very active in the not so distant future.
There certainly are many scenarios that can be imagined as to why it has been so quiet in that area lately.

According to the seismologists it takes a long time for the pressures to build up to the breaking point, if there have been small quakes in the area recently then that activity has released the energy and it will take longer to make a big quake.

Your suspicion seems to be that perhaps there is some black project somewhere in the states where they are experimenting with Tesla technology.

I can not comment on the Tesla technology, because I’m not fully familiar with everything he did.
I have heard that Tesla claimed that he could make a machine that could split the Earth, the device was some type of a very low frequency oscillator that caused a sympathetic vibration in the structure that it was attached to.
I would call such a system a VASARA to reflect the way it works, that is: Vibrational Amplification by Stimulating Resonanting Areas.

Why anyone would want to split the Earth is beyond my comprehension, but if such a machine was made in a very much smaller scale, then perhaps it could be used to build pyramids or move mountains.

My suspicion is that the air density in that area is greater than in the areas where the Earth quakes and volcanoes are very active.
The carbon dioxide and monoxide that pollutes the California atmosphere has a greater density (or weight) than clean air that exists elsewhere and most likely in the areas that have more geological activity.

The basic idea is that the heavier the air is, the more pressure it places on the tectonic plates.
To know how much pressure difference there is because of the heavier gasses ,we would need to know the surface area of the land under consideration and the quantity of the heavier gasses in the area, also it would be good to know the difference in the weight of clean air and the polluted air.

Something for the mathematically idling mind to think about.

If there is more weight on top of the tectonic plate in the California area, then it could be that it is easier for the moving mass underneath to push itself deeper into the interior of the continent, like the Yellowstone National Park area for instance.

Perhaps there is a super volcano forming right now under the Yellowstone National park.

This is naturally a speculation on my part, but without factual numbers that have been obtained from scientific instruments, all explanations countering this possibility will also be simple speculation, regardless of how large or small the speculated numbers may be.