John...you link to the total seismicity for tens of years....of course a patten that appears briefly for a week a month or so ahead of time will not show up. Look at the map on Don's second post on this thread...I guess he took quakes provided by Petra. Or, ask Don to make this graphic with all quakes, or all quakes >3 or 4, for a 1 week interval of time when Petra posted this. When Petra first noticed this, it was a pretty clear ring. What I have not done is checked the epicenter and rupture area against the ring...but am assuming the "x" on Don's map is the epicenter.
Chris