-reading Marineford and the sphere effect called my attention.
There's a sound effect used whenever Whitebeard conjures the bubble, maybe someone can check out what it's meant for?