Is it likely that there will be another to wreak the damage at San Francisco in 1906? Are building methods now stable enough to prevent most of the damage?
California has very strict building codes designed to prevent damage from earthquakes. That said, there are many old structures that are not "up to code". There could be a big earthquake here at any moment. They've been saying "the big one is coming" for years now; no one really knows when anything is going to happen. You can't live your life being afraid of it, but you make sure infrastructure is built solidly.
Considering earthquakes, mud slides, brush fires, forest fires and tsunamis, it is unreasonable to expect a house in California to outlast its mortgage.
I've no idea about their civil engineering, but I've often visited San Francisco.....the roads are winding and walking up the roads is in itself an exercise, this is how the buildings look, stacked against each other.