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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. ???, XXXX, DOI:10.1029/,
A Decade of GPS Measurements in S.E. Asia: (Re)Defining Sundaland
Motion and its Boundaries
W.J.F. Simons, 1 A. Socquet, 1 C. Vigny, 2 S. Matheussen, 1 B.A.C. Ambrosius, 1 C.
Subarya, 3 R.W. Matindas, 3 D.A.C. Sarsito, 4 J. Kahar, 4 S. Haji Abu, 5 H. Bin Ali, 5 Chaiwat
Promthong, 6 Phanusak Swangnet, 6 M. Iwakuni, 7 T. Kato, 7 P. Morgan 8 and W. Spakman 9
Abstract. An updated geodetic solution on crustal velocities in S.E. Asia is presented. Parts
of the existing GEODYSSEA network in S.E. Asia were re-measured, and episodical and/or
permanent data from new GPS points in Indonesia, Malaysia, Myanmar and Thailand were
added. The expanded GPS database on S.E. Asia now provides more than 100 velocity estimates
with horizontal accuracies of 0.5-2.5 mm/yr. To achieve this, both the GIPSY GPS
software package and the International Terrestrial Reference Frame solution of 2000 (ITRF-
2000) were used, thereby using improved processing and mapping strategies. Based on 28 velocity
vectors on its rigid part, a refined pole for Sundaland in ITRF-2000 was computed, located
at 48.9ÆSand 85.8ÆE and with a clockwise rotation rate of 0.341Æ/Myr. The Sundaland
block is composed of a rigid core, characterized by very slow strain rates and residual
velocities < 3 mm/yr, which covers the Indochina and Malaysian peninsulas in the North
and West, the Sunda shelf, the major part of Borneo in the East and extends to the South almost
until Java. However, strain rates increase from the core of Sundaland outwards, with significant
deformation occurring close to its boundaries. With respect to GPS Eurasia, Sundaland
rotates clockwise at 0.106Æ/Myr around a pole located at 108ÆE, 36ÆS. The predicted Sundaland
/ Eurasia motion confirms an Eastward motion, increasing from south to north, of Sundaland
with respect to Siberia. With respect to South China, the motion is small but significant
and increases from very small values within the South China Sea in the pole area, to
higher strain rates in the Red River area.
1. Introduction
The plate tectonics concept [McKenzie and Parker, 1967; Morgan,
1968; Le Pichon, 1968; Chase, 1972, 1978; Minster and Jordan,
1978] was a fundamental advance in understanding global
Earth behavior, however it still lacks in complexity to describe
continental area’s kinematics and deformation. For example, the
NUVEL-1A model [DeMets et al., 1990, 1994] presents a global
plate motion model, averaged for the last 3 Myrs, based on geological
constraints. For Eurasia, this kinematic model predicts a rigid
plate from Western Europe until South-East Asia. However, it was
recognized early that the spectacular Asiatic relief pattern attests for
intra-continental deformation extending from the Himalayas to the
Baikal rift zone to the North, and until the Red River Fault in the
South East, resulting from the collision between India and Eurasia
[Argand, 1924].
Deformation of Asia has been extensively studied from the 70’s by
Department of Earth Observation and Space Systems (DEOS),
Delft University of Technology, Delft, The Netherlands
École Normale Supérieure (ENS), Paris, France
National Coordination Agency for Surveys and Mapping
(BAKOSURTANAL), Cibinong, Indonesia
Institute of Technology Bandung (ITB), Bandung, Indonesia
Department of Survey and Mapping Malaysia (DSMM), Kuala
Lumpur, Malaysia
Royal Thai Survey Department (RTSD), Bangkok, Thailand
Earthquake Research Institute, University of Tokyo, Tokyo, Japan
University of Canberra (UC), School of Computing, Canberra,
Australia
Faculty of Earth Sciences, University of Utrecht, Utrecht, The
Netherlands
Copyright 2004 by the American Geophysical Union.
0148-0227/04/$9.00
1
analysis of satellite imagery [Tapponnier and Molnar, 1977, 1979],
geological and seismological studies [Molnar and Tapponnier,
1978; Molnar and Lyon-Caen, 1989]. To explain the geological
features and the geophysical data set, end-members models assume
that continents deform either by viscous flow of a continuously
deforming medium [England and Houseman, 1985, 1986; Houseman
and England, 1986, 1993] or by motion of rigid lithospheric
blocks along narrow fault zones [Tapponnier et al., 1982; Tapponnier,
1986; Peltzer and Tapponnier, 1988; Avouac and Tapponnier,
1993; Peltzer and Saucier, 1996; Meyer et al., 1998]. Discriminating
these end-members models requires spatially dense measurements
of surface strain rate. High accuracy GPS measurements can
constrain models for a better understanding of the mode of deformation
of the lithosphere and of the plates kinematics.
The Sundaland block, making up a large part of South-East Asia,
has been the subject of discussions whether or not it has a significant
motion with respect to the Eurasian plate and how the deformation
is distributed between Siberia and South-East Asia.
Initial GPS results in S.E. Asia (eg. [Tregoning et al., 1994; Genrich
et al., 1996]) let to the conclusion that this region seemed rigidly
connected to the Eurasian plate. However, this conclusion was obtained
from using mostly local GPS data, many of which are located
in deformation zones (Sumatra, Java, Sulawesi, Banda Arc)
and hence not belong anymore to rigid Sundaland. Later, the results
of the GEODYSSEA project [Wilson et al., 1998; Chamot-Rooke
et al., 1998; Simons et al., 1999; Michel et al., 2001] showed clearly
that the Sundaland block presents a rigid motion with respect to
Eurasia and is separated from the Siberian platform through a series
of deforming and moving blocks, invalidating by the way the
NUVEL-1A model [DeMets et al., 1994] for present-day deformation.
This project, led between 1994 and 1998, used a GPS network
systematically distributed over Sundaland, which is most suited to
accurately determine a rigid plate motion.
Since then, the GPS database on South-East Asia has been expanded
by including new high-quality GPS measurements of both
episodically and continuously operated sites. Besides actively carrying
out GPS surveys through international cooperation, this was