While relative velocities across tectonically active regions are typically of the order of 5-50 mm yr-1 (that can be generally resolved with annual GPS campaign data over a three to five year period), relative velocities across intra-plate regions are typically less than 1 mm yr-1. Previous studies of crustal deformation in intra-plate seismic regions, such as New Madrid, centre of the US, have shown that the current strain level in regions of past large earthquakes is at or below the resolution of geodetic methods (Hamburger et al., 2002; Newman et al., 1999). At the same level of importance of the amplitude and patterns of crustal strain, a robust estimation of the uncertainties on geodetic measurements is a major issue for seismo-tectonic studies in intra-plate environments.
Hamburger, M. W., Rybakov, V., Lowry, A., Shen-Tu, B., and Rupp, J. A. (2002). Preliminary Results from a GPS Geodetic Network in the Southern Illinois Basin. Seismological Research Letters, 73(5), 762-775. doi:10.1785/gssrl.73.5.762.
Newman, A., Stein, S., Weber, J., Engeln, J., Mao, A., and Dixon, T. H. (1999). Slow Deformation and Lower Seismic Hazard at the New Madrid Seismic Zone. Science, 284(5414), 619-621. American Association for the Advancement of Science. doi:10.1126/science.284.5414.619