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The toll from the Iranian earthquake in December — at least 30,000 dead
and an estimated 40,000 homeless in just a few seconds — is difficult to
comprehend. Unfortunately, we can predict with reasonable certainty that sometime
in the next few years, in a country with buildings unprepared to withstand disaster,
a catastrophic quake will happen again. It’s one more way in which the
gap between the developed and the developing worlds makes a profound difference,
and we seismologists have to decide how best to deal with that sad fact.
The evidence of this gap is startling. The 1989 Loma Prieta earthquake in California
(magnitude 6.9) left 63 dead and more than 3,700 injured, while the 2001 quake
in Bhuj, India (magnitude 7.6), killed roughly 20,000 and injured more than
100,000.
As devastating as these recent events have been, they almost pale compared to
the largest earthquake losses on record. How does one conceptualize the 1976
earthquake in Tangshan, China, which killed somewhere between 250,000 and 500,000
people? Or the 1556 quake in China’s Shensi province, considered by many
to be the greatest natural disaster in history, that left an unimaginable 800,000
dead?
Yet here is perhaps the most sobering fact: If those earthquakes were to recur
today at the same magnitude, the losses might be nearly as severe.
That’s because in many parts of the developing world, sun-baked mud bricks
and clay tile roofs still serve as shelter for millions of people. In earthquake
country, these masonry structures are death traps waiting to happen. So are
some larger buildings: Floors are added until the first signs of the lowest
levels yielding. Even a moderate amount of shaking is enough to cause a collapse.
One image imprinted on my mind is that of relief workers standing atop a once
six-story building in Mexico City that was literally pancaked in 1978 by an
earthquake 200 miles away.
In stark contrast, the impact of large earthquakes in the developed world is
never as severe, evidence of the clear value of earthquake engineering. Reinforced
structures almost never collapse, and even if they sustain heavy damage, they
usually protect the lives of occupants as they are designed to do. Take, for
example, the 1995 earthquake in Kobe, Japan, which effectively destroyed more
than 100,000 buildings and killed 5,500. Nearly all of those deaths could be
traced to older buildings whose construction predated the enactment of modern
building codes. While tens of thousands of newer structures were damaged beyond
repair, they did not crumple.
Despite the clear-cut evidence that earthquake engineering is effective, deploying
it in the developing world is a complicated matter. The extensive retrofitting
that has strengthened dangerous buildings and infrastructure in California and
Japan is often seen as prohibitively expensive in the developing world, although
international groups are working to implement low-cost solutions to some of
the most egregious hazards in earthquake-prone areas.
Even the best engineering, however, can’t work without vigilance. Having
essentially the same building codes as California doesn’t protect anyone
if lax enforcement or corruption prevents their implementation.
The final reason it is often difficult to implement earthquake engineering in
the developing world is geological, not human. The devastating earthquakes in
China and India were “intraplate” events — occurring far from
the boundaries of the great tectonic plates where earthquakes are more common,
such as the San Andreas fault system in California. In many cases, intraplate
earthquakes are not associated with previously known faults, and the geological
reasons for their occurrence are not well understood (such as three severe earthquakes
that struck New Madrid, Mo., in the winter of 1811-1812).
Large earthquakes on intraplate faults occur infrequently, and the killer faults
responsible for history’s most damaging events may not have moved for thousands
of years. December’s earthquake that ravaged Iran’s ancient city of
Bam occurred in the Zagros collision belt and destroyed a 2,000-year-old citadel.
Moving forward
As efforts to implement earthquake engineering and preparedness move forward
in the developing world, what else might be done to limit the devastating consequences
of such events? The answer may be earthquake prediction. It would not prevent
much of the physical damage that has accompanied earthquakes in the developing
world, but such prediction would be enormously effective in reducing the death
tolls. The successful prediction of the 1975 Haicheng earthquake in China undoubtedly
saved thousands, if not tens of thousands, of lives.
Unfortunately, since that event, there have been no scientifically acknowledged
accurate earthquake predictions. There is even widespread doubt among many seismologists
that earthquakes are predictable. The Haicheng prediction may have been fortuitous
as the area had experienced numerous foreshocks (relatively small quakes that
sometimes precede a main shock).
At one level, it is difficult to argue with this logic. From a scientific perspective,
not only do we not know how to predict earthquakes, but we also do not even
know if, in general, earthquakes are predictable. We do know prediction is not
easy. It has been difficult to “catch” an earthquake early with detailed
monitoring systems. For example, despite the high probability of earthquakes
on various sections of the San Andreas fault system, none of the significant
earthquakes that have struck California in the past 15 years actually occurred
on the San Andreas.
Given the paucity of direct observations of earthquake processes at depth, it
has also been impossible to test many of the theories about such processes that
have been proposed over the past several decades. Today, we still do not know
if all, most, some or any damaging earthquakes will ever be predictable in a
way that would benefit people.
Still, there are many reasons for optimism. Like our colleagues in astronomy,
earthquake scientists are living in an era of unparalleled progress due to the
data now coming in from exciting new observational systems. For example, permanently
installed, high-resolution GPS instruments have recently discovered episodic,
slow-slip events at depth on the great subduction faults threatening Japan,
the U.S. Pacific Northwest and Central America.
Time will tell if such slow movements play a role in initiating earthquakes
on these major faults. It is heartening to know that the discoveries being revealed
by the roughly 1,000 permanent GPS instruments installed throughout Japan will
soon be complemented by about 800 such instruments installed along major fault
systems and volcanic centers in western North America as part of the Plate Boundary
Observatory of the National Science Foundation’s EarthScope initiative
(see page 30). Satellite radar observations have shown us “breathing volcanoes”
(episodes of inflation and deflation without eruption) as well as large portions
of the Earth’s crust deforming slowly in response to large earthquakes.
Might they also show anomalous deformation prior to earthquakes?
Another component of the EarthScope initiative, the San Andreas Fault Observatory
at Depth, will soon penetrate the fault to address long-standing questions about
the physics of earthquake processes. In addition, for the very first time, it
will be possible to make direct observations at the depth of the initiation,
propagation and arrest of earthquake ruptures, and to test for observable phenomena
that might someday lead to reliable earthquake predictions.
Taking action
The tragedy in Iran emphasizes the fact that the stakes are simply too high
to leave earthquake prediction to quacks and charlatans. So what should we do
to limit future catastrophes? In military parlance, we attack across a broad
front. We support efforts to implement earthquake engineering and preparedness
programs, especially in the developing world, and we continue to do everything
we can to better understand the physics of earthquakes.
If we can do that, perhaps some day we will develop prediction capabilities
we can trust, with widespread benefit to the hundreds of millions of people
who live in quake-threatened areas around the world. At worst, this research
will lead to a better understanding of long-term earthquake hazards and dramatic
improvements in our knowledge of how the earth works.
Not bad for a fallback position.
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