Fractal geometry of the Sumatra active fault system and its geodynamical implications

The Sumatra active fault system is a 1650 km long northwest trending dextral active strikeslip fault which accommodates the oblique convergence between the Indo-Australian and the Eurasian plates. It consists of 11 fault segments connected northward to the Andaman extensional back arc basin and southward to the extensional fault zone of the Sunda Strait. The geometries of the 11 segments are quantified using a fractal approach and it is found that their fractal dimensions (D) range from 1.00±0.03 to 1.24±0.03. Larger D values are associated with more irregular fault geometry. There are six discontinuities, reflected by sharp changes of fractal dimensions, observed along the segments. The locations of the discontinuities correspond to sites of major structural breaks in Sumatra mainland and its fore arc and back arc. The discontinuities and variations of D values suggest that the Sumatra mainland is not rigid. Instead it appears to be segmented into several blocks which may correlate to the segmentation in the Sumatra fore arc. This segmentation may explain the large discrepancy among the displacements and velocities of the Andaman Sea opening, the Sumatra fault motion and the Sunda Strait opening. This research also demonstrates the applicability of the fractal approach for analyzing the variations of fault geometry due to geodynamic processes.