The 1989 Loma Prieta earthquake caused billions of dollars in damage and claimed more than sixty lives. But was it "the big one"? Take a look at the comparison between the images below for the 1989 Loma Prieta and the 1906 San Francisco earthquakes, and decide for yourself.
The colors on the map indicate Modified Mercalli Shaking Intensity (MMI) at each point, which is usually (but not always) written as Roman numerals to avoid confusion with earthquake magnitudes. The "Instrumental Intensity" indicated in the Bay Area images is determined by a slightly different technique, but is designed to be virtually identical to the traditional Modified Mercalli scale.