New Madrid

That's Maa-drid, emphasis on the first syllable, not pronounced like the capital of Spain, don'tcha know.

The greatest earthquake risk east of the Rocky Mountains is along the New Madrid fault system. Damaging earthquakes are much less frequent than in California, but when they do occur, the damage can be far greater, due to the underlying geology.

The New Madrid fault system, or the New Madrid seismic zone, is a series of faults beneath the continental crust in a weak spot known as the Reelfoot Rift. It cannot be seen on the surface. The fault system extends 150 miles southward from Cairo, Illinois through New Madrid and Caruthersville, Missouri, down through Blytheville, Arkansas to Marked Tree, Arkansas. It dips into Kentucky near Fulton and into Tennessee near Reelfoot Lake, and extends southeast to Dyersburg, Tennessee. It crosses five state lines, and crosses the Mississippi River in at least three places.

Here's the USGS link to the story of the great (magnitude 8) quakes of the winter of 1811 - 1812.

The Mississippi Valley-"Whole Lotta Shakin' Goin' On"

In the winter of 1811-12, the central Mississippi Valley was struck by three of the most powerful earthquakes in U.S. history. Even today, this region has more earthquakes than any other part of the United States east of the Rocky Mountains. Government agencies, universities, and private organizations are working to increase awareness of the earthquake threat and to reduce loss of life and property in future shocks.

The 400 terrified residents in the town of New Madrid (Missouri) were abruptly awakened by violent shaking and a tremendous roar. It was December 16, 1811, and a powerful earthquake had just struck. This was the first of three magnitude-8 earthquakes and thousands of aftershocks to rock the region that winter.

Severe shaking accompanied the powerful New Madrid earthquakes that struck during the winter of 1811-1812. By winter's end, few houses within 250 miles of the Mississippi River town of New Madrid (Missouri) remained undamaged.

Survivors reported that the earthquakes caused cracks to open in the earth's surface, the ground to roll in visible waves, and large areas of land to sink or rise. The crew of the New Orleans (the first steamboat on the Mississippi, which was on her maiden voyage) reported mooring to an island only to awake in the morning and find that the island had disappeared below the waters of the Mississippi River. Damage was reported as far away as Charleston, South Carolina, and Washington, D.C.

These dramatic accounts clearly show that destructive earthquakes do not happen only in the western United States. In the past 20 years, scientists have learned that strong earthquakes in the central Mississippi Valley are not freak events but have occurred repeatedly in the geologic past. The area of major earthquake activity also has frequent minor shocks and is known as the New Madrid seismic zone.

Earthquakes in the central or eastern United States affect much larger areas than earthquakes of similar magnitude in the western United States. For example, the San Francisco, California, earthquake of 1906 (magnitude 7.8) was felt 350 miles away in the middle of Nevada, whereas the New Madrid earthquake of December 1811 (magnitude 8.0) rang church bells in Boston, Massachusetts, 1,000 miles away. Differences in geology east and west of the Rocky Mountains cause this strong contrast.

[Continued]

UPDATE: From the BU Bridge comes this tidbit:

But New England doesn’t have serious earthquakes, does it? “Not compared to California,” says Abercrombie. “The rock here is much more stable.” While California earthquakes occur along major faults, those in New England do not. New England is near the center of the North American tectonic plate, and earthquakes here are “internal plate quakes” produced by stress that builds up under the continent, rather than near a major boundary separating two of Earth’s tectonic plates, as is the case in California.