http://www.washingtonpost.com/wp-dyn/content/article/2010/02/22/AR2010022204828.html?wpisrc=nl_pmheadline
Under the world's greatest cities, deadly plates
By Joel Achenbach
Washington Post Staff Writer
Tuesday, February 23, 2010
Megacities are something new on the planet. Earthquakes are something very old.
The two are a lethal combination, as seen in the recent tragedy in
Port-au-Prince, where more than 200,000 people perished -- a catastrophe that
scientists say is certain to be repeated somewhere, and probably soon, with
death tolls that once again stagger the mind.
In 1800, there was just one city with more than a million people -- Beijing.
Now there are 381 urban areas with at least 1 million inhabitants. Urbanization
crossed a threshold last year when, for the first time, more people lived in
city settings than rural ones. About 403 million people live in cities that
face significant seismic hazard, according to a recent study by seismologist
Roger Bilham of the University of Colorado.
The next Big One could strike Tokyo, Istanbul, Tehran, Mexico City, New Delhi,
Kathmandu or the two metropolises near California's San Andreas Fault, Los
Angeles and San Francisco. Or it could devastate Dhaka, Jakarta, Karachi,
Manila, Cairo, Osaka, Lima or Bogota. The list goes on and on.
"You can name about 25 cities that are like Port-au-Prince. They're not going
to shake but every 250 years [on average]. But if you can name 25 of them,
you're going to have an event like this every 10 years," said David Wald, a
seismologist with the U.S. Geological Survey.
In many vulnerable cities, people are effectively stacked on top of one another
in buildings designed as if earthquakes don't happen. It is not the tremor that
kills people in an earthquake but the buildings, routinely constructed on the
cheap, using faulty designs and, in some cities, overseen by corrupt
inspectors. The difference between life and death is often a matter of how much
sand went into the concrete or how much steel into a supporting column.
Earthquakes might be viewed as acts of God, but their lethality is often a
function of masonry.
"In recent earthquakes, buildings have acted as weapons of mass destruction,"
Bilham writes in the journal Nature.
Difficult to predict
For years, earthquake scientists have shouted their warnings about the strong
likelihood that a major quake would level an impoverished city and kill
hundreds of thousands of people. They have said, for example, that Kathmandu,
where masonry structures expand so haphazardly that some eventually cantilever
over narrow city streets, is every bit as vulnerable as the surrounding
Himalayas are majestic. They have said that a million people could die in a
major quake in Tehran.
What's impossible, however, is knowing precisely which of these cities will be
the next to crumble. Or when. For all practical purposes, scientists can't
predict earthquakes.
The theory of plate tectonics, largely developed since the 1960s, explains why
earthquakes happen in general. The major plates of the earth's crust move
constantly, creeping along at about the speed of fingernail growth. They rarely
move smoothly past one another but are usually locked in place. On a
strike-slip fault of the type that ruptured in Haiti, strain builds on the
fault line for decades or centuries. The fault in Haiti had not ruptured in 240
years. An earthquake is a sudden, stress-relieving event. The fault is said to
"break."
Scientists can map faults and estimate how much strain has accumulated since
the last quake. What they can't do is say that a given fault will break
tomorrow or next year or 10 years from now. Any calculation of earthquake
probabilities has a lot of slop in the numbers.
"The problem is, the slop is huge on a human time scale," said Susan Hough, a
seismologist with the U.S. Geological Survey. "We're wired to deal with the
immediate. We're not geared to plan and stress about things likely to happen in
30 years."
Some large earthquakes have small precursors, called foreshocks, but others
happen without warning. There is one famous case of earthquake prediction, in
Haicheng, China, in 1975. A local official sounded the alarm after many
foreshocks and reports of snakes emerging from hibernation. But that prediction
was more akin to a hunch than a scientific argument. There have been countless,
less publicized instances when predicted earthquakes did not materialize.
As Hough notes in her book "Predicting the Unpredictable," the successful
prediction of earthquakes was an official government mandate in Mao Zedong's
China, but no one foresaw the killer quake that took at least 240,000 lives in
Tangshan in 1976.
Port-au-Prince had not been hit with a major quake since the days of French
rule in the 18th century. Only in recent years have scientists mapped the fault
that runs near the city.
"Just the beginning of work had been done. But enough was known that it could
produce a big earthquake," said Carol Prentice, a geologist with the U.S.
Geological Survey. "We knew it would be bad, but I didn't imagine that it would
be this bad."
Time bombs
Prentice had been to the island of Hispaniola and had studied a different,
roughly parallel fault called the Septentrional, which runs along the island's
northern edge. It had been difficult getting into Haiti, she said, so she and
her fellow scientists focused their work on the Dominican Republic. That fault
is another time bomb, threatening the Dominican city of Santiago, with a
population of more than 1 million, Prentice said.
The entire Caribbean is seismically active. So is much of Central America. The
next Big One could be on the isthmus of Panama, where Panama City sits just six
miles from a major fault that hasn't ruptured in four centuries, said Mary Lou
Zoback, a seismologist who works for the California-based Risk Management
Solutions.
Or the next catastrophe could be in Caracas, Venezuela, where millions of
people live in poverty near a boundary of two tectonic plates, including the
one that created the fault that broke in Haiti. The last catastrophic quake was
198 years ago. Zoback said that relief groups have donated bricks to poor
people in Caracas to help them build homes but that unreinforced brick
dwellings are death traps in an earthquake.
Another seismic bull's-eye is Mexico City, which sits on the worst possible
soil, a drained lake bed that will intensify seismic waves. The city also is in
a basin in the mountains, which essentially traps the seismic waves. The
devastating earthquake of 1985, which killed about 10,000 people, was centered
hundreds of miles away but managed to ring Mexico City like a bell.
Earthquakes can turn up closer to home than many Americans realize. Several
major tremors have been recorded off the East Coast, including near
Newfoundland in 1929 and Boston in 1755. Charleston, S.C., had a quake in 1886
that killed 60 people. Hough, of the USGS, said it might be that all three
earthquakes were associated with the edge of the continental shelf and that any
coastal city, including Washington, could get rattled by a quake someday.
Another hazard is right in the Mississippi River valley. Memphis is close to
the New Madrid fault, which caused powerful earthquakes in 1811 and 1812.
By some measures, the American city at greatest risk of a disastrous earthquake
is New York.
Although New York City is rarely thought of as earthquake country, the region
experiences many small tremors that indicate that larger ones are possible. The
good news is that a magnitude-6 earthquake should happen only every 670 years
or so. A magnitude-7 tremor should happen every 3,400 years. That's the
calculation by scientists at Columbia University who studied 383 much smaller
tremors recorded in the New York area from 1677 to 2007.
The bad news is that there is a massive amount of infrastructure built without
earthquakes in mind.
"A lot of old brownstones -- they crumble well," Zoback said.
Mitigating destruction
Urbanization is a steady process. In the next half-century, the planet will add
about 5 billion people and build about 1 billion housing units, Bilham
estimates. The question is whether those people will live in buildings designed
for a sometimes shaky world.
Brian Tucker, an earth scientist who leads GeoHazards International, said 10
percent of the money going to help Haiti rebuild should be dedicated to
mitigating the destruction in earthquakes. But he also knows from many years of
sounding warnings about possible earthquakes that people tend to be complacent
about catastrophes that have yet to happen.
"People who advocate diet and exercise are chumps, and heart surgeons are
heroes," Tucker said.
Bilham said he would like to see the United Nations develop a
building-inspection program akin to its efforts to look for banned nuclear,
biological and chemical weapons. Zoback, likewise, is impatient for action that
could save lives:
"We know where the problems are. We know what to do. We know how to fix it. We
just need the political will."
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http://www.washingtonpost.com/wp-dyn/content/graphic/2010/02/23/GR2010022301120.html?sid=ST2010022204582
Mega-growth in a seismic world
In 1950, the world was home to seven metropolitan areas with a population of 5
million people. Today there are more than 50. The potential of a significant
earthquake occurring near or in a megacity is seen as inevitable as urban
populations continue to rise.
SOURCE: Global Seismic Hazard Assessment Program, United Nations Population
Division | Laris Karklis/The Washington Post - February 23, 2010
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