Fault Lines in the United States

With Tuesday’s 5.9 temblor rattling nerves along the East Coast, attention is being turned to other parts of the United States and North America that may be at risk for damaging earthquakes. Most people have heard of the well-known San Andreas fault in California and the New Madrid Seismic Zone in the central United States, but there are other faults that are worth knowing about:

Wabash Valley Seismic Zone

Most of the southern third of Illinois and a large chunk of southwestern Indiana is nestled right in the Wabash Valley Seismic Zone. Wabash Valley butts right up against the northern edge of the New Madrid fault system that was responsible for historic earthquakes in 1811 and 1812. The last sizeable earthquake to shake in the Wabash Valley fault system was a 5.2 magnitude temblor on April 18, 2008.

While the potential risk for a major earthquake in the Wabash Valley is uncertain, the proximity to the more well-known New Madrid Seismic Zone causes concern among residents. It is uncertain if a large quake along either fault system could trigger a quake within the nearby system but the potential is always worth making note of.

Cascadia Subduction Zone

The Pacific Northwest may be one of the most overlooked fault zones in the United States. This system of faults known as the Cascadia Subduction Zone runs roughly between Vancouver, British Columbia, and northern California along the West Coast of the United States. The Cascadia zone is situated where the Juan de Fuca tectonic plate subducts underneath the North American plate — creating both volcanic activity and earthquakes in the Pacific Northwest. Most recently, a 3.5 magnitude quake was registered at the northern edge of this fault zone on Vancouver Island on Aug. 17. This quake had an epicenter about 48 miles southwest of Campbell River, British Columbia.

Realistically, the 680-mile-long Cascadia is at risk for a major earthquake that could rival the 9.0 Tohoku earthquake in March. Past history has shown massive quakes that created 15-foot high tsunami waves and the last major and damaging rupture of this fault system occurred in 1700 when a 9-magnitude quake sent a tsunami crashing into Japan. Some experts have asserted that there is an 80 percent chance of a deadly quake in the southern Oregon and northern California portion of this fault system — within the next 50 years.

Sangre de Cristo Fault

The Sangre de Cristo fault located at the New Mexico and Colorado border region is a 59-mile-long fault and runs along the Sangre de Cristo mountains that are situated running north and south between Colorado and New Mexico.

The last sizeable earthquake with an epicenter near this fault system occurred on Aug. 22, 2011 — just one day prior to the earthquake that rattled Virginia. This quake was registered as 5.3 in magnitude. This particular temblor in Colorado was the largest in the state since the early 1970s.

Gulf-Margin Normal Faults

The Gulf-Margin Normal faults in the Gulf of Mexico area in the southeastern United States is a little-heard-of fault zone. This is a group of faults that border the northern edge of the Gulf in western Florida, southwestern Alabama, southern Mississippi, the whole state of Louisiana, southern Texas and a portion of southern Arkansas. This grouping of seismic faults have only produced about four damaging earthquakes prior to 1989. These were located in western Florida in 1780, the southern part of Louisiana in 1930, eastern Texas in 1891 and 1932. A 4.9 magnitude quake in southwestern Alabama in 1997 may have been triggered by oil and gas fracking, so it is difficult to determine the definite risks for this series of faults. Like any seismic fault, an earthquake of any size and intensity could occur without warning.

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