Well, the Marianas swarm did not lead to something large, but there was a foreshock to a foreshock to the Andeanoff/Aleutian M6.6. There was a 4.0 two hours 21 minutes before the M6.4 which was strike-slip. It was rather far from the epicenter of the M6.4... 0.8 deg longitude. But, this is within the area of aftershocks. The next day there was a M6.6 strike-slip. These quakes are north of the historic thrust epicenters.

I know that as you go west on that subduction zone the motion gets more oblique. It is common for oblique convergence across a subduction zone to be partitioned between near pure thrust and strike-slip: Sumatra comes to mind. Must be what this is about. I wonder if they even knew this strike-slip fault(s) existed.

John, compare to Cascadia? I think convergence is Oblique there. Is Seattle fault strike-slip?
Chris

• historic Andreanoff