The INL operates both seismic and accelerograph networks for the purpose of documenting earthquake information in support of INL operations and programs. The INL seismic network began in 1971 with a single station and evolved into a three-station network by October of 1972 for the purpose of developing a historical earthquake database. Throughout the 1980’s and early 1990’s additional seismic stations were installed to improve earthquake monitoring of earthquake sources that may affect INL facilities. These sources include the volcanic rift zones within the eastern Snake River Plain, range-bounding faults along the southern portions of the Lost River Range, Lemhi Range, and Beaverhead Mountains, and background seismicity in the Intermountain Seismic Belt. Currently, the INL operates 27 seismic stations located throughout southeastern Idaho.
The INL accelerograph network began in 1973 when 11 strong-motion accelerographs were installed in buildings at the INL Site. Additional strong motion accelerographs were installed at the INL Site following the 1983 M 7.3 Borah Peak, Idaho earthquake and at seismic stations in 2002. At the INL Site, the strong-motion accelerographs are located within buildings at basement, floor and rooftop levels and outside of buildings at ground surface level (referred to as free-field sites). The strong-motion accelerograph locations at the INL Site have been selected to provide information on the building, ground surface, and soil-building responses to strong ground motions of future large earthquakes. At seismic stations, three-component accelerometers were installed to record near-field acceleration data from small to large magnitude normal faulting earthquakes. The INL currently operates 31 strong-motion accelerographs.
INL seismic stations (red triangles) are located near potential sources of earthquakes such as range bounding faults and volcanic rift zones. Accelerometers (inverted red triangles) and continuous GPS receivers (yellow solid circles) are co-located at some INL seismic stations.
INL Seismic Station Instrumentation
A view to the southeast of seismic station Italian Canyon located along the Beaverhead fault.
The INL short-period seismic stations are composed of one or three seismometers. A single-component station has a vertically oriented seismometer that is either a Teledyne Geotech model S-13 or S-13 borehole Jr. Eleven stations within the eastern Snake River Plain have vertical seismometers located in 20-m (or 65 ft) deep boreholes. The remaining stations have vertical seismometers buried within 3 m (or 10 ft) of the ground surface near rock outcrops or set upon concrete pads affixed to rock outcrops. Five seismic stations have three-components, one vertically oriented sensor as described previously and two horizontally oriented Teledyne Geotech model S-13 seismometers located within concrete vaults. Additionally, six seismic stations have Applied MEMs Inc. model SF1500A tri-axial accelerometers (described below) and two have UNAVCO continuous recording GPS (Global Positioning System) (see crustal deformation) receivers collocated at them.
The seismic stations have DAQSystems NetDAS recording units with an embedded LINUX computer, a GPS clock and Symmetric Research 24 bit digitizer. The NetDAS time stamps the seismic data with accuracies greater than 0.001 seconds. The seismic data are transmitted to the INL Research Center in Idaho Falls, Idaho using the FreeWave Technologies DGR115 900 MHz Wireless Modem. The wireless modem uses standard IP (Internet Protocol) networking features included in the embedded LINUX. INL uses both the 4 and 8 channel NetDAS recorders that boot from flash memory providing high reliability and low power consumption. NetDAS employs a highly efficient Generic Recording Format (GRF) that is interfaced with the U.S. Geological Survey’s EARTHWORM data acquisition software. At the INL Research Center located in Idaho Falls, seismologists analyze the earthquake data using the SEISAN program.
INL Strong Motion Accelerographs
Strong motion accelerograph located at the INL Research Center in Idaho Falls.
The 25 strong motion accelerographs at the INL Site consist of DAQSystems NetDAS four-channel recorders that contain Applied MEMs Inc. model SF1500A tri-axial accelerometers. The accelerographs are set to trigger at approximately 0.005 g. At some facility areas, several strong motion accelerographs are interconnected so that when one accelerograph is triggered, they all turn on to record earthquake data. Several strong motion accelerographs are also connected to phone lines providing quick access to acceleration data in the event of a large earthquake. The remaining accelerographs save the data on memory cards for INL personnel to retrieve. Acceleration data are analyzed using the SEISAN program that can produce both corrected and uncorrected acceleration, velocity and displacement time histories and amplitude spectra.
Earthquake Data Sharing
INL exchanges data in real-time with several nearby seismic networks using the U.S. Geological Survey’s EARTHWORM program. INL records earthquake data from seismic stations owned and operated by BYU-Idaho in Rexburg, Idaho, Montana Bureau of Mines and Geology in Butte, Montana, the University of Utah Seismograph Stations in Salt Lake City, Utah, and the National Earthquake Information Center in Golden, Colorado. INL also provides data from some its seismic stations to these seismic networks. Real-time data exchange with surrounding networks helps to fill in gaps between seismic networks and assists with determining more precise locations of earthquakes.
Seismogram for seismic station Taylor Mountain (TMI) displaying primary (P) and secondary (S) waves of a recent earthquake.
Accelerogram for seismic station Grays’ Range (GRRI) displaying primary (P) and secondary (S) waves of a recent earthquake.
- Contacts:
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Suzette Payne, (208) 526-4293, Send E-mail