Earthquake Shakes Local Region

Published by Editor on November 26, 2012. · · Share this Article

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Some Jefferson County residents slept thought the earthquake, while others were awoken by the thunderous noise. The earthquake, which struck on Saturday morning November 24th, had an epicenter was five miles from Sevierville. The quake registered a 3.0 magnitude and provided an early wake up call as it arrived at 6:03 a.m. A second quake in nearly the same spot occurred later that same morning at 9:56. Registering a 2.5 magnitude, the second quake was only four miles from Sevierville. This is the second and third recent earthquakes in East Tennessee in recent weeks, with a 4.3 magnitude earthquake happening earlier this month on November 10th. With all of the earthquake activity in our area recently, it brings to light the question of how long East Tennessee has dealt with earthquakes. How big have they gotten? What is the past history and what can we expect to come?

What exactly is an earthquake? An earthquake is caused by the breaking and shifting of rock beneath the Earth’s surface. Several thousand shocks of changeable sizes occur annually in the United States, and 70 to 75 damaging earthquakes occur throughout the world each year. All 50 states and all U.S. territories are susceptible to earthquakes. Where earthquakes have occurred in history, they will likely happen again.

What can be expected from earthquakes? Most earthquakes in our region are small tremors. Often there are complaints of cracked walls, shaken homes, upset animals, but very few reported injuries. But most earthquake-related injuries result from collapsing walls, flying glass, and falling objects. Earthquakes strike suddenly, violently, and without warning at any time of the year and at any time of the day or night. Smaller earthquakes habitually follow the main shock. Ground shaking from earthquakes can collapse buildings and bridges, disrupt gas, electric, and phone service and sometimes trigger landslides, avalanches, flash floods and fires.

Past history of Earthquakes in our region consist of many larger quakes on the west side of the state, while there have been smaller tremors locally. The quakes have been monitored beginning in the mid 1800’s. Since that time earthquakes from as small as 1.0 to over 8.0 have been recorded. The Eastern Tennessee seismic zone extends across Tennessee and Northwestern Georgia into Northeastern Alabama. It is one of the most active earthquake areas in the Southeast. Earthquakes too small to cause damage are felt about once a year. Earthquakes too small to be felt are abundant in the seismic zone, and seismographs have recorded hundreds of them in recent decades. Earthquakes in the Central and Eastern U.S., although less frequent than in the western U.S., are typically felt over a much broader region. Earthquakes everywhere occur on faults within bedrock, usually miles deep. Most of eastern Tennessee’s bedrock originated several hundred million years ago, as the Appalachian Mountains were formed. The Eastern Tennessee seismic zone is far from the nearest plate boundaries, which are in the center of the Atlantic Ocean and in the Caribbean Sea. The Eastern Tennessee seismic zone is laced with known faults but numerous smaller or deeply buried faults remain undetected. Even the known faults are poorly located at earthquake depths. Accordingly, few, if any, earthquakes in the Eastern Tennessee seismic zone can be linked to named faults. It is difficult to determine if a known fault is still active and could slip and cause an earthquake ref CITATION USG12 l 1033 (USGS.gov)

Because earthquakes are relatively commonplace in East Tennessee it is important to be knowledgeable about their potential impact. Due to the location of the most recent earthquakes and their proximity to the Douglas and Cherokee Dams, TVA confirmed that an inspection of the areas surrounding the dams, as well as the Watts Bar Nuclear Plant had been investigated for possible compromise from the quake. TVA will be releasing pertinent information as it becomes available, however no current damage has been reported. The Report Card for American Infrastructure produced by American Society of Civil Engineers has reported that of Tennessee’s dams, there are 148 high hazard dams in Tennessee. A high hazard dam is defined as a dam whose failure would cause a loss of life and significant property damage. In addition, 6 of Tennessee’s 658 dams are in need of rehabilitation to meet applicable state dam safety standards.

On the national level, The National Earthquake Hazards Reduction Program (NEHRP) leads the federal government’s efforts to reduce the fatalities, injuries, and property losses caused by earthquakes. Congress established NEHRP in 1977, directing that four federal agencies coordinate their complementary activities to implement and maintain the program. These agencies are FEMA, the National Institute of Standards and Technology, the National Science Foundation, and the U.S. Geological Survey. New building codes have been put into place, but only for new construction. The federal government’s FEMA plays a key role in developing the seismic provisions of model building codes and associated design standards FEMA also maintains several grant programs that help state and local governments plan and implement earthquake mitigation measures. FEMA has produced many of the publications used to document and promote seismic rehabilitation methods and the consensus recommendations that the agency helps to develop on improving building codes. FEMA works with code- and standards-development organizations to incorporate these recommendations into nationally applicable model building codes and standards.

Source: Robin Archer, Jefferson County Post Staff Writer