See the link; interesting summary. The mainshock was only slightly oblique: it was mostly thrust (not stated in summary: that is what the focal mechanism shows). The plate boundary is mostly right lateral but is somewhat oblique. The summary says quake could be on subduction zone, or it could be above subduction zone in crust. It does not say this, but subduction zone might be mostly ancient from when the Farallon plate was subducting also beneath all of California before the San Andreas. I don't know how long ago the Queen Charlotte right-lateral plate boundary formed (this would be known) and the main subduction stopped.

The largest aftershock is 6.2 and is normal slip (stretching). Given its location within the main aftershock zone of a thrust, a normal quake this large seems unusual.

Chris

• summary