FRACTAL GEOMETRY OF THE SUMATRA ACTIVE FAULT SYSTEM AND ITS GEODYNAMICAL IMPLICATIONS

The Sumatra active fault system is a 1650 km long northwest trending d extral active strikeslip fault which accommodates the oblique converge nce between the Indo-Australian and the Eurasian plates. It consists o f 11 fault segments connected northward to the Andaman extensional bac k are basin and southward to the extensional fault zone of the Sunda S trait. The geometries of the 11 segments are quantified using a fracta l approach and it is found that their fractal dimensions (D) range fro m 1.00 +/- 0.03 to 1.24 +/- 0.03. Larger D values are associated with more irregular fault geometry. There are six discontinuities, reflecte d by sharp changes of fractal dimensions, observed along the segments. The locations of the discontinuities correspond to sites of major str uctural breaks in Sumatra mainland and its fore are and back are. The discontinuities and variations of D values suggest that the Sumatra ma inland is not rigid. Instead it appears to be segmented into several b locks which may correlate to the segmentation in the Sumatra fore are. This segmentation may explain the large discrepancy among the displac ements and velocities of the Andaman Sea opening, the Sumatra fault mo tion 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. Copyright (C) 1996 Elsevi er Science Ltd