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.
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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 ÂŁ50,000 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, anything that improves the odds has got to be good news.