Results acquired using global positioning system (GPS) data taken over a large part of SE-Asia, indicate that Sundaland, i.e. Indochina along with the western and central part of Indonesia, constitutes a stable tectonic block moving approximately east with respect to Eurasia at a velocity of 12 þ 3 mm yr 31 . With respect to India and Australia this block moves due south. Significant motion has not been detected along the northern boundary to South China i.e. along the Red River Fault, whereas nearly 50 mm yr 31 of right lateral motion has to be accommodated between India and Sundaland in the Andaman^Burma region. ß

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Repeated GEODYSSEA-GPS measurements and additional GPS data from the IGS and APRGP97/98 constrain the motion of SE-Asia within a global reference frame. Sundaland i.e. Indochina as well as the western and central part of Indonesia, together with South-China, constitute an apparently stable tectonic block that is decoupled from Eurasia. In the ITRF97 this block moves to the east about an Euler pole approximating that of Eurasia, but with a velocity that is one third higher than the eastward directed movement of Eurasia. With respect to India and Australia the Sundaland-South China block is moving due south. This suggests that a) Sundaland-South China are moving coherently to the East along the boundaries studied and b) the eastward motion of India is compensated by the eastward motion of Sundaland-South China. The current rather homogeneous kinematic behaviour of SundalandSouth China that differs in rate (no more than 5 mm) rather than direction from the movement of N-China differs from the kinematics proposed by different modelling approaches throughout the literature. The data help to constrain locations and behaviour of the active fault zones and give information on the interplate and intraplate deformation in the area.

A major geodynamic study has provided significant new information about the location of active plate boundaries in and around Southeast Asia, as well as deformation processes in the Sulawesi region of Indonesia and tectonic activity in the Philippine archipelago. Results also have confirmed the existence of the so‐called Sunda Block, which appears to be rotating with respect to adjacent plates. The study, known as the Geodynamics of South and South‐East Asia (GEODYSSEA) project, has been a joint venture of the European Commission and the Association of South‐ East Asian Nations. It began in 1991 and involved a large team of European and Asian scientists and technicians studying the complex geodynamic processes and natural hazards of the region from the Southeast Asia mainland to the Philippines to northern Australia. Earthquakes, volcanic eruptions, tsunamis, and tectonically induced landslides endanger the lives of millions of people in the region, and the tectonic activity behind these natural hazards results from the convergence and collision of the Eurasian, Philippine, and Indo‐Australian Plates at relative velocities of up to 10 cm per year.

In the framework of the GEODYnamics of South and South-East Asia (GEODYSSEA) project a network of 42 stations was observed by GPS during two field campaigns in 1994 and 1996. BKG and GFZ realized a third observation of the complete network in 1998. The data was analyzed independently by two analysis centers and a precision of the coordinate solutions was found to be 4-7 mm for the horizontal, and 10 mm for the vertical component. Subsequently, these campaign solutions were merged into one unique solution, which was accurately mapped into the International Terrestrial Reference Frame of 1997 (ITRF97). The global accuracy of this solution with respect to ITRF97 is of the order of 10 mm, while the resolution of the relative horizontal velocities is estimated to be at the level of 2-3 mm/yr. Comparison of the new solution with the previously published GEODYSSEA solution indicates, that improved results for the motion of Sundaland, South China and the overall deformation in the area could be found. Improvements are due to the increased time span and due to a better connection to and the advances in the ITRF reference frame. The new set of coordinates and velocities is used as the basis for scientific interpretations, which have been and will be published in separate papers.