LOS ANGELES -- The earth moves every day in California, though usually the tremors are imperceptible. Seismologists in Southern California are expecting the Big One to hit within the next 50 years. Lucile Jones not only anticipates that quake, she's impatient for it.

"There are so many questions to be resolved by that big earthquake on the San Andreas," says the 35-year-old seismologist from the U.S. Geological Survey. She sounds almost wistful. "And I'd hate to miss it."

Not far from Jones's home, other fault lines, far less famous than the notorious San Andreas -- although virtually as dangerous -- etch their way across the Los Angeles area. "It was pretty clear you couldn't buy in Pasadena and not be within a few miles of a fault," she says. She can reel off the names of those faults and the years when some of them produced earthquakes you could feel.

She says her curiosity about the big earthquake is founded on acceptance of the inevitable. The ground simply will not lie still forever.

"It's not that I want people to be killed," she says, but given that a major earthquake is inevitable, "I'd rather be there when it happens so that I can find out the answers to some of those questions."

For instance: Exactly where does the San Andreas Fault go through the San Bernardino Mountains? "It disappears in the mountains and we're not really sure what it does through there," she says.

"And we've been saying that we think the Elysian Park fault is an active fault," says Jones. "Well, are we right? That one goes right under the city."

The largest recorded earthquake in the United States was in Alaska in 1964 and measured 9.2 on the Richter scale. But, Jones predicts, "we're not going to have anything that size." What is most likely on the southern San Andreas Fault, she speculates, is a magnitude 8 earthquake -- last year's Loma Prieta was a 7.1 -- focused in the San Bernardino area. What might be more dangerous is an earthquake under a more densely populated part of Los Angeles -- for instance, downtown. "What could the Elysian Park fault do? Could it produce a 7.5 or an 8?" she wonders.

In the past few years, the familiar predictions that as many as 20,000 people would die if an 8-magnitude earthquake -- which is about 10 times as strong as a 7-magnitude -- shook Los Angeles have been challenged by some experts as much too high. They contend that such predictions don't account for today's better-constructed buildings and sophisticated emergency medical services. Jones shares that optimism.

"The emotional reaction to earthquakes is out of proportion to the damage that they do," she says. "I don't know how many people are going to die. But focusing on deaths tends to keep people from doing the preparedness that will help them."

The notion of "predicting" an earthquake is actually misleading. "We can't predict an earthquake in the sense of saying, 'There's going to be an earthquake tomorrow at 3 o'clock.' If somebody says that, they're not doing it on science. But there are situations that are more hazardous than others. And we've started to be able to assess the probability."

For instance, she says, "6 percent of the Southern California earthquakes are followed by something larger within three days ... at the same place -- within 10 kilometers. Therefore if you feel an earthquake you've got a 6 percent chance you're going to feel something bigger in the same place. Qualitatively, if that earthquake happens on the San Andreas or some other fault capable of producing a big earthquake, we're more nervous about it."

The idea is to warn people so they will prepare for the quake beforehand, not flee when it happens. "You wouldn't want to leave the state anyway -- even if we came and said 50 percent chance -- because more people are going to be killed in a traffic jam than in the earthquake."

As the USGS's geophysicist in charge of earthquake hazard assessment for Southern California, Jones analyzes the probability of a quake's occurrence -- the closest that scientists get to predictions.

Her expertise has turned her into a kind of public earthquake analyst. Although the Loma Prieta earthquake occurred in Northern California, beyond her area of responsibility, she was seen frequently on Los Angeles area television in the aftermath -- a youthful, fresh-scrubbed woman in brightly framed glasses calmly discussing the dramatic events. In fact, the writers of "The Great Los Angeles Earthquake," an upcoming television movie, approached her for advice and ended up modeling one of the lead characters after her. Actress Joanna Kerns of the TV comedy "Growing Pains" plays the role, and Jones notes the similarities with a chuckle -- "blond, glasses, studies foreshocks."

She is amused by fictional conceptions of earthquakes, and some years ago she and a group of fellow geophysics graduate students almost got thrown out of a movie theater showing "Superman" because they hooted so loudly when the hero tried to repair the San Andreas Fault.

Jones is a fourth-generation Southern Californian, and her love of the place and her fascination with earthquakes are inextricably linked. Her earliest memory is of an earthquake that occurred while her family was living near Malibu. She guesses she was 2.

"I've always sort of liked earthquakes," she muses. "I guess I just never got imbued with the fear of them." Jones boasts that her mother lived her whole life in California never fearing earthquakes, despite being in the severe 1933 Long Beach temblor, which prompted the region's building code changes. When Jones was a student in oft-shaken Taiwan, she cavalierly ignored earthquakes strong enough to crack the flimsy staircase of her apartment building. "I should have been a little more afraid in Taiwan because the buildings weren't as good," she says now.

She ventured east for college and graduate work (she has a PhD in geophysics from MIT), and she's spent several long periods in Asia. But it was important to her that her children be born in California. She and her 41-year-old Icelandic-born husband, Egill Hauksson, a California Institute of Technology seismologist, have lived here since 1983 and have two boys -- an infant and a 4-year-old. She and Hauksson met at a gathering of geophysicists and later "started flirting" at a symposium on earthquake predictions. Now they work on opposite sides of a Caltech campus street.

An earthquake has to be rather big to get Jones's attention. The other night her husband mentioned to her that "there'd been a 3.1 somewhere around Point Magu," she recalls. " 'Oh, that's nice,' I said and went back to changing diapers." When the 5.9-magnitude Whittier Narrows quake hit 12 miles east of downtown Los Angeles in 1987, Jones was driving her toddler son to his day-care center. As the quake rattled her car, she fumed that the car was breaking down. But when she pulled into the parking lot, the radio was announcing news of an earthquake. Then she felt aftershocks.

"Before we had a kid, it was easy," she recalls. "We never really bothered with a lot of earthquake preparedness at home. ... But once we had a kid it was different, and I wondered how I would respond." That day, with her son, she found out. "Of course, I knew {the earthquake} wasn't that bad. I ran in and practically threw him at the day-care teacher -- 'I've gotta get to work!' " She laughs. "I did run by the office of the day-care center and suggest they move the kids outside just in case it was a foreshock. In any earthquake you've got a 5 percent chance it's a foreshock to something bigger, and the most likely time is within the next hour."

And with that, she jumped into her car and sped back to the office. "I did, like, 90 miles an hour to work. I was almost there and I thought, 'I didn't even think about keeping him with me.' The instinct that came through was a seismologist's. I was sort of embarrassed."

Jones's route to seismology took as many twists as the San Andreas Fault. She grew up a math whiz who played math games with her aerospace engineer father, who came from a family of experts on China.

Jones spent a year during high school in Taiwan with an aunt and uncle. In college she went back again while majoring in Chinese language study -- and taking enough science courses to be a physicist. "I was 14 when they landed on the moon," she says. "I very seriously and solemnly told my dad that I was going to be a physicist and go to the moon."

She didn't take her first geology course until her senior year at Brown University. Within a week, she was hooked. "It was earthquakes that really got me," she remembers. "It was obvious right away that I wanted to go into seismology." As a graduate student at MIT, she won a Fulbright Fellowship in 1979, which allowed her to be the first American scientist to work in China after the normalization of relations. She, of course, studied earthquakes. "In geology, there are so many questions waiting to be answered," she enthuses. "Some very fundamental things in geology and geophysics just aren't known: What starts an earthquake?" She chuckles. "We don't even know that."