Strainmeter Helps NASA Identify Continental Drift

TEGAM 1949-0001 ratio transformer
Geneva, OH

The EarthScope Project is an undertaking funded by the National Science Foundation in partnership with the United States Geological Survey and NASA to characterize the geology of North America, including continental drift caused by earthquake faults. Capturing the slow movement (which in some areas happens over centuries) can be done by measuring strain. Capturing strain (the deformation caused by stress) also can highlight areas that are moving faster along a fault relative to other areas.

GTSM Technologies in Brisbane, Australia, developed a tensor strainmeter to measure stress in this application. The strainmeter has a resolution of 0.02 nanostrain — the equivalent of 0.02 mm of motion per 1,000 km of distance, or 0.02 parts per billion (ppb). It also includes a TEGAM Ratio Transformer as one of its main components. Each GTSM sensor has three strain gauges oriented 120 degrees apart, providing detailed three axis information on the strain that results from earth movement.

The strainmeter is put into service by drilling a borehole into the earth. Although initial accuracy is important, it is critical that the ratio transformer have extremely low drift. Once the GTSM device is embedded in the rock, it is there for the life of the device. Component drift would produce unacceptable results, and the ratio transformer assures there will be insignificant drift for that component over the life of the project. Combined with GPS data that measures the overall motion of the earth surface, the equipment can distinguish regions of energy accumulations from regions of simple deformations.

The EarthScope project has funded a significant increase in the number of strainmeter sites. As the density of strain measurements grows, changes in earthquake models are likely as a result of better information, particularly over long time frames.

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