The quake machine

June 28, 2001

The Earth needs a good massage to release all that pent-up tension and prevent catastrophic quakes. But do we dare try it? Nicola Jones reports

YOU can count yourself lucky if you don't live in an earthquake zone. When I was growing up in Vancouver we watched newscasts of quakes that had devastated California, and were told that when our time came it could be worse. We scrambled under our school desks during practice drills while our mothers stockpiled bottled water. There wasn't much else we could do. We held our breath and waited for the city to be flattened.

Vancouver is still standing but others aren't so fortunate. Every year quakes kill or injure about 10,000 people, yet researchers seem to come no closer to predicting them. In fact, geologists have all but given up trying to tell when, where, and how badly quakes will hit. "More and more experts agree that prediction is impossible," says Valerio De Rubeis, a seismologist at the National Institute of Geophysics in Rome.

But is there another way to avert destruction and death? If you can't predict the "big ones" or brace against them, then how about stopping them in the first place? De Rubeis is coordinating an international team of geologists who think they may have found a way to do just that. They want to gently ease the stress out of the Earth a little at a time-by skewering the ground with artificial lightning and triggering their own mini-quakes.

This radical plan is not without its risks. Their earthquake machine has a switch labelled "start", but so far it doesn't seem to have one labelled "stop". Legally, too, they are on shaky ground. If you lost your home or family to a man-made mini-quake gone wrong, who could blame you if you sued? But these could be risks worth taking. If De Rubeis and his colleagues can massage the strain out of the planet's shoulders early enough, they hope there will be no build-up of pressure to trigger a deadly tremor. Every year they could save billions of dollars and thousands of lives.

The first hint that it might be possible to control earthquakes came in 1966, when geologist David Evans noticed a cluster of tremors near the Rocky Mountain Arsenal in Denver, Colorado. Staff were pumping waste water into the Earth, and Evans suspected that this was triggering the quakes. It turned out that the fluid was squeezing into a fault line below the base and the resulting pressure was pushing the two plates on either side of the fault apart. With less friction, the plates could slip past each other more easily.

A year later, three geologists from the US Geological Survey put that theory to the test. They pumped water into the ground at an oilfield in Rangely, Colorado, and recorded seismic activity in the area. They found that within a kilometre of the injection site the water triggered an average of 28 mini-quakes per month. When they stopped pumping it in, the quakes dropped to 1 per month. For the first time, earthquake control seemed possible.

This idea was particularly appealing in the late 1960s, when geologists were beginning to suspect that it was impossible to predict quakes. Things haven't changed much. Over the years, people have tested a thousand ways of predicting quakes, from measuring radon concentrations in well water to watching animals for signs of bizarre behaviour. But nothing has proved reliable.

Today most seismologists simply throw their hands up in despair at the thought of predicting quakes, which is why the concept of releasing the pent-up energy in the crust in a controlled fashion is so attractive. But fluid injection probably isn't the answer. For starters, it only seems to work over a small region. To control something like the San Andreas-with over 1200 kilometres of fault lines-the cost of drilling wells and pumping water would be huge, and a logistical nightmare. And even drilling the holes might trigger a quake.

But a new look at a series of experiments in Tajikistan in central Asia in the mid-1970s is bringing fresh hope. A team of Soviet geologists were shooting intense pulses of electromagnetic energy more than 50 kilometres into the ground to measure the electrical conductivity of the crust, hoping to better understand how and why quakes happen.

To create these pulses, they used an exotic machine called a magnetohydrodynamic generator, originally developed by the Soviet military as an energy source for advanced weaponry. The machine is powered by rocket engines that blast exhaust gases between the poles of an extremely powerful magnet. Just as moving a wire through a magnetic field creates a pulse of current, this jet of charged gas creates an intense but short-lived electric field.

By sticking two electrodes four metres into the ground a few kilometres apart, the geologists directed the electromagnetic pulses-effectively a blast of artificial lightning-into the Earth. Throughout the years of trials the mountains rumbled with weak tremors, but no one thought that unusual in an area prone to quakes.

That changed in 1993, when Nikolay Tarasov, a seismologist at the Institute of Earth Physics in Moscow, began a study to pin down how nuclear explosions influence earthquakes. He had developed a statistical method to determine whether seismic activity in a given area had gone up or down after a blast. To get some background data he turned to seismic records from his colleagues in central Asia. Much to his surprise, Tarasov realised that the seismic activity following these electromagnetic pulses was no fluke.

In fact, the results were staggering. The electromagnetic pulses were brief-lasting 10 seconds at most-and the total energy input was a modest 10 million joules, about the power of a single flash of lightning. But the total seismic energy released afterwards was up to a million times greater than the energy they had put in.

Tarasov delayed publication while he searched for other explanations. Nothing turned up. Then in 1996 he looked at records from a site in northern Tien Shan, where the same kind of generator had been fired between 1983 and 1990. He found exactly the same effect. About two-thirds of the pulses were followed by a significant increase in rumblings-on average, seismic activity in the region increased three-fold.

His first results came out in 1997 and by 2000 all of the work was published (Volcanology and Seismology, vol 21, p 627). By then Tarasov had teamed up with other geologists and, led by De Rubeis, they began to study this phenomenon. Last year, De Rubeis secured £50,000 from the European Union to explore the effect with Vladimir Zeigarnik from the Russian Academy of Sciences' Institute for High Temperatures in Moscow, Gennady Sobolev of the Academy's Institute of Physics of the Earth, and other Georgian, Greek and Israeli colleagues.

Their first task is to figure out what is going on. It is already well established that quakes can be triggered by all kinds of events such as nuclear tests and dam construction. But triggering quakes with electromagnetic energy is a far sketchier proposal.

In the past, a few researchers have claimed that a spate of earthquakes in the early 1900s could be attributed to an increase in sunspots. The Sun was going through a spell of intense electromagnetic activity at that time, which they believed was somehow triggering quakes. But most geologists are sceptical. "The physics would argue that this is pretty much impossible," says Malcolm Johnston, a seismologist at the US Geological Survey in Menlo Park, California.

Geologists assume that if electromagnetism is doing anything at all, the most likely mechanism would be the "electrokinetic effect" in which electric and magnetic fields force polar liquids such as water to move about. If this mechanism is responsible, the physics behind these mini-quakes would be much the same as that behind quakes triggered by fluid injection.

But the currents required to move liquids in any substantial manner are huge: "of the order of hundreds of amps", says Johnston. Not the kind of input you can get from a solar storm, but just the jolt you could get from a magnetohydrodynamic generator.

Johnston has seen the electrokinetic effect in action-but only in the crust near the surface, not tens of kilometres down where the Russian earthquakes originated. So could there be another explanation?

Alan Jones from the Geological Survey of Canada in Ottawa suggests that the pulses could be striking a chord with rocks in the crust and making them vibrate like a tuning fork, thanks to what's known as the piezoelectric effect. These vibrations could trigger seismic activity. But the piezoelectric effect only occurs in well-ordered structures, like the aligned atoms in a crystal-not in the jumbled mess of rock more typical of the Earth's crust. "There is some evidence that rocks deep in the mantle-about 45 to 150 kilometres down-might be ordered," says Jones. But he can't believe that this ordering would survive the crushing forces at a fault.

Electromagnetic pulses could influence rocks in other ways, says De Rubeis. Some seismologists suggest that the crust can act as a giant capacitor, with huge multilayered sandwiches of water and solid rock just micrometres thick storing up charge. It's thought that these zones of charge tend to become aligned as stress builds up just before an earthquake. The Russian generators could be helping to align the charges, suggests De Rubeis, speeding that process. Or the energy could be heating water trapped in the rock, raising the pore pressure and-like fluid injection-reducing friction along the fault. Eventually, De Rubeis thinks they will find several causes. "There is not one mechanism-it is a combination," he says.

To put their theories on more solid ground, Sobolev and his crew have begun to explore the problem in the lab. In their first tests they applied pressure to a concrete block and recorded changes as they passed a pulse of electricity through it. A blast of 0.9 joules seemed to increase the rate at which cracks spread by between 2 and 5 per cent. And a burst of almost 150 joules increased the cracking by up to 15 per cent. More experiments are needed, they say, using realistic rock samples which contain water. The mechanism is still a mystery, but at least they've confirmed that electromagnetic pulses can actually affect rock.

"Sobolev is one of the leading experimentalists in the field," says Carl Kisslinger, a seismologist from the University of Colorado who is familiar with artificially induced quakes. But he's never heard of electromagnetic quake triggering, and has little idea how it might work. "It's just weird," he says. "But you have to keep an open mind about anything that doesn't violate the basic laws of physics."

"To be honest," admits De Rubeis, "when I first saw this project I was sceptical-I thought this argument was a little crazy." But the more he learns about it, the more convinced he becomes. "Sometimes good results come out of strange research."

Not surprisingly, De Rubeis and his team are treading carefully. They say they need to work out the mechanism and put their statistical data through a more rigorous analysis before they attempt more experiments in the field. But some day they hope to address the most important question of all: can these induced quakes be controlled?

In the US, it was the fear of runaway earthquakes that halted the fluid injection experiments. Some level of control can be achieved by pumping water out of surrounding areas before pumping the water in, says John Booker, a geophysicist from the University of Washington in Seattle, but there are no guarantees. And in a state where people sue because their coffee is served too hot, trying to crack the spine of the San Andreas would be a risky business. "As a seismologist, I wouldn't turn a garden hose on up there," says Kisslinger. "I might spend the rest of my life in court."

Even if you could relieve some of the crust's stress, you might end up transmitting it elsewhere: triggering one quake could make neighbouring stretches of a fault more likely to blow. "By triggering thousands of small events, odds are that one of them would grow into a damaging event," says Ellsworth. "I doubt that even Lloyds of London would be interested in covering this bet." But De Rubeis and his team hope that their technique will prove reliable. The tests in Tien Shan were in highly earthquake-prone areas and, in retrospect, firing pulses into the ground might not have been the brightest idea. But, says Zeigarnik, the lack of any catastrophic event during the years of trials might be more than good luck. It might mean that something restricts the induced quakes to mini-tremors.

If, as he suggests, electromagnetic radiation has a built-in safety brake that stops triggered quakes from getting too big, then that will make it far more useful than any other method of earthquake induction-regardless of logistical problems.

But it would come at a price: almost constant rumbling. To release the energy stored in a potential magnitude 7 quake, for example, would take about 30 earthquakes of magnitude 6. Or 10,000 magnitude 4 quakes. Or a million magnitude 2s. "Since even magnitude 4 events can cause damage, you wouldn't want to stimulate events much larger than this," says Booker. But playing it safe with magnitude 2s would mean triggering 10 quakes a day for 300 years to drain off the stress.

Sobolev's colleague Alexey Nikolaev admits that they will probably never stop quakes altogether. But in places such as California, Japan or Central America, even a small reduction in their magnitude could make all the difference. "If, for example, an earthquake would normally have a magnitude of 7, we could reduce it to 6.7 by using earthquakes of magnitude 4 or 5. Reduce the magnitude by 0.3 and damage will be reduced by 2 times." That's half as many fallen bridges, flattened buildings and lost lives. And if you live under the constant threat of a deadly quake, any-thing that improves the odds has got to be good news.
New Scientist issue: 30 June 2001


New Scientist

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