Hi Mary Jane. You're correct, but it's purely speculation that the second 4.0Ml may have been a far-field after shock from the Mariana quake. As a rule most far-field aftershocks occur with quakes above 7.0. In all probability this whole series of quakes started with the first the quake in this swarm.

There are times I wish I were a microbe so I could go down into the fault and see what's going on. Then again I might see more then I would care to see and it would scare the heck out of me. Take Care…Don in creepy town