Science: The Palmdale Bulge

Located some 35 miles north of downtown Los Angeles at the edge of the Mojave Desert, Palmdale (pop. 13,500), Calif., is a sleepy town where the loudest sounds are usually the whistling of desert winds and the popping noise of exhausts as teen-age dragsters race their cars. But Palmdale has been lifted, quite literally, out of obscurity. Scientists have recently discovered that it is in the center of a 120-mile-long, kidney-shaped area of land that rose as much as ten inches in the early 1960s. The phenomenon has earned the desert town a dubious notoriety. The Palmdale bulge, as the uplift is called, could be an early warning signal of a major—and potentially disastrous—earthquake.

Recent studies have shown that the ground rose noticeably before the 1971 San Fernando quake that killed 58 people in California’s last major trembler. Before a 1964 quake that destroyed much of Niigata, Japan, the ground lifted two inches, and the Chinese discovered an elevation of the land in Liaoning province before the Manchurian earthquake of February 1975.

The location of the Palmdale bulge has added to scientists’ concern. The swelling lies along a stretch of the 600-mile San Andreas Fault, a deep fracture that runs from below the Mexican border to about 100 miles north of San Francisco, where it meets the Pacific Ocean. The fault is actually the boundary of two tectonic plates, huge sections of the earth’s outer layer that are sliding in opposite directions. A western sliver of California, on the Pacific plate, is moving northwest. The remainder of the state is being carried by the North American plate toward the southeast.

Sticking Plates. As the two plates grind past each other, friction causes them to stick together briefly at some places. Then, driven by powerful and little-understood forces deep within the earth, they tear apart to resume their journeys, causing minor to moderate tremors. But in the Palmdale region, they have apparently been firmly locked for more than a century, while adjoining parts of the plate have slid as much as 30 ft. Some day, seismologists warn, the stalled sections are going to have to catch up with the main bodies of the plates. Strains are inexorably building up in the crustal rock. When—as it must —the rock finally fractures, the plates will jolt ahead, causing a major earthquake. In fact, the last significant plate movement in the Palmdale vicinity occurred in 1857, when a huge earthquake jolted the then sparsely populated area.

What scientists fear is that the Palmdale bulge could be caused by dilatency, a phenomenon that takes place in rocks before they break under stress. Tiny cracks open in the rock, increasing its volume; this could account for the uplift of land. Dilatency has already been linked to such quake precursors as unexpected variations in velocities of seismic waves through the earth and changes in local magnetic fields as well as in electrical conductivity of rocks; all have been used to make successful forecasts in the emerging science of earthquake prediction (TIME cover, Sept. 1).

The Chinese, for example, managed to predict the Manchurian quake with such extraordinary precision that the big jolt came only a few hours after their warning. As a result, says MIT Geologist Frank Press, more than a million people were evacuated from their vulnerable homes and tens of thousands of lives were saved.

Tilt Meters. Geologist Robert Castle, who with colleagues at the U.S. Geological Survey discovered the Palmdale bulge while examining old geodetic records, is keeping an open mind on the subject. The swelling could be caused by dangerous strains and dilatency, he says, or might be merely a “false pregnancy,” resulting from other, less menacing geological quirks. He points out that there have been instances of land rising—including an earlier uplift south of Palmdale at the turn of the century—without subsequent earthquakes.

To find out just what is occurring around Palmdale, scientists are now installing additional tilt meters, seismometers, magnetometers and other instruments in the little-monitored bulge area. These efforts have so far been badly handicapped by a lack of funds, but President Gerald Ford, after a plea from USGS scientists, has authorized an additional $2.6 million for earthquake research in fiscal 1977—$2 million of it specifically for studying the bulge.

Most Californians are displaying characteristic indifference to a possible quake. Indeed, Los Angeles is continuing land acquisition in the Palmdale area for a new jetport. But a few officials are openly worried. Last week the California Seismic Safety Commission, urging Los Angeles to prepare for the worst, warned that a major earthquake of 8 on the Richter scale could kill 12,000 people, injure or leave homeless thousands more and cost $12 billion in property damage. Said Roger Pulley, a state earthquake preparedness official: “There is no sense of alarm, but we are treating the Palmdale bulge as a threat.”