The Pacific Geosciences Center on Pat Bay years ago started using alpha and gamma spectroscopy to look at changes in the Pacific Plate and in particular the northern end of the San Andreas fault which extends off the coast of the Island. They showed that a part of the plate off the fault line was stuck. Whereas the plate should be subducting, the tip of it was stuck with the rest of the plate still heading under the Continental Plate. Big stresses being built up there! Every smaller quake is a godsend relieving some of that stress.
But when the BIG ONE comes and rest assured it is coming, as in a 100% chance in the next 50 years, it will be a doozy like 9+. My new house is at about 700 ft above sea level and if it's still standing after that one hits I figure I can watch the tsunami go by from my front yard.