Earthquake Massacre

Science World, Nov 1, 1999 by Van Neistat

Scientists examine one of the deadliest quakes of the 20th century.

A man and his wife leap from a third-story stair-well as their apartment building literally crumbles beneath their feet. Miraculously they survive, and look back to watch their home crash into a mound of concrete and steel.

Forty-eight hours later, rescuers unearth a 7-year-old boy and his 3-year-old sister from a mass of rubble. The children are dehydrated and terrified--but alive.

Nearby, searchers extract a mother and her infant son, both trapped below slabs of what was once their house. The woman had kept her son alive with just breast milk.

These are tales with miraculous endings. But for the estimated 15,000 people who died August 17, 1999, after an earthquake struck western Turkey, there were no such miracles. The quake was centered in Izmit, a populous suburb of Istanbul, Turkey's largest city (see map, p. 18). It struck at 3:02 a.m., while most of the city's citizens slept.

In 45 seconds, nature's brute force leveled more than 40,000 buildings. Scientists labeled the quake a magnitude 7.4 on the Richter (RICK-tur) scale, a measure of the amount of energy released during an earthquake. That's almost 4 times stronger than the 6.9 quake that hit California's San Francisco Bay Area in 1989, killing 62.

In the days that followed Turkey's quake, death was so widespread, rescuers stored decaying bodies on an icehockey rink to prevent an outbreak of cholera, a deadly bacterial disease.

The earthquake that struck Turkey's North Anatolian fault, a deep fracture in the Earth's crust, now ranks as one of the five deadliest quakes of the 20th century. (Three struck China, each hitting over 8.0 on the Richter scale and killing more than 200,000 people.) In its aftermath, Turkey has become a classroom for teams of seismologists (earthquake scientists) trying to glean lessons from the fury of a rumbing Earth. The pressing question: Does this quake increase the likelihood that subsequent trembles could demolish nearby Istanbul with its population of 12 million? And could the disaster in Turkey happen elsewhere in the world?

SLIDING DRAWERS

Massive quakes are as old as Earth itself. The planet's surface, or crust, is broken into sections called tectonic plates, huge slabs of rock that push against each other. These plates are about 100 kilometers (62 miles) thick. Tectonic plates "float" atop the mantle, a gooey layer between Earth's crust and core, or center.

Turkey sits on a relatively small plate called the Turkish Microplate, which is surrounded by three larger plates (see map, bottom left). Those plates--the Eurasian, Arabian, and African--squeeze and slide against Turkey, and the resulting pressure can cause massive earthquakes--like a sticky silverware drawer that thrusts open after a strong pull. Just as the silverware flies out after a tug, buildings, bridges, and freeways pry apart atop a sliding tectonic plate.

But it's not simply moving landmasses that cause great destruction. In fact, where there are no buildings, earthquakes are essentially harmless. "Earthquakes don't kill people--buildings do," says Ross Stein of the United States Geological Survey (USGS). On vacant land you could safely stand atop the epicenter--the spot where a quake originates and is usually most violent. "An earthquake would be a wonderful experience to go through in a tent," Stein says. In 1964, an 8.6 monster-quake in sparsely populated Alaska killed fewer than 10 people even though it was 16 times stronger than the quake in Turkey.

CLOSE TO HOME

Like the North Anatolian fault, California's San Andreas fault--which runs through Los Angeles and San Francisco--has rocked the Earth before, and could very likely quake again. "They're an astonishingly similar set of beasts," says Stein. Both faults are known as strike-slip faults: tectonic plates slip past each other horizontally like a pair of trains passing in opposite directions (see diagram, p. 17). The fault lines in Turkey and in California both measure 1,000 km (620 mi) long and 12 m (40 ft) deep, and move at the same speed.

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So far, the San Andreas fault seems to have infrequent, but relatively large-scale quakes. San Andreas' largest recent quakes occurred in 1906 and 1989, when the fault released huge amounts of pent-up pressure that ran beneath and along adjoining tectonic plates. In contrast, Turkey's North Anatolian fault experiences generally smaller, more frequent quakes.

Seismologists have also noticed that each Turkish quake occurs just west of the previous one. Experts now fear that Istanbul, which lies directly in the "line" of cities hit, will be the site of the next calamitous quake. California's fate is far less certain. "What will happen in the next century depends on how long it takes the [San Andreas] fault to rebuild the stress released by the big earthquake in 1989," Stein explains.

At present, scientists have no method to predict earthquakes anywhere on Earth. But they hope to find clues from Turkey's latest disaster to better prepare them in years to come.