A comparison of model estimates of ocean-tide loading displacements in New Zealand

We analyze the regional accuracy of the global ocean tide models TPXO7.2, GOT00.2, NAO.99b, FES2004, and EOT10a using the tide-gauge records from 7 stations along the coastline of New Zealand. The comparison reveals that TPXO7.2 provides the bestfit with the tide-gauge data in this part of the world. The TPXO.7.2 ocean tide model is then used for computing and analysis of the vertical and horizontal ocean-tide loading displacements in New Zealand. The ocean-tide loading is calculated for the semi-diurnal and diurnal tidal harmonic constituents M2 , S2 , N2 , K2 , K1 , O1 , P1 , and Q1 , the long-period tidal components Mf and Mm , and for the shallow-water (nonlinear) components M4 , MS4 , and MN4 . The charts of the ocean tide (offshore) and the ocean-tide loading (onshore) are compiled on a 5×5 arc-min geographical grid at the study area of New Zealand. The results reveal that the major contribution to the ocean-tide loading displacements up to a few centimeters is attributed to the semi-diurnal and diurnal harmonic constituents. The contribution of the long-period tidal components is to about 1 mm, and the effect of the shallow-water components is less than 0.2 mm. The maxima of vertical and horizontal displacements are typically of the same order of magnitude with larger amplitudes of vertical motions. The maximum amplitudes of vertical motions up to 5.6 cm are found in the upper north region of the North Island. The maximum horizontal motions up to 2.1 cm are in the northwest part of the South Island The ocean-tide loading displacements in New Zealand are finally compared with the crustal deformations due to geodynamic, atmospheric and other phenomena.