The earth can hardly move without Susan Hough noticing.

From her office in a tiny outpost of the far-flung U.S. Geological Survey, Hough spends her days studying and tracking what's known in her unusual trade simply as an "event," any shift, rumble, or twitch far below ground in California that could be classified as an earthquake.

The big ones are few and far between, but she and the small band of federal seismologists based here have no shortage of urgent work to do. There are hundreds of seismic recording devices planted along the many fault lines of this giant state that must be monitored by computer almost daily.

And hardly a week passes without the arrival of another batch of tremors way too minor to break windows or make headlines but still important to analyze in the hope they will offer insights into what is the most earthquake-prone region of the country.

It is a kind of endless chess game with the Earth, and predicting its next dangerous move is never easy.

"We knock on wood a lot in this office, because knowing what we know, none of us wants to be in the middle of a big quake," Hough said. "But professionally, this is the place to be."

It is the closest she will come to professing academic delight in a job that most Californians would prefer had no reason to exist, for nothing strikes more fear in the hearts of the Golden State's 33 million residents than the sudden rattle and roar of earthquakes.

Twice in the last decade, major temblors have pounded metropolitan areas: San Francisco in 1989 and Los Angeles in 1994. And no doubt there will be more.

At the end of one recent week, Hough had tallied more than 50 relatively minor tremors around California and Nevada, enough to frighten the layman but nothing extraordinary in the eyes of seasoned seismologists who know just how turbulent the Earth gets in this part of the world. "That's pretty normal," she said.

Hough and her colleagues are hardly thrill seekers. Because of advances in technology, most of their work these days involves sitting for hours in front of colorful computer maps, and not rushing over to the shaky San Andreas Fault to record ground motion. They are a crew of sober, buttoned-down federal workers, and their tasks are part science, part math and part just plain guesswork.

"Even with all the data we collect here on earthquakes, we can't say what's probable because we just can't see things that far into the Earth," Hough said. "We can only say what's possible in the years ahead."

Along with analyzing and cataloguing even the smallest quakes, she and other seismologists advise local governments on what kind of building codes would help structures withstand tremors, as well as where the riskiest areas seem to be for residential and commercial developments to avoid. Although the state is vulnerable to a large quake, the kind of massive devastation that one just caused in Turkey is unlikely here because buildings are much sturdier.

Hough, 38, has been stationed at the Geological Survey's field office in Pasadena, which is just east of Los Angeles, for seven years. She stumbled upon her vocation during a collegiate whim. At the University of California at Berkeley, Hough was a math major looking for career direction when a listing for a course in geophysics caught her attention. About the same time, an earthquake that was serious enough to shake her apartment struck near the San Francisco Bay Area.

"I needed something to do with my interest in math," she said, "and I got pretty curious about why earthquakes occur."

She went on to earn a doctorate in earth science from the University of California at San Diego and became a research scientist at Columbia University in New York. She returned to quake work in the West. It is a daunting assignment but hardly a high-profile one.

The Geological Survey's office here, tucked away in a modest two-story Pasadena town house with just a small sign out front, is deliberately low-key.

In earthquake-crazed Southern California, it might be difficult to get much research done any other way. Yet now and then a few fearful residents somehow manage to find the site and all but beg the seismologists for reassurance that the Big One is not about to occur right under their feet.

"We had one lady from Palm Springs call us a while back and ask which of two homes might be better for her to buy along the San Andreas Fault," Hough said with dismay. "People think we have all the answers, but we don't. There's a lot we're still trying to understand."

But she is hoping to offer some guidance in a book that she is busy writing--after hours--about earthquakes, one that she hopes will make the science of them more accessible and remind those who think tremors are only a California problem not to be indifferent to the phenomena.

Major quakes have occurred around Missouri and South Carolina in the past 150 years, and there are fault lines beneath New York City and around parts of New England. The coastline of the Pacific Northwest is potentially vulnerable to a sizable quake.

"It wasn't until the big 1906 earthquake in San Francisco that people even thought this was a California problem," Hough said.

And where does a seismologist with an insider's knowledge choose to live around here? "It doesn't matter," Hough said. "I hate to say this, but there's really no place to hide."

Players

Susan Hough

Title: Geophysicist, U.S. Geological Survey, Interior Department.

Age: 38.

Education: Bachelor's degree in geophysics, University of California at Berkeley; doctorate in earth science from University of California at San Diego.

Family: Married; two children.

Previous job: Research scientist, Columbia University, 1988-92.

On predicting earthquakes: "People think we have all the answers, but we don't. There's a lot we're still trying to understand."