this ancient slab of the Pacific finally dives down to oblivion, dragging on the earth above and tugging at New Madrid.

Then, from the east. The Mid-Atlantic Ridge is a colossal underwater mountain range in the middle of the Atlantic Ocean that runs from the Arctic to nearly the Antarctic. It has been pushing North America away from Europe and Africa for 200 million years. The stress from that distant mid-ocean push might be transmitting all the way to the middle of the United States. And so New Madrid buckles. From the north, there used to be tremendously heavy sheets of ice more than a mile thick that covered the top half of North America until a very recent 12,000 years ago. As these ice sheets have retreated, andNorth America has been relieved of its Ice Age burden, the continent still unbends—a strain that might be tweaking New Madrid. Finally, from above. The writhing Mississippi River, which whips sediment back and forth throughout the delta, constantly shifts the load atop the ancient faults of the Reelfoot Rift, potentially setting them off. Whatever the reason, the rift came alive a few thousand years ago. Though New Madrid earthquakes undoubtedly came as a surprise to European settlers in the 19th century, they were a recurring peril for the epic civilization that came before. * * * From the top of Monks Mound in southern Illinois, the St. Louis Arch is a hazy mirage on the horizon. At almost 100 feet tall the mound itself is a terraced pyramid