First geodetic measurement of convergence across the Java Trench

Abstract

Convergence across the Java Trench has been estimated for the first time, from annual Global Positioning System (GPS) measurements commencing in 1989. The directions of motion of Christmas and Cocos Islands are within 1° 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 Java differs significantly from the NNR NUVEL‐1 prediction for the Eurasian plate with a 21° difference in direction and a 40% increase in rate. We infer that either West Java moves with a distinct Southeast 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°E ± 4° which is orthogonal to the trench. The magnitude of convergence agrees with the rescaled NUVEL‐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 northerly than the N20°E±3° predicted by NUVEL‐1. On June 2, 1994, almost a year after the last GPS survey, an Mw=7.5 earthquake with slip vector direction N5°E occurred south of central Java.