Series of Earthquakes Rocks Northern California

THE second big earthquake to jar California in less than a week has reminded residents of the perils of living in a fault-veined state, sent scientists puzzling over their seismographs, and underscored the importance of being prepared for a force that is both unpredictable and powerful.

Residents of rattled Humboldt County in northern California are cleaning up after a 6.9-magnitude quake that struck Saturday, one of the largest temblors to hit the state this century.

Two major aftershocks were reported early Sunday morning. The first measured between 6.0 and 6.3; the second, 6.5 on the Richter scale.

The quake was only slightly smaller than the 7.1 earthquake that rocked the San Francisco area in 1989.

A fire in a shopping district, gas leaks, and bridge damage were reported following the aftershocks, but no injuries. Highway 101 was closed in some sections due to damage. The logging town of Scotia, 25 miles south of Eureka, lost a market and hardware store.

Centered 35 miles south of Eureka, the quake caused widespread structural damage in the region's picturesque coastal hamlets, triggering rockslides and injuring 53 people, though few seriously. No one was killed.

Gov. Pete Wilson quickly declared Humboldt County a disaster area. The state set a preliminary damage figure of $3.5 million. Quakes not related

The quake struck only three days after a 6.1-magnitude shook southern California. That temblor also hit a predominantly rural area, in the desert just north of Palm Springs, causing only minor damage and injuries.

Although both quakes occurred near the notorious San Andreas Fault, scientists say the two events were not related. The northern California quake hit in one of the most seismically active areas in the state. The region is a veritable tuning fork - vibrating with scores of small temblors, usually less than 3 on the Richter scale, each month. Previous quakes

Last Aug. 17, a 6.1-magnitude temblor jolted the area. Less than three hours later, a 7.1 quake struck offshore. Only minor damage resulted from both. A 7.0 temblor was recorded in the area in 1980.

The latest shaker hit just onshore somewhere within a cluster of faults at the "Mendocino escarpment," a geological formation near Cape Mendocino.

An earthquake usually occurs in a crack, or fault, in the Earth's surface where two giant slabs or plates meet. At Cape Mendocino, a relatively small plate called the Gorda is sandwiched between two larger plates. Its edges have been ground as the two larger plates move.

Saturday's quake rattled a rugged, mountainous corner of California where redwoods outnumber people. Called the state's Lost Coast, 4,000-foot peaks rumple the region which receives as much as 100 inches of rain a year.

Petrolia, a river valley hamlet just south of Cape Mendocino, was hardest hit. Fire consumed a small general store, post office, and restaurant, and more than a dozen homes were destroyed.

In the logging town of Ferndale, the temblor knocked down buildings and burst water pipes. Several Victorian homes were jolted off foundations. The quake struck just as residents were gathering on main street to celebrate a "Best of the West" parade. Eureka and Fortuna also suffered damage.

The quake could be felt from Oregon to San Francisco, 230 miles to the south, and as far East as Reno, Nev. The aftershocks could be felt in Santa Cruz, Calif.

Residents in the isolated communities, a resilient lot, are already pulling together to restore communities. In Ferndale, residents are hoping to salvage some of the stately Victorian homes that were damaged. 'Big One' speculation

As with any substantial quake, the question naturally arises: Is this a precursor to an even bigger one - a magnitude 7 or more? Scientist don't think so. But dozens of aftershocks are expected over the next few days.

Still, the back-to-back temblors in the north and south have Californians nervously thinking about the "Big One" that is supposed to strike some time, probably along the San Andreas Fault.

Scientists estimate there is a 40 percent chance that a magnitude 7.5 or greater quake will hit southern California in the next 30 years, while the probability is slightly lower for one in northern California.

Even though the state has among the toughest earthquake building codes in the country, these two temblors will likely once again touch off soul-searching over just how prepared the state really is.