If an earthquake like the one that devastated San Francisco in 1906 struck today, the toll would be staggering: tens of thousands of buildings damaged and hundreds of people dead, according to a new study.

The report, released Monday, calculated that a repeat of that 7.9-magnitude temblor would cause 1,800 to 3,400 deaths, damage more than 90,000 buildings, displace as many as 250,000 households and result in $150 billion in damage.

"We already witnessed the effect of the displacement of hundreds of thousands of people from last year's hurricanes," said Bill Ellsworth, a geophysicist with the U.S. Geological Survey in Menlo Park. "It would have huge social and economic effects on the entire country."

The study, "When the Big One Strikes Again," was released the day before the 100th anniversary of the 1906 San Francisco earthquake. It was prepared for what is being billed as the biggest earthquake conference ever.

The three-day 100th Anniversary Earthquake Conference, starting Tuesday in San Francisco, was expected to draw more than 2,500 scientists, engineers, government officials and emergency response professionals. Gov. Arnold Schwarzenegger, Sen. Dianne Feinstein and other politicians were scheduled to speak.

The conference is one of a long list of events being held around the Bay Area to commemorate the 1906 quake and promote earthquake preparedness. On Tuesday, survivors will lay wreaths at Lotta's Fountain in downtown San Francisco to mark the moment the temblor struck shortly after 5 a.m. 100 years ago.

The latest report, prepared by the engineering firm Charles Kircher & Associates in Mountain View, was commissioned by the earthquake conference's organizers: the Earthquake Engineering Research Institute, Seismological Society of America and California Governor's Office of Emergency Services.

Using computer models, the study estimated how a 1906-size earthquake would impact today's nine-county San Francisco Bay area, where the population has mushroomed to more than 7 million people.

The report found that a 7.9-magnitude quake would cause up to $34 billion in building-related losses in San Francisco, $28 billion in Santa Clara County, $26 billion in San Mateo County and $15 billion in Alameda County.

Most of the deaths would result from the collapse of old buildings made with unreinforced masonry or concrete, or structures not tied to their foundations, according to the report. Structures built after the 1970s are generally considered safe.

"We need to recognize the buildings that are the most dangerous and would cause the most loss of life," said conference chairman Chris Poland, chief executive officer at Degenkolb Engineers in San Francisco. "They need to be identified, then strengthened or replaced."

Estimates of the death toll from the 1906 quake and fire range from 478 to 6,000. In addition, 28,000 of San Francisco's 53,000 buildings were destroyed; 225,000 of San Francisco's nearly 400,000 residents were left homeless and estimated property damage was the equivalent of $8.2 billion in today's dollars.

Experts said the Bay Area has made a lot of progress strengthening buildings, roads and bridges since the 1989 Loma Prieta quake, but the study's findings indicate the region still has a lot of work to do.

"The Bay Area is probably better prepared than most urban areas for a natural disaster," Poland said. "But it's not prepared enough."