It was not only the biggest quake in San Fernando Valley history at the time, but it was the first strong one in the Valley since 1893.
In fact, the area where the fault broke had been the locale of only 10 earthquakes of magnitude 3.0 or greater in the previous 37 years.
But at 42 seconds after 6 a.m. on a Tuesday morning 25 years ago this week, Feb. 9, 1971, the Sylmar-San Fernando earthquake hit the Valley and other parts of Greater Los Angeles for 12 seconds, killing 64, injuring 2,543 and doing $553 million in damage.
Scientists now believe what they call simply the San Fernando earthquake was a magnitude 6.7, identical in strength to the Northridge quake.
"San Fernando and Northridge have to be related somehow, but we don't understand the process well enough to know why they were 23 years apart," said Thomas Heaton, a Caltech professor of geology.
And Lucy Jones of the U.S. Geological Survey commented, "San Fernando clearly nudged the Northridge plane toward having an earthquake. It didn't happen for 23 years, but it could have happened almost immediately as an aftershock.
"For some reason, Northridge wasn't quite ready to go, and we were fortunate it wasn't, because had Northridge occurred right away, then it's pretty clear we would have killed a lot more people."
The San Fernando quake, in fact, could have been a catastrophe instead of just a costly disaster. That conclusion arises from its most striking episode: the near-collapse of the lower dam at the Van Norman reservoir.
The 1,100-foot dam held 3.6 billion gallons of water on the morning of Feb. 9, 1971, but it was only half full; the water level was 36 feet below the lip.
The top 30 feet of the edifice crumbled, leaving the water only six feet from the top and fresh chunks of earth falling off with each aftershock.
With leading seismologists of the day warning there could be a much heavier aftershock at any time, authorities ordered 80,000 people living below the dam in an area bounded by the San Diego Freeway on the east, Victory Boulevard on the south, Balboa Boulevard on the west and Rinaldi Street on the north to evacuate.
The evacuation lasted three days while engineers tried furiously to pump water from the dam through a 24-inch hole cut in an aqueduct pipe and another in the dam face. They succeeded in lowering the water level by about three feet a day.
A year to the day before the quake, the dam held 6.5 billion gallons of water, and its level was eight to 10 feet higher than the level to which the top of the dam slumped in the quake. Engineers recognized that had such a vast quantity of water spilled over the top, the entire dam would have quickly been washed away.
Later, a UCLA study estimated that collapse of the dam would have brought flooding that could have killed between 71,600 and 123,400 people.
Clarence Allen, Caltech professor emeritus of seismology, said the toll might not have been that high, but a dam failure would have been "a disaster unique in American history."
"It was an awful close call," Allen said. "A big aftershock may have let the thing go. I was there. I can remember as if it were yesterday, the water six feet from the top."
It remains a pungent memory too to Tammy Williams Poppen, then a 12-year-old girl living in the evacuation zone in Granada Hills.
Trying to find her three cats, which had disappeared when the quake struck, she suddenly heard loudspeakers telling everyone in the neighborhood to get out.
" 'Dad,' I yelled, 'they're telling us we have to leave,' " said Tammy, now manager of a downtown Los Angeles credit union. " 'No, they can't be,' he said. But then he heard the loudspeakers, too."
Three days later, the Williams family returned to their home and found their cats, safe and sound.
The Van Norman Dam experience led to an inspection of dams across the state and to the rebuilding or retrofit of many.
As for the new dam that was constructed on the site, Allen notes happily, "It came through the Northridge quake without a scratch."
The results were not as fortunate at the San Fernando Veterans Administration Hospital, where 47 of the 64 fatalities attributed to the San Fernando quake occurred.
Built with reinforced concrete structural frames in 1925, before seismic protection was written into building codes, the sides of two big buildings collapsed, trapping many of the patients.
Eventually, the hospital's laundry and chapel were the only buildings among 50 at the site that were not demolished.
Frank Carbonara, 68, survived in the rubble 58 hours before he was rescued.
At first, he recalled after he was safe, "I thought I was dead. . . . I closed my eyes and waited, said a prayer God would forgive my sins. Nobody lives forever. But after a while, I noticed I was still breathing."
Another hospital that was hard hit was Olive View in Sylmar, where a six-story building opened only a few weeks before collapsed, killing three.
Surgical resident Philip Ching, sleeping on the fifth floor, remembered "the tremendous noise."
"I later found that it was the day room wing," he said. "The whole thing toppled over. The noise lasted at least 30 seconds, perhaps a minute. Things were falling. My room was a shambles. Then, I could hear people screaming."
Olive View was rebuilt and reopened in 1987. It sustained some damage during the Northridge quake but was reopened then in just 41 hours.
Four freeways were temporarily closed as a result of the San Fernando quake, including the Golden State, the Antelope Valley, the San Diego and the Foothill.
Altogether, 12 overpass bridges fell into freeway lanes, one of them killing two men who were passing in a pickup truck, and 62 bridges were damaged.
Other vital statistics of the earthquake:
* Power outages affected 890,189 customers, most only briefly, but some as long as three days. The Los Angeles Department of Water and Power initially lost 12.7% of its total electrical capacity when equipment was destroyed at its Sylmar Converter Station, the southern terminus of the 846-mile Northwest Intertie.
* Some 9,500 customers lost telephone service for several weeks. The volume of telephone calls in the Los Angeles area jumped 300%, clogging many lines. After the earthquake, the telephone companies set up a priority system that limited the number of calls that went through.
* Only 13 of the city's 619 schools suffered severe structural damage, a notable success for seismic standards implemented after the 1933 Long Beach earthquake.
The earthquake was centered in the San Gabriel Mountains about nine miles north of San Fernando. The surface of the earth ruptured for about 10 miles, from Sunland through Sylmar.
Caltech's Heaton notes that the mountains above Sylmar and San Fernando rose by seven feet as a result of the quake.
The impact on individual homeowners was probably worst in Sylmar.
A Times article described the scene:
"Devastation . . . was complete: Many houses and businesses were without windows, chimneys, roofs and walls; streets were buckled; power lines were down and there was no water, gas, electricity or telephone service.
"Homes that appeared from the outside to have survived the earthquake intact were wrecked inside. The quake had sent refrigerators, washing machines, china cabinets, pianos and even toilet bowls crashing about.
"Kitchen pantries and cupboards were emptied of canned food, dishes and glasses to such a degree that many residents shoveled, rather than swept out their homes."
Actually Los Angeles was lucky, concluded Douglas DeNike, a clinical psychologist at County-USC Medical Center.
"The quake was the luckiest event in Los Angeles' long history of undeserved good luck," he contended in an essay that appeared soon in The Times.
"A more favorable time for its occurrence could not have been chosen. It took place beneath clear skies, with no wind to fan fires, and out of the brush fire season. It hit just at dawn, permitting maximum daylight for first day emergency operations. The freeways were uncrowded, and families were together at home. Partly because of the good weather, the Van Norman Dam held and did not inundate the 80,000 residents beneath it. More importantly, this was a 'moderate' temblor . . . by latest calculations, and it was centered far from the center of the sprawling metropolis."
Scientists make these other points about the impact of San Fernando:
* Strong-motion recorders clearly showed that shaking intensities were greater than the building codes had prepared structures to withstand. The long process of strengthening the codes was pushed after San Fernando, and much more bridge retrofitting was undertaken.
* Problems with certain kinds of buildings--particularly unreinforced masonry, tilt-ups, and even reinforced concrete--became more evident as a result of the earthquake. Ten years afterward, Los Angeles passed an ordinance requiring the retrofit of 8,000 unreinforced masonry buildings. The program was substantial, but it took the Northridge quake to show how much more work needed to be done.
* The weakness of steel frame buildings that was one of the most unpleasant surprises of the Northridge quake might have been discovered after the San Fernando temblor had more comprehensive inspections been undertaken, some scientists said.
Allen said much was learned from San Fernando, but he also observes that "the realism of what it was going to cost to take corrective measures is something we didn't have after San Fernando."
"Strengthening dams and hospitals are things we could do within reasonable budgets," he observed last week. "The cost and benefit ratios of more complicated and extensive retrofits (indicated by Northridge) pose a more difficult problem."