Rebuilding to survive quakes

Improved methods can save lives in the most tremor-prone areas


The powerful earthquake that killed as many as 30,000 people in northern Pakistan over the weekend is the latest manifestation of a continental collision that began 55 million years ago, geologists say.

That was when, it is believed, the Indian subcontinent, drifting northward on a slab of Earth's crust, first slammed into the southern flank of the Eurasian continent.

Like a slow-motion car wreck, the impact has continued ever since, piling up Earth's crust at the impact zone into the highest mountain ranges on the planet, from the Hindu Kush in Afghanistan and Pakistan to the Himalayas of Nepal and Tibet.

Tragically for residents of the region, the clash of continents brings violent shaking, death and destruction.

In addition to as many as 30,000 dead, Pakistani officials said yesterday that thousands of injured, homeless and desperate quake survivors were suffering from cold and hunger.

Some had begun looting local shops in search of food and supplies.

The United Nations said 2.5 million people would need shelter as winter approaches.

Pakistani officials called for international assistance, but it was slow to arrive in many areas. Survivors were being pulled from beneath the rubble of fallen buildings, and the injured were being airlifted from remote areas.

Saturday's quake measured 7.6 on the Richter scale, roughly the same as the famous San Francisco quake of 1906.

Geologists say the same collision of plates that devastated northern Pakistan is also to blame for the 9.0 quake that shook the Indonesian island of Sumatra in December, killing as many as 229,000 people in 11 countries, most of them in the tsunami that followed the earthquake.

And geologists say more such quakes are inevitable.

"The mechanisms that create them are still active," said University of Maryland geologist Aaron J. Martin. "They're going to keep going for a long time."

Less damage, death

With no means to prevent them, the best option for people and governments in the region is to improve building codes and construction standards so that earthquakes do less damage and kill fewer people.

"At the very least, we should link our [reconstruction] help with an assurance that they're going to rebuild correctly," said Brian E. Tucker, founder and president of GeoHazards International, a California-based nonprofit promoting the construction of safer school buildings in quake-prone developing countries.

Saturday morning's quake in Pakistan was followed by dozens of aftershocks of magnitudes ranging from 4.2 to 5.9 on the Richter scale. One tremor seven hours after the main quake registered 6.2.

Globally, the U.S. Geological Survey typically records one magnitude 8.0 quake per year, 18 of magnitude 7.0 or larger and about 170 of magnitude 6.0 or greater, said Harley Benz, the scientist in charge of the National Earthquake Information Center, in Golden, Colo.

A gigantic puzzle

Most occur where continental plates meet. Scientists learned in the 1960s that the planet's crust is not a single structure, like the shell of an egg.

Instead, it's a sort of jigsaw puzzle, composed of rigid "tectonic plates" that float on the liquid magma beneath. They have been splitting apart, drifting and colliding for eons.

The Indian plate continues to drive into and beneath the Eurasian plate at a rate of about 40 millimeters (1.6 inches) per year. But the convergence is not going smoothly.

When portions of the plates get stuck, the strain behind them builds. When it releases, it's in a lurching motion that's felt as an earthquake.

In a 2001 article in the journal Science, University of Colorado geologist Roger Bilham and colleagues listed 23 quakes in the Himalayan region between 1803 and 2001 with measured or estimated magnitudes of 7.0 or greater. Four were estimated at 8.0 or more.

(One whole-number increase in the Richter scale reflects a 32-fold increase in the energy released by the quake.)

Several lines of evidence show that one or more great earthquakes [magnitude 8.0 or higher] might be overdue in a large part of the Himalayas, threatening millions of people in that region, the study said.

The last big earthquake in the same region of northern Pakistan as Saturday's was a 6.2 event in 1974.

"That quake caused about 5,800 casualties," Benz said.

Other quakes in the 7.0 to 8.0 range occurred there in 1803, 1833, 1897, 1905, 1934 and 1950, he said, and there's evidence of similar and larger events going back thousands of years.

"You can see where streams have cut new channels because of offsets [movements across a fault line]," he said, "or whole landforms being changed due to uplifts due to faults."

"We know they've occurred in the past, and since the rates and style of deformation haven't changed, we expect them to occur in the future," he said.

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