GMT Based Comparative Geomorphological Analysis of the Vityaz and Vanuatu Trenches, Fiji Basin

The study is geographically focused on the two deep-sea trenches: Vanuatu and Vityaz, Fiji Basin, East Australia, located in the area of the double conver- gent complex boundary of Pacific and Indo-Australian plates in the North Fiji back- arc basin. Complex geophysical settings results in the formation of the trenches, seismicity, geodynamic complexity and instability of the region. The work aimed at modelling and comparative statistical analysis of the bathymetry and geomorphology of two trenches. Technically, the methodology of this work is based on the Generic Mapping Tools (GMT) using cartographic mapping of the geophysical, tectonic and geological settings, 2D and 3D modelling, visualizing raster grids GEBCO, ETOPO1, ETOPO5. Histogram topographic equalization (equalized, normalized, quadratic) was done using module ’grdhisteq’. Modelling geoid and gravity was based on EGM96 by sequence of GMT modules. The cross-spectrals of 2D binary raster grids were compared and their coherency plotted by ’grdfft’. The automated cross-section- ing was done using ’grdtrack’ module. The results include modelled transects visu- alizing trenches asymmetry, bathymetric and geomorphic variations. Vityaz Trench is shallower with depths <–6,100 m, has ’bell-shape’ data distribution with two peaks at ranges –3,500 m to –3,700 m, and –4,800 m to –5,000 m. Vanuatu Trench reaches up to –7,000 m with majority of values between –5,000 m to –3,000 m, even data distribution with depth increasing at –2,200 m to –800 m. Geomorphic form of both trenches varies: Vityaz has flat wide bottom similar to a trough, steeper gradient eastern slope. Vanuatu has V-form classic shape with gentle shapes on both slopes. Selected segment of Vityaz has shallower depths with maximal <–5,000 m while Vanuatu is deeper (–6,000 m). Cartographic functionality of the GMT is presented by various cartographic projections: Mercator, Behrman, Cylindrical Stereographic, Hammer retroazimuthal. 3D modelling was done using GMT module ’grdview’. Trenches were visualized and rotated at 160°/45°azimuth. Presented maps, 2D and 3D models and graphics are plotted and visualized by GMT with selected code snip- pets explained. Current work contributes to the methods of the modelling of deep-sea trenches geomorphology.