"We just had an earthquake, so we're safe for a few years."
"It's earthquake weather."
"The moon and planets are lined up."
"We're way overdue."
Have you heard these statements? Maybe said them yourself? People are intensely interested in foreseeing earthquakes. Like lottery strategies, everyone has a theory—and also like lottery strategies, none of them work. After a century of close study, earthquakes look just like random events.
Do earthquakes correlate with the phase of the Moon? No they don't. Do they tend to occur during a particular type of weather? No they don't. What about time of year? No effect. Previous seismic events? Outside of aftershocks, no. Sunspots and solar cycles? Nope, nope. Not even psychics do better than chance. Every prediction method makes lucky hits, but none of them really work.
Lay people reinvent these hypotheses anyway. They ask the real experts about them every day—they even ask me—and we try to educate them.
Earthquake Prediction in the 1990s
Scientists have moved on to more sophisticated guesses, but with little more success. It doesn't matter, for instance, how long it has been since the last earthquake along a particular stretch of geologic fault. It doesn't matter what fluid pressures underground are doing—rising, falling, or fluctuating. It doesn't matter what the electrical conductivity of the ground is doing. The behavior of earthquake faults is a stubborn mystery. Seismologist Yan Kagan of UCLA said a few years ago, "It may require the development of completely new mathematical and theoretical tools. We should not expect significant progress in this direction in the near future." (That doesn't stop him from trying new schemes, though.)
A team of Greek seismologists, known as the VAN group after the names of its leaders (Panayotis Varotsos, Kessar Alexopoulos, and Kostas Nomicos of the University of Athens), has long claimed to make useful predictions from a complicated network of signal detectors in electric power lines of many kilometers length. But a dedicated group of critics has kept the VAN group on its mettle. The debate was formalized in 1996 in Geophysical Research Letters. The VAN group responded to each of 16 Comments with a formal Reply. In some cases the exchange continued further, a sign of strong disagreement over basic matters. These days their work seems to be ignored generally, although Seiya Uyeda continues similar research with his group in Japan.
Later that year—November 7–8 at a "discussion meeting" in London sponsored by the Royal Astronomical Society and the Joint Association for Geophysics—researchers agreed to put the whole question aside: earthquakes appear to be inherently unpredictable. Prominent seismologist Robert Geller reported on the RAS-JAG meeting in the pages of Eos:
The overwhelming consensus of the meeting was that earthquake prediction, in the popular sense of deterministic short-term prediction, is not possible at present. Most of the participants also agreed that the chaotic, highly nonlinear nature of the earthquake source process makes prediction an inherently unrealizable goal. . . . The mass and trade media's highly optimistic reports on prediction differ greatly from the extremely pessimistic consensus of the meeting. Participants agreed that efforts should be made to correct the media's misconceptions, but there was pessimism about the prospects for real improvement.
The word "chaotic" is significant, because the mathematics of chaos is a step forward. The pattern of earthquakes along a fault resembles other chaotic phenomena like the avalanching of a sand pile under a random rain of sand grains—while each individual occurrence is unpredictable, the bulk result can be modeled quite precisely. In the case of the sand pile, the bulk result is a cone with sides at the angle of repose. For earthquakes it is an overall level of energy release that matches the tectonic movement of the earth's plates. From that information we can confidently map the expected long-term hazards for a region—that is, we can construct long-term forecasts. This is vitally useful for planners, emergency agencies, and designers of buildings and other structures.
A related development was a 1996 paper from Science, by the all-star cast of Robert Geller, David Jackson, Yan Kagan, and Francesco Mulargia, was about as strong a statement as scientists can make on the subject, starting with its title—"Earthquakes Cannot Be Predicted."