Abstract

The Sumatra Fault System (SFS) is a 1650 km long, northwest trending, dextral strike-slip fault zone which accommodates the oblique convergence between the Indo-Australian and the Eurasian plates. The geometry of the SFS plays a key role in the development of a major structural pattern in Sumatra. This study applies the fractal method for quantifying the Sumatran active fault geometry and for this purpose 1:250,000 maps showing the traces of a Sumatran active fault were constructed based on the interpretation of SAR imagery and aerial photographs. Eleven segments are distinguished based on the segment geometry, seismic history, and fractal dimension. There are six fractal discontinuities, reflected by sharp changes of fractal dimensions and gravity anomaly patterns, observed along the segments. The variations of segments' fractal dimensions and the occurrence of these discontinuities suggest that the Sumatra mainland is not rigid. Instead, it appears to be segmented into several blocks in which each block has specific physical properties which are different and separated from the adjacent blocks by major structural discontinuities. The discontinuities which are orientated roughly N-S to NNE-SSW correspond to locations of major structural breaks in the Sumatra fore-arc. It suggests a close correlation between the segmentation of the Sumatra active fault zone and the Sumatra fore-arc. This segmentation may also explain the large discrepancy between the displacement and velocity of the Andaman Sea opening, the Sumatra fault motion and the Sunda Strait opening.