Crustal deformation rates in Central and Eastern U.S. inferred from GPS

Analysis of continuous GPS observations between 1996 and 2000 at 62 stations distributed throughout the central and eastern United States suggests that the area is generally stable. Seven of the 62 stations show anomalous velocities, but there is reason to suspect their monument stability. Assuming the remaining 55 stations are stable with respect to interior North America, we have found the North America-ITRF97 Euler vector (-1.88^o ± 1.04^oN, 77.67^o ± 0.39^oW, 0.201^o ± 0.004^o Myr^-1) that minimizes the RMS station velocity. Referred to fixed North America, all of these velocities are less than 3.2 mm yr-1. Motion of several stations suggests the Mississippi embayment may be moving southward away from the rest of the continent at a rate of 1.7±0.9 mm yr^-1. The motion of the embayment produces a large gradient in velocity which, in turn, implies the highest seismic moment accumulation rate that we found. Although the highest rate is only marginally significant, the fact that it occurs near New Madrid, where earthquake risk is thought to be high, argues that the anomaly may be real. Nevertheless, the identification of the anomaly remains tentative.