Hi Petra. As you well know from our contacts with various seismologist around the world the answer more then a couple of years ago to was earthquake prediction a probability was “no way” but now, today the answer is “not yet.”

The mini PBOs in the Bay Area are not the finial answer, but they are just one tool in the hopes of being able to predict the next large quake in the Bay Area. There are still 6 more sites to be put in, but the money for them isn’t there.

To say that the public wouldn’t be warned if a large quake could, or was about to occur isn’t quite true. However I must admit I would hate to be the person who called for an evacuation of the Bay Area and then not have the quake occur. Some how I don’t think there would be a second chance and as such I would have to have a lot data that makes the probability of quake occurring darn good. I would be for telling the people and let them fend for themselves. You would probably get better mileage out of it.

To date there have been 4 earthquake predictions made in California that I’m aware of. One did occur, but not when it was thought that it might. The other never occurred. Quakes are funny that way. They have their own schedule to follow and they aren’t telling anyone in ways that can be understood. Take Care…Don in creepy town

The following is from the USGS web page.

Some large earthquakes are preceded by foreshocks. Knowledge of past earthquake patterns allows scientists to estimate the odds that an earthquake striking today is a foreshock and will soon be followed by a larger mainshock in the same area. These odds depend on the earthquake's magnitude and the seismic history of the fault on which it occurred. When a moderate earthquake hits California, scientists immediately estimate the probability that a damaging mainshock will follow. If the threat is significant, a warning is issued.

This warning process was put into action in June 1988 when a magnitude 5.1 shock--one of the largest in the San Francisco Bay region since the great 1906 earthquake--struck 60 miles south of San Francisco. Alerted by the USGS that there was a 1 in 20 chance of a larger earthquake in the next 5 days, the California OES issued an advisory to warn the public. (The usual daily odds of a large quake in the Bay region are 1 in 15,000.) The warning period passed without further activity. In August 1989, another earthquake hit the same area and a similar advisory was issued. Again nothing happened in the specified warning period. However, 69 days later, the area was rocked by the magnitude 7.1 Loma Prieta earthquake, which killed 63 people and caused $6 billion damage in the San Francisco Bay region.

The town of Parkfield, population 34, was chosen as the site of this innovative experiment because six magnitude 6 earthquakes have struck in its vicinity since 1857. Some of these quakes were preceded by foreshocks and possibly by other precursors. Because the time between a precursor and a mainshock may be short, earthquake warnings must be communicated rapidly. To accomplish this, a plan was developed specifying when and how warnings are to be issued in response to possible precursors to earthquakes in the Parkfield area. This plan was activated in 1992 and again in 1993 by possible foreshocks; state and county officials conducted rapid, well-planned responses.

The lessons learned from the Parkfield experiment have already enabled earth scientists and emergency response officials to build a framework within which they communicate rapidly and effectively. Based on this experience, similar alert plans have been devised for geologic hazards in other areas of the United States. With the development of modern seismic monitoring networks and the knowledge gained from past shocks, earthquake forecasts and warnings are now a reality. Continued effective communication of these forecasts to the public will help reduce loss of life and property in future earthquakes.

Andrew Michael, Paul Reasenberg, Peter H. Stauffer, and James W. Hendley II

COOPERATING ORGANIZATIONS
California Office of Emergency Services
California Division of Mines and Geology

For more information contact:
Earthquake Information Hotline (415) 329-4085
U.S. Geological Survey, MS 977
345 Middlefield Road, Menlo Park, CA 94025
USGS Menlo Park Earthquakes Home Page

U.S. Geological Survey Fact Sheet-242-95, 1995

• USGS Web Page