Description of the data examples from SW Sumatra is found in Susilohadi, S., C. Gaedicke and A. Ehrhardt, 2005. "Neogene structures and sedimentation history along the Sunda forearc basins off southwest Sumatra and southwest Java." Marine Geology 219(2-3): 133-154.
Schlüter, H.U.,Gaedicke, C., Roeser, H.A., Schreckenberger, B., Meyer, H., Reichert, C., Djajadihardja, Y., Prexl, A., 2002. „Tectonic features of the southern Sumatra–western Java forearc of Indonesia." Tectonics 21 (1047), 11-1–11-15.
Description of the data examples from NW Sumatra is found in
Berglar, K., C. Gaedicke, R. Lutz, D. Franke and Y. S. Djajadihardja, 2008. "Neogene subsidence and stratigraphy of the Simeulue forearc basin, Northwest Sumatra." Marine Geology 253(1-2): 1-13.
Contributor: Dieter Franke (BGR)
Fig. 4. Uninterpreted SW-NE seismic line: bgr06-135. This line is situated in the south of Simelue Island. Data courtesy: BGR
by Gordon Brown, WesternGeco
Within days following the earthquake, humanitarian relief poured into the region surrounding the Indian
Seismic Expression of Some Geological Features of Andaman-Offshore West Sumatra Subduction zone
Herman Darman (Shell International E&P) - Berita Sedimentologi #20, February 2011
duction zone developed in the south of
The Andaman - Offshore
eneath the southern tip of Eurasian continental plate.
This region is also an active p
etroleum exploration area. Recently, there are a number of companies (e.g. Spectrum, TGS and Geco) provide new and reprocessed seismic lines to the market. These seismic lines show the geological features in this subduction system.
1. Andaman Section
2010 articles in Geo-ExPro and AAPG Explorer displayed seismic sections of
Indian authority. The regional seismic section shows a submarine volcanic arc, which separates the back-arc basin from the fore-arc basin. East Andaman fault system developed bathymetric high called ‘invisible bank’ in the middle of the fore arc basin. Part of the fore-arc is shown on the west of the section. Further west of this section the fore arc ridge appear to the sea surface as
The interpretation suggest Pliocene-Recent stratigraphic interval at the shallowest section. This unit thins in parts due to volcanic activity and fault movement. Neogene units are thicker in the back arc basin compare to the fore-arc basin. The majority of the back-arc basin is deeper than 3000 MSec. TWT.
A seismic section published in AAPG Explorer show a Miocene Limestone unit which this towards the deeper water. The interpretation also indicates a shelf deposit, shelf edge and an isolated shoal (Figure 4). The shelf unit is about 3-4 Msec. TWT deep.
The Neogene unit is underlain by
Pre-Neogene sediments which is thins towards the volcanic arc. In parts the pre-Neogene sequence has been completely eroded away. This unit seems thicken to the west of the section in the fore-arc ridge zone. It is believed that the deeper stratigraphic unit has limited data control.
2. West Aceh Section (Profile Sumenta 32)
A seismic section published by Malod et al is a result of Baruna Jaya shallow seismic survey in 1991. The survey is part of collaboration between Indonesian and
This short section shows a reverse fault which bound the west part of the fore-arc basin (Figure 5). The fault goes all the way to the sea floor at about 3.5 sec. TWT, separating the accretionary prism from the fore-arc basin. The accretionary prism in the SW of this section is clearly shown as a bathymetric high and the fore-arc basin appear as a flat sea base.
The fore-arc basin was filled with Late Miocene and younger deposits. Flat reflectors shows that there were very little tectonic impact on this area despite the major earth quakes and tsunami developed in this region.
Unfortunately the seismic section is too short and too shallow to show the regional picture. The complex geology in the accretionary complex result in unclear seismic expression in this area.
3. Simeuleu Section
In July 2006, Geco acquired 3 deep seismic sections in offshore west Aceh. (Bunting et al, 2007) to image active faults along the subduction zone, quantify the volume of water that penetrated along these faults and provide information to optimize the location of future borehole location for the Integrated Ocean Drilling Program (IODP).
The seismic section is more than 16 sec. TWT deep and show the oceanic Moho on the SW of the section. An indication of continental Moho appears in the NE of the section. The section also shows the trench and the accretionary wedge of the
Slightly to the south of this line, TGS shot some seismic which was focused on the fore-arc basin. The seismic section clearly shows the fore-arc ridge and major regional NW trending fault zone in the SW of the section (Figure 7). In the NE, present day shelf deposit is well imaged. Meulaboh fore-arc basin has thick post late Miocene deposit adjacent to the NW trending fault zone as this fault generate an accommodation space fore about 2 sec. TWT deep.
Recent seismic sections published by Spectrum, Geco and TGS, shows different element of the Andaman-Offshore West Sumatra. Indonesian BPPT Baruna Jaya shallow seismic, acquired in 1991, shows sea bottom profiles which are controlled by tectonic features. These seismic lines clearly show the subsea volcanic arc, accretionary wedge, fore-arc basin, the trench, and boundaries of each element.
Both carbonate and clastic deposits are shown on the seismic sections with indication of potential hydrocarbon.
Bunting, T, Chapman, C; Christie, P., Singh, S., Sledzik, J., 2007, The Science of Tsunamis, Oil Field Review, Autumn 2007
Malod, J. A., Kemal, M., Beslier, M. O., Deplus, C., Diament, M., Karta, K., Mauffret, A., Patirat, Pl., Pubellier, M., Rgnauld, H., Aritonang, P., Zen, M. T., 1993, Deformation fo the Fore-arc Basin, NW of Sumatra, response to oblique subduction, Sumenta Cruiese – Baruna Jaya III – 1991.