The New Madrid fault -- near where Missouri, Kentucky, Arkansas, and Tennessee meet -- witnessed an 8.0 or greater magnitude quake nearly 200 years ago. The shaking spread so far that church bells reportedly rang in Boston, more than 1,500 miles away! It had dramatic effects on the area's geography, lifting up land enough to make the Mississippi River appear to flow upstream. Fortunately, the sparsely populated area suffered only one death and minimal property damage.
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The San Andreas is the most famous and closely watched fault line in the world. HowStuffWorks looks at how overdue we are for the next big quake.