An item Twitter is pushing is the study on San Andreas fault quakes. The Twitter splash language:

New study suggests the chance of a big San Andreas quake has tripled
Out of the many faults in California, the San Andreas is singularly poised to be the one that unleashes a megaquake in our lifetime.

Very misleading.

San Andreas fault quakes are due to slippage along the fault. While these can be quite large, they are not “megaquakes”.

The really big quakes, like the Honshu quake that cause such damage in Japan a few years ago, are due to plate subduction. There is a risk of this in the US: in the Pacific northwest and in Alaska.

But not in California.

So yes, a large earthquake in California, say an 8.0, will cause a lot of damage. But top of the scale quakes, close to 9.0, only happen in the subduction zones.