Although earthquakes in this part of the country are generally less frequent and not as strong as earthquakes on the West Coast, scientists from the U.S. Geological Survey have concluded that a strong quake is likely to occur in the Charleston, S.C., area within 50 years.

Walter Hays, the chief USGS geophysicist, said, "While it is recognized that the Charleston area remains the most likely area for future large earthquakes, the probability of such events elsewhere along the East Coast also needs to be addressed."

The USGS has been trying to increase local leaders' awareness of the potential dangers of earthquakes and to encourage them to adopt more stringent construction standards.

Since record-keeping started in 1700, there have been more than 3,500 earthquakes east of the Mississippi River. Most were rated at III or IV on the Modified Mercalli Scale, which ranges from I quakes, which can't be felt, to XII quakes, in which all structures are demolished.

Most of the research is done by sophisticated seismographic monitoring equipment in 35 earthquake-susceptible belts across the country. The stations include 514 along the San Andreas fault near the Pacific coast and 31 in Virginia and West Virginia.

Hays, who has studied a major quake that killed 60 people in Charleston in 1886, said the technology for predicting quakes hasn't been able to catch up with nature's ways because of the varied geological formations in the East.

But, Hays said, "Because many tectonic aspects of the Charleston area are similar to other parts of the East Coast, a full understanding of the cause of the large Charleston earthquake is important to much of the eastern United States."

Tectonic plates are slabs of the Earth's crust on or under the ground or the seabed. The plates shift over time, and when they rub together, an earthquake usually occurs.