1ST GEODETIC MEASUREMENT OF CONVERGENCE ACROSS THE JAVA TRENCH

Convergence across the Java Trench has been estimated for the first ti me, from annual Global Positioning System (GPS) measurements commencin g in 1989. The directions of motion of Christmas and Cocos Islands are within 1-degree of that predicted by the No-Net Rotation (NNR) NUVEL- 1 plate motion model for the Australian plate although their rates are 25% and 37% less than predicted, respectively. The motion of West Jav a differs significantly from the NNR NUVEL-1 prediction for the Eurasi an plate with a 21-degrees difference in direction and a 40% increase in rate. We infer that either West Java moves with a distinct Southeas t Asian plate or this region experiences plate margin deformation. The convergence of Christmas Island with respect to West Java is 67 +/- 7 mm/yr in a direction N11-degrees-E +/- 4-degrees which is orthogonal to the trench. The magnitude of convergence agrees with the rescaled N UVEL-1 relative plate model which predicts a value of 71 mm/yr between Australia and Eurasia. The direction of motion matches the direction inferred from earthquake slip vectors at the trench but may be more no rtherly than the N20-degrees-E+/-3-degrees predicted by NUVEL-1. On Ju ne 2, 1994, almost a year after the last GPS survey, an M(W) = 7.5 ear thquake with slip vector direction N5-degrees-E occurred south of cent ral Java.