You can't "turn off" that bunker, it has multiple diesel generators and lots of fuel reserves. It also has clean water reserves and air filtering capabilities, so you can't gas the people inside.
Physically cutting its uplink lines would be IMHO the most efficient way to neutralize that datacenter.
Or just getting all their peering exchanges to null route packets in and out. Advantage being that it's cheaper, more effective and less lawsuit prone.
There is, of course, the other end of the cable connecting to the rest of the world... no need to actually cut the cable. You could do it with software alone really.