2010 Metro Mitigation Plan

The Southern Appalachian Seismic Zone (SASZ) extends from Alabama to Virginia with the
most recent activity extending from northwestern Georgia through east Tennessee (the portion
known as the East Tennessee Seismic Zone or ETSZ) (Figure 4.7b). The ETSZ is the most
active seismic region in the eastern United States. Given the rate of seismicity in the ETSZ, it
is somewhat surprising that the largest known earthquake in the ETSZ was the 1973 Alcoa,
Tennessee earthquake, which had a magnitude of only 4.6 on the Richter magnitude scale.
Figure 4-7b. Schematic Map of East Tennessee Seismic Zone
Several methods, compared in Table 4-19, have been developed to quantify the strength of an
earthquake. The most recognized methods for measuring earthquake strength are:
Richter Magnitude is a measure of earthquake strength or the amount of energy
released. Charles Richter originally developed this scale in 1935. Magnitude is
expressed in whole numbers and decimals, with each succeeding whole number
representing a tenfold increase in the energy released. There is only one Richter value
calculated for the epicenter of a specific earthquake. (The epicenter is the location on
the surface of the earth directly above where an earthquake originates. It is
determined by measuring the amplitudes of ground motion on seismograms.)
Modified Mercalli Intensity Scale is an evaluation of the severity of ground motion
at a given location measured relative to the effects of the earthquake on people and
property. This scale was developed by Wood and Nueman in 1931, based on
Mercalli‟s 1902 original version. Intensity is expressed in Roman numerals I – XII.
Metropolitan Nashville - Davidson County
Hazard Identification
Multi-Hazard Mitigation Plan Page 4-44
April 2010