Hi All. While doing some research for our next “fault of month” segment I came across this report. The report was compiled by a group of scientists known as a "working group" or "WG99," comprised of more than 70 geologists, seismologists, geophysicists and statisticians. The group is chaired by Dr. David Schwartz, a USGS geologist who heads that agency's San Francisco Bay Area Earthquake Hazards Project.

Schwartz said an important difference between the new probabilities figures and previous earthquake estimates is that the earthquake hazard is spread broadly across the entire Bay region, from the Pacific coast to the Sacramento Delta, not just restricted to those areas closest to the Bay.

"Since much of this broad region is becoming heavily urbanized and many of these faults run right through urban areas, future earthquakes have the potential to cause much more damage than the 1989 Loma Prieta earthquake," Schwartz said. "For example, there is a 30 percent chance of a damaging earthquake on one of the four newly characterized faults along and east of the rapidly growing I-680 corridor."

Coastal areas from Half Moon Bay to Monterrey are also included in the new probabilities study, with a 25 percent chance of one or more earthquakes centered on the nearby San Andreas or San Gregorio faults. "These areas are also experiencing rapid growth," said Schwartz, "and thus increasing the odds for damage from earthquakes."

While the new study concludes that there is a 70 percent chance (plus or minus 10 percent) for at least one large earthquake across the region in the next 30 years, it also lists the odds for earthquakes on individual faults in the San Francisco Bay area, with those odds having an uncertainty factor of 5-10 percent. Those faults are:

The Hayward-Rodgers Creek fault that runs from Fremont to Santa Rosa, with a 32 percent probability of a 6.7 or larger earthquake, has the highest odds for any Bay area fault.

A 21 percent probability of a 6.7 or larger earthquake occurring on the San Andreas fault, from San Jose to north of San Francisco.

An 18 percent probability of a 6.7 or larger earthquake occurring on the Calaveras fault, which runs from Gilroy on the south to Mount Diablo.

A 10 percent probability of a 6.7 or larger earthquake occurring on the San Gregorio fault, which runs offshore, from Monterey on the south to the Golden Gate.

A 6 percent probability of a 6.7 or larger earthquake occurring on the Greenville fault, which runs through the East Bay hills from south of Livermore to east of Mt. Diablo, and also a six percent probability for the Concord-Green Valley fault which runs northward from Walnut Creek, across Suisun Bay to an area east of Napa.

A 4 percent probability of a 6.7 or larger earthquake occurring on the Mt. Diablo thrust fault. This "blind thrust" fault under the landmark East Bay mountain is similar to the fault that caused the 1994 Northridge earthquake.

Here is a list of past quakes in the Bay Area. You may want to compare the list of quakes before the 1906 quake to the current list of quakes after 1906.

Pre 1906 quakes
1836 6.75 Hayward
1838 7.00 San Andreas
1865 6.50 San Andreas
1868 7.00 Hayward
1892 6.50 Possible Great Valley fault
1898 6.50 Fault unknown
1906 8.25 San Andreas

Post 1906 quakes
1911 6.50 Calaveras
1979 5.70 Calaveras
1980 5.80 Calaveras
1984 6.10 Calaveras
1989 7.10 San Andreas
1998 5.40 San Andreas, not sure if you would want to count this as Bay Area as it occurred in the Hollister area
2001 5.20 Fault unknown, but may have been West Napa fault

As you can see from 1906 to 1979 there was a quiet period. Starting in 1979 with the 5.70 near Morgan Hill the quakes have been progressively getting larger with a moderate quake or two thrown in here and there.

USGS says there is the potential for a major quake in the Bay Area in the next 30 years. There is one little problem with this. They have been saying this for at least the last 20 years, or more.

It seems to me we are running out of time. For all we know the next major quake could be on 12/12/2001. Take Care…Don in creepy town