Nicholas Sitar is a professor of civil engineering at UC Berkeley, and he likes to joke that “earthquakes don’t come with due dates.” Yet he and other scientists say it’s only a matter of time — maybe days, more likely a few years — before a major Earth-shaking catastrophe hits the East Bay.

Their words are not scare tactics. The Hayward Fault runs nearly right through the heart of the region, splitting the flatlands from the hills. This 74-mile-long zone has been quiet since 1868, when it generated its last large earthquake. But scientists explained to the Express that the average time frame in which a large tremblor occurs on the Hayward Fault is about 140 years. And that period lapsed in 2008. “Yes, in terms of the statistical average, we are now well past the average period between earthquakes,” is how Sitar put it.

This means that, in layman’s terms, the proverbial Big One is overdue.

The professor is among many scientists who spend their time considering what would happen if a quake similar in size to, or perhaps substantially more powerful than, the 1868 Hayward Fault shaker struck Oakland and the greater region today. Nearly all agree that it would be a terrible disaster.

The shaking of a 7.0 magnitude earthquake would cause tremendous and unprecedented destruction. Thousands of buildings — even dozens of hospitals that are rated by state officials as seismically unstable — could be destroyed. Gas and water lines would break, and fires would leave the region reeling, if not wholly crippled, for days. Looters and thieves almost certainly will take advantage of abandoned homes and busy police and emergency officials.