The Why Files The Why Files --

Earthquakes: Preventing building collapse.

POSTED 22 MAY 2008

Lesson from China's tragedy: Prevention is the only solution
As the last few survivors are pulled from horrific heaps of concrete in China, we wonder why so many buildings collapsed. Most earthquakes, after all, occur in distinct, well-known patterns, and even though it's impossible to know exactly when the next earthquake will strike, in Sichuan and many other regions quakes are not just likely, but practically inevitable.

Two dozen people holding umbrellas stand before giant heap of collapsed rubble, twisted metal, concrete blocks and building debris
May, 2008: This building collapsed in Dujiangyan, Sichuan, China. Photo: Wikipedia

Yet as the death toll attests, hundreds, even thousands, of homes, schools and apartments in Sichuan province were poorly designed, with a severe shortage of the steel reinforcement that concrete buildings need to survive the wrenching forces of a severe earthquake.

Well-built structures may crack during an earthquake, but they do not collapse, giving residents time to escape.

Requiring the right steel in the right places is central to building codes in Japan and California, and even in China, according to some newspaper reports.

But code does not always become reality. Good building material is expensive. Some builders are ignorant, and others are corrupt. Because the reinforcing is quickly hidden by concrete, the construction process needs repeated inspections by an outsider, not the builder's cousin or a "friend" who gets paid under the table.

"What is happening is a systematic failure to build correctly," says Roger Bilham, a professor of geology and earthquake specialist at the University of Colorado at Boulder, "and it's usually caused by a very simple problem. Although there may well be a good building code, and there are engineers who know how to build, the person who assembles it is the lowest paid person on the totem pole, and he does not know what he is doing, so even if he is told how, he may not do it right. As a result, the mid-level buildings are the ones that always collapse, and these are the dwellings."

A two-story school with four doors and very small windows is perched precariously on a dozen concrete stilts, surrounded by a playground
A school in Quito, Ecuador, shows a common structural defect: a collapse-prone first story that lacks cross walls. If the ground shakes while this school is in session, parents will soon be grieving. Photo: GeoHazards International

The irony, Bilham says, is that "one- to four-story concrete-framed buildings are very simple to build correctly. But if you don't know what you're doing, you won't do it right. If you want to save cost, you reduce the amount of steel and reduce the amount of cement in the sand, and buy any old sand," rather than the clean sand necessary for strong concrete.

A tall order
Convincing builders in earthquake zones to adopt collapse-resistant technologies is the goal of the non-profit GeoHazards International. As founder and president Brian Tucker described in a talk at the University of Wisconsin-Madison last week, "Our mission is to reduce death and suffering due to geological hazards in the most vulnerable communities through preparation."

The organization does not help in recovery after earthquakes, but rather advocates -- in advance -- for safe buildings, and strong building codes that are well enforced. It's an ounce-of-prevention strategy that attempts to enlist tons of steel to avoid replays of last week's catastrophe in Sichuan.

Prediction problem
Although the timing of earthquakes is unpredictable, they do not happen at random. Most earthquakes serve to relieve stresses that build up at borders between the giant, shifting tectonic plates of Earth's crust. As the plates gradually move past each other, the junctions can snag, but when they suddenly slip, that's an earthquake.

As the plates continue moving, another earthquake becomes largely a matter of time.

Earthquakes are among the deadliest of natural disasters, and Tucker expects the death toll to rise because most of the projected rise in world population -- more than 2 billion people -- will occur in cities in developing countries, including large swaths of earthquake territory. "When you overlay where people will live and where earthquakes are going to be, there is a tremendous overlap in the developing countries."

The problem is accentuated by the worldwide trend toward building with heavy concrete floors.

Oval-shaped map of the world,  circles in blue, purple and yellow bloom over areas in southeast Asia and the west coast of South America.
Since 1900, Asia and Latin America have been headquarters for deadly quakes. Officially, 255,000 died in China's Tanshen earthquake in 1976, but the actual loss may have been much higher. Map: USGS

As the death toll in China takes a giant leap forward, engineering improvements and code enforcement can save lives. In 1988, for example, 40,000 died during the collapse of schools and dwellings in Armenia. In 1989, the slightly weaker Loma Prieta earthquake in California, a citadel of earthquake engineering, claimed only 62.

Persuasion problems
Even in the shadow of the Himalayas, which are being lifted by the collision of two tectonic plates, Tucker has found difficulty in persuading local people that earthquakes will return in time. Yet the equation is pretty simple, he says: "Where there was a large earthquake, there will be a large earthquake."

Many countries in Asia, where hundreds of millions are living in concrete multi-story apartments, are in danger, Tucker says, because dangerous faults underlie heavily populated nations like Iran, Pakistan, India and China.

Although earthquakes repeat, future quakes are likely to exact a much greater death toll, due to the increase in population and the shift toward multi-story building construction. If the 1897 Shillong earthquake in Northern India (death toll 1,500) happened today, the death toll is projected to be 60 times higher, Tucker says.A forest of reinforcing rods on the floor and walls of a building under construction

Prevention trumps prediction
The timing of earthquakes is unpredictable, says Clifford Thurber, a seismologist and professor of geophysics at University of Wisconsin-Madison. "We don't have a good understanding why they start where they do, why they stop where they do, and why they break the fault where they do. There is a fundamental lack of knowledge about the physical state of the fault zone, and the processes that happen during an earthquake."

If predicting earthquakes is impossible, preventing disaster is the only alternative. And in this era of concrete construction, that means adding steel members -- reinforcing rod -- to knit the building together.

California's building codes focus on preventing collapse during earthquakes. These Santa Monica apartments are a densely engineered forest of reinforcing rods. Since the forest will be concealed by concrete, inspection must occur during construction. Photo: © Joel Grossman

These changes may not be prohibitively expensive if applied to new construction: In California, Tucker says, estimates of the added cost range from four to eight percent. (But California's buildings codes are already rather tight, and it's not clear if upgrading from building-as-usual in Sichuan or Iran would be more expensive.)

Schools are a focus of concern, as we learned from photos of grief-stricken parents outside the piles of rubble that entombed their children in Sichuan.

Is it possible to mobilize a poor village to construct safer schools?


Megan Anderson, project assistant; Terry Devitt, editor; S.V. Medaris, designer/illustrator; David Tenenbaum, feature writer; Amy Toburen, content development executive

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