Is this a core explosion from a mech I am assuming?
Yes.
If so which mech and will they all be the same or will they be Mech size specific?
It really doesn't matter which Mech exploded there as for now, all core explosions look the same. Not that I could remember anyways.
I also noticed the texture on the ground appears to have been changed by the blast is that just looking down through the blast effect
Yes.
or is there an observable change in the ground texture after an explosion? I thought I read somewhere that you were doing a deformable terrain.
If so, this might have been an earlier post. While we'd certainy like to have something like this, I know that this is not at all being worked on or even discussed about. There are a lot more urgent problems at hand than this, so don't expect to see this anytime soon, definitely not in the beta or in 1.0.