Contrary to popular belief, earthquakes are not rare events, says Father James A. Rigert, CSC, associate professor of civil engineering and geological sciences at Notre Dame and an expert on quakes.
According to Rigert, who holds a Ph.D. in geophysics from Texas A&M University and is a member of the American Geophysical Union, earthquakes of magnitude 6 or greater on the Richter Scale (capable of causing severe damage) occur every few days. Fortunately, the majority are not near heavily populated areas and cause little destruction.
Other misconceptions about quakes Rigert would like to see crumble:
-- The greatest destruction from an earthquake occurs at the surface directly above the center of the quake.
Not necessarily. Workers in a deep mine near a fault may actually feel much less shaking than someone at the surface, he says. That's because a quake can quadruple in perceived strength if energy waves reflected back from rock get in synch with waves emanating from the fault. In the 1989 Loma Prieta earthquake, centered near Santa Cruz, California, the greatest damage occurred to structures built on landfills in the San Francisco Bay area, more than 60 miles away.
-- The first, most violent shakes from an earthquake cause the greatest damage.
The first waves are often the strongest, Rigert says, but most damage occurs later, when structures have been weakened. A much weaker aftershock can cause the collapse of a severely damaged structure.
-- The atomic bombs dropped in World War II released much more energy than most large earthquakes.
Actually, an earthquake of moderate strength releases 100 times the energy of the Hiroshima bomb, according to Rigert.
-- Animals can feel earthquakes coming before humans can.
This may be true for animals with different types of sensory methods than we have, Rigert acknowledges. Some, such as homing pigeons, can detect changes in the Earth's magnetic or electrical fields, which sometimes precede quakes. But when it comes to sensing quakes, we don't do too badly: Many people can detect vibrations equal to a thousandth the strength of gravity.
-- Scientists will soon be able to predict earthquakes.
Twenty-five years ago, several geophysicists suggested that we need only look for a small number of precursory phenomena to predict earthquakes, Rigert says. Since then, a few earthquakes have been predicted, but most have not.
By studying plate movements and stresses near the surface, as well as records of past earthquakes, he says, we now have some pretty good ideas as to where earthquakes will occur. But there is no magic formula yet to pinpoint the location -- or the time.