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Earth Sense: Severe quakes are common in Pakistan

POSTED: October 12, 2013 5:18 p.m.

Recently, southwestern Pakistan was rocked by a 1-2 punch of major earthquakes. The first one Sept. 24 had a magnitude of 7.7. For comparison, the Loma Prieta Quake which struck the Santa Cruz-San Francisco, Calif., area in 1989 was a 6.9. That was sufficient to collapse parts of Interstate 880, burying motorists beneath concrete. On the Bay Bridge, an entire section disengaged, causing cars to fall into the gap.

The Pakistan quake, with an epicenter about 150 miles from the country’s western coast, was almost 10 times as powerful. Every full number increase on the Richter magnitude scale stands for a tenfold rise in strength.

More than 300 lives were lost in the one of Sept. 24. The region, southern Belochistan, had been a setting for such a disaster all along. Loose, unconsolidated sediment and rock debris covers much of the ground. In a quake, this tends to make the shaking worse by shifting and collapsing. Many buildings were made of mud brick that offers little structural strength.

When a second quake followed Sept. 27 with a magnitude of 6.8 (U.S. Geological Survey), there were few houses left to collapse, but further damage and a terrorized local population were inevitable.

The region has an unfortunate predestination for severe earthquakes. Pakistan is located northwest of India. The Arabian Sea ends at the country’s main coastline, which runs from east to west. At that exact location, not two but three major tectonic plates come together. The boundaries of these plates, which form the mosaic of the earth’s solid crust, are prone to motion and friction.

Where two plates rub against one another, like in California, quakes are common. But Belochistan is at the intersection of the massive African Plate, the smaller Arabian Plate, and the huge Indian-Australian Plate which in the earth’s past has heaved the world’s tallest mountains out of the ground. Little wonder then that a new island rose from the ocean just offshore from the town of Gwadar. It mimics, on a small scale, how the world’s large mountain chains have formed.

In Eurasia, it’s the Himalayas, north of India and Pakistan. On our continent, these chains are the Sierra Nevada and the much older Appalachians.

Being a focus of global geology is of little help to the population of Belochistan right now, though, who needs disaster relief more than anything else.

Rudi Kiefer, Ph.D., is a professor of physical science and director of sustainability at Brenau University. His column appears Sundays and at gainesvilletimes.com.


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