SAN FRANCISCO -- a powerful and damaging earthquake that could cause billions of dollars in damage has a 62 percent chance of striking the San Francisco Bay area within the next 30 years, according to a study released on Tuesday.

The U.S. geological survey forecast said these odds referred to an earthquake of at least magnitude 6.7 or greater -- the same size as the 1994 Northridge earthquake in Los Angeles that caused an estimated $20 billion in damage.

While the study showed the likelihood of a major quake in the region dipping from a 70 percent estimate four years ago, scientists warned the danger of a powerful earthquake remains. "Probabilities of 62 or 70 percent are high numbers," the study said. "Regardless of where earthquakes occur in the bay area, they will produce damaging ground motions over broad areas and substantial distances from the source of the earthquake."

The researchers also said there is a more than 80 percent chance of one or more magnitude 6.0 to 6.6 quakes occurring over the same period that could wreak havoc if any of them strike on faults that run near heavily populated areas.

These smaller temblors might be especially devastating depending on where and when they strike, said the researchers, who gathered data from a variety of public and private sources to calculate new earthquake probability and damage estimates.

The last big quake to hit the region was the magnitude 6.9 loma prieta temblor in 1989 that caused billions of dollars in damage, caused part of the bay bridge to collapse and killed 63 people.

"In the bay area loss of life is predicted to be highest if an earthquake occurs in the early afternoon when people are working in commercial buildings with varying susceptibility to quakes," the researchers said.

The point of the study, the researchers added, was to spur better understanding of the risks posed by earthquakes and give public safety agencies more information to prepare.

The region is no stranger to quakes. San Francisco last week commemorated the giant magnitude 7.9 temblor in 1906, which killed at least 3,000 people, destroyed almost 30,000 buildings and remains one of the worst natural disasters ever to strike a U.S. city.

A newer worry for the researchers is a growing population along major fault lines. The scientists noted much of the expansion is occurring in places of significant seismic hazard in the eastern and northern parts of the area-- something they said they did not fully appreciate before the study.

"The cumulative 30-year probability of an earthquake of magnitude 6.7 or greater occurring somewhere within these rapidly growing northern and eastern areas is alone nearly 50 percent," the researchers said.