HAYWARD, Calif. -- The cracks in Elke DeMuynck's ceiling appear every few weeks, zigzagging across her living room, creeping toward the fireplace, veering down the wall. Month after month, year after year, she patches, paints and waits.

"It definitely lets you know your house is constantly shifting," DeMuynck said. So does the gate outside that now swings uselessly 2 1/2 inches from its latch. And the strange bulges in the street, and the geology students who make periodic pilgrimages to her cul-de-sac.

DeMuynck could throw a putty knife from her front stoop and hit the Hayward Fault, the most dangerous in the Bay Area, if not the nation. Like others who live here, she gets by on a blend of denial, hope and humor, putting earthquake anxiety on a long list of modern-day worries.

It's the geologists, emergency planners and historians who seem to do most of the fretting, even in this year of heightened earthquake awareness, when the region is marking the 100th anniversary of San Francisco's Great Quake on April 18.

Several faults lurk beneath this region, but geologists say the Hayward is the most likely to snap.

"It is locked and loaded and ready to fire at any time," said U.S. Geological Survey seismologist Tom Brocher.

The Hayward Fault runs through one of the country's most densely populated areas, slicing the earth's crust along a 50-mile swath of suburbia east of San Francisco. Experts say 2 million people live close enough to be strongly shaken by a big Hayward quake.

It runs directly under thousands of houses, from exclusive hilltop manors overlooking the bay to Hayward's humble flatlands. It snakes beneath interstate bridges, strip malls, nursing facilities, retirement centers, and it splits the uprights of the University of California, Berkeley's football stadium, official capacity 67,537.

"A lot of these structures are going to come down," said David P. Schwartz, the chief of the USGS's Bay Area Earthquake Hazards Project. He spoke with one foot on either side of the fault, straddling a thin crack that snaked through a parking lot in Hayward's business district.

Before San Francisco's Great Quake of 1906, on the San Andreas fault, there was the Great Quake of 1868 on the Hayward, a magnitude 6.9 rumbler that killed five people. Severe quakes have happened on the Hayward Fault every 151 years, give or take 23 years, meaning it is now into the danger zone.

Experts forecast the next big one will be in the potentially lethal 6.7 to 7.0 range. The Association of Bay Area Governments estimates it would wipe out some 155,000 housing units, 37,000 in San Francisco alone.

It's a time bomb waiting to go off. Historically, severe quakes have occurred on the Hayward Fault every 151 years, give or take 23 years, meaning it is now into the danger zone. Experts forecast the next big one will be in the potentially lethal 6.7 to 7.0 range.

In a big quake, the earth on either side of the fault could shift three feet. Two objects sitting on different sides before the quake could be abruptly carried a total of six feet apart, he said.

"You can visualize what would happen if it moves six feet," Schwartz said, gesturing toward the telltale asphalt crack, which disappears underneath businesses.

The Hayward Fault runs directly beneath Eden Jewelry and Loan, but the men working in the pawn shop shrugged when asked whether they fear a quake.

"I better get a new job!" said Saul Gevertz, 64, flashing a smile at his co-worker. "Honestly, it's a nonissue."

One of the building's co-owners, Darrell Davidson, 47, said that ever since a renovation and retrofit about five years ago, the structure is essentially an enormous steel cage, designed to flex in an earthquake.

"I'm not worried-worried. I've thought about it," said Davidson, his eyes scanning the steel beams. "I think we're in good shape. I hope to God we are."

Nickey Avila, 23, confessed some alarm when a reporter informed him the fractured pavement outside his house was the fault. Avila had just returned from a tour with the U.S. Army in Iraq; the "welcome home" banner and balloons still hung from the house.

"I knew I was close to the fault, but I didn't know I was this close," Avila said.

"I'm thinking one day it's going to move, but if I survive it, I'll be able to say I survived one of the biggest quakes of all time," he said. "For my family -- I'm third-generation military -- it's like, 'bring it on."'

That could be any moment, seismologists say.

"If it moved while we were walking, it wouldn't surprise me," Schwartz said during a tour of Hayward's misaligned street curbs, warped concrete gutters and abandoned buildings. Among the shuttered structures was the former Hayward City Hall, a grand art deco complex deemed too dangerous to occupy. The fault runs right underneath.

Built in 1930, it was part of a 20th century Bay Area building boom nurtured by an unusually quake-free period. The Great San Francisco Earthquake of 1906 released stresses on all faults in the region, resulting in few earthquakes, Schwartz said.

The legacy of the boom, and the fault menacing from below, are both visible in an unnerving new "virtual tour" of the fault developed by the USGS. Meant to simulate a helicopter flight, the new images show the Hayward Fault represented as a bright red line, slashing through specific, identifiable structures, like DeMuynck's house.

DeMuynck, 62, is resolved not to worry.

"There's dangers all around us, all the time, so if we thought about those dangers all the time, we wouldn't have anything else to think about," she said. "We just come home and say, the house is still here. We're OK for another day."