PAPER 1
THE PROJECT GEODYSSEA: IT'S ORIGIN, DEVELOPMENT AND FUTURE
by Dr. Peter Wilson
No abstract available
PAPER 2
LITHOSPHERE AND MANTLE STRUCTURE OF SOUTH EAST ASIA
by W. Spakman and Bijwaard
Abstract: We present results from the tomographic inversion of about 7.5 million
P and pP data for global mantle structure (Bijwaard, Spakman, and Engdahl, in
prep) with a focus on the southeast Asian region. We use data from a new data
set derived by Engdahl, Van der Hilst and Buland (submitted JGR). They
reprocessed about 100,000 earthquakes from the ISC data base by re-identifying
seismic phases and relocating all events in the AK135 model. The re-processing
leads to a data set for tomography which has two main advantages with respect
to the ISC data set. Firstly, the use of later arrivals, specifically pP data,
in the location procedure leads to much better located earthquakes which reduces
the nonlinear relation between tomographic data and event location. Secondly,
the use of a modern reference model (AK135) for location reduces the nonlinear
relation between tomographic data and earth structure. Both advantages lead to
a closer linearization with respect to AK135 of the relation between
observations and tomographic model parameters. We use an innovative model
parameterization of the mantle in terms of cell (block) shapes and sizes
depending on the sampling of the mantle by seismic ray paths. Cell sizes vary
between 60*60*35 km in well sampled regions to cells with dimensions of many
hundreds of km in poorly sampled regions. This allows a considerable reduction
of the number of cell parameters to only 150,000 while allowing for imaging
details on the order of 50 km in potentially well resolved regions (e.g. most
subduction zones). Further, the data are binned into composite rays (bundles of
rays from a source region 30*30*30 km to one station) which reduces the number
data for inversion to about 4 million. The inversion solves jointly for the
seismic velocity anomalies in cells, event relocation parameters, and station
statics. The inversion is regularized using first derivative damping which
penalizes the gradient of seismic slowness in regions poorly sampled by the
data. A comparison of the tomographic results with previous findings (e.g.
Fukao et al. 1992, Widiyantoro and Van der Hilst 1996) leads to a general
agreement on the larger scale patterns imaged (e.g. the large scale subduction
of Indian plate below the Sunda Arc). Specifically, the results presented by
Widiyantoro and Van Der Hilst display a comparable degree of detail imaged.
However, we do not find one of their main observations,: the detachment of (or
tear in) the slab around 400 km below Sumatra. Instead we find that below
northern Sumatra the Sunda slab makes a clear bend westward toward the Andaman
island arc. Subduction below the Sunda arc is imaged down to at least 1500 km
indicating penetration into the lower mantle. The morphology of subduction
below the Philippines is very complex in the upper few hundred kilometers of the
mantle. At the latitude of Mindoro island the subduction zone makes a distinct
EW-jump of about 250 km, correlating with the sharp bend in Philippines island
arc. This jump in morphology is also visible in the intermediate depth
seismicity. The subduction below Sulawesi is the southern extension of
subduction below the Philippines. East of Sulawesi a slab is also imaged below
Halmahera island (Molucca collision zone).
PAPER 3
TOMOGRAPHIC IMAGING OF THE LITHOSPHERIC SLAB BENEATH S. AND EAST ASIA
by Sri Widiyantoro, R. Van der Hilst
No abstract available
PAPER 4
THE GEODYSSEA NETWORK: GFZ RESULTS AND DATUM DEFINITION
GFZ RESULTS OF GEODYSSEA 94 AND 96 CAMPAIGNS
by D. Angermann, J. Klotz, G. Baustert, Ch. Reigber, and P. Wilson
Abstract: In scope of the GEODYSSEA project an extensive GPS network has been
established in South and South East Asia. In November/December 1994 and April
1996, two large GPS measurement campaigns have been carried out by GFZ and IfAG
with the support of ENS, Paris and relevant institution in the host countries.
The GEODYSSEA 94 and 96 campaign data were processed at the GeoForschungsZentrum
Potsdam using GFZ software EPOS (Earth Parameter and Orbit System). The precise
GPS software package is based on undifferenced phase and pseudo-range
observations. The GEODYSSEA network station position were computed
simultaneously with station data of the IGS (International GPS Service for
Geodynamics) and AUSLIG (AUstralian Survey and Land Information Group) stations.
The results gave a daily repeatability of the station coordinates in the order
of 3-6 mm for the horizontal components and 9 mm for the height. The
fiducial-free network solutions were transformed to the ITRF94 (International
Terrestrial Reference Frame of 1994) using transformation parameters computed
for the five IGS stations that were included in the computations. The global
network accuracy is of the order of 1cm.
THE DATUM DEFINITION OF THE GEODYSSEA NETWORK
By D.Angermann, GeoForschungsZentrum Potsdam, Div.1, Telegrafenderg A17,D-14473
Potsdam, Germany
Abstract: In this paper two major questions concerning the datum defination of
the GEODYSSEA network are discussed:
• 1) What is the effect of different IGS orbits on the station coordinates?
• 2) What is the effect of a regional or global distribution of the IGS stations
included in the solution?
The data from 25 stations of the GEODYSSEA 96 network were processed with the
GFZ software EPOS to study the effect of the IGS orbits on the network
coordinates. Fiducial-free network solutions were performed using fixed IGS
orbits computed by different IGS analysis centres and using the combined orbit.
The mean station coordinate residuals of a Helmert transformation of the
different solution fall within 2-3 mm.
Concerning the second question, the data from 20 stations of the GEODYSSEA 96
network were computed simultaneously with the 5 IGS sations (Regional Solutions)
and with 14 globally distributed IGS stations (Global solution). Both solutions
were transformed to the ITRF94. In the case of the global solution the Helmert
transformation parameters are closer to zero and their mean errors are smaller
by a factor of 3 compared with the regional solution. Another advantage of the
global solution is that the influence of individual stations on the
transformation results is significantly reduced. The differences in the
absolute station coordinates between the regional and the global solutions are
about 1 cm. The internal network geometry varies by 1-2 mm.
PAPER 5
ANALYSIS OF THE RESULTS OF THE 1994 AND 1996 GEODYSSEA GPS CAMPAIGNS AT IfAG
by M. Becker, P. Neumaier, E. Reinhart
Abstract: In the ASEAN-EU project „GEODYSSEA" two GPS campaigns have been
conducted in South-East Asia. In two 5 day campaigns in November/December 1994
and in April 1996 more than 40 stations have been repeatedly observed. The
homogeneous dataset of both epochs has been analyzed at the Institute of Applied
Geodesy (IfAG), Frankfurt using the Bernese Software Version 4.0. The results of
the individual campaigns show a high internal consistency at the 5 mm level of
the rms. The station velocities are determined with respect to the ITRF94
coordinates of 5 IGFS common to both epochs. Station displacements are compared
to the NUVEL1A displacement vectors. The accuracy, the optimal estimation
strategy, the transformation to the ITRF94 and the significance of the
velocities estimated are discussed. The IfAG solution is compared to the final
combined solution of all analysis centers. Special emphasis is put to the
vertical component and the study of possible systematic effects in the
observations and the results. These are set up of baselines, troposphere
estimation, ionosphere estimation and the datum selection.
PAPER 6
CRUSTAL MOTIONS IN SOUTH-EAST ASIA DERIVED FROM THE GEODYSSEA OBSERVATIONS BY
DUT
by Simons, W.J.F., B.A.C. Ambrosius, and
R. Noomen
Abstract: In the framework of the GEODYSSEA Project, a dense network of geodetic
points in South-East Asia was measured twice in campaign style with GPS in
November 1994 and in April 1996. At DUT, the complete data sets, which also
include observations from 4 additional stations in Australia and 5 nearby IGS
stations, have been processed with the GIPSY-II software. For the network
deformation analyses, the so-called 3D-Motion software, developed at DUT, was
used. First, independent free-network solutions were computed for every single
day of the campaigns. The GPS orbits were held fixed using the IGS precise
ephemerides. Also, since the networks included different receiver antenna types,
the latest version of the antenna phase center variation tables, recommended by
the IGS, were applied in the analyses. Next, the daily solutions were combined
into two separate campaign solutions which were subsequently transformed into
the ITRF-94 reference frame using the IGS stations as fitting points. In a final
step, the relative motions of the stations were computed using the 3D-Motion
software. In this paper, an overview of the data analysis is given in which the
quality of the coordinate solutions is addressed. Also, an interpretation of the
observed station velocities is presented. The observed motions are in general
agreement with the motions predicted by the NUVEL-1A model, except for stations
at or near the deformation zones. The vectors recovered for the latter stations
provide significant new information which may be used as constraints in the
development of better geodynamic models. The results also provide new evidence
that the motion of the Sundaland block is somewhat different from that of the
Eurasian plate. This was confirmed by the results of an additional analysis
using a global network of IGS stations for reference. From these results a new
independent pole and vector of rotation for the Sundaland block has been
derived.
PAPER 7
NEWCASTLE PROCESSING OF THE GEODYSSEA GPS DATA
by Prof. Dr. P. Cross, Dr. Luhut Perluhutan
No abstract available
PAPER 8
REPORT ON THE ENS SOLUTION OF THE GEODYSSEA GPS MEASUREMENTS
by Christophe Vigny and Andrea Walpersdorf
Abstract: The complete data set from the two GEODYSSEA GPS campaigns (November
94 and April 96) were analysed at ENS, including data from additional stations
observed in the main sessions and appended sessions in the Sulawesi area. The
data were processed using MIT's GAMIT / GLOBK / FONDA package. Software
specificities will be detailed along with data editing and data processing
strategies. The quality of the solution is assessed by the excellent
repeatabilities (scatter of independent daily measurements) obtained both for
the 94 and 96 campaigns for baselines as long as 10,000 km. The 2246 (resp.
2138) baselines measured in 94 (resp. 96) show mean repeatabilities of 3.9
(resp. 4.3), 5.8 (resp. 7.4), and 11.1 (resp. 16.7) millimeters on the North,
East, and vertical component. The precision of the inferred velocities is
therefore estimated around 5 mm/year. Precision and accuracy of the ENS solution
with respect to the combined solution will be presented. Especially, the
influence of orbits (fixed precise IGS orbits vs. locally adjusted orbits),
antenna phase center tables, and ambiguity resolution on the final solution will
be discussed. The GEODYSSEA solution shows a relatively poor agreement with the
global models (ITRF/NUVEL1) for the fiducial stations used in the analysis (IGS'
KIT3 TAIW TIDB TSKB YAR1 and AUSLIG's COCO KARR XMAS DARW). This result will be
discussed in terms of real, short time scale, local, crustal deformations and/or
large scale network deformations induced by erroneous external reference frames.
PAPER 9
FINAL GEODETIC RESULTS OF THE GEODYSSEA PROJECT: THE COMBINATION SOLUTION
by Ambrosius, B.A.C., D. Angermann, M. Becker, P. Neumaier, R. Noomen, E.
Reinhart, W.J.F. Simons, C. Vigny, A. Walpersdorf, P. WILSON
Abstract: The GPS measurements acquired in the framework of the GEODYSSEA
project have been processed by four different analysis groups, using various
software packages and applying different analysis strategies. The data were
collected during two 5-day campaigns in November/December 1994 and in April
1996. The main network consists of 41 designated GEODYSSEA stations covering the
region of the triple junction of the Eurasian, Philippine and Indo-Australian
tectonic plates. In addition, data were used from 4 more stations on the
Indo-Australian plate and from 5 IGS stations around the area. The computations
resulted in four independent series of unconstrained daily station coordinate
solutions for the complete network. Day-to-day repeatability of the coordinates
was found to be of the order of 3 to 5 mm for the north and east components and
9 mm for the vertical. In the following step, these results were merged into
separate combination solutions for each of the two campaigns. This was done in a
careful analysis and weighting process, using special software. It provided a
unique possibility to cross-check the performance of the different software
packages and to identify anomalous results in the individual solutions. Allowing
for systematic effects, the various solutions were found to be quite consistent,
the rms differences being even less than the day-to-day repeatability, i.e. 2.5,
4 and 7 mm, respectively. Finally, a kinematic model for the motion of the
stations was derived from the differences in the station coordinates between the
two combined solutions. The observed displacements range from a few millimeters
up to more than one meter. Although the results are only based on two campaigns,
the accuracy appears to be remarkably good. An important indication for this is
the strong coherence between the recovered velocity vectors of individual
stations located on the same tectonic block. Also, for the more stable regions
the observed horizontal motions are in close agreement with the motions
predicted by global plate tectonic models. The overall uncertainty of the
horizontal velocities is estimated to be about 2 - 3 mm/yr. The results provide
significant new information on the precise location of the active plate
boundaries, deformation processes in the Sulawesi region and tectonic activities
in the Philippine archipelago. Also, several 'anomalies' in the results have
been related to earthquakes in the vicinity of some of the stations during the
one-and-a-half year interval between the observations. The coordinate solutions
and velocity fields described in this paper represent the 'official' final
geodetic results of the GEODYSSEA project.
PAPER 10
A FIRST ORDER STUDY OF THE INDIAN AND AUSTRALIAN PLATES
by Russell Tiessler and Peter Morgan
Abstract: The tectonic history of Australia and India is quite different
although both areas were part of the Gondwana super continent that split away
from Antarctica. The rates of the fragments have accelerated and decelerated
over time as various obstacles slowed each of the components. In developing the
current tectonic model the early model lumped these two fragments together. The
common name being the Indo-Australian Plate although many referred to the plate
as either the Australian or Indian plate. Kinematic plate models now
differentiate between the two plates.
This study seeks to delineate the deformation zone between the Australian and
Indian plates and precise estimates of the Euler pole from GPS observations.
This has been done by computing velocity vectors and
closure/extension vectors for a number of stations on both plates including
stations in the Maldives and at Diego Garcia, both generally thought to be close
to transition zones between the two plates. Both the Maldives and Diego Garcia
are new stations with the former only having intermittent occupations. However
these stations in conjunction with stations on the African plate and the
principal blocks of the Australian and Indian plates as well the South East
Asian craton of the Eurasian plate enable the boundary to correctly placed and
the appropriate Euler rotation rates to be determined.
PAPER 11
INVERSION OF THE GEODYSSEA RELATIVE DISPLACEMENTS INTO STRAINS, INCREMENTAL
ROTATIONS AND SLIP ON ACTIVE FAULTS
by M.C.J. Nyst, W. Spakman, W.J.F. Simons, B.A.C. Ambrosius
Abstract: We are currently developing a new inversion method, which allows a
joint estimation of the deformation gradient field and the slip on active faults
from geodetic displacement data. From the deformation gradient field the
elastic strain and incremental rotations can be easily computed. The method is
based on an integral formulation of relative base-line displacements. The
novelty of the method is that it allows estimates of continuous (e.g. elastic)
deformation in crustal blocks and at the same time of slip on faults bordering
the crustal blocks. Further, the method is unbiased with respect to the
relation between fault slip and crustal strain, e.g. it does not invoke elastic
dislocation models for fault slip. At present the method is being tested,
studied and refined using synthetic models and synthetic data. We intend to
apply the new inversion method to the relative displacement data available from
the GEODYSSEA project. The results will be presented at the meeting.
PAPER 12
THE ASIA AND THE PACIFIC REGIONAL GEODETIC NETWORK
by Ramesh Govind
No abstract available
PAPER 13
EARTHQUAKE REFORMATION DERIVED USING GPS: EXAMPLES FROM SE-ASIA, CENTRAL ASIA
AND THE ANDES
by G.W. Michel, D. Angermann, J. Klotz,
C. Reigber, H. Schelle and P. Wilson
No abstract available
PAPER 14
ONGOING ACTIVITIES IN CHINA
by Ye Shuhua
No abstract available
PAPER 15
DATA EVALUATION OF THE RED-RIVER GPS CAMPAIGNS IN VIETNAM
By M. Becker, P. Neumaier, E. Reinhart, Nguyen Trong Yem, Duong Chi Cong, To
Linh, Tran Dinh To
No abstract available
PAPER 16
INDONESIAN RESEARCH ON GEODESY AND GEODYNAMICS: STATUS AND ITS DEVELOPMENT
By R. Matindas
No abstract available
PAPER 17
CRUSTAL DEFORMATION IN THE INDONESIAN ARCHIPELAGO BY GPS
by Yehuda Bock
Abstract: Annual GPS fields campaigns were organized across the Indonesian
archipelago by Scripps Institution of Oceanography (SIO), Rensselaer Polytechnic
Institute (RPI), and the National Coordination Agency for Surveying and Mapping
(BAKOSURTANAL), and in Australia by Univ. of New South Wales (UNSW), between
1989 and 1994. Crustal deformation results inferred from site velocity
estimates are summarized. We discuss (1) Pacific-Australia plate boundary
deformation in Irian Jaya (Puntodewo et al., 1994), (2) convergence across the
Java trench (Tregoning et al., 1994), (3) accretion of the southern Banda arc to
the Australia n plate boundary (Genrich et al., 1996), (4) interseismic strain
segmentation at the Sumatran subduction zone (Prawirodirjo et al.,1997),(5)
relative motion of the Sunda Shelf block with respect to Eurasia (Calais et al.,
1997), (6) Australia-Eurasia collision at the Banda arc (Calais et al., 1997),
and (7) strain partitioning and oblique convergence in Sumatra.
PAPER 18
SUNDALAND MOTION DETECTED FROM GEODYSSEA GPS MEASUREMENTS: PART I
- IMPLICATIONS FOR MOTION AT SUNDA TRENCHES
by N. Chamot-Rooke, C. Vigny, A. Walpersdorf, X. Le Pichon, P. Huchon and C.
Rangin
Abstract: 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.
PAPER 19
PRESENT-DAY PLATE MOTIONS IN THE PHILIPPINES INTERPRETATION OF GPS RESULTS OF
GEODYSSEA
by M. Aurelio
No abstract available
PAPER 20
SUNDALAND MOTION DETECTED FROM GEODYSSEA GPS MEASUREMENTS : PART II - RELATIVE
MOTION OF SUNDALAND AND SOUTH CHINA BLOCKS; IMPLICATIONS ON INDIA/EURASIA
COLLISION AND ON THE TECTONICS OF TAIWAN
by X. Le Pichon, N. Chamot-Rooke, C. Vigny, A. Walpersdorf, P. Huchon and C.
Rangin
Abstract: In part I, we have defined the motion of the Sundaland block with
respect to Eurasia. We compare this motion to the motion of the South China
block with respect to Eurasia as defined by Holt et al. (1995). We note that the
motion predicted by Holt et al at Shanghai is on excellent agreement with the
recent VLBI solution of Heki (1996) and that the motion predicted at Taipei also
agrees with the Geodyssea solution there. The results of local GPS measurements
at Taiwan by YU et al. (1995) confirm that Taipei belongs to the main South
China block. We then note that the pattern of motion revealed is such that the
boundaries, between India and Sundaland on the one hand and between Tibet and
South China on the other hand, are purely transform along a N/S direction. In
other words, the eastward component of motion of the indenter is compensated by
an equal eastward component of motion of the South China and Sundaland blocks.
The poles of motion are situated in such a way that this eastward component is
maximal at the latitude of the eastern Himalayan syntaxis and decreases
northward and southward. Thus Taiwan is now situated at the latitude of maximal
eastward velocity. We discuss the geodynamic implications of these kinematics on
the tectonics of Taiwan based on the relative motion history between the
Sundaland and South China blocks along their common Red River Fault boundary
PAPER 21
DISTRIBUTION OF DEFORMATION ACROSS THE SUNDALAND / PHILIPPINE SEA PLATE BOUNDARY
FROM GPS RESULTS
by Rangin Claude, M. Pubellier, C. Vigny, X. Le Pichon, M. Aurelio, R. Quebral
and. A. G. Bader
Abstract: Convergence between rigid Sundaland and the Philippine Sea plate (PSP)
is distributed across a 600 km wide zone including the stretched continental
margin and the Sulawesi - Luzon deformed volcanic belt. GEODYSSEA simple
baselines study indicate a variation from South to North (Philippines / Molucca
/ Sulawesi) of the location of maximum shortening.
• Across the northern Philippines, 70% of the shortening is absorbed along the
Manila Trench/Philippine fault system, the remaining being accommodated along
the northern segment of the Philippine trench.
• Across the central Philippines, the Manila trench is pinned and 70% of the
convergence is absorbed along the Philippine trench. There, 30% corresponds to
thrusting and folding in the Visayas.
• In the Southern Philippines 30% is also taken across Mindanao and another 25%
along the Negros - Sulu trench, allowing only 45% of convergence along the
Philippine trench.
The Molucca Sea accommodates 75% of the convergence within a less than 250 km
wide zone. Taking into account the 25% of the Negros - Sulu trench, the
Philippine trench is inactive and the Celebes sea floor may be considered rigid.
South of the Molucca Sea the effect of the PSP convergence with Sundaland is
transmitted trough Australian microblocks (Sula - Buton) to the North Sulawesi
trench, and to a lesser extend to the Makassar strait, accommodating 4.5cm/y and
1.2cm/y respectively. At this latitude a minor but geologically significant part
of the shortening is absorbed as far as 1000km from the PHSP in the Crocker belt
of Brunei.
Differential motion across this wide deformed zone individualize segments
separated by transfer zones (Southern Luzon, Cotabato, Sorong - Palu).
PAPER 22
ACTIVE FAULTING IN CENTRAL SULAWESI (EASTERN INDONESIA)
by Olivier Bellier, Michel Sebrier, Thierry Beaudouin, Michel Villeneuve, Eka
Putranto, IR Wan Bahar, and Indyo Pratomo
Abstract: In the framework of the GEODYSSEA program (an EU-ASEAN program of SE
Asia GPS survey) a subprogram was set up to study the active tectonics of the
Central Sulawesi fault system, in eastern Indonesia. This system consists of
complex distributed left-lateral strike-slip fault zones located within a triple
junction area between three tectonic plates: the Pacific, Indo-Australian, and
Eurasian plates. Seismicity in Central Sulawesi documents shallow earthquakes
located on and around the Central Sulawesi faults. To characterise the active
fault trace geometry and to localise the high seismic potentiality zones, we
analyse SPOT images covering Sulawesi. This analysis shows, from west to east,
the occurrence of two major active fault zones: The NNW-trending Palu-Koro and
the WNW-trending Matano fault zones. However, deformations are distributed on
three fault zones in the east-central part and SE arm of Sulawesi. The
northernmost segments of the Palu-Koro zone appears geomorphologically more
active and bounds the western part of Palu basin. Study of the Palu-Koro
segments evidences late Quaternary left-lateral geomorphologic feature offsets
ranged between 50 and 600 m (streams, alluvial fans, etc.), as well as faceted
spurs, shutter ridges and 300-400 m high triangular and trapezoidal facets. The
western edge of the Palu basin is controlled by a N-trending 2000-2500 m high
escarpments. The significant dip-slip component of the Present-day faulting is
confirmed by Quaternary uplifted marine and alluvial terraces that reach up to
200 m high. Thus, these geomorphologic characters evidence combined strike-slip
and normal faulting for the Palu-Koro fault Present-day activity. This
transtensional tectonic regime has been confirmed by the fault slip-vector
analyses. We perform an along strike survey of the Sulawesi faults analysing and
dating fault offsets to subsequently determine fault long-term slip-rate.
Datings were done using the U/Th and ESR methods on the offset marine terraces.
In addition, fission track analysis applied on granodiorites which form the
escarpment should constrain the vertical slip rate. To define precisely the Late
Quaternary seismic history, we excavated seven trenches across the North
Palu-Koro fault zone which exposed paleosoils and colluvial wedges in fault
contact with a poorly weathered alluvial bedrock. This indicates the occurrence
of seismic event during the Late Quaternary, even if the seismic history did not
report any earthquake around the Palu zone.
PAPER 23
GPS OBSERVATIONS OF THE TECTONIC ACTIVITY IN THE TRIPLE JUNCTION AREA IN
INDONESIA
by Andrea Walpersdorf and Christophe Vigny, Luhut Parluhutan, Cecep Subarya and
Sobar Sutisna
Abstract: The point of convergence of three major tectonic plates (the Eurasian,
the Philippine and the Australian plate) is situated in Indonesia. The relative
plate velocities are estimated by NUVEL1 to 7 to 8 cm/yr. The complex tectonic
mechanism of the triple junction has been observed during a two years time span
on the GEODYSSEA network, including some densification points, and on a local
subnetwork. A remeasurement of a local subnetwork confirms a high degree of
deformation in the contact zone between the 3 plates. The deformation in this
area is analysed in terms of rigid blocks rotation and deformation. The
influence of 2 large earthquakes in the area (Mw = 7.8 01/01/96 and Mw = 7.0
22/07/96) on the motion of the Tomini station (North Sulawesi) is also
discussed. The block movement is also constrained by observations on the main
fault system on its western limit, the Palu-Koro fault. Previous studies predict
left lateral movements of up to 5 cm/yr (Silver et al., 1983). The GPS
measurements on a transect across this fault show a present day left lateral
displacement of 3 cm/yr. The observations on the intermediate stations help
constrain the localisation of the deformation and the locking depth of the main
fault. Geomorphological observations show clear traces of active opening in the
Palu fault zone. The GPS measurements will be able to confirm if the opening
corresponds to the present day activity of the fault.
PAPER 24
INSTANTANEOUS AND FINITE KINEMATICS IN THE NORTHERN ARM OF SULAWESI
by Andrea Walpersdorf, Christophe Vigny, Claude Rangin, Herve Bellon, and
Bambang Priadi
Abstract: Geodetic data acquired in the Northern Arm of Sulawesi are compared
with the geologic and paleomagnetic data obtained in North Sulawesi and the
Celebes Sea. The objective of this study is to try to extrapolate the
instantaneous motions measured by GPS to the finite motion deduced from
paleomagnetic and geological arguments. The instantaneous motion in Sulawesi
reveals in between 2.5 cm/yr and 5 cm/yr of relative displacement on the
Palu-Koro fault. Paleomagnetic data collected in the Northern Arm (Surmont et
al., 1995) show a 20 degree semi-rigide rotation of the Northern Arm with a pole
located right North of Manado, and this since 5 million years. This suggests
around 150 km of left lateral displacement along the Palu-Koro fault and
consequently a velocity of 3 cm/yr. This fits quite well the 4 years average
instantaneous motion obtained by GPS on this fault.
A higher relative displacement on the Palu fault is given by the asymmetric
magnetic anomaly of the Celebes Sea. It implies that 200-250 km of oceanic
crust was subducted along the North Sulawesi Trench. The time interval of
rotation of the Northern Arm could be reduced by radiometric data on the
calc-alcalic-potassic volcanisme in West Sulawesi which continues up to 2
million years. If this valcanisme is present in the Northern Arm, the long term
velocity on the Palu-Koro fault, which is offsetting this volcanisme, could be
higher by a factor of two. Although on the upper boundary, this estimate could
still be compatible with the rates inferred from recent GPS measurements.
PAPER 25
EASTERN INDONESIA EVOLUTION SINCE THE LATE EOCENE
by Villeneuve M., J.P. Rehault, J.J. Cornee, W. Gunawan, J. Girardeau, A.H.
Harsolurnakso, C. Honthaas, J.A. Malod, and C. Monnier
Abstract: Since the late Eocene time, the eastern part of Indonesia which is
located at the triple junction of the Asiatic, Australian and Pacific plates,
has undergone several geodynamic changes within a large convergent tectonic
regime. During the Oligocene time, the Banda block which is a large continental
fragment drifted away from the Gondwana by the Jurassic time, reached the
Asiatic margin in the Sulawesi Island. A part of Asiatic marginal basins
(Celebes sea) were directly abducted onto the Northern part of this Banda block.
By the early Miocene, due to local collapses, several graben like basins
developed in the Sulawesi Island and Banda block. By the middle Miocene, the
Tukang Besi block moving from the East, collided the southern part of the Banda
block. By the late Miocene and the early Pliocene, the new block including the
formers Banda and Tukang Besi blocks was dismembered and large basins have
occurred (for example Banda sea North and South). By the mid Pliocene, these
basins began to close meanwhile the Bangai Sula block, coming from the East,
reached the Eastern part of Sulawesi. To the Southern part, the Australia
continent collided the Banda/Tukang Besi block mainly in Timor Island. The late
Pliocene is a period of molassic deposition mainly around the mid Pliocen
collisions zones. During the Holocene, the Northwestward motion of the
Australian continent is the main factor of tectonic changes in the eastern part
of Sulawesi. This scenario shows rapid changes from extensional to
compressional regimes. GPS measurement will allow us to understand and to
quantify the present day tectonic changes in this far east country.
PAPER 26
MONITORING THE DEFORMATION OF MT. GUNTUR, INDONESIA, USING REPEATED GPS SURVEY
METHOD : PRELIMINARY RESULTS
by Hasanuddin Z. Abidin, Ony K. Suganda, Mipi A. Kusuma, R. Sukhyar, J. Kahar
Abstract: Indonesia is decorated with 129 volcanoes, where 80 of them are the
type A volcanoes. Since quite many peoples are living around and closed to
these volcanoes, the volcano monitoring is absolutely very important matter to
Indonesia. Several methods have been used in monitoring the volcanoes in
Indonesia, which one of them is the deformation method. This deformation method
is usually implemented by utilizing the terrestrial measurements of distances
and height differences. With the wide spread use of GPS (Global Positioning
System), the GPS-based volcano deformation monitoring system is now started to
be implemented in Indonesia. This paper will describe the use of Repeated GPS
Survey Methods for monitoring deformation of Mt. Guntur, a type-A volcano which
is located about 60 km South-East of Bandung, the capitol city of West Java,
Indonesia. The GPS deformation monitoring network consists of seven points
covering the volcano and its surrounding area, and it is planned to be observed
several times with a time interval of about three months between two consecutive
surveys. The preliminary results of deformation analysis based on two epochs
observation of this GPS monitoring network will be presented and discussed in
this paper. The operational constraints experienced during the establishment
and observation of this GPS monitoring network will also be explained. Some
conclusions and recommendations will also be given.
PAPER 27
PEAK GROUND ACCELERATION OF MALAY PENINSULA DUE TO LONG-DISTANCE EARTHQUAKES
by Tso-Chien PAN and Jichun SUN
Abstract: In this paper the potential ground motion at three geographic points
on Malay Peninsula due to long-distance Sumatra earthquakes is investigated,
following the probabilistic seismic hazard assessment approach. The case
investigated differs from a conventional one, in that no attenuation equations
are available for long-distance earthquakes. Firstly, the attenuation
relationships developed for other regions of the world are reviewed. It is
found that the existing attenuation equations, when extrapolated to
long-distance earthquakes, tend to underestimate peak ground accelerations
(PGAs). By comparing with the PGAs recorded by Japan Meteorological Agency
stations at long distance for major Japan earthquakes, one attenuation equation
is selected for this study. With the chosen attenuation equation, the
probability of PGA exceeding certain levels for various exposure periods of time
at the three geographic points is the computed. At the northern, central and
southern points along the west coast of Malay Peninsula, there is a 10%
probability in 50 years for the peak ground acceleration at rock sites to exceed
1.7% g, 2.5% g, and 1.1% g respectively.
PAPER 28
GPS MEASUREMENT FOR GEODYNAMIC MONITORING IN WEST JAVA
By Bambang Setyadji
Abstract: Two geological structures are predominant in West Java, Indonesia,
that are Cimandiri fault and Lembang fault. These faults are highly assumed as
one of the compensation of the subduction system of the Indo-Australia plate
beneath the Eurasian plate at south of Java Island.
Some GPS campaigns have been done several times since 1992. Every measurement
is done at about 14 stations which are designed to observe the "behavior" of
these two faults. The western part of the network covers the Cimandiri faults
meanwhile the eastern part is related to the study of Lembang Fault.
The 1994 campaign gave a baseline accuracy below 3mm using Lc processing
algorithm. The three days repeatability shows the variation of baseline length
at about 40mm. Displacement vectors which are derived from 1993 and 1994
campaign show that the CIAWI point moves nearly to the North-East direction
(103mm E, 193mm N) and the TUGU point nearly moves to the East (97mm E, 1mm N)
relative to ITB1 Point. The resulted displacement vectors show that there is a
compressing force process from the south in this area, which is considered to be
in agreement with the global tectonics.
The GPS network has been expanded southernly to a volcano area, the Mt. Guntur.
The first Campaign for this network has been done on November 1996.
PAPER 29
CREATION OF GEODETIC SCIENTIFIC NETWORK IN EAST MALAYSIA USING RESULTS OF
GEODYSSEA CAMPAIGNS
by Dr. Majid Kadir, Samad Abu, Azhari Mohamed, Soeb Nordin
Abstract: 1n 1995, the Department of Survey and Mapping Malaysia (DSMM) has
embarked a GPS observation campaign using four Trimble 4000SSE dual frequency
GPS receivers in an effort to provide a modern and precise reference frame for
East Malaysia. The objectives of this campaign were to establish a new GPS
network with a relative accuracy of better than 1 ppm, to analyse the existing
geodetic network and to densify control points for the purpose of production of
topographical maps. A total number of 171 stations which consist of 6 existing
Doppler, 73 existing triangulation and 92 new GPS stations have been observed
during the campaign. The Trimble GPSurvey processing software with broadcast and
precise ephemerides were used to process the acquired GPS data . The GEOLAB
Network Software were used to adjust the network in the constrained adjustment.
The coordinates obtained from the Squadron of Technical Royal Engineers (STRE)
GPS campaign in 1994 were used for the fixed stations. In order to relate the
network to the International Terrestrial Reference Frame (ITRF), the coordinates
of the fixed points were obtained from the results of the GEODYSSEA campaign.
This paper presents the results of the processing, adjustment of the GPS
campaign and the establishment of a first-order network for East Malaysia.
Comparisons were made between the results of the processing using broadcast and
precise ephemerides and the two adjustment.
PAPER 30
TOWARDS VISION 2000 - A FUTURE GEOCENTRIC GEODETIC DATUM AND REDEFINATION OF THE
VERTICAL DATUM FOR PENINSULA MALAYSIA?
by Zarina Ahmad-Berger, Chris Rizos, A. H. W. Kearsley
Abstract: This paper attempts to raise questions, assess the situation and set
the scene on the feasibility of implementing a Zero-order Network, the necessity
of redefining the vertical datum and the possibility of providing a direct link
between the geodetic network and mean-sea-level, in the first instance, for
Peninsula Malaysia. In addressing these issues, the applicability of GPS in its
state-of-the-art form are reviewed and assessed in terms of technology
configuration, operational issues, quality control and institutional issues.
Some results from the investigations of the Malaysia Height Datum Project
carried out at UNSW are discussed, and the validity of the existing vertical
datum for Peninsula Malaysia is appraised. The relevance of establishing a
Zero-Order GPS Network in Peninsula Malaysia, given the current situation that
the datum adopted is only "quasi-WGS84" is accentuated. Both satellite datums
(WGS84 and ITRF) are purely a geometrical system, with no deflection of the
vertical or geoid information (ie no vertical datum in the satellite datums).
In this case, how could GPS complement the process of vertical datum
determination? This is only one of the many issues being looked at.
Considerable Research and Development (R&D) is needed not only to assess the
requirements and impact of a transition to a new datum for the surveying, GIS
and mapping communities, but to also better understand the current expertise of
the local organisations in satellite positioning technology, such as the NAVSTAR
Global Positioning System, to be able to provide sufficient training and
education. The R&D and output from this project will provide invaluable
experience in developing a conceptual framework, workable methodology, strategic
procedures and training modules, applicable not only in Malaysia, but also to
other developing countries in the South East Asian region.
PAPER 31
LOW-COST DENSIFICATION OF PERMANENT GPS NETWORKS FOR NATURAL HAZARD MITIGATION
by Chris Rizos, Shaowei Han, Craig Roberts
Abstract: Crustal deformation is a phenomenon ideally suited for study using
GPS. An experiment can be devised in order to measure the rate of deformation,
by using GPS to measure the change in length (as well as height difference and
orientation) of baselines connecting receivers in a carefully monumented ground
network. This is done by repeatedly measuring the same baseline components to
an accuracy commensurate to, but preferably much higher than, the expected
baseline component changes. Such GPS techniques are based on the "campaign"
principle : the periodic (often annual) re-survey of a network of control
points. After several years, the rate of shortening, or lengthening, of the
baseline components can be reliably estimated. In the past half decade or so
there has been increasing interest in the use of permanent, continuously
operated GPS stations, and a small number of continuous networks have been
deployed in the USA, Japan, Canada and several other developed countries for
large scale crustal motion studies. An important justification for permanent
arrays is that natural hazards research will be furthered because of the
continuous measurement of a deformation phenomenon, rather than a periodic
measurement. However, only Japan has it been possible to establish a
country-wide continuous GPS network to support seismic research, and ultimately
contribute to hazard mitigation through the implementation of an earthquake
warning system. Even with such a dense network of high quality dual-frequency
GPS receivers as established by Japan's Geographical Survey Institute, the
station separation is of the order of 15km or more. There are, however,
applications of GPS deformation systems which require receiver densities of the
order of just a few kilometres. Furthermore, the high cost of such GPS systems
means that most countries cannot possibly afford to establish such systems.
Applications of permanent GPS arrays include monitoring of volcano flanks,
micro-faults, ground subsidence due to underground mining or fluid extraction,
slope stability, and even engineering structures such as dams, etc. Therefore
the cost of an automatic, continuously operating GPS array system must be
reduced significantly (ideally by at least a factor of five to ten) if the
technology is to contribute to hazard mitigation. This paper described design
for a Permanent Automatic GPS Array System which is a significant advance on
earlier designs. The basis of the design is to deploy a mixed network
consisting of a large number of low-cost GPS receivers across the area of
interest, each costing around US$3,000 each, surrounded by a small number of
dual-frequency GPS receivers. Through the application of innovative operational
strategies and data processing algorithms, the network will be able to deliver
centimetre level accuracies (or better), at considerably lower cost.
PAPER 32
CONNECTION OF THE INDONESIAN GEODETIC REFERENCE SYSTEM TO THE ITRF-94 SYSTEM AND
ITS QUALITY MEASURES
by Sobar Sutisna
No abstract available
PAPER 33
IFAG PERMANENT GPS NETWORK ACTIVITIES AND THEIR IMPLICATIONS TO GEODYSSEA FOLLOW
ON PROJECT
by E. Reinhart, M. Becker, H. Seeger, and G. Weber
Abstract: The Institute of Applied Geodesy (IfAG) presently maintains more than
10 permanent GPS sites and contributes to the IGS and the EUREF activities in
view of the definition and monitoring of the geodetic reference frame as well as
of the monitoring of geokinematics. A network of about 20 permanent stations for
the realisation of a reference frame in Germany and the monitoring of its
stability is being installed presently. The data of a regional sub-network of
13 stations as densification of the IGS in EUROPE is analysed regularly on a
daily basis at IfAG. The experiences of this analysis are presented and the
results are discussed with respect to the development of a permanent network as
required for the densification of the IGS in the area of South-East Asia with
respect to the active geokinematics in this area and the reference frame
realization.
PAPER 34
DENSIFICATION OF REGIONAL GPS NETWORK - THE FUTURE OF GEODYSSEA
by P.A. Cross
Abstract: Regional GPS networks are important for a number of reasons. The most
obvious of these is that they can give information on the overall deformation of
the region in question and so help to refine regional tectonic models -
especially regarding the exact nature and location of plate boundaries. It is
the case, however, that in most parts of the world such networks mainly confirm
theories already developed from other (largely seismic and geological)
evidence, i.e. they add little that is intrinsically new. Of course they do
help to assess current levels of activity by allowing comparisons between
current motions and those over geological timescales and they also perform a
useful geodetic role (in defining deforming reference frames).
Their real value is that they can form a framework for future densification and
it is these more dense networks that have the potential for real practical
benefit. In particular they can be used (in conjunction with other data
sources) for a variety of environmental monitoring applications - including
seismic hazard monitoring, global warming (through sea level rise), weather
forecasting and transport of pollutants. Such monitoring actually requires a
dense network of permanently located and recording GPS receivers something that
is currently probably beyond the financial resources of most of the publicly
funded bodies charged with the monitoring of such environmental phenomena.
This paper summarises the environmental benefits of permanent networks and
offers partial, and less expensive, solutions (especially for the case of
seismic hazard assessment) for regions such as SE Asia. These solutions are
based on continuously observing mobile GPS receivers and either
point-positioning type solution strategies or more formal IGS regional
solutions.
PAPER 35
APSG AND GEODYSSEA
by Ye Shuhua
No abstract available
PAPER 36
SOUTH EAST ASIA/ASIA-PACIFIC GPS ACTIVITIES AND THE IGS
by Ruth Neilan and Jim Zumberge
Abstract: Within this venue of 'Geodyssea,' it is appropriate to consider the
longer term benefits of the IGS to South East Asia/Asia-Pacific GPS
applications. Similarly, it is timely to encourage greater participation of
these groups within the IGS to strengthen the international infrastructure and
to foster multi-national cooperation in this region. We will provide an
overview of the IGS, our data products and resources available to users, and how
to access this information. New activities of the IGS will be described such as
densification of the ITRF, aspects of the March, 1997 sea level monitoring
workshop at JPL, and efforts to support ionospheric studies. How the above
activities relate to South-East Asian projects will be addressed.