SAN JOSE, Calif. -- Mother Nature delivered another jolt to San Francisco's South Bay residents Wednesday as a 3.7 aftershock -- one of more than three dozen following Tuesday's magnitude-5.6 tremor -- rattled homes, businesses, stores and schools.

Such is life in the Bay Area where the "Big Seven" earthquake faults slash the like claw marks on a map, tracing lines that parallel the coast. Most are little-known to residents, but each has the potential to trigger disaster.

Tuesday's magnitude-5.6 quake struck on one of them, the Calaveras Fault, just east of San Jose. It was a seismic throat-clearing of sorts, a warning to the more than 7 million people who inhabit the nine-county Bay Area region, from Silicon Valley to wine country.

The quakes produced no reports of serious injuries or damage, officials said, but Tuesday's temblor rattled nerves, homes and businesses when it struck shortly after 8 p.m. The shaking was felt as far away as Santa Rosa, Sacramento and Monterey.

The magnitude-7.0 quake that experts anticipate will hit one of the region's seven major faults in the next 25 years will pack 60 times the force, said Tom Brocher, a senior U.S. Geological Survey seismologist.

The quake also threw a spotlight on geologists' emerging understanding of how the faults interact. Recent research shows the Calaveras Fault intersects with the Hayward Fault, currently considered the most dangerous in the region.

Scientists give the Hayward Fault a 27 percent chance of a magnitude-6.7 or greater quake -- higher odds even than its storied neighbor, the San Andreas Fault.

"In the last 10 or 15 years we've gotten a better appreciation of how these faults actually talk to each other," said David P. Schwartz, chief of the U.S. Geological Survey's Bay Area Earthquake Hazards Project.

Under certain circumstances, a quake on one fault can transfer energy to another, adding instability and potentially triggering events on the other fault, seismologists said.

The linkages remain murky, even to experts.

"Is it the straw that breaks camel's back, or do we have to add 5,000 more straws?" said David Oppenheimer, a USGS seismologist.

So Tuesday's quake immediately raised questions among experts about whether it would increase the likelihood of a quake on the Hayward Fault, which cuts through one of the country's most densely populated areas, including the city of Oakland. Experts say 2 million people live close enough to be strongly shaken by a big quake.

By Wednesday morning, a consensus had emerged at the U.S. Geological Survey that the previous night's quake did not significantly elevate the likelihood of a dreaded Hayward Fault quake. Tuesday's temblor sent ripples of energy largely to the south, while the Hayward Fault extends north from the epicenter, Brocher said.

Still, state officials issued an alarming warning.

The California Earthquake Prediction Evaluation Council, a panel of scientists that advises the governor on earthquake forecasts, warned that Tuesday's earthquake "has significantly increased the probability above the normal level for a damaging earthquake along the Calaveras and/or Hayward faults within the next several days."

However, the panel said, "the overall likelihood of such an event is still low."

Other big faults intersect in the Bay Area, possibly raising the stakes when quakes hit near their intersections.

California's best-known fault, the San Andreas, is thought to touch the San Gregorio Fault, which skirts the coast along Half Moon Bay and Monterey. The Rodgers Creek Fault and the Hayward Fault meet at the north end of San Pablo Bay, near Vallejo.

Oppenheimer listed the latter intersection as a particular concern.

Asked to single out the fault that keeps him up at night, Oppenheimer said: "Personally, I don't lose any sleep over them because I've taken the advice that the experts give -- I've bolted my house down, I have 20 gallons of water, and while I expect things to fall off shelves, I don't expect injuries."

In addition to the Big Seven, hundreds of smaller faults form a latticework of cracks beneath the region, perhaps a dozen of which could snap and generate moderate quakes, Schwartz said.

He recalled a magnitude-4.2 quake that jolted the East Bay town of Lafayette in March. And the name of the fault on which it occurred?

"Who knows?" shrugged Schwartz. "It just has no name."

A hypothetical trench dug around the Bay Area would reveal hundreds of these small fissures, Schwartz said.

"The earth's crust, which has been around for millions of years, has been pushed and pulled in all different directions, and is very broken up," he said. "It's literally cracked up."

The faults, he said, "occasionally just pop off."