AS107, Tuckaleechee Caverns,
Tennessee, United States
Thumbnail profile: Tuckaleechee Caverns, Tennessee
Carved out over tens of thousands of years in one of the Earth's oldest mountain chains, Tuckaleechee Caverns at Townsend, Tennessee are known as the "Greatest Site Under the Smokies".
Estimated to be between 20 and 30 million years old, the Cherokee Indians knew of the Caverns and used them as a hiding place before the white man discovered them about 1850.
Cherokees lived in this part of the United States until the 1840s when most of them were forced to move to Oklahoma in a bitter winter trip known as “The Trail of Tears.” Some who refused to leave were eventually granted land in western North Carolina at the town of Cherokee.
Whitemen began to settle this area in the late 1700s and the early 1800s. They discovered the caverns around the middle of the 19th century when sawmill workers watched water from a heavy rain pour into a sink hole in the area. The hole was filled with debris but one of the men found an opening in the rock and made his way to what is now the entrance of the caverns.
Geology and Environment
Tuckaleechee Caverns are located in Tuckaleechee Cove, one of five geological windows through overlying Precambrian strata, which exposes the older limestone of the Knox formation. The cave is a typical karst formation, a landscape formed by the dissolution of layers of soluble bedrock, such as limestone or dolomite, by water.
The climate is moderate and continental with hot, humid summers. Winters are mild with scant snowfall. Strong winds and hurricanes occasionally hit the area.
Within the cave (where sensor and digitizer are installed), the temperature is constant at approximately 15°C year round, which is beneficial for the precision of seismic measurements. Although humidity is close to 100%, due to the low temperatures, there is little condensation on equipment.
The United States hosts more International Monitoring System (IMS) facilities than any other Comprehensive Nuclear-Test-Ban Treaty (CTBT) Member State: these include five primary and 11 auxiliary seismic stations in addition to AS107, two hydroacoustic stations, eight infrasound stations, 11 radionuclide stations and one radionuclide laboratory.
Mandate of Auxiliary Seismic Stations
Auxiliary seismic stations are mandated to provide data to the International Data Centre (IDC) upon request only but then with immediate availability. The purpose of this additional data is to improve location accuracy of seismic events detected by the primary seismic network. It is also to characterize the seismic sources with greater precision in order to ascertain what kind of event has taken place; for example, an earthquake or an explosion.
IMS Station Location
AS 107 is the only IMS seismic station to cover the large eastern part of the United States. The station is privately owned but can be accessed any time of the year by prior arrangement with the owners. The cave is generally open daily to the public from mid-March to mid-November.
The original seismic station was established in 1978 by the Tennessee Earthquake Information Center (TEIC) as part of its network in cooperation with Tennessee Valley Authority (TVA). The University of Tennessee at Knoxville (UTK) took over responsibility for the TVA seismic network in 1995.
All seismic stations, including this one at Tuckaleechee Caverns, have three basic parts: a seismometer to measure the ground motion, a recording system which records the data digitally with an accurate time stamp, and a communication system interface.
AS 107 is connected to the public AC power grid and is equipped with a back-up capacity of approximatively two hours.
This station is, in principle, a very quiet site although regional mining activities create a certain amount of “noise” during weekday mining operations. To a lesser extent, occasional car traffic in the Cavern’s parking lot seems to show up on seismograms.
Testing and Certification
The AS107 station upgrade was completed in July 2005 for seismic equipment and in June 2006 for the Global Communications Infrastructure (GCI). In June 2006 the station was connected to the IMS lab and has been sending continuous data ever since. The station parameters were accepted by the IDC in August 2006.
The first station visit was conducted in July 2005 in order to install equipment. The GCI had to be relocated to a new location with a better view of the satellite, which was completed in 2006. A second station visit was undertaken in June 2006 to complete the GCI installation, implement network connections and carry out certification tests. The station started sending data to the IDC in June 2006.
In terms of data availability, continuous data have been received in the IMS lab since June 2006 without any interruption (i.e. 100% data availability) and all automatic data requests have been satisfied promptly. Accordingly, AS107 was certified on 22 August 2006.