SUNDALAND MOTION DETECTED FROM GEODYSSEA GPS MEASUREMENTS : PART I - IMPLICATIONS FOR MOTION AT SUNDA TRENCHES
N. CHAMOT-ROOKE, C. VIGNY, A. WALPERSDORF, X. LE PICHON, P. HUCHON AND C. RANGIN 1)
The deformation pattern obtained from GEODYSSEA GPS measurements shows that
a set of stations located in Vietnam, Malaysia, Borneo, Eastern Sumatra and
Java have small relative motions. To a first approximation, these stations
belong to a rigid block hereafter called the "Sundaland block". Since
Sundaland stations are tied to stations belonging to different tectonic
plates, GEODYSSEA solution can be used to constrain the kinematics of this
block with respect to surrounding plates. We first put GEODYSSEA solution
in an Australia reference frame by minimizing the misfit with NUVEL-1A
global plate model at Australian sites (COCO, KARR, YAR1, WAME and TIDB).
The residual motion (adjusted solution versus NUVEL-1A) is small for all
stations (within one to two sigma's) except for TIDB (Tidbinbilla) on the
Eastern coast of Australia. We then invert the motion at 12 Sundaland
stations (in the adjusted solution) and find that the Sundaland block is
rotating clockwise with respect to Eurasia around a pole located South of
Australia. The motion is towards ENE and is ranging from 1.2 cm/yr to 2.2
cm/yr from Eastern Java to Northern Sumatra. The mean residual motion
(adjusted rigid rotation versus observed vectors) is about 3 mm/yr and the
azimuth is adjusted within less than 10 degrees.
We discuss the implications of this Sundaland motion for the subduction of
Indian and Australian plates beneath Java and Sumatra. Slip vector azimuths
of interplate thrust earthquakes along the Java trench consistently show a
10 degrees westward deviation with respect to the predicted NUVEL-1A
Australia-Eurasia motion. This discrepancy is fully resolved if Sundaland
motion is included. Subduction velocity is reduced along the entire
subduction system with respect to NUVEL-1A predictions. In an India
reference frame, Sundaland is moving due south so that the motion is pure
dextral strike-slip north of Sumatra. The predicted velocity of India at
the latitude of Myanmar is close to the rate of opening of the Andaman Sea,
suggesting low subduction rate along the Andaman front.
1) Laboratoire de Geologie,
Ecole Normale Superieure - CNRS,
Paris, FRANCE
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