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Mountain or No Hill? : New Technology May Settle 7-Year Debate About Existence of Palmdale Bulge

July 14, 1986|ANDREW C. REVKIN | Times Staff Writer

When its existence was first announced 10 years ago, the Palmdale bulge, a purported periodic swelling of the Earth north of Los Angeles from Ventura County to the Mojave Desert, generated headlines and predictions of a great earthquake.

When a UCLA geologist claimed three years later that the Palmdale bulge did not exist, that it was an illusion created by faulty data, the phenomenon seemed to fade away, leaving in its wake an atmosphere of doubt.

One headline read: ". . . new study turns geological 'mountain' into molehill."

Actually, the battle over the Palmdale bulge was never won or lost.

Two geologists--Robert Castle at the U.S. Geological Survey in Menlo Park, who discovered the bulge, and David Jackson at UCLA--have been locked in a stalemated debate for seven years, each with a retinue of critics and supporters.

"Both sides got pretty tired," Jackson said. "Everybody is sort of on the ropes."

Although the existence of the bulge is disputed, recent work by USGS geologists seems to be confirming, at least, that the landscape north of Los Angeles is in continual motion, heaving up and down as much as half a foot a year. And new space-based technology may soon put to rest any doubts.

If the bulge turns out to be real, and not a phantom result of imprecise measurement, as Jackson contends, the periodic swelling--although only a foot or less in height--may be linked to seismic events such as the destructive Sylmar earthquake of 1971 and Tuesday's moderate temblor in Palm Springs, Castle said.

Its behavior could also provide important clues about the structure of the San Andreas Fault. This 600-mile-long scar, where two shifting sections of the Earth's crust are in perpetual collision, is the predicted source of the "Big One," the devastating earthquake that geologists say is likely to hit the Southland in the next few decades.

Even Jackson agreed. "It would tell us a lot about how the Earth works and stresses build up," he said. "If it were real," he quickly added.

The battle of the Palmdale bulge provides a good view of the long, painful course that a scientific theory must run before it becomes established as a scientific fact.

Castle's discovery of the bulge came in the wake of the Sylmar earthquake. He was conducting a post-earthquake study of the San Fernando Valley that included analysis of old measurements of elevations across the Valley and north and east into the desert.

Castle said he noticed many changes in elevations in the 10 years leading up to the earthquake, with a particularly dramatic change in the "tilt"--the difference in elevations--between Saugus and Palmdale.

8-Inch Tilt

From 1961 to 1964, the tilt between the two towns, just 18 miles apart, appeared to change by more than eight inches. In the geological scale of things, where a mountain range might rise the width of a fingernail in a year, this finding was startling, Castle said. Palmdale appeared to be sitting on top of a bulge in the Earth.

Along with other USGS scientists, he began to examine surveys of the region from as far back as 1902. The result was a picture of an area thousands of square miles in extent--rising around Santa Barbara in the west and descending again east of the Salton Sea--that seemed to have swelled and receded twice, peaking once in 1905 and again in 1974.

Records for the recent bulge were much more complete, Castle said, showing remarkable spasmodic growth, with peaks in 1961 and 1973 as well as local "blisters" and "dimples." In 1974, the whole region began to collapse like a pierced crust on a fresh-baked pie.

Gone in Some Spots

Currently, measurements of the bulge indicate it has shrunk to a third of its greatest dimensions, with some sections--for instance, the region around Bakersfield--actually lower than they were before the bulge began, Castle said. Even at the time of its discovery in the early 1970s, the bulge was already almost gone. That has been the biggest roadblock to confirming or debunking the phenomenon, Castle said.

"We didn't recognize the existence of it until it had almost disappeared," he said.

In 1976, Castle published the first accounts of this "Southern California uplift." The discovery created a huge stir, prompting a large government study. In January, 1978, 36 teams of scientists fanned out across the region in what Time magazine then called "one of the most extraordinary surveys in the annals of U.S. geology."

$1.5-Million Study

More than $1.5 million went into the effort to measure the bulge.

"The goal was to try and cover the vast area within a short period of time, producing a detailed snapshot" of the bulge, Castle said.

Ironically, the survey, which was meant to be the final word on the bulge, was marred by some balky equipment and "the worst weather in years." And that was only the beginning of Castle's troubles.

Then along came Jackson. In 1979, he started what would become a series of challenges to the Palmdale bulge, most based on flaws in the method used to take its measure.

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