Elastic Deformation of the Earth\u27s Crust from Surface Loading Phenomena

The Earth’s crust deforms in response to changes imposed upon it by the cryosphere, the atmosphere, and the hydrosphere. In this study, we consider the load exerted on the Earth by water masses. The resulting deformation signal of the Earth can be measured with high precision, using Global Positioning System (GPS) instruments.GPS observations show annual, inter-annual and in some cases, multi-year elastic displacement signals, characterized by periodicity. These elastic signals can be easily separated from tectonic and post-glacial rebound signals that may be present in the GPS observations. We focus our study on a regional scale, considering two prime examples of regions with surface loading phenomena: The Mississippi River basin and the Great Salt Lake basin. We make use of 13 and 16 year 3-component displacement time-series, measured using GPS stations in the New Madrid Seismic Zone (NMSZ) and the Great Salt Lake (GSL) regions respectively (16 stations in the NMSZ around the Mississippi River and 39 stations around the GSL). The changes in the vertical displacements are inversely correlated with the changes in river and lake stage measurements in the respective regions and decay with distance from the load. We model the interaction of the Earth’s surface with the load and use topographic, river/lake stage, groundwater and atmospheric data, together with a half-space model of the earth, to estimate the surface loading and response in the respective regions. We invert the observed response to obtain Young’s modulus values of ~133Gpa and 138Gpa respectively for the NMSZ and the GSL