for National Geographic News
Californians know earthquakes. Many residents living near the infamous San Andreas Fault have likely felt their share of minor tremors and maybe even a few violent quakes.
But the approaching anniversary of the great 1906 earthquake that leveled San Francisco has some seismologists turning their attention to a completely different section of the United States.
It's the middle of the country, these scientists say, that could be at risk from the next "Big One"and cities there aren't ready for the shock.
The New Madrid seismic zonewhere Missouri, Kentucky, Arkansas, and Tennessee meetlies in the middle of the North American tectonic plate, thousands of miles from the plate boundaries where earthquakes usually occur.
The zone has three to five faults stretching about 120 miles (193 kilometers).
Mark Zoback is a geophysicist at Stanford University in Palo Alto, California, who has studied the New Madrid system for three decades.
He and other experts warn that the region has a recent history of recurring seismic events, including three massive quakes that hit Missouri in 1811-1812.
But modern cities in the New Madrid zone are ill-prepared and could be destroyed if a similarly big earthquake hit them today, the scientists say.
Zoback and his colleagues presented their latest findings at the annual meeting of the American Association for the Advancement of Science this past February in St. Louis, Missouri.
Most earthquakes occur at the edges of the tectonic plates that move across the surface of the Earth. Quakes are produced when the plates move over, under, or against each other.
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