John,
Warren Buffett is reported as saying that 'diversification' was invented by sales people on Wall Street so they can sell you stuff. He prefer to focus on opportunities where he can create alpha (apply what he knows to gain an advantage) rather than trying to reduce his upside to the market averages.
There is a lot of friction to selling a property you already own (taxes, transaction fees, an asset you already know vs the unknown).
Given your age, you have a 'long runway' before you need to live on your savings. As SF is bounded by water on 3 sides and hills on the fourth, values there will be fine long term.
Grow your knowledge, consider other investments and keep the rental occupied. I would not be in a rush to exit the property. And I would not be in a rush to drain all the equity from it. The logic there is you can lose the property to the bank if you over leverage.
I lived in SF for a while and was there for the 7.1 earthquake. Look into the insurance options rather than sell the property. You do not need perfect coverage to largely protect the asset. There were fine choices for insurance in the past. I expect there will be some now. Note: Insurance companies will close access to new policies for 90 days after an earthquake. Most people fail to think about insurance until after a big one. Get it sorted now and rest easier.
Two other things. Earthquakes are a big risk yet they are not that often. Other risks exists. Review your coverage so you are well protected. A lawsuit might be a bigger risk than an earthquake. Second, you can do things to improve the resiliency of a building to earthquakes. Bolting the house to the foundation, bracing if there is a garage below the house, etc. Nothing too complex. Lots of info out there.