(CNN) It's 4:18 in the afternoon in Oakland, California. Deep below the city, the Hayward Fault -- one of the most active fault lines in the country -- suddenly slips, setting off a magnitude-7.0 earthquake.

Violent shaking is felt throughout the San Francisco Bay Area, a region packed with more than 7 million people. The shaking is so extreme that solid ground moves like liquid near the San Francisco Bay, while landslides tumble down area hills and mountains. Hundreds are killed, tens of thousands are injured and nearly half a million people are left homeless. Aftershocks plague the region for two years.

The start of another Hollywood disaster flick? No, it's what the US Geological Survey predicts what will happen if a major quake hits along the Hayward Fault. But researchers at the USGS didn't just dream up this nightmare out of thin air. They conducted a scientifically realistic scenario, using computer simulations of the way seismic waves travel, in an effort to spur Bay Area residents to prepare for the "big one" that is long overdue to strike the region.

A matter of when, not if

In the USGS's hypothetical earthquake disaster , about 800 people are killed and 18,000 injured when the tremor hits on the Hayward Fault at Oakland. The fault -- which runs for 52 miles along the east side of the Bay Area through one of the most densely populated stretches of the West Coast -- ruptures along its entire length, unleashing hellish destruction, especially in East Bay cities like Oakland and Berkeley.

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