GPS Height and Gravity Variations Due to Ocean Tidal Loading Around Taiwan

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This study presents predicts ocean tidal loading (OTL) effects using a Green's function approach and validates a novel tidal model for Taiwan. Numerical integration of OTL is performed using the Gauss quadrature method and a local tidal model for the inner zone and a global model for the outer zone. Observed time series of GPS-derived vertical displacements and gravity variations (3–7 days) at five co-located GPS-gravimeter stations along the South East China and Taiwan coasts were utilized to assess the accuracy of the proposed models and two other models. The OTL-induced gravity variations are 3–16 μgal and the vertical site displacements are 13–27 mm. Generally, an OTL model using a mixed global and local tidal model generates better agreement with the observations than an OTL model using a global tidal model only. However, containing a local model inside a global model does not always produce a good agreement with the observations. The relatively large discrepancies between modeled and observed OTL values at some stations indicate that there is a need for an improved local tidal model in the study area.

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