CUPERTINO, Calif. — The circular building housing Apple’s headquarters in Silicon Valley is so big, it’s nearly a mile in circumference. So it’s hard to fathom that it is not actually attached to the ground.

The spaceship, as the building is often called, is a mammoth example of a technology that reduces earthquake shaking by as much as 80 percent.

While other buildings in Silicon Valley are likely to suffer damage and be nonfunctional for days, if not months, after an earthquake, Apple’s headquarters, which were completed early last year, are designed to be usable immediately after the Big One.

The building is one of a relatively small number in the United States that use so-called base-isolation technology. We explore the system in an article here.