International Journal of Geosciences, 2016, 7, 598-614 Published Online April 2016 in SciRes. http://www.scirp.org/journal/ijg http://dx.doi.org/10.4236/ijg.2016.74046 How to cite this paper: Widarto, D.S., Yudistira, T., Nishida, J.-I., Katsura, I., Gaffar, E.Z. and Nishimura, S. (2016) Imaging Rock Density Distribution beneath Liwa Fracture Zone in the Southern Part of the Great Sumatran Fault System, Indonesia. International Journal of Geosciences, 7, 598-614. http://dx.doi.org/10.4236/ijg.2016.74046 Imaging Rock Density Distribution beneath Liwa Fracture Zone in the Southern Part of the Great Sumatran Fault System, Indonesia Djedi S. Widarto 1* , Tedi Yudistira 2 , Jun-Ichi Nishida 3 , Ikuo Katsura 4 , Eddy Z. Gaffar 5 , Susumu Nishimura 4 1 Upstream Technology Center, PT Pertamina (Persero), Jakarta, Indonesia 2 Department of Geophysical Engineering, Bandung Institute of Technology, Bandung, Indonesia 3 Faculty of Literary, Ohtani University, Kyoto, Japan 4 Kyoto Institute of Natural History, Kyoto, Japan 5 Research Centre for Geotechnology—LIPI, Bandung, Indonesia Received 1 March 2016; accepted 25 April 2016; published 28 April 2016 Copyright © 2016 by authors and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY). http://creativecommons.org/licenses/by/4.0/ Abstract We have imaged rock density distribution beneath Liwa fracture zone in the southern part of the the Sumatran Fault Zone by modelling and inverting Bouguer gravity data in two-and three-di- mensional environments, respectively. The purpose of this study is aimed to figure out the subsur- face distribution of rock densities associated with subsurface basement structure representing the evidence of trans-tensional tectonic product in the SF. In the gravity modeling, to eliminate distortions to the measured gravity values before modelling and inverting the data, Bouguer ano- malies obtained in field measurements are reduced to the horizontal plane of z = +800 m as a re- presentation of the average elevation in Liwa. For the inversion, we used algorithm implementing depth-and minimum volume weighting parameters in order to obtain a smooth model with better vertical resolution. The two-dimensional models show clearly surface topography of the basement rocks and the presence of normal faults. The reduced Bouguer anomaly of +800 m elevation shows the presence of structural lineaments extending primarily in a northwest-southeast direction, pa- rallel to Sumatran Fault Zone and older graben faults showing a negative flower structure. From the three-dimensional inversion, the model illustrates an increase of density contrast, lower val- ues being found near the surface and higher values in the deeper parts. The lower density contrast of 0.15 to 0.3 g/cm 3 found in the rock groups at depths of 2 km and less is characteristic of rela- tively homogeneous and poorly compacted rocks. Rocks with moderate to high density contrast (>1.0 g/cm 3 ) are recognized at depths of over 2 km. This model suggests a change of basement morphology as a function of depth, and delineates structural lineaments extending in north- * Corresponding author.