I'll second Mahagogo's advice. Do you have an emergency plan at home (for earthquakes)? If so, if you think it might help, share the plan with your ds (if you don't have a plan, you could come up with one - have your ds help you gather an emergency kit, talk about how you can use the water in your water heater if water supply is temporarily disrupted, stock up on some non-perishable-type food supplies that will last just in case, find a spot to store flashlights etc.
Re tsunamis, unless you are in a very low-lying area within a few miles of the coast, I would reassure your ds that the likelihood of a tsunami is very very VERY low (both due to the set of circumstances required to generate a tsunami and your geographic location if you are on high ground or a distance away from the coast). You can also let him know what your tsunami plan is (drive away) - and let him know that there is a national tsunami warning system in place, so you'll most likely have advance warning (unlike the devastating tsunami in Thailand a few years ago where there was no warning system in place). You can also let him know that historically, we're not aware of any devastating tsunamis hitting California/Oregon/Washington.
I'd also let your ds know that scientists can't accurately predict earthquakes. We keep trying, and our knowledge keeps growing so that our predictions gain reliability, but the reality is - we don't know when or if the "big one" will hit LA or SF or wherever. You can let your ds know that the small earthquakes you feel are the earth releasing pressure along stressed fault lines which means in some cases a fault system is less likely to implode into a large earthquake (pressure released gradually over time instead of building up and exploding all at once).
Gotta run - I probably have more thoughts! Will be back later if I think of anything else
polarbear
