While many easterners look upon California as the home of tremors, slip-sliding faults and earthquakes, seismologists are warning again that the East Coast should prepare itself for a Big One.

Based on an analysis of seismic activity since 1727, two geologists report that there is a 40 to 60 percent chance that the eastern or central United States will experience a major devastating earthquake before the year 2020. In other words, the likelihood of a catastrophic temblor east of the Rocky Mountains is about two-thirds the likelihood that one will occur in California.

In California, the San Andreas fault can be viewed at the surface, making earthquake study and prediction easier. But the eastern United States is also laced with faults, although they are smaller, scattered and buried miles below the surface. While quakes do not occur as frequently in the East -- the last big one was 95 years ago -- they definitely occur. Since 1727, there have been at least seven major earthquakes to rival the Loma Prieta temblor last year.

"We know frequency in the East is less, but that doesn't mean we can forget," said G.A. Bollinger of Virginia Polytechnic Institute, whose report with S.P. Nishenko of the U.S. Geological Survey appeared in last week's edition of Science. "We're due for a major one."