Brian L. Murphy

Estimation of current plate motions in Papua New Guinea from Global Positioning System observations

Plate tectonic motions have been estimated in Papua New Guinea from a 20 station network of Global Positioning System sites that has been observed over five campaigns from 1990 to 1996. The present velocities of the sites are consistent with geological models in which the South Bismarck, Woodlark, and Solomon Sea Plates form the principal tectonic elements between the Pacific and Australian Plates in this region. Active spreading is observed on the Woodlark Basin Spreading Centre but at a rate that is about half the rate determined from magnetic reversals. The other major motions observed are subduction on the New Britain Trench, seafloor spreading across the Bismarck Sea Seismic Lineation, convergence across the Ramu-Markham Fault and left-lateral strike slip across the Papuan Peninsula. These motions are consistent with a 8.2° Myr -1 clockwise rotation of the South Bismarck Plate about a pole in the Huon Gulf and a rotation of the Woodlark Plate away from the Australian Plate. Second order deformation may also be occurring; in particular, Manus Island and northern New Ireland may be moving northward relative to the Pacific Plate at ∼5-8 mm yr -1 (significant at the 95% but not at the 99% confidence level) which may suggest the existence of a North Bismarck Plate.

Errata/Addendum - Australian Geodetic Datum Technical Manual

Abstract The Australian Geodetic Datum Technical Manual (Special Publication 10) was produced by the former National Mapping Council of Australia in 1984. Since that time this publication has served as the standard technical reference for the definition of the Australian Geodetic Datum (AGD), the Australian Map Grid (AMG) and the Australian Height Datum (AHD).

Antarctica—Where is it, and where is it going?

Abstract Antarctica plays a critical role in the study of global climatic change, regional oceanography and plate tectonics. A fundamental requirement for the study of plate tectonics in this region is the determination of a set of precise geodetic coordinates for a number of carefully selected sites located both within Antarctica and on adjoining tectonic plates. Ideally, the coordinate set should be determined in a global terrestrial reference system which remains stable over many decades. This paper outlines the development and current status of the application of space geodetic techniques to Antarctica, and descibes how the GPS system is currently being used to provide first epoch data for the study of plate tectonics in the region.

FORMATION OF A COLLISIONLESS MAGNETOHYDRODYNAMIC SHOCK WAVE.

Points out a certain necessary condition for a detached magneto-hydrodynamic shock to form in front of a magnetic field which acts as a piston moving a collisionless plasma. This condition takes the form of a requirement that the time during which the piston accelerates to the Alfven speed be greater than a certain value determined by the plasma parameters. Unless this condition is met in an experiment a detached shock will not form, so that any interpretation of the observations which uses shock theory will be incorrect.