Publications

The existence of a major structural discontinuity around North Sumatra, as the effect of a split in the descending oceanic plate along the continuation of the Investigator Ridge Transform Fault, has been observed by many studies. The discontinuity is reflected by a sharp change of the Sumatra Fault segment's geometrical fractal dimension, volcanic line offset and major changes to the strike of the Batee fault and Batee trench. This paper presents the results of a gravity study conducted for the purpose of analyzing the discontinuity. A gravity anomaly map of Sumatra has been constructed using 2,400 gravity stations and 2.67 grlcc Bouguer density. The area around the discontinuity is characterized by a very low gravity anomaly closure (up to -96 mgal) with a relatively higher anomaly in the center. It indicates the existence of a low density body of mantle material intruded by a higher density igneous material in the center. The maps of density variation with depth constructed from 3-D deconvolution of gravity anomalies and a 2.5 D gravity model, show that this pattern reflects the thinning of the crust beneath the North Sumatra area due to regional tensional stresses of the mantle depth at a depth of approximately 20 km. The constructed Bouguer anomaly map and crust model should be useful for assisting in hydrocarbon prospecting around the study area.