Just a guess........
With all the quakes last week in South America in Chile (7.7, 6.8, 6.2) which then moved northward and gave us a 6.7 in Equador and Peru and a 6.3 in Equador and Columbia.
The whole southern hemisphere seems active, including the six pointers in the Antarctic earlier this month. And Indonesia, and deep quakes there and now the volcano blowing.
Maybe the stresses will be relieved, but California sems long overdue.
It's the only ridge/plate that hasn't seen any release of tectonic pressure in ages.
It's just a guess, not a prediction.
http://www.iris.edu/seismon/