“As solid as the earth,” we say. That’s why even mild earthquakes are often frightening and always memorable. Suddenly you can’t rely on the earth any more: it’s not rock-steady, it’s dancing. And it might be about to dance you to death.
But Robert Musson, author of this excellent guide to the history and future of seismology, points out that even in a big earthquake you’ll usually be safe in the open away from buildings. The problem is that few people spend much time like that. Cities are getting bigger and more crowded, which is why he suggests that one day an earthquake could kill a million people or more. Tehran is one candidate. So is this:
The case of Istanbul is unnerving for another reason. The North Anatolian Fault, the great strike-slip fault that starts in eastern Turkey and dies out in the middle of the Aegean, has an interesting property. Earthquakes along it tend to occur in sequences, starting in the east and moving progressively west. Each quake, as it occurs, throws more stress on the next section of fault to the west, which then fails a few years to a decade or so later. it’s like a series of dominoes toppling. […] The current sequence began with a 7.8 magnitude event near Erzincan, at the eastern end of the fault line, in 1939. This was followed by quakes progressively further west in 1942, 1943, 1944, 1957 and 1967. Then, after a lull, the next most westerly stretch of fault broke in 1999 with the Izmit earthquake. The next stretch of fault to the west goes straight through the Sea of Marmara, just south of Istanbul. This is the next domino to fall, and it could happen at any time. (ch. 12, “Stay Safe”, pp. 233-4)
Or there could be another lull. That is one of the interesting things about earthquakes: their unpredictability. The subtitle of this book is misleading, because there is no reliable science of prediction for earthquakes. Seismologists can say in great detail why and how they occur, but they can’t say where or when or what size. We are far better at predicting the behaviour of the sky above our heads than we are at predicting the behaviour of the earth beneath our feet. Meteorologists are refining and extending their forecasts further all the time. Astronomers have been accurately predicting eclipses and planetary orbits for thousands of years.
Seismologists would like to make their discipline predictive rather than reactive, but it’s proving very difficult. Masson discusses one team of Greek seismologists who claimed to be able to predict quakes using “seismic electrical signals, or SES for short” released by “rocks once they are stressed beyond a certain degree” (ch. 8, “Next Year’s Earthquakes”, pg. 172). But the team, led by Professor Panayotis Varotsos, made their predictions by sending telegrams to each other rather than informing an official body. When the earthquake occurred, they would produce the telegram and its date-stamp: “The question that was whispered in the corridors at conference sessions was this: How many telegrams were quietly burned when the prediction failed?”
Then a “moderate earthquake” hit Athens in 1999 and although the team claimed to have predicted it, they hadn’t said so in public. Apparently stung by the criticism that followed, Professor Varotsos issued a public prediction of a larger earthquake on its way in central Greece. But it never happened and the team were no longer taken seriously.
It’s not difficult to understand why earthquake prediction is so difficult: rocks aren’t transparent and gathering data from the depths of the earth is much harder than gathering data from the sky. Seismologists would be delighted if they could realize the suggestion made by Arthur C. Clarke in his short story “The Fires Within” (1949):
Sonar, as you will know, is the acoustic equivalent of radar, and although less familiar is older by some millions of years, since bats use it very effectively to detect insects and obstacles at night. Professor Hancock intended to send high-powered supersonic pulses into the ground and to build up from the returning echoes an image of what lay beneath. The picture would be displayed on a cathode ray tube and the whole system would be exactly analogous to the type of radar used in aircraft to show the ground through cloud.
Nearly seventy years on, we’re still waiting for a geoscope like that. Seismology is still a hobbled science and earthquakes are still mysterious and frightening things. As Sherlock Holmes says in “The Adventure of the Copper Beeches” (1892): “Data! data! Data! … I can’t make bricks without clay.” But seismologists have done a lot with the limited data they’ve got, as you’ll learn here. Writing clearly and colloquially, Masson traces the history of mankind’s attempts to understand earthquakes, describes their effects on history, discusses related phenomena like volcanoes and tsunamis, and explains why seismologists don’t use the “Richter scale”. The Million Death Quake has a hyperbolic title and a misleading subtitle, but it’s one of the best popular science books I’ve come across.