>Gary Fuis
>Earthquakes: Preparation and Prediction
>Earthquake prediction has been an elusive goal for earth scientists. Given the
>lack of certainty that we will ever be able to predict earthquakes, scientists and
>engineers are concentrating on mitigating the well known effects of earthquakes.  
>Earthquakes do not kill people, buildings do.  We need to design buildings to
>withstand earthquakes, and we need to know the level of earthquake threat that
>exists for each building.
>Dr. Gary Fuis, a geophysicist with the U.S. Geological Survey in Menlo Park,
>will review the hopes and failures of earthquake prediction during the last half
>century and talk about what scientists are now doing to determine the risks for
>buildings.  Earthquake prediction is not dead, however.  Scientists (and the
>public) are ever hopeful that prediction can be done at some level, and there
>are some new leads that are now being pursued.
Dr. Fuis began his talk by explaining that until about 1968, predicting earthquakes was considered to be impossible. Then during the 1970s there was a period when they thought we would get there, but since then the probability that near term (days to weeks) earthquakes would be predicted turned out to be slight. Long term predictions (within a decade or two) are now beginning to be made.

For a while they thought they would be able to predict earthquakes by looking at the speed at which sound moved through the rock, but that turned out to be a dry hole. Another group he knows of studied the way animals react to earthquakes, but that didn't produce results any better than listening to the hunches of people. Other studies have concluded that earthquakes are more likely to happen when tidal stresses are largest, but there are several thousand tides per earthquake, and nobody has learned how to figure out which tide is likely to be the one. Despite all this, a Chinese team did successfully predict one large earthquake, and a New York team predicted a couple of others. However, this has not proven to be repeatable to the point where the predictions have the credibility of weather forecasts.

Dr. Fuis has spent much time studying the Los Angeles basin, where many earthquakes have happened. His team gave the area the seismic equivalent of an ultrasound and a CAT scan, exploding charges all across the basin to map out rock formations and faults from wave speeds and echoes. He showed us many well done charts of the area, illustrating how the Pacific Plate is colliding with the North American plate along the San Andreas fault, raising the Transverse Ranges of southern California and causing many large compressional earthquakes, such as the 1971 San Fernando and 1994 Northridge earthquakes.  These quakes are driven from below by silent slip on a deep slip surface, or "decollement", that approximately divides the brittle upper crust from the ductile lower crust.
He explained that most large earthquakes in California happen on "blind" thrust faults, young compressional faults that have not yet been exposed at the surface and are hidden from view. Scientists have been successful in identifying locations on the earth's surface where earthquake shaking will be amplified, as it was under the Cypress structure and Marina District during the Loma Prieta earthquake.  Amplification occurs on very soft soil that can be natural, such as under the Cypress structure, or man-made, as under the Marina District.  Amplification also occurs atop deep sedimentary basins, such as the Los Angeles basin and, closer to home, the Evergreen and Cupertino basins of San Jose.  Scientists are now also able to produce maps, immediately following an earthquake, showing where the epicenter is and where shaking and damage are likely to  be greatest. He showed us the maps of predicted shaking that were produced after the the Loma  Prieta and Northridge earthquakes.  These maps are useful for emergency responders.  The map for the Loma Prieta earthquake showed the damage greatest in Santa Cruz.

Another area where earthquake research has paid off is in understanding how buildings behave when shaken and how to counteract damage from shaking by improving building designs and standards. Building standards were first upgraded as a result of the 1933 Long Beach, California, earthquake and have since been revised as a result of other earthquakes in the State, because "Earthquakes don't kill people, buildings kill people." He showed us pictures of large buildings with interesting earthquake protections measures built in. One was an office building in Utah with shock absorbers in the walls, and another was a large stone government building in San Francisco that was put on skids so the ground underneath it could move without the building moving as much.

Tian Harter