Concern and even apprehension was expressed 13 years ago when scientists said they had detected a huge bulge in the Earth’s crust centered near Palmdale and that it might be the precursor of a giant earthquake in Southern California.
The Palmdale Bulge was eventually said to have developed during the early 1960s and to have uplifted an area extending along the San Andreas Fault from Point Arguello southeastward to the Salton Sea, but to have had the most effect in the Palmdale area, where the uplift was supposedly about 10 inches.
Now, however, following years of dispute as to whether there actually was a bulge, the phenomenon has faded from public attention. Federal research grants have mostly dried up, and even those who believe the most in the bulge say they doubt whether it could say much about where and when a big earthquake may strike.
“I think most scientists in the field would like to know whether the thing really existed,” said Thomas Heaton of the U.S. Geological Survey’s Pasadena office. “If it did, I’m not sure whether it would have predictive value. I’m not sure we understand it well enough yet.
“Certainly it’s an interesting notion to think large-scale changes in the Earth’s crust are occurring. But it’s kind of hard to say too much when the interpretation of the data is so ambiguous.”
The greatest public defender of the bulge remains Robert Castle of the Geological Survey’s Menlo Park office, who says he is sure there was one, part of which has now collapsed, but that what research efforts are still going on are devoted more to explaining the phenomenon than charting any rise or fall of terrain.
“We have not been generating any new data,” said Castle, “just using what exists in historic record.” But asked whether the bulge would be of value in predicting an earthquake, Castle said, “I really don’t know. If I read my entrails correctly, I’d say limited at best.”
“It’s great when we can find something to agree on,” responded David Jackson, the UCLA geologist who, beginning in 1979 and continuing for years thereafter, sharply questioned whether there was a bulge at all.
“We haven’t found anything in all the measurements we’ve taken that has led to earthquake predictions, or has taught us about earthquakes.”
Jackson said there has been a recent study that shows “no rapid ups and downs” such as Castle and others say have occurred, but just “a very small, steady rise, just barely measurable, not any bulging or debulging.”
The effort to find a means of predicting earthquakes, in the meantime, has gone on to other concentrations. The latest is a theory that moderate earthquakes on smaller faults may trigger within hours the “big one” on the San Andreas.