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Hayward Fault Tours Available Online: EAST BAY: Geological Survey Combines Research With Google Earth Technology to Educate Viewers

Posted on: Friday, 10 March 2006, 09:00 CST

By Betsy Mason, Contra Costa Times, Walnut Creek, Calif.

Mar. 10--How close is your house to the fault geologists have deemed most likely to unleash a large Bay Area earthquake in the coming decades? Now you can answer this question to within a few meters on your own computer using a new virtual flyover of the Hayward fault.

The U.S. Geological Survey has combined its most updated fault map with Google's three-dimensional satellite imagery tool, called Google Earth, to create a simulated helicopter tour of the fault. And anybody with a computer and Internet access can be the pilot.

Flyovers of the other major Bay Area faults, including the San Andreas fault, are in the works; but the USGS decided to begin with the Hayward fault because it is the most likely to host the next big Bay Area quake.

"The Hayward fault is locked and loaded. It is ready to fire at any time," Tom Brocher of the USGS said Thursday.

The USGS has estimated roughly a one in four chance that a magnitude 6.7 or greater earthquake will occur before 2032 somewhere along the Hayward and Rogers Creek faults between Santa Rosa and San Jose. This is the highest probability for any fault in the Bay Area.

In addition to being ready to rupture, the Hayward fault runs under some highly populated terrain. "It is the most urbanized fault in the Bay Area and perhaps the entire country," Brocher said.

The Hayward fault runs along the East Bay hills from San Pablo Bay south to Fremont, crossing under four highways, more than 500 local roads, BART and UC Berkeley. In fact, Memorial Stadium straddles the fault.

Instructions for downloading Google Earth and the Hayward fault map can be found on the USGS Web site at http://quake.wr.usgs.gov/research/geology/hf_map/. Both are free and take just minutes to download and install before you can follow the fault in your virtual helicopter.

In addition to being able to zoom in on neighborhood streets and individual houses, users can click on camera symbols along the fault trace that link to close-up photos of the fault on the ground.

Many of the photos are of streets and buildings that have been cracked and deformed by movement along the fault. Movement that is very slow and doesn't cause earthquakes is known as creep.

"Creep is good," Brocher said. "If all your energy was dissipated by creeping, you wouldn't have earthquakes."

The creep may damage roads and houses, but it also helps relieve stress caused by the land to the east of the fault moving northward relative to the land west of the fault. However, fault parts are locked and don't creep much, which stores up strain that will eventually be released as an earthquake.

USGS geologist Jim Lienkaemper has been hunting for traces of past earthquakes by digging trenches across the Hayward fault.

He has found evidence of 11 large quakes over the past 1,700 years. He estimates the average time between the big earthquakes on the Hayward fault is 151 years, give or take 25 years.

The last big earthquake on the Hayward fault struck 137 years ago in 1868, which means it could be ready for another one any day now.

"The earth is ready for an earthquake," Lienkaemper said. "And because the earth is ready, we should be too."

The 1868 quake moved the fault as much as six feet in some areas, and geologists have estimated it was a magnitude 7. It killed five people, injured 30 and did extensive damage in San Jose and San Francisco and the communities in between. The 1868 quake was known as the "Great San Francisco Earthquake" until 1906, when it was outdone by the magnitude 7.8 quake that devastated the city.

Reach Betsy Mason at bmason@cctimes.com or 925-847-2158.

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Copyright (c) 2006, Contra Costa Times, Walnut Creek, Calif.

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Source: Contra Costa Times (Walnut Creek, Calif.)

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