America's 'most dangerous fault'

By Jonathan Amos
Science reporter, BBC News

It's a big white building on Mission Boulevard. You can't miss it; the Art Deco style is really striking. The grass is trimmed and it all looks perfectly inviting, except this is a lock-out.

The first Hayward City Hall in California has long been off-limits to occupants because its foundations sit right atop an earthquake fault and it's gradually splitting in two.

"Look up at the stairwell," says geologist Russ Graymer, as we peer through a window.

"There are huge cracks, several centimetres broad and many metres long - basically showing the evidence that this building is being torn in half."

The Hayward Fault is one of a network of cracks in the Earth's surface running through the San Francisco Bay Area. The San Andreas Fault is probably the best known, but right now the Hayward is the one everyone's talking about.