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Comment

Earthquake Prediction and the Developing World
Mark Zoback

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.


Zoback is a professor of geophysics at Stanford University and one of the principal investigators of the San Andreas Fault Observatory at Depth project. Email: zoback@pangea.stanford.edu. This piece is modified and reprinted from an Op-Ed in the Jan. 4 Washington Post.

Opinions and conclusions expressed in Comment by the authors are their own and not necessarily those of AGI, its staff or its member societies.

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