Page 30 - Sumatra Geology, Resources and Tectonic Evolution

GRAVITY FIELD 17

Fig. 3.1. The gravity field of Sumatra and the surrounding seas, based on data from sources discussed in the text. Contours are of free-air gravity offshore and Bouguer
gravity onshore. The Bouguer reduction density is 2.67 Mg m -3. Faint white contours are bathymetry, at 200 m and at intervals of 500 m thereafter, from the GEBCO digital
atlas prepared by the British Oceanographic Data Centre. The continuous black line running the length of Sumatra marks the approximate surface trace of the Sumatran Fault.
The yellow line crossing the forearc basin near the equator marks the location of the interpreted profile of Figure 3.6. The black outlines enclosing the letters 'O' and 'B'
indicate the locations of the gravity surveys of the Ombilin and Bengkulu basins shown in Figures 3.3 and 3.4 respectively. The letter B also indicates the approximate
position of the town of Bengkulu. TS and T indicate, respectively, Lake Toba (including Samosir Island) and Lake Tawar. The letters 'IFZ' at about 97 ~ 30'E mark the central
trough of the Investigator Fracture Zone. The inset shows the GEM-T3 long wavelength gravity field in the Sumatra region (see Lerch et al. 1994).