thank you so much for such a great explanation!
he has just moved there. would you recommend I ask to be on the ping list for this sort of thing?
I think plate tectonics, volcanoes and geology in general is most interesting, so yes but not out of great concern for your son. Unfortunately, earthquakes can only be generally predicted within an area. A "based on history and geology, you can expect so and so" sort of a thing. The San Francisco area is far better prepared for a bad earthquake than most of the world. Up here in the Pacific Northwest, we are far less prepared but we will eventually have a large destructive quake.
It hasn't cost me any sleep.