[G01-P] Poster

[G01-P-10] Modeling vertical displacements at stations of the Geocentric Reference System for the Americas (SIRGAS) due to hydrological load

Claudio Brunini^{1, 2, 3}, ^○Laura Sanchez⁴, Romina Galvan^2,3, Hermann Drewes^4,5, Mauricio Gende^2,3 (1.Argentinean - German Geodetic Observatory, Argentina, 2.Consejo Nacional de Investigaciones Cientificas y Tecnicas, Argentina, 3.Facultad de Ciencias Astronomicas y Geofisicas de la Universidad Nacional de La Plata, Argentina, 4.Deutsches Geodaetisches Forschungsinstitut, Technische Universitaet Muenchen, Germany, 5.International Association of Geodesy, Germany)

The usual assumption of constant station velocities in reference frame realizations has proved to be inefficient for many sites where geophysical processes cause significant non-linear motions, either seasonally (e.g., due to oceanic, hydrological or atmospheric loads) or episodically (e.g., due to co-seismic and post-seismic processes). Seasonal displacements are usually described using harmonic functions with annual and sub-annual periods. This work presents an alternative description based on the modelling of the hydrological process underlying the seasonal displacement. The study focuses in a first stage on the vertical displacements of the SIRGAS stations associated with the seasonal variations of the hydrological load. The developed methodology combines two sources of information: GNSS normal equations of the SIRGAS network (NEQ) to describe the geometric displacements; and monthly grids of equivalent water height (EWH) provided by GRACE to describe the hydrological load. The proposed model relates the response of the Earth's crust to the hydrological load and relies on a numerical solution of the static equilibrium equation for an elastic medium (i.e. the Earth's crust) characterized by an 'elastic parameter', which results from the combination of the Poisson ratio and the Young modulus. The NEQ are calculated on a weekly basis and remain weakly constrained to avoid deformations of the network geometry. These equations are then combined with the EWH values and some fiducial station positions are constrained to define the datum of the network. This leads to a common adjustment of 7 parameters per station, namely: 3 positions at a certain epoch, 3 velocities, and 1 elastic parameter. The vertical positions calculated after the adjustment agree with the weekly vertical positions published by SIRGAS within +/- 3 mm at the one sigma level, which is interpreted as a first satisfactory evaluation of the method here presented.