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Earthquakes in Chile
 
Chile earthquake, 2010. (Photo courtesy: Claudio Núñez)
 

By Ernenst Gurulé
egurule@lavozcolorado.com
 
11/18/2015

Sitting on the western-most coast of South America, it stands out; elongated and looking geographically undernourished. From north to south, its length exceeds the distance between New York and San Francisco. Yet from east to west, it averages just 112 miles in width.

But in this sliver of a country, there are three distinct and awe inspiring geographic regions, including one that holds the Atacama Desert, perhaps the driest spot on earth where less than two millimeters of moisture – hardly enough to fill a thimble – falls annually.

But this remarkable country has another side which is dark and malevolent and periodically rains down torrents of human suffering. Its fault – actually five faults – make it one of the most earthquake-prone zones on the planet. As a result, two of the most powerful earthquakes ever recorded – including one last September – have occurred in Chile.

Around sunset last September 16th, gigantic underground plates, some forty miles off Chile’s coast, began shifting and creating an unstoppable, rolling wave of energy that moved the earth for hundreds of miles in each direction. In its path stood coastal and slightly inland hamlets, including Illapel and Coquimbo.

In minutes, homes and buildings collapsed, tenements crumbled, countless structures were compromised. Fishing boats, once placid in the water, were left awkwardly docked on sidewalks. Nearly a dozen people were killed. And the aftershocks continued.

More than a hundred miles away in the capital, Santiago, residents were put on notice, as well. Buildings swayed and people fled into the streets, but no major damage was recorded. In Chile, lessons taught by an unforgiving nature, have been learned well.

“Most new construction in Central and South America,” says the University of Colorado-Denver’s Phil Gallegos, “now falls under seismic building code requirements.” The long-time professor of architecture has studied building construction throughout the two regions. A history pocked with earthquakes has forced a total rethinking of how building takes place. No longer, says Gallegos, can corners be cut or codes ignored in “new construction or reinforcement of historic, older buildings, like colonial buildings.”

Of course, these new requirements were adopted only after scores of painful earthshaking lessons. Because Chile lies just a zip code away from the Nazca and South American plates – among the world’s most active fault lines – earthquakes have been a fact of life.

In a five-year period beginning in 1570, scientists say Chile was rocked by three major quakes, the mildest registering at 7.3, the most severe at 8.5. Scientists have measured them according to what is called the Moment Magnitude Scale, a system that takes into account the total moment.

The U.S. Geological Survey, located in Golden, Colorado, defines ‘moment’ as a product of the distance a fault moved and the force required to move it. The long-used Richter scale is considered an inaccurate and obsolete measurement and is no longer used.

The U.S.G.S. says the difference between a 7.1 earthquake and one measuring 7.2 is not subtle. Basically, a 7.2 quake is 100 percent more severe than a 7.1 and releases 3.1 times more energy. The difference between a relatively minor 5.8 temblor to one measuring 8.7 is nearly 800 percent. And Chile has experienced both. In fact, the largest earthquake in modern history occurred in 1960 in Chile.

On May 22, 1960, “The Great Chilean Earthquake” hit. It measured 9.5 on the MMS. Across the country, thousands of buildings swayed or simply collapsed from the force leaving more than 2 million people homeless. So strong was its impact that buildings shook in Buenos Aires, more than 700 miles away. And it could have been worse.

Luckily, the quake hit in mid-afternoon and not when most of the country was sleeping. Nonetheless, it was a real-time nightmare with the aftershocks and tsunamis which ran well inland drowning untold numbers of people. In today’s dollars, damages would total upward of $6 billion.

The time when an earthquake hits is crucial. China’s Tangshan earthquake in 1976 – measuring 7.8 – hit at 3:42 a.m. Within 15 seconds, much of the city of a million people was destroyed. An aftershock measuring 7.1 hit later that day. It’s estimated that more than 240,000 deaths occurred with another nearly 170,000 serious injuries. Tangshan is the largest earthquake of the 20th century. It also occurred on a fault that, until then, was unknown.

Chileans know they live in a seismic hot zone, says U.S.G.S. researcher Gavin Hays. “The Nazca plate is converging with (the) South American (plate) and thrusting beneath South America along a very shallowly dipping fault plane.” As such, a good portion of the continent is on stand-by for the next ‘big one.’

But as fault planes go, Chile’s is rather diminutive, says Hayes, compared to others, stretching only 150 kilometers in length. The Sumatra fault, which generated the 2004 tsunami in Indonesia and killed more than 300,000 people, measures more than 1,300 kilometers. Japan’s – part of the so-called ‘Ring of Fire’ – is listed at 400 kilometers. It was responsible for the 2011 earthquake that killed 19,000 and resulted in billions in damage.

Earthquakes occur every single day in some part of the world, including Colorado. The state’s most active region for the ground shaking is around Trinidad, about three hours south of Denver. But, they have also happened intermittently across the state including Commerce City and Grand Junction. But the chance of a major quake hitting here, is probably remote, says Hayes. “We’re far away from global plate boundaries.”

Seismologists say the New Madrid fault, a 150 mile line that goes through five Midwestern states, and the west coast are the most likely spots for a major U.S. quake. The last significant quake to hit the Midwest occurred in 1812 and measured 8.0. Along the Pacific Coast they are regular occurrences. Earthquakes have been recorded along the Pacific Coast on a regular basis for years. (California has recorded nearly 275 5.0 quakes or larger in the last one hundred years.)

Because earthquakes measuring 5.0 occur on an irregular basis in Seattle, they must be taken seriously. And because a 6.8 quake took place in 1872 in the nearby Cascade Mountains, emergency planners know it could happen again. A straight line between Seattle and the quake is just 120 miles.

“It’s one of the top hazards,” says Barbara Graff, Seattle’s Director of the Office of Emergency Management. Graff says the recently discovered Seattle fault zone, which bisects Puget Sound and crosses the city, is a day-to-day concern.

While Seattle is a far cry from Chile or even southern California where quakes have caused major damage, the city’s location and natural geology present an omnipresent threat. Each time the ground shakes in Seattle, says Graff, the city upgrades its building codes. “I don’t want to allay fears,” she says, “because I don’t want to lessen people’s concerns.”

Despite the fact that science has come to understand earthquakes and their residual properties, including aftershocks that can sometimes continue weeks after the initial jolt, predicting the next one or even ‘the big one’ remains elusive. “We’re nowhere near being able to do that,” says Hayes.

What science can do, says Hayes, is study historic earthquakes and the faults they occur on. That may hasten learning about the time scales that they occurred on. For the time being, predicting “the big one” will be left to soothsayers, television hucksters or alarmists.

In the meantime, science has learned that when a major earthquake has occurred the chances of it repeating itself in the same place soon after is remote. Hayes likens it to an exhausted budget. “You have to spend time accumulating that budget before you can release it again.” Of course, he adds, an equally devastating quake can occur just a bit farther up or down the same fault line.

 

 

 

 

 
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