These periods of changing tectonic activity would be a result of variations in gravity. The variations in gravity are induced -- see also, Spiral Galaxy Accelerations -- by changes in the solar system's velocity as it:
Is gravity going up right now? The importance of knowing this question is obvious. This is potentially one of the most important short-term implications of the Ball-of-Light Particle Model. If we knew, for example, that earthquakes were going to become more severe, and more frequent, governments should legislate stricter codes for making buildings. My guess is the earth is going into a stage of lesser gravity.
I would like to see very sensitive satellites put in space that precisely monitor whether the earth is slightly swelling or contracting. I bet there is a measurable change taking place.