Don't forget that buildings in California today are built to far higher standards (though not necessarily perfect) than the structures present in 1906 San Francisco, which included many unreinforced masonry buildings.

For what area of destruction are you deriving your casualty figures? You will get maximum destruction at or near the epicenter, but damage will tail off in surrounding areas, subject of course to local factors, such as geology and soils.

I would be very surprised if authorities have not already gamed this scenario, perhaps at an even higher level of sophistication that we are capable of, incredible as that might seem.

Of course, I am no stranger to surprises......