I saw the 8.4 had occured this morning on-line and then had to go to the end of the SCEC meeting and then travel back to the heartland...back to my new home for the first time since Aug 1 (home is where the heartland is?). I would have suggested that the aftershocks to the 8.4 suggested that it rupture northwest: the focal mechanism is low angle thrust for the NE-dipping plane so a subduction quake...the large aftershocks only went to 3 something south...the March 2005 M8.7 only went south about as far as the equator...or a little north...so that left a big area between the equator and 3 deg south that would be stressed from both sides. Looks like the M7.8 occured there....there is still a big chunk of subduction zone that probably has not broken yet...given the pattern, it would be unsurprising of it failed...there is room for another M8 or so. Might failt any time...or in a couple years...or not for decades. My unscientific opinion is that it will go in the next days or weeks. I suppose I should check the IRIS page to see what is known, but it is 3:30 AM in the heartland. A M4 at Coalinga, and I have to check nhc.noaa.gov to see the hurricane that blew up in 12 hours from just a disturbance this AM....and something in the tropical atlantic...
Chris