Approximately 33,000 buildings in the City of Los Angeles--or about 5%--would be destroyed, and damage would be in the $4-billion range, if the city's central business district were the epicenter of an earthquake with a 6.3 magnitude, a report for the National Science Foundation has concluded.
A 6.3-magnitude earthquake would be about twice the severity of last week's Palm Springs temblor.
The as-yet unreleased report adds that an 8.3-magnitude "big one" on the San Andreas fault near the city would destroy about 1,600 buildings in Los Angeles, with a citywide damage price tag of more than $1 billion. An 8.3-magnitude quake would be about the severity of Southern California's Fort Tejon temblor almost 130 years ago or the San Francisco earthquake of 1906.
The study, now circulating among Los Angeles city officials, did not project personal injuries or deaths.
It serves as "a starting point" to prepare for the area's next big earthquake, its architect, urban planning consultant William Spangle, said in a telephone interview from his Portola Valley office.
Postulating the impact of a major temblor on specific areas of Los Angeles "hadn't been calculated before," said principal city planner Glenn O. Johnson, who is studying a draft copy of the report. "It provides us with useful information about the extent of damage. It could help us better plan the resources needed to meet (earthquake) disasters in different parts of the city."
The report is timely, he said, because a committee of city officials, including planners, engineers and safety experts, was recently formed to see if city ordinances and regulations need overhauling to facilitate rebuilding and recovery after a major earthquake.
The two-volume report, "Pre-Earthquake Planning for Post-Earthquake Rebuilding," carries the acronym, the Pepper Report, and is essentially complete. It was underwritten in 1981 by a $365,000 National Science Foundation grant and is scheduled to be made public in the fall.
The report states that a great Southern California earthquake, such as the Fort Tejon temblor of 1857--the strongest quake to hit this area in recorded history, which was felt from Los Angeles to San Francisco and Sacramento--is "almost certain to occur" near Los Angeles in the next 50 years.
And a "moderate-sized" earthquake, such as the one in San Fernando Valley in 1971, can be expected to hit the Los Angeles area much sooner, the report said. That quake caused about $500 million in damage, killed 58 people, destroyed almost 800 homes and apartment buildings and made nearly 1,200 structures unsafe for occupancy.
The report's earthquake forecasts are generally consistent with previous studies. One of the earlier studies, made in 1981 by the Federal Emergency Management Agency, also predicted that as many as 14,000 people in Southern California would be killed if an earthquake of 8.3 magnitude occurred on a weekday afternoon.
The Pepper Report pointed out that the location of the epicenters of such temblors is far more important than their sheer size in terms of the devastation which could be expected in Los Angeles.
'Could Be More Severe'
"A 6.3 earthquake could be more severe than . . . an 8.3 (along the San Andreas Fault) with its epicenter some distance from the city," it said.
Asked to comment on whether a major temblor could strike downtown Los Angeles, Caltech seismologist Kate Hutton said, "I think it's plausible, it's not totally off the wall."
Looking at a state Division of Mines and Geology earthquake fault map, Hutton said, shows that the Whittier Fault line runs about 10 miles east of downtown and "could produce" a temblor in the 6.3-magnitude range. When the Whittier Fault slipped in 1929, she added, a temblor in the upper-5 magnitude range was recorded.
Two other moderately active fault lines run near central Los Angeles: the Raymond Fault, which runs through Pasadena about seven miles northeast of downtown; and the Newport-Inglewood Fault, which tracks through Culver City about seven miles southwest of Los Angeles' core.
"And there may be other faults down there we may not know about," said Henry Degenkolb, chief of a San Francisco structural engineering firm which helped produce the Pepper Report. "Coalinga happened where we didn't know a fault existed," he said, referring to the 6.7-magnitude earthquake that severely damaged that Central Valley community in 1983.
The Pepper Report's disaster analysis is based on several scenarios.
One is that sometime in the next 50 years there will be an 8.3-magnitude earthquake on the southern segment of the San Andreas Fault about 35 miles north of Los Angeles.
Other scenarios include three magnitude-6.3 earthquakes focused in Los Angeles' central business district, in West Los Angeles and in Long Beach, all triggered by nearby faults. Such "moderate-sized local earthquakes," the report said, "occur much more frequently in California" than "great earthquakes" with a magnitude of 8 or more.