While Earthquakes are sometimes believed to be a West Coast phenomenon, there are 45 states and territories throughout the United States that are at moderate to high risk from earthquakes. An earthquake is the sudden, rapid shaking of the Earth, caused by the braking and shifting of subterranean rock.

The Cumberland Plateau is located within a close proximity of the New Madrid Seismic Zone (NMSZ). The NMSZ extends southward 150 miles from Cairo, Illinois down the Mississippi River to Dyersburg, Tennessee. Today this area includes the metropolitan populations of St. Louis and Memphis. Along the line is a series of geological rifts running through the Mississippi River Valley. These rifts are in the middle of a geological plate, not on the edge where most earthquakes occur. In 1811 a “bubble” began to rise near the frontier town of New Madrid, Missouri not far north of Tiptonville, Tennessee. When it burst the pressure was not fully relieved for years. The earthquakes came in heavy waves, and there nearly 2,000 quakes from November 16, 1811 to March 15, 1812. “The probability of magnitude 6.0 or greater in the near future is considered significant; a 90% chance of such an earthquake by 2040 has been given.( http://en.wikipedia.org/wiki/New_Madrid_Fault_Zone )”

The Southern Appalachian Fault also has a large affect on the Cumberland Plateau. “The southern Appalachians contain one of the most active seismic zones in eastern North America. Twenty years of monitoring has revealed a belt of seismicity in northeastern Alabama, northwestern Georgia and much of eastern Tennessee. The Eastern Tennessee seismic zone presents many questions. Since 1982, 44 felt earthquakes have occurred in the denser zone of activity and 35 have had magnitudes exceeding 3.0. However, the largest historical shock was magnitude 4.6, and occurred in 1973. (http://gsa.confex.com/gsa/2002NC/finalprogram/abstract_32405.htm ).”

A broad map of the Seismic Hazard of the Southeastern US can be seen below…

Below is a more detailed map showing the Seismic Hazard for Cumberland County…

Percent G is a measure of the gravitational forces caused by the shaking of the earth. The intensity of an earthquake is typically measured in the United States using the Modified Mercalli Scale.

What is the relation to building damage?

“NOTE: The 10 percent g value was chosen because on the average it corresponds to
Modified Mercalli Intensities VI to VII, levels of threshold damage, in California, for
ground motions within 25 km of the earthquake epicenter. (http://earthquake.usgs.gov/research/hazmaps/haz101/faq/parm02.php )”

A Hertz is a unit of measurement commonly used in earthquake measurements that expresses the frequency per second in the rise and fall of an electromagnetic wave, as can be seen in the following picture…

“Electromagnetic waves range from less than one hertz (used speculatively in seismology for earthquake prediction) through visible light near 10¹⁵ Hz. to cosmic ray radiation up to 10²⁵ Hz. (http://ptolemy.eecs.berkeley.edu/eecs20/sidebars/hertz )”

The maps below depict the probability of a 5 Hz Earthquake in 25 years, 50 years, and 100 years…

Since it is not possible to predict when an earthquake will occur, it is essential that you and your family are prepared ahead of time.

Prepare for Earthquakes

• Securely fasten shelves to walls.
• Keep large or heavy objects on lower shelves.
• Store breakable items in lower cabinets with doors and latches.
• Inspect and repair electrical wiring and gas connections; these can be potential fire hazards during an earthquake.
• Secure your water heater by strapping it to wall studs and bolting it to the floor.
• Check your home or building for structural defects and repair cracks in your ceiling and foundation.
• Keep toxic and flammable items securely stored in cabinets with doors and latches.
• Identify safe places in your home or office where you will ride out an earthquake. The best protection is under heavy furniture where you are protected from falling debris.
• Learn how to turn off electricity, gas and water.
• Get an emergency supply kit.

Plan to act Quickly

• During or immediately after an earthquake, the best protection is to get under heavy furniture, such as a desk, table or bench, staying away from large windows, mirrors or other glass.
• The greatest danger is directly outside buildings, at exits and along exterior walls, due to falling debris.
• If you are already outside, stay clear of buildings, power lines, overpasses and elevated expressways.
• Most deaths and injuries are due to falling walls, flying glass or debris.
• Expect aftershocks – smaller quakes (and sometimes larger ones) can often follow hours or days after the initial shake, causing further damage to weakened buildings and structures.
• Check for gas leaks – if you smell gas or hear a hissing or blowing noise, open a window and leave the building immediately; turn off the gas at the outside main valve, if possible and call the gas company.

Stay Informed

Local authorities may not immediately be able to provide information on what is happening and what you should do. However, you should watch TV, listen to the radio or check the Internet often for official news and instructions as they become available.

Information on this page was obtained from Ready.gov

For further information on how to plan, prepare and stay informed about earthquakes, visit: Federal Emergency Management Agency or visit NOAA Watch for more weather-related information.