Earth tide observations in Tierra del Fuego (Argentina)

A. RICHTER; R. PERDOMO; J. L. HORMAECHEA; L. MENDOZA; D. DEL COGLIANO; M. FRITSCHE; M. SCHEINERT; R. DIETRICH

Mar del Plata

Congreso; International Geological and Geophysical Congress on the Southern Hemisphere; 2010

Instututo Nazionale di Oceanografia e di Geofisica Sperimentale, OGS, Trieste, Italy, Instituto de Geofísica "Daniel A. Valencio", Universidad de Buenos Aires, Argentina; Dipartamento di Scienze Geologiche, Universita di Urbino, Italy

The solid earth tides, originating from luni-solar forcing, manifest themselves in different effects, such as gravity variations, deformations of the earth crust, and variations in the tilt of the earth surface with respect to an equipotential surface. The ocean tidal loading generates an additional contribution to these effects. The load tides depend on the ocean tide signal and the elastic rheological properties of the earth crust.These tidal effects are contained in geodetic (e.g. GPS), astronomical (e.g. zenith tube) and geophysical (e.g. gravity metre) observations and exceed nowadays achievable measurement uncertainties. They must therefore be accounted for in high-accuracy observations of different geophysical phenomena. On the other hand, such observations provide the opportunity to gain new insights into the response of the solid earth to the tidal forcing.The first systematic investigation of tidal effects in Tierra del Fuego was based on lake-level observations in Lago Fagnano. Based on pressure tide gauge records at three sites in the lake the amplitudes, phase angles, and circulation patterns for the four main tidal waves were determined. In this way we utilized the lake as a 100 km long tidal tilt sensor. The comparison of the observed lake tide signal with a model accounting for both solid earth tides and load tides revealed a significant deviation of the observations from the theoretical prediction. It suggests that this difference is due to an anomalous amplification of the load tides in the order of 20%. One possible explanation of this anomaly consists in a deviation of the elastic crustal properties in the Lago Fagnano region from the global earth model assumed in our load tide model.With the aim to shed light onto the cause of the detected anomaly additional earth tide observations were commenced at a number of sites in the Argentine part of Tierra del Fuego main island in November 2009. Here we present the continuous tidal gravity metre and GPS records obtained so far. The results of a preliminary tidal analysis of these records are compared to model predictions. They are discussed with an emphasis on their possible implications for the effective elastic crustal rheology in the region under investigation.