Almost like an explosion.
Except for all the aftershocks over several hours. I would negate any idea of an explosion that was man made. However, magma is definitely under the ground there as evidenced by all the hot springs in the region. A sudden movement of magma perhaps?
That is if those are true aftershocks rather than magma movement a/o tremors that were induced by a rather large possibly artificial initial event that took place in already seismically active area. There doesn't seem to be the characteristic P & S wave tracings of a common EQ. Its just one big bang that started it all.