Battle of Palmdale Bulge: Geologists Argue If It’s Real
When its existence was first announced 10 years ago, the Palmdale Bulge, a reported periodic swelling of the Earth north of Los Angeles from Ventura County to the Mojave Desert, generated headlines and predictions of a great earthquake.
But three years later, when a UCLA geologist claimed 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 claims to have 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.
Although the existence of the bulge is disputed, recent work by USGS geologists seems to be confirming that at least 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, Castle said, 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, last week’s temblor in Palm Springs and Sunday’s quake off the coast of San Diego.
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.”
The battle of the Palmdale Bulge provides a good view of the long, painful course that a scientific theory must run before it is accepted as fact.
Castle discovered the bulge while conducting a study after the Sylmar quake to analyze, among other things, 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.
From 1961 to 1964, the tilt between the two towns, just 18 miles apart, appeared to change by more than eight inches--a startling finding in the geological scale of things. Palmdale appeared to be sitting on top of a bulge in the Earth.
Along with other USGS scientists, Castle began to examine surveys of the region from as far back as 1902. The result was a picture of an area covering thousands of square miles--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.
More Complete Records
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 the pierced crust of a fresh-baked pie.
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.
When Castle published the first accounts of this “Southern California uplift” in 1976, it created a huge stir, prompting a large government study.
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. At a professional meeting in 1979 and in a series of journal articles, he asserted that there were many sources of error in the data gathered during the old surveys that Castle had used to trace the evolution of the bulge.
The job of measuring the finest features of the Earth’s surface is given to geodesists. Periodically, teams of surveyors crisscross an area, charting their course and measuring elevations as they go. The result is a precise contour map.
Their equipment is simple and has hardly changed in 100 years: two three-meter rods marked off in millimeters and a small telescope that is kept horizontal by a leveling device, either a pendulum or a bubble enclosed in a liquid-filled chamber.
A survey team starts at a point with a known elevation. Many of the lines used to study the Palmdale bulge originated at a bench mark at sea level on the San Pedro waterfront, winding from there along railroad tracks or roads or open country, Castle said.
The rods are usually placed less than 200 feet apart, with the viewing instrument between. Each rod is viewed through the horizontal telescope. The difference between the heights spotted on each rod denotes the rise in elevation between them. The first rod is then carried beyond the second one and the procedure is repeated--sometimes more than 1,000 times, depending on the distance covered.
“For one thing,” Jackson said, “the rods should be calibrated every year. Some were not calibrated for 18 years.”
Another source of error is atmospheric refraction, he said. When someone is sighting through the telescope at a rod, the line of sight can be distorted by variations in atmospheric conditions, such as temperature. Although the error is slight, over the course of surveying a line--say, from San Pedro to Saugus to Palmdale--these tiny errors can add up to account for something as big as the Palmdale Bulge, Jackson said.
“It’s a human issue as well as a scientific issue,” he said. “People want to believe it. . . . There seems to be something in people that likes excitement. When they get some data that’s got some wiggles in it, they blame it on the Earth.”
But Castle insists that when the data is adjusted to compensate for these errors, the bulge persists. He added that Jackson and other critics of the bulge are using “the antithesis of the scientific method. . . . If they can’t explain data, they don’t believe the data.”
A survey of some geologists familiar with the terrain of Southern California--but outside the fray over the bulge--turned up no bulge disbelievers and only a couple who were neutral on the issue. One fence-sitter is Bradford Hager, associate professor of geophysics at Caltech.
“It’s one of those things that’s right on the edge of resolution as to whether it occurred or not,” Hager said.
The question of whether such a bulge can be linked to seismic activity is still unresolved, geologists say. The original flurry surrounding the bulge was caused by a widespread feeling that an uplift of such massive proportions might presage an equally massive earthquake, Castle said. A small-scale bulge had been noted before the Sylmar earthquake. Also, the 1905 bulge seemed to be associated with unusual earthquake activity.
But when the recent swelling subsided in 1974, it did so quietly, “singularly free” of any direct link to local seismic activity, Castle said.
The earthquake that shook Palm Springs last week “is near the point of maximum cumulative uplift” of the bulge, said Wayne Thatcher, a USGS geophysicist. But if there is a link, no one knows what it is. “Certainly there’s an indirect relation,” he said. “Both are parts of the tectonic activity in the region--mountain-building forces.”
More recent surveys of the area, conducted over the last few years by Thatcher and others at USGS, have continued to show dramatic rises and falls of up to six inches in the landscape, Thatcher said. This time, measurements of variations in Earth’s gravity and of changes in horizontal distances are also being taken.
“The more simultaneous things we can measure, the better,” Thatcher said. These measurements are confirming that the region is active, but it is too early to know if the Palmdale Bulge is on the rise again, he said.
A new technology, employing lasers and satellites, may help put an end to the battle of the Palmdale Bulge, Hager said. A pinpoint beam of laser light is bounced from points on Earth to Defense Department satellites that are part of what is called the Global Positioning Satellite System.
By timing the return of the light reflected back to Earth from four different satellites, the system can determine the distance between two points or the elevation of a point to within a few centimeters, Hager said.
Even with the new technology, the putative Palmdale Bulge will not be the last geological phenomenon to generate debate. A dispute has already arisen over the accuracy of some measurements obtained with the satellite system, Hager said. The data seem to show that the speed at which the two sides of the San Andreas Fault slip past each other has dropped over the last four years from six centimeters a year to two or three centimeters a year.
If this is true, he said, it would be another instance in which “the Earth doesn’t move in some smooth way” and would make an already complex phenomenon even harder to understand.