Calculating geomorphic indicies in West Sulawesi using SRTM derived DEM

Filippo Vecchiotti, completed PhD project


SRTM DEM of the Palu-Koru Fault zone, West Sulawesi

The study of equatorial South East Asian regions offers an opportunity to assess SRTM derived DEMs. Because of widespread rain forest cover, there have been few attempts to use remote sensing for evaluation of geomorphic indices and neotectonic analysis.

Quantitative measurement and analysis of geomorphic indices like stream length gradient index(SL), mountain front sinuosity (Smf) and ratio of valley floor width to valley height (Vf) are highly valuable for planning geologic exploration in large areas where there is rapid change in geomorphology.

West Sulawesi was chosen because is possible to test the accuracy of automatic river extraction methods from a DEM with 90 m horizontal grid size by comparison with recently acquired topographic maps at 1:50,000.

Neo-tectonic activity on the Palu-Koro fault in West Sulawesi was assessed using geomorphic indices calculated for major river systems. Mountain front sinuosity indices are similar whether derived from SRTM-DEM or topographic survey-DEM. Likewise, although the ranges differ, valley floor width to valley height ratios returns the same average value. Stream length gradientindices even though influenced by systematic sensor errors in areas of extreme local relief on SRTM-DEM were a useful tool for characterisation of the most important lithologies and detection of major fault-lineaments systems. From the correlation of Smf and Vf was also possible to validate recent GPS measurement where the tectonic activity in Palu-Koro fault area decreases from north to south.

Geomorphic indices calculated for various sectors of the Palu-Koro Fault Zone

Geomorphic indices calculated for various sectors of the Palu-Koro Fault Zone