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| Earthquake Predictions |
Hi All. The University of Toledo, Ohio has a fairly good set of guidelines for what constitutes a good earthquake prediction and for the most part is close to the criteria used by many of the countries around the world. First, the rules: an earthquake prediction is not valid (scientifically testable) unless all of the following conditions are met. 1. Time window specified. A window is either open or it is closed. Claiming a hit for an event that occurs close to the window is cheating. 2. Location specified. Knowing when an earthquake is going to strike is useless unless we also know where. Isoseismals from the event that occurs should overlap those that would have been at the 'predicted' epicenter. If you are going to predict an earthquake, the location must be specific enough that I can set up my single portable seismograph and record some strong ground motions. 3. Size. I'll be generous - within 0.5 of a magnitude unit. Claiming a 'hit' when a 4.7 occurs after someone predicts a 6.5 is like claiming that a 1 oz sirloin really weighs nearly 4 pounds. 4. Statement on significance. How does the prediction compare with the historic record? Stating that there is 1 chance in 4 that a magnitude 6.0 or greater will strike southern California during 1999 is not a significant prediction because this is nearly the historic frequency for the region. The recent prediction by an astronomer in Japan for a major quake to strike the Tokyo area was ignored by the population in general. The reason being was that the theory had never been tested. He had no track record of how many predictions made and of those how many were right and how many were wrong. It had never been used by others, or put to the test by others. After the Loma Prieta earthquake, the panel of experts was again convened to determine whether they should change the estimate of the probabilities of future large earthquakes in the San Francisco Bay Area because of the earthquake and other new data. Their report, issued in July 1990, was endorsed by the National Earthquake Prediction Evaluation Council and the California Earthquake Prediction Evaluation Council. The panel identified four fault segments in the Bay Area along which they now believe large earthquakes are most likely: the peninsula segment of the San Andreas fault between Los Gatos and Hillsborough; the Hayward fault between Fremont and San Leandro; the Hayward fault between San Leandro and San Pablo Bay; and the Rodgers Creek fault between San Pablo Bay and Santa Rosa. They estimated that the probability is about 25 percent for a large earthquake on each one of these fault segments within 30 years. More importantly, when the probabilities of earthquakes on all of these segments are combined mathematically, there is a 67 percent chance for at least one earthquake of magnitude 7 or larger in the San Francisco Bay Area between 1990 and 2020. Such an earthquake could strike at any time, including today. The panel also concluded that: There could be more than one earthquake of magnitude 7 or larger in this 30-year period. Earthquakes of magnitude 7 are considered possible, but not as likely, on other Bay Area faults such as the Calaveras, Concord, and San Gregorio. A repeat of the magnitude 8.3 San Francisco earthquake of 1906, which broke several segments of the San Andreas fault from south of San Jose to Cape Mendocino (a distance of more than 270 miles), is not likely during the next few decades. Numerous earthquakes with magnitudes of about 6 are also likely; these smaller earthquakes could cause some damage, especially near their epicenters. As one can see there are a lot of probabilities, but nothing you can take to the bank. Something that I have gotten real good at in the last couple of years or so is to lean back, put my heels and wait. That’s what I’m doing right now. Take Care…Don in creepy town Reference: http://quake.wr.usgs.gov/prepare/future/likely/ |
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