INL GPS Sites
The INL Seismic Monitoring Program has a geodetic network for the purpose of monitoring crustal deformation in support of INL seismic hazards assessments. GPS data are used to investigate active crustal deformation that is on the order of millimeters of movement per year within the Snake River Plain, the surrounding Basin and Range, and the Yellowstone Plateau. GPS data delineate regions of high velocity gradients (or strain rates), which have more frequent damaging earthquakes than regions of low velocity gradients. The regional spatial patterns of GPS data also help constrain the fundamental geodynamic processes contributing to active continental deformation in the western United States.
The INL geodetic network consists of 14 GPS receivers that are located at INL seismic stations. INL operates 13 of these GPS receivers and assists with operation of 1 GPS receiver (at GTRG), which is currently operated by EarthScope. Additionally, INL Seismic Monitoring Program personnel have conducted several campaign GPS surveys on the Snake River Plain and surrounding Basin and Range regions. A recent study of horizontal GPS velocities indicates that the Basin and Range is extending at a rate that is an order of magnitude greater than the Snake River Plain. The slower rate may explain why the Snake River Plain has very few earthquakes.
A typical GPS station consists of a Trimble NetRS GPS Receiver connected to a Trimble L1/L2 dual frequency choke ring antenna (model 41249.00). The antenna is attached to a 2.4 m (8 ft) steel rod, which is drilled into rock outcrops to a depth of about 1 m (3 ft). Above ground, the antenna is stabilized within a much larger PVC pipe filled with sand. This reduces the amount of wind noise in the GPS data, improving the accuracy. The NetRS receivers continuously collect data, which are downloaded daily and archived by University NAVSTAR Consortium.