The Last of the Earthquake Predictors

July 19, 2016

In late winter of 1975, a seismologist named Cao Xianqing tracked a series of small earthquakes near Haicheng, China, which he took to presage a much larger one to come. On the morning of February 3, officials ordered evacuations of the surrounding communities.

Despite the subfreezing weather, many residents abandoned their homes, although others refused, dismissing the warning as another cry of “wolf” in a string of false alarms.

Yet this time, around dinnertime the very next day, Cao’s prognosis materialized in the form of a massive, magnitude 7.3 quake. Bridges collapsed, pipes ruptured, and buildings crumbled. But the accurate early alert—the first ever documented—spared thousands of lives: Of the 150,000 casualties predicted for a disaster of comparable size, only about 25,000 were tallied, including just over 2,000 deaths.

The successful forecast of the Haicheng quake seemed to justify the optimism felt by earthquake researchers around the world, who believed they were on the brink of unlocking the secrets of Earth’s tectonic motion.

Just a few years earlier, in 1971, geophysicist Don Anderson, who headed the California Institute of Technology’s renowned Seismology Laboratory, had boasted that prediction science would soon pay big dividends. With enough funds, he told a local reporter, “it would in my opinion be possible to forecast a quake in a given area within a week.”

Those funds duly arrived. In 1978, the United States Geological Survey (USGS) allocated over half its research budget ($15.76 million) to earthquake prediction, a level of spending that continued for much of the next decade.

Scientists deployed hundreds of seismometers and other sensors, hoping to observe telltale signals heralding the arrival of the next big one. They looked for these signs in subterranean fluids, crustal deformations, radon gas emissions, electric currents, even animal behavior. But every avenue they explored led to a dead end.

In one sudden and violent motion, all that tension is released. The rock snaps apart, shifting the earth as much as several feet in a matter of seconds.

“In our long search for signals, we never saw anything that could be used in a reliable way,” says Ruth Harris, a geophysicist at the USGS. “Either the method wasn’t repeatable or it looked like the original thing was just a case of noise.”

Even the famous Haicheng prediction turned out to be little more than fabulously good luck. Cao later admitted he had based his warning partly on foreshocks, which precede some large quakes by minutes to days, and mostly on superstition. According to a book he’d read called Serendipitous Historical Records of Yingchuan, the heavy autumn rains of 1974 would “surely be followed” by a winter earthquake.

Since the early 20th century, scientists have known that large quakes often cluster in time and space: 99 percent of them occur along well-mapped boundaries between plates in Earth’s crust and, in geological time, repeat almost like clockwork. But after decades of failed experiments, most seismologists came to believe that forecasting earthquakes in human time—on the scale of dropping the kids off at school or planning a vacation—was about as scientific as astrology.

By the early 1990s, prediction research had disappeared as a line item in the USGS’s budget. “We got burned enough back in the 70s and 80s that nobody wants to be too optimistic about the possibility now,” says Terry Tullis, a career seismologist and chair of the National Earthquake Prediction Evaluation Council (NEPEC), which advises the USGS.

Read More: Here

0 comment