Determining the Sula Block Kinematics in the Triple Junction Area in Indonesia by GPS
A. Walpersdorf, C. Vigny, P. Manurung, C. Subarya, and S. Sutisna
The point of convergence of the Eurasian, Philippine, and Australian Plates, is situated adjacent to the island of Sulawesi, Indonesia. The relative plate velocities are estimated by NUVEL1 to be 7 to 9 cm/yr.
The complex tectonic mechanism of the triple junction has been studied over a two year period in the course of the GEODYSSEA South-East Asian Project. The GPS investigations concentrate on measurements of both the Sulawesi (Eastern Indonesia) part of the inter-regional GEODYSSEA network, and a local subnetwork on Sulawesi. Motions derived using data from the subnetwork confirm what the results of the inter-regional GEODYSSEA network have suggested: that is, that current deformation is high, and there are distinct deformation domains in the study area on Sulawesi.
The tectonic mechanism of the triple junction has been analysed using a rigid micro-block model. The triple junction area can best be interpreted as a headland of the Australian plate deflected by its collision with the Philippine Plate, thereby identifying the driving forces of the current deformation. The northern part is domminated by the Sula domain, which shows clockwise rotation. To the south, it is connected to the Australien Plate by an ensemble of microblocks undergoing counter-clockwise rotation.
In addition to the above, our tectonic model permits the determinination of the local influence of two large earthquakes (on 1 Jan. with M=7.8 and 22 Jul. 1996 with M=7.0) on the motion of the station Tomini (North Sulawesi). More observations and a denser GPS network are planned in order to study the behaviour of the Palu-Koro Fault, the main fault on the western limit of the Sula block.
Complete PostScript version (texte+figures)