At that time, only the Morman Temple in Utah was built to withstand a direct 8.0 hit.
Also there's ground soil composition, terrain, and a host of other factors to consider. Where you live in Napa is a 35 mile fault that was discovered just after your encounter. There's not much one can do unless you're willing to quake proof your speakers but it won't look good. Tethers, wires mounted to walls or ceilings, and just how to mount them to the speakers, etc.
When the '71 Sylmar earthquake hit, my mom woke up my dad and said, "Tom, there's an earthquake!" to which my dad replied, "Back on Iwo Jima the sky was falling! Go back to sleep!", which he did. He was pragmatic when it came to the big stuff.
All the best,