We buried the Hayward fault last week. It's not going to rest in peace, though. Like a demon with a day planner, it'll reappear on a regular schedule to haunt Bay Area Realtors and their clients. We exhumed it in April for the "Great 1906 San Francisco Earthquake Centennial." Since then, some 20,000 viewers filed past to pay their respects and listen to the eulogy, 15 feet below the surface in Fremont's Central Park.

As far back as geologists have peered into its prehistoric past, this fault has ruptured the ground in a huge quake every century and a half, on average. We're not guessing here. It's as close to clockwork as disasters get. In dozens of backhoe trenches dug across the fault, hard science from broken layers of ancient sand and soil proves its regularity.

Eleven times in the last 16 centuries the fault has lost its grip. Each time, the land on one side suddenly slips past the other, by 3 to 6 feet, slicing a 20 to 30 mile gash through the East Bay, now a sprawling urban corridor. The result? A dozen seconds of interminable terror across the region. Timber-splitting violence. An earthquake of magnitude 7, or near enough. This demon last visited around Halloween in 1868, on October 21st at 7:53 a.m. to be precise.

Let's see. Every 150 years. Last one in 1868. That puts the next Hayward fault earthquake out...well, probably within the 30-year mortgage on that post-war rental I just sold, a half-mile from the fault.

Shouldn't somebody warn the buyer about this? ("Seller discloses that experts know a violent earthquake will thrash parcel within foreseeable future, likely sinking the property value if old house isn't strengthened to modern seismic codes.") California is one of more than 30 states with a "Seller Disclosure" law. I checked a box for each statutory question. I signed the form. My agent delivered it to the buyer before the close of escrow. We satisfied our disclosure duty. Didn't we?

I'm a geologist. Hazard disclosure's my bag. This is my blog.

Coming up, I'll say more about the fault we buried here, as well as other seismic zones that threaten both U.S. coasts and the region in between. Landslides, tsunamis, floods, fires, sinkholes, subsidence, environmental contamination, these and other property hazards will also get their due. And we'll chat about liability disasters just waiting to happen in that gray zone -- the one between what we "shall" disclose, and what we probably should've but didn't.

(Oh, and let's be fair. This isn't just Fremont's fault, or Hayward's. It cuts through pricey neighborhoods in Oakland, Berkeley, and every other city along the eastern Bay margin. Nor is it the biggest fault. The San Andreas, which caused the 1906 and 1989 disasters, bisects the San Francisco Peninsula and extends through coastal California for a total of 800 miles. These faults are just two of hundreds nationwide capable of shaking profits out of the U.S. real estate industry. And future earthquake shaking is just one of many hazards that may affect the judgment or decision of a buyer or the price or terms offered, "material facts" as the lawyers call them. You disclosed everything. Right?...)

NOTE: The collective "we" in the first paragraph is the "1906 Earthquake Centennial Alliance": the U.S. Geological Survey, American Red Cross, City of Fremont, the Math/Science Nucleus, and a host of other agencies and corporations united in earthquake hazard awareness and disaster preparedness. They invited me to be a Lead Docent for "The Hayward Fault Exposed!" in Fremont -- the only public exhibit inside of an active fault, outside of Japan! (It remained open through the end of October, thanks in part to generous support from the real estate community by way of Summerhill Homes and Robeson Homes. We're now looking for funds to bring it back for good.)

Here's more about the fault exhibit.

Here are zoomable air photos of the faulted neighborhoods.

...and a cool GoogleEarth rooftop flight along the fault.