surface uplift history of the incipient banda arc continent collision geology and synorogenic foraminifera of rote and savu islands indonesia abstract field mapping and analysis of foraminifera from synorogenic pelagic units of rote and savu islands indonesia reveals high rates of surface uplift of the incipient banda arc continent collision during the past 1 8 myr new geological maps of these islands document accretion to the banda forearc of triassic through tertiary sedimentary cover units from the down going australian continental margin foraminifera rich synorogenic deposits of the batu putih formation unconformably overlie these accreted units we use paleodepth versus time estimates from benthic and planktic foraminifera s to measure long term surface uplift rates for the accretionary wedge although strong currents in the region cause some problems with reworking several distinctive species have been found synorogenic deposits in savu and rote yield foraminifer s of biozone neogene n 18 to n22 5 6 1 0 myr that were deposited at estimated depths of around 3000 m these deposits are unconfomrably overlain by uplifted coral terraces the highest coral terraces in savu are 300 m above sea level and perhaps as old as 0 8 myr in rote the highest coral terrace is 200 above sea level and 0 2 myr old these data indicate that collision of the australian continental margin with the banda arc which initiated much earlier in timor has propagated westward towards rote where it is in the initial stages of accretionary wedge emergence collision of the scott plateau propagated se from sumba 2 3 ma to savu 1 0 0 5 ma and then to rote 0 2 ma average rates of surface uplift of the batu putih formation pelagic deposits during the past 2 myr in rote and savu are 1 5 and 2 3 mm a respectively the rise of these islands is clogging the indo pacific seaway

earthquakes gravity and the origin of the bali basin an example of a nascent continental fold and thrust belt we infer from the bathymetry and gravity field and from the source mechanisms and depths of the eight largest earthquakes in the bali region that the bali basin is a downwarp in the crust of the sunda shelf produced and maintained by thrusting along the flores back arc thrust zone earthquake source mechanisms and focal depths are inferred from the inversion of long period p and sh waves for all events and short period p waves for two of the events centroidal depths that give the best fit to the seismograms range from 10 to 18 km but uncertainties in depth allow a range from 7 to 24 km the p wave nodal planes that dip south at 13 to 35 7 strike roughly parallel to the volcanic arc and are consistent with thrusting of crust of the bali basin beneath it the positions of the earthquakes with respect to crustal features inferred from seismic and gravity data suggest that the earthquakes occur in the basement along the western end of the flores thrust zone the slip direction for the back arc thrust zone inferred from the orientation of the earthquake slip vectors indicates that the thrusting in the bali basin is probably part of the overall plate convergence as it roughly coincides with the convergence direction between the sunda arc and the indian ocean plate summation of seismic moments of earthquakes between 1960 and 1985 suggests a minimum rate of convergence across the thrust zone of 4 2 mm a the presence of back arc thrusting suggests that some coupling between the indian ocean plate and the sunda arc occurs but mechanisms such as continental collision or a shallow subduction of the indian ocean plate probably can be ruled out the present tectonic setting and structure of the bali basin is comparable to the early forelands of the andes or western north america in that a fold and thrust belt is forming on the continental side of an arc trench system at which oceanic lithosphere is being subducted the bali basin is flanked by the tertiary java basin to the west and the oceanic flores basin to the east and thus provides an actualistic setting for the development of a fold and thrust belt in which structure and timing of deformation can change significantly along strike on the scale a few hundred kilometers

itrf2000 a new release of the international terrestrial reference frame for earth science applications 1 for the first time in the history of the international terrestrial reference frame the itrf2000 combines unconstrained space geodesy solutions that are free from any tectonic plate motion model minimum constraints are applied to these solutions solely in order to define the underlying terrestrial reference frame trf the itrf2000 origin is defined by the earth center of mass sensed by satellite laser ranging slr and its scale by slr and very long baseline interferometry its orientation is aligned to the itrf97 at epoch 1997 0 and its orientation time evolution follows conventionally that of the no net rotation nnr nuvel 1a model the itrf2000 orientation and its rate are implemented using a consistent geodetic method anchored over a selection of itrf sites of high geodetic quality ensuring a datum definition at the 1 mm level this new frame is the most extensive and accurate one ever developed containing about 800 stations located at about 500 sites with better distribution over the globe compared to past itrf versions but still with more site concentration in western europe and north america about 50 of station positions are determined to better than 1 cm and about 100 sites have their velocity estimated to at or better than 1 mm yr level the itrf2000 velocity field was used to estimate relative rotation poles for six major tectonic plates that are independent of the trf orientation rate a comparison to relative rotation poles of the nuvel 1a plate motion model shows vector differences ranging between 0 03 and 0 08 m y equivalent to approximately 1 7 mm yr over the earth s surface itrf2000 angular velocities for four plates relative to the pacific plate appear to be faster than those predicted by the nuvel 1a model the two most populated plates in terms of space geodetic sites north america and eurasia exhibit a relative euler rotation pole of about 0 056 0 005 m y faster than the pole predicted by nuvel 1a and located about 10 n 7 e more to the northwest compared to that model

fore arc deformation at the transition between collision and subduction insights from 3 d thermomechanical laboratory experiments 1 three dimensional thermomechanical laboratory experiments of arc continent collision investigate the deformation of the fore arc at the transition between collision and subduction the deformation of the plates in the collision area propagates into the subduction collision transition zone via along strike coupling of the neighboring segments of the plate boundary in our experiments the largest along strike gradient of trench perpendicular compression does not produce sufficiently localized shear strain in the transition zone to form a strike slip system because of the fast propagation of arc lithosphere failure deformation is continuous along strike but the deformation mechanism is three dimensional progressive along strike structural variations arise because coupling between neighboring segments induces either advanced or delayed failure of the arc lithosphere and passive margin the modeling results suggest that orogenic belts should experience deeper subduction of continental crust and hence higher pressure metamorphism where the two plates first collided than elsewhere along the plate boundary where collision subsequently propagated furthermore during the initial stage of collision the accretionary wedge is partially subducted which leads to lubrication of the interplate zone and a reduction of shear traction therefore a large convergence obliquity angle does not produce a migrating fore arc sliver rather the pressure force generated by subduction of the buoyant continental crust causes fore arc motion it follows that convergence obliquity during collision does not yield trench parallel deformation of the fore arc and its influence on the collision process is limited however convergence obliquity may control the geometry of the active margin during the oceanic subduction stage prior to collision and inherited structures may influence the propagation mechanism

evolution of atauro island temporal constraints on subduction processes beneath the wetar zone banda arc abstract atauro is a key to understanding the late stage volcanic and subduction history of the banda arc to the north of timor a volcanic history of bi modal subaqueous volcanism has been established and new whole rock and trace element geochemical data show two compositional groups basaltic andesite and dacite rhyolite 40ar 39ar geochronology of hornblende from rhyo dacitic lavas confirms that volcanism continued until 3 3 ma following the cessation of volcanism coral reef marine terraces have been uplifted to elevations of 700 m above sea level continuity of the terraces at constant elevations around the island reflects regional scale uplift most likely linked to sublithospheric processes such as slab detachment local scale landscape features of the eastern parts of atauro are strongly controlled by normal faults the continuation of arc related volcanism on atauro until at least 3 3 ma suggests that subduction of australian lithosphere continued until near this time this data is consistent with findings from the earthquake record where the extent of the wetar seismic gap to a depth of 350 km suggests slab breakoff as a result of collision commenced at 4 ma leading to subsequent regional uplift recorded in elevated terraces on atauro and neighbouring islands

temporal association of arc continent collision progressive magma contamination in arc volcanism and formation of gold rich massive sulphide deposits on wetar island banda arc whole rock 87sr 86sr and 18o analyses of volcanic rocks and 3he 4he analyses of sulphides and sulphates from mineralized rocks on wetar indonesia indicate a variable contribution of assimilated crustal material or sediment sourced from the subducted australian craton to the south these new data support the idea of progressive source contamination with precisely dated events showing that wetar island hosts the most extreme examples of crustal assimilation in the region the increased continental contamination occurs during the pliocene zanclian to piacenzian during distinct magmatic events between 5 and 4 ma and at 2 4 ma when 87sr 86sr ratios in unaltered lavas with whole rock 18o values between 5 7 and 9 6 increase from 0 707484 to extreme radiogenic values of 0 711656 the earlier of these magmatic events is important in the generation of the hydrothermal systems responsible for the mineralization recorded on wetar samples from this yield radiogenic 3he 4he ratios between 0 5 and 1 4 r ra similar to the data from volcanic rocks on nearby romang the later magmatic event coincides with the arrival of the australian continental margin at the subduction zone along the banda arc progressive incorporation of continental sourced components into the source region below the wetar island edifice coincides with the formation of gold rich volcanogenic massive sulphide deposits hosted within the contaminated volcanic pile

modeling of large scale accretionary wedge deformation instantaneous stress and velocity fields within an active accretionary wedge can be calculated using plastic slip line theory given the assumptions of a perfectly plastic rheology and plane strain conditions after selecting a plastic yield stress and an average density a stress field slip line field can be computed for a wedge of known cross sectional configuration from known stress boundary conditions on the upper surface basal surface tractions are derived without basal boundary conditions the geometry of the computed slip line field can then be used to constrain the lower limit of the yield stress the known velocity boundary conditions are insufficient for calculation of a velocity field because the coupling between the wedge and the subducting plate is unknown consequently basal velocity distributions must be assumed to permit the construction of velocity fields these assumed distributions are constrained by known rates of surface uplift and rates of tilt as well as inferred patterns of instantaneous strain rates within a wedge the sunda accretionary wedge west of central sumatra is used to illustrate the plasticity approach a minimum average yield stress of 20 30 mpa and a weaker basal layer of variable effective strength are indicated for this example surface uplift rates may be affected significantly by regions of high basal strain rate finite velocity discontinuities and underplating the known pattern of uplift rates near nias island located on the outer arc ridge is consistent with the constraint that 90 of the total incremental shortening of the wedge is concentrated within 20 km of the trench given a sufficient number of uplift and tilt rate observations across a particular wedge the relative influence of underplating tectonic erosion and basal strain rate variations could be assessed using the perfectly plastic model

u pb dating of a terminal pliocene coral from the indonesian seaway abstract pristine detrital platygyra corals were discovered in an exhumed package of syn orogenic marine sediments on the island of timor in the eastern indonesian region and dated using u pb techniques a single coral from the upper part of the sequence yields a 238 u 206 pb 207 pb 206 pb concordia age of 2 66 0 14 2 ma that is supported by coral 87 sr 86 sr chemostratigraphy and foraminiferal biostratigraphy from bounding strata minor u series disequilibrium is best explained by u mobility within the last 150 ka as pore water chemistry was altered during exhumation and is unlikely to have affected 238 u 206 pb and the apparent sample age by more than 1 2 the ability to date corals beyond the limits of 14 c and u th techniques provides the opportunity to improve the temporal resolution of associated marine chronostratigraphic records in this instance we refine the timing of timor s emergence from beneath the waters of the indonesian seaway is and the initiation of turbiditic deposition at the study site to between ca 3 35 and 2 66 ma these results have implications for the evolution of topography and is oceanic pathways in the active orogenic belts along the northern fringes of the australian plate

one century of tectonic deformation along the sumatran fault from triangulation and global positioning system surveys an analysis combining historical triangulation and recent global positioning system gps survey measurements in west and north sumatra indonesia reveals a detailed slip history along the central part of the sumatran fault the arc parallel components of the combined velocity field are consistent with slip rates inferred from gps data ranging from 23 to 24 mm yr between 1 0 s and 1 3 n the sumatran fault appears to be characterized by deep locking depths of the order of 20 km and the occurrence of large mw 7 earthquakes the long term 1883 1993 strains show simple right lateral shear with rates similar to gps measured 1989 1993 strain rates coseismic deformation due to the 1892 tapanuli and 1926 padang panjang earthquakes estimated from triangulation measurements taken before and after the events indicates that the main shocks were significantly larger than previously reported the 1892 earthquake had a likely magnitude of mw 7 6 while the 1926 events appear to be comparable in size to the subsequent m 7 1943 events and an order of magnitude higher than previously reported

strain partitioning during oblique plate convergence in northern sumatra geodetic and seismologic constraints and numerical modeling global positioning system gps measurements along the subduction zone of northern sumatra 2 s to 3 n reveal that the strain associated with the oblique convergence of the australian plate with eurasia is almost fully partitioned between trench normal contraction within the forearc and trench parallel shear strain within a few tens of kilometers of the sumatran fault kinematic analyses of interplate earthquake slip vectors provide slip rates on the sumatran fault within a few millimeters per year of gps and geologic rates giving us more confidence in the use of slip vectors for inferring slip partitioning elsewhere the inferred slip rate on the sumatran fault is 1 3 less than the full margin parallel component of plate motion an across forearc rotation in the slip vectors suggests that the missing arc parallel shear occurs seaward of the geodetic network between the forearc islands and the trench simple finite element models are used to explore the conditions under which the change in the principal strain rate directions between the forearc and the arc region can occur modeling suggests that neither a preexisting strike slip fault nor a zone of thermally induced lithospheric weakness in the overriding plate is needed for strain partitioning to occur in general forearc slivers form over the region of interplate coupling and are driven along strike by the basal shear a volcanic arc can help the partitioning process by localizing the margin parallel shear strain in the upper plate if its crust and mantle are weaker than its surroundings interplate slip vectors and geodetic results from sumatra together suggest that the highest coupling on the plate boundary occurs beneath and seaward of the forearc islands consistent with inferences about the rupture zones of great nineteenth century earthquakes there the sumatra example suggests that geodetic measurements of interseismic margin parallel shear strain at oblique convergent margins can be used to map the landward extent of the relatively high basal stress beneath the overriding plate if one can correct for strain localization caused by weak upper plate strike slip faults

crustal deformation at the sumatran subduction zone revealed by coral rings analyses of coral rings grown in the interval 1970 1997 reveal a geographically distinct pattern of interseismic uplift off sumatra s western coast at distances less than 110 km from the sumatran trench coral reefs are submerging as fast as 5 mm y at 130 and 180 km distance from the trench they are emerging at similar rates we suggest that a locked or partially locked patch located above 30 km depth on the upper surface of the subducting oceanic plate generates this pattern

collisional melange development geologic associations of active melange forming processes with exhumed melange facies in the western banda orogen indonesia analysis of block assemblages matrix clay mineral composition and microfauna and offshore seismic reflection profiles reveal that the bobonaro melange in the timor region is sourced from mud rich australian continental margin sequences that are remobilized during accretion and form various facies depending on the structural conditions of emplacement melange facies include broken formation matrix rich mud injections and classic mixed block in clay facies each of these are distinguished by varying degrees of remobilization mixing and dispersion at different structural positions across the orogenic wedge the most important structural control is whether melange was generated beneath or in front of upper plate banda forearc basement banda terrane at the present collisional deformation front in the timor trough seismic reflection profiles show that melange forms mostly by stratal detachment and fluid assisted remobilization above a basal decollement propagating laterally along overpressured jurassic to cretaceous clay rich sequences of the distal australian continental margin the broken clay rich material injects upward through faults to form intrusive bodies at the base of slope cover sediment to form mud ridges at the surface similar patterns of stratal disruption are exposed onshore in the pliocene kolbano fold and thrust wedge of southern timor which is structurally contiguous with the timor trough deformation front melange in the kolbano mountains is mostly broken formation and matrix rich injections of mud from jurassic and cretaceous units deformation mechanisms include intense layer parallel extension associated with emplacement by mud diapirs that rise from near the decollement upward to the surface along fault conduits in the hinterland of the orogenic wedge east timor and northern west timor melange is dominantly of mixed block in clay facies with large blocks derived from roof thrust sheets of intermixed banda terrane and maubisse formation units at the structural base of these thrust sheets is the sonnebait disruption zone sdz which formed the initial suture between the banda terrane and structurally underthrust australian continental margin sequences during the late miocene to early pliocene the thickest accumulations of mixed block in clay melange in the timor region are found at the southern edge outlet of the sdz near the central and viqueque synorogenic basins the extent of block dispersion and mixing in the sdz is indicative of intense shear strains perhaps induced by an oversupply of accretable material when the suture zone was clogged by underthrusting of the australian continental margin

reassessing the chronology of the archaeological site of anzick found in 1968 the archaeological site of anzick montana contains the only known clovis burial here the partial remains of a male infant anzick 1 were found in association with a clovis assemblage of over 100 lithic and osseous artifacts all red stained with ochre the incomplete unstained cranium of an unassociated geologically younger individual anzick 2 was also recovered previous chronometric work has shown an age difference between anzick 1 and the clovis assemblage represented by dates from two antler rod samples this discrepancy has led to much speculation with some discounting anzick 1 as clovis to resolve this issue we present the results of a comprehensive radiocarbon dating program that utilized different pretreatment methods on osseous material from the site through this comparative approach we obtained a robust chronometric dataset that suggests that anzick 1 is temporally coeval with the dated antler rods this implies that the individual is indeed temporally associated with the clovis assemblage

gps measurements of crustal deformation within the pacific australia plate boundary zone in irian jaya indonesia abstract global positioning system gps measurements made in 1991 1992 and 1993 provide preliminary estimates of slip distribution between the australian and pacific plates in irian jaya indonesia we interpret the gps results with constraints from earthquake mechanisms and slip vectors recent marine surveys and geology three gps sites in southeastern irian jaya show motions that are within 10 mm yr of the expected motion of australia a coast to coast n s baseline along 140 5 e crosses all known onland regions of active deformation but reveals no more than 15 mm yr of shortening and 20 mm yr of left lateral shear in the 27 month period the remaining 40 mm yr of expected convergence between the pacific and australian plates probably occurs at the new guinea trough gps sites on the island of biak at 136 e and at sorong near the western tip of bird s head at 131 e both move 90 100 mm yr in a wsw direction relative to irian jaya but less than 15 mm yr relative to each other these sites are on either side of the sorong fault and demonstrate that it is not presently the major boundary between the australian and pacific plates instead the plate boundary is now south of the sorong and biak sites earthquakes suggest possible structures that accomodate motion between bird s head and australia but the relative importance of them remains uncertain

observing plate motions in s e asia geodetic results of the geodyssea project this paper presents the final geodetic results of the geodyssea project the gps data from a 42 station network observed during two field campaigns 1994 1996 were analyzed by four groups using different software packages and analysis strategies the precision of both campaign coordinate solutions was found to be 4 7 mm for the horizontal and 1 cm for the vertical component the campaign solutions were merged into one unique solution which was accurately mapped into the itrf 96 reference frame the global accuracy of this solution with respect to itrf 96 is 1 cm while the resolution of the relative horizontal velocities is estimated to be at the level of 2 3 mm yr this solution was used as the basis for all scientific interpretations which are published in separate papers the velocity estimates of a part of the network provided the first direct measurement of a relative motion of the sundaland block with respect to eurasian plate

tectonic collision processes after plate rupture abstract rupture of a continental plate subducted below a forearc produces a fold and thrust mountain belt with fast overthrusting of nappes post rupture plate unflexing leading to reflexure provides a mechanism for foreland basin formation application to the australia banda arc collision accounts for the origin of the timor trough its imbrication and contemporaneous extension in outer arc as well as reversal of subduction direction after the emplacement of nappes

accretion of the southern banda arc to the australian plate margin determined by global positioning system measurements global positioning system geodetic measurements at thirteen locations in indonesia and four in australia reveal that the australian continent has accreted the banda island arc to its margin small relative velocities of five sites on west java south kalimantan bali and south sulawesi define a rigid sunda shelf that moves relative to northern australia in a manner consistent with pole locations from nuvel 1 australia eurasia but at a rate that is about 7 slower block like northward motion of the southern banda arc toward the sunda shelf at nearly the same rate as australia suggests that the timor trough is now inactive as a thrust little of the convergence of australia with eurasia is accommodated by strain within the banda arc structure most of the convergence appears to occur as northward translation of the rigid arc with shortening on the flores and wetar thrusts and possibly on faults within the back arc basin

slip partitioning and fore arc deformation at the sunda trench indonesia oblique subduction at the sunda trench has produced transpressive deformation of the plate leading edge a major feature is the right lateral great sumatran fault gsf which probably absorbs a significant fraction of the trench parallel shear the kinematics of sunda relative to australia are discussed on the basis of available gps data and geologically determined slip rates on the csf in spite of the uncertainty on the plate motion several robust conclusions can be drawn the predicted obliquity of the convergence increases northward along the sumatra trench up to about 30 slip partitioning is nearly complete along the northern segment of the sumatra trench where the csf probably accommodates most of the trench parallel shear along the southern segment where obliquity is less than about 20 slip partitioning is not complete as indicated by oblique thrusting at the subduction there only a fraction of the trench parallel motion of australia relative to se asia is accommodated along the csf these observations suggest that the leading edge behaves like a plastic wedge except that slip partitioning although incomplete is observed even at low obliquities

gps compared to long term geologic motion of the north arm of sulawesi geodetic data acquired in the north arm of sulawesi are compared with geologic and palaeomagnetic data from north sulawesi and the celebes sea the objective of this study is to assess whether the long term motion deduced from palaeomagnetic and geological studies is coherent with the extrapolation of the current motions measured by gps palaeomagnetic data that have been collected in the north arm of sulawesi indicate that since 5 ma about 20 to 25o of semi rigid rotation occurred about a pole located north of manado this suggests 200 to 250 km of left lateral displacement along the palu koro fault with a displacement rate of 4 cm year a rather similar displacement on the palu fault is derived using the distribution of the asymmetric magnetic anomalies of the celebes seafloor the distribution implies that 200 to 250 km of oceanic crust was subducted at the north sulawesi trench another marker for the rotation is derived from the opening of the gulf of tomini and the nw migration of the calc alkaline subduction related volcanism the far field observation by gps of 4 cm year of left lateral strike slip motion over 17 months and the 5 year average of 3 4 0 3 cm year on a transect across the palu fault fit well with the geological observations that indicate a motion of 4 to 5 cm year of the north arm we therefore conclude that the current rates deduced from gps measurements approximate the long term rates and may hence be extrapolated over a few million years 1998 elsevier science b v all rights reserved

estimates of terrestrial heat flow in northern chihuahua mexico based upon petroleum bottom hole temperatures bottom hole temperature data from deep petroleum tests are used in conjunction with estimated and measured thermal conductivity values to estimate heat flows at 12 sites in northern chihuahua the errors and uncertainties associated with these estimates and measurements are discussed from these heat flow estimates several geothermal regions are proposed which appear reasonable in terms of data statistics and the geologic environments in northeastern chihuahua an area of considerable tectonic activity with no cenozoic volcanic activity the heat flow mean is 73 mw m 2 westward in north central chihuahua the heat flow values become 85 mw m 2 farther westward in northwestern chihuahua heat flows 105 mw m 2 are estimated however there is only a modest probability that mean heat flow values for northwestern and north central chihuahua differ very high heat flows 250 mw m 2 and low heat flows 2 are not observed in north central or in northwestern chihuahua the deep temperature data may be removed from the effects of hydrothermal activity in sediments and along faults which can cause very high or low values it may also be possible that potential magma sources in the crust of the study area are not as young and hot as the sources associated with the volcanics along the rio grande rift in new mexico although heat flows of 105 mw m 2 do suggest crustal magmatic sources additional geophysical data will be needed to consider these possibilities

assembling north china craton within the columbia supercontinent the role of double sided subduction abstract an evaluation of recent s wave receiver functions s wave velocities and two versions of p wave tomographic images along various transects in the north china craton provides some clues on the subduction collision history of the different crustal blocks and their final amalgamation within the paleoproterozoic columbia supercontinent interpretation of a n s seismic section of the craton suggests thick slab debris sinking to various depths in the mantle the w e seismic corridors show the preservation of a thick 200 km lithospheric root tectosphere beneath the ordos block and its variable and extensive erosion towards the yanliao block eastern block this zone is characterized by layers with marked velocity contrast and suggests repeated stacking of the remnants of underplated and accreted paleoproterozoic oceanic lithosphere the present day lithosphere asthenosphere boundary beneath this region probably marks the erosional plane along which decratonization occurred through subduction erosion from the east and thermal and material erosion by upwelling asthenosphere from below resulting in the partial destruction of the tectosphere and its thinning towards the east within the asthenosphere below the yanliao block younger and thinner slabs predominate in the absence of any prominent thick high velocity layers these younger slabs define a westward polarity and constitute a mega scale duplex formed by underplating through phanerozoic subduction process particularly the pacific plate subduction from the east the lithologic associations within the inner mongolia suture zone dividing the yinshan block to the north and ordos block to the south correspond to an accreted ocean plate stratigraphic sequence with the tonalite trondhjemite granodiorite ttg gneisses charnockites and calc alkaline granites representing a continental arc built up through subduction from the north the seismic transects bring out a contrasting polarity in the subduction regime with an oblique east to southward subduction of the yinshan block and a westward subduction of the yanliao block here i propose a double sided subduction history for the ncc similar to the ongoing subduction process in the western pacific such double sided subduction is considered to promote rapid amalgamation of continental fragments within supercontinents and the subduction polarities and mantle dynamics of ncc are therefore considered to be critical in evaluating the final assembly of the paleoproterozoic supercontinent columbia

gps determined eastward sundaland motion with respect to eurasia confirmed by earthquakes slip vectors at sunda and philippine trenches abstract gps measurements acquired over southeast asia in 1994 and 1996 in the framework of the geodyssea program revealed that a large piece of continental lithosphere comprising the indochina peninsula sunda shelf and part of indonesia behaves as a rigid sundaland platelet a direct adjustment of velocity vectors obtained in a eurasian frame of reference shows that sundaland block is rotating clockwise with respect to eurasia around a pole of rotation located south of australia we present here an additional check of sundaland motion that uses earthquakes slip vectors at sunda and philippine trenches seven sites of the geodyssea network are close to the trenches and not separated from them by large active faults two at sumatra trench three at java trench and two at the philippine trench the difference between the vector at the station and the adjacent subducting plate vector defines the relative subduction motion and should thus be aligned with the subduction earthquake slip vectors we first derive a frame free solution that minimizes the upper plate or sundaland motion when corrected for australia eurasia and philippines eurasia nuvel1 a motion the misfit between gps and slip vectors azimuths is significant at 95 confidence indicating that the upper plate does not belong to eurasia we then examine the range of solutions compatible with the slip vectors azimuths and conclude that the minimum velocity of sundaland is a uniform 7 10 mm a eastward velocity however introducing the additional constraint of the fit of the geodyssea sites with the australian igs reference ones or tie with the ntus singapore station leads to a much narrower range of solutions we conclude that sundaland has an eastward velocity of about 10 mm a on its southern boundary increasing to 16 18 mm a on its northern boundary

deformation and exhumation in timor distinct stages of a young orogeny abstract timor island in the outer banda arc bordering the timor sea preserves the orogenic product of an arc continent collision between the australian plate and the banda arc that commenced after 10 9 9 8 ma gts2004 but emerged above sea level only 3 1 ma ago the orogenic pile includes large tracts of material from the australian margin including the permian to middle jurassic gondwana megasequence and the late jurassic to early late miocene australian margin megasequence which occur in thrust slices in addition material from the banda arc side of the plate margin referred to as the banda terrane occurs throughout the island and includes both seafloor metamorphosed igneous material and cover sediments also in thrust sheets however the distribution of thrust slices is unclear in many areas perhaps because only the uppermost nappes of the thrust pile are currently emergent and also because the thrust piles have been disrupted by later high angle faulting evidence from east timor suggests that the major break between deformed pre collisional strata and the relatively undeformed overlying deposits was during the late miocene 9 8 5 5 ma we present evidence for the timing of three distinct phases of orogenic development as determined from east timor including initial collision and emplacement of the early nappes creating loading and diapirism within the 9 8 5 5 ma interval a tectonic quiet interval 5 5 ma 4 5 ma that extended for about a million years during the middle of the collision and may represent the time of locking of the subduction system and a post 4 5 ma phase of uplift unroofing and further diapirism in response to isostatic rebound our conclusions offer an alternative model for the evolution of this part of the banda arc

nature and distribution of deformation across the banda arc australian collision zone at timor recently acquired seismic reflection and seamarc ii side scan and swath bathymetry profiles near timor show that the banda arc australia collision zone has a tectonic framework similar to that of a typical oceanic subduction system deformation is occurring at present most intensely at the foot of the inner slope of the timor trough this deformation front is discontinuously advancing southward as new thrust slices develop within the subducted australian margin strata in contrast present deformation is apparently negligible in the savu basin the complex fore arc basin north of timor a possible significant exception is a postulated right lateral northeast trending fault zone offsetting the outer arc high between savu and roti although back arc thrusting has been documented north of the volcanic arc this component of convergence is minor compared with the scale of ongoing deformation in the timor trough the detailed nature of these surveys has also led to the recognition of along strike variations in deformation in the timor trough and in the savu basin these variations may be related to the variable degree of involvement of the australian continental margin along the arc

new constraints on the timing of flexural deformation along the northern australian margin implications for arc continent collision and the development of the timor trough abstract numerous extensional faults offset the passive margin strata of the northern bonaparte basin this extensional deformation has been attributed to lithospheric flexure of the descending australian plate in an overall convergence setting here we use an extensive 2d and 3d seismic dataset calibrated with well biostratigraphy and strontium sr isotope age data to constrain the timing of deformation along the northern australian margin during the neogene analysis of fault throw and differential thickness variations give new insights on the propagation and slip history of the faults along dip throw profiles exhibit d shape distributions skewed towards the top positive throw gradients above the throw maxima coinciding with intervals of growth strata indicate multiphase fault activity results indicate that post rift extensional deformation initiated during the latest miocene ca 6 ma the development of the modern timor trough as a foreland basin and cartier trough also commenced during this period a second episode of increased tectonic activity occurred around the pliocene quaternary boundary ca 3 ma and the deformation continued intermittently to the present day these new results are in agreement with the timing of initiation of collision between the australian plate and the banda arc and uplift of the timor island recently derived from stratigraphic analysis in timor these regional tectonic events have profoundly affected the paleogeography of the timor sea and may explain major changes in oceanic circulation and climate during the neogene

back arc thrusting in the eastern sunda arc indonesia a consequence of arc continent collision the structure of the eastern sunda back arc region is dominated by two large north directed thrusts the wetar and flores thrusts and one or more minor thrusts which may represent early stages of subduction polarity reversal of the arc the relationships between thrusting and magmatic activity surface slopes cross arc faulting uplift forearc structure and collision by the australian continental margin provide constraints on the likely driving mechanisms of thrust formation driving mechanisms are considered in two broad categories one set of possible mechanisms originates within the upper plate and includes gravity sliding gravity spreading and magmatic intrusion the other set focuses on stress propagation between the upper and lower plates and for this arc system the major mechanism is that of continental collision while no one mechanism explains the range of observations we see in the back arc region all of these aspects play some role in the development of the thrusts we can eliminate upper plate mechanisms as primary driving forces because slope effects are similar in areas of both thrusting and nonthrusting in addition the wetar thrust shows a negative relation between thrusting and volcanism and side looking airborn radar images show no evidence of postvolcanic rifting that could accompany intrusion without volcanism collision between the arc and the australian continent provides the clearest driving mechanism but it does not explain the discontinuous nature or the particular location of the thrusts we suggest a sequence that appears to account for the data and to provide insight into the controversies often associated with other such thrust belts thrusting was initiated in those areas where the crust of the forearc region was thick a factor that facilitated stress propagation across the arc and where the crust of the back arc was thin which facilitated back arc thrusting thrusting concentrated at the base of the slope where the slope stress is maximum the early thrusting may have been helped also by thermal weakening of the crust due to volcanism as convergence proceeded volcanism waned then ceased in the eastern part of the arc the crust then strengthened and thrusting required higher stress to maintain and propagate this later stage should show higher seismic energy release which appears to be the case for the wetar thrust region displacement on the flores thrust appears to be matched by deflection of the volcanic arc we have estimated shortening in the back arc from interpretation of reflection profiles and for the flores thrust the value of approximately 30 km is consistent with that estimated for deflection of the arc compressional deformation continues west of the collision zone across the bali basin and into java it is reported in ne sumatra as well this deformation involves much less convergence than the eastern sunda thrusts and it may be related to magmatic processes to subduction of oceanic plateaus such as the roo rise or in the case of the bali basin to efficient lateral propagation of the flores thrust

switching between alternative responses of the lithosphere to continental collision summary we study possible responses to arc continent or continent continent collision using numerical models our short term integration models show that the initial stage of deformation following continental collision is governed by the competition between three potential weakness zones 1 mantle wedge 2 plate interface and 3 lower continental crust depending on which of these is the weakest zone in the system three different responses can be recognized 1 subduction polarity reversal 2 continuation of subduction and 3 delamination and back stepping subduction polarity reversal occurs if the mantle wedge is the weakest zone in the system this happens only if the viscosity of the mantle wedge is at least one order of magnitudelowerthantheaverageviscosityofthelithosphere incontinent continentcollision one additional condition needs to be satisfied for subduction polarity reversal to occur for the subducting lithosphere the ratio of the viscosity of the lower continental crust to the viscosity of the upper lithospheric mantle must be equal to or higher than 0 006 the time required for polarity reversal depends on several parameters the convergence rate the sinking velocity of the detached slab and the relative strength of the mantle wedge arc and backarc the response to collision is continued subduction if the plate interface is the weakest zone and is delamination and back stepping if the lower continental crust is the weakest area in the system our finding that a low viscosity wedge is a prerequisite for a reversal of subduction polarity agrees with inferences about regions for which subduction polarity reversal has been proposed

crustal motion and block behaviour in se asia from gps measurements results acquired using global positioning system gps data taken over a large part of se asia indicate that sundaland i e indochina along with the western and central part of indonesia constitutes a stable tectonic block moving approximately east with respect to eurasia at a velocity of 12 3 mm yr 31 with respect to india and australia this block moves due south significant motion has not been detected along the northern boundary to south china i e along the red river fault whereas nearly 50 mm yr 31 of right lateral motion has to be accommodated between india and sundaland in the andaman burma region fl 2001 elsevier science b v all rights reserved

orogeny in arc continent collision the banda arc and western new guinea eastern indonesia contains a modern continent island arc collision that demonstrates how a complex juxtaposition of continental and oceanic elements can occur in an orogenic belt shallow earthquakes show that strike slip faulting transports large crustal blocks into out of and along the collision zone while crustal shortening and thickening occur by steep angle thrust faulting near the strike slip faulting whereas strike slip faulting is paramount in positioning australian continental rocks so as to enclose the oceanic and island arc rocks of eastern indonesia its role may be overshadowed by the contemporaneous thrusting and may confuse geologic interpretations of the resulting orogenic belt

the sumba enigma is sumba a diapiric fore arc nappe in process of formation abstract the anomalous updomed morphological expression of sumba island its enigmatic lack of strong neogene deformation and the northward morphological indentation of southern sumbawa and flores require explanation the stratigraphy of sumba may be correlated with the cretaceous to miocene part of the timor allochthon the sedimentary and eruptive rock succession in sumba shows remarkable similarities with the allochthonous palelo wiluba and cablac deposits of timor in both islands the cretaceous parts of these sequences are regarded as characteristic of fore arc deposits built on thin continental crust the timor nappe is interpreted as a 5 km thick tectonic flake of the banda fore arc thrust onto the australian continental margin in the mid pliocene collision the postulated sumba nappe has not yet been thrust onto the australian margin which in the sumba region has not yet converged as close to the arc as in the timor area the postulated sumba nappe is interpreted as a diapiric elongated dome of the sunda fore arc that is being squeezed by the converging margin of australia against the volcanic islands of sumbawa and flores the absence of indications on the seismic reflection profiles for the presence of the thrust fault of the sumba nappe may perhaps be explained by the thrusts being nearly horizontal within flat lying strata the savu thrust is correlated with the probably older pre late pliocene wetar suture as a major southward dipping lithospheric rupture east of 124 e this suture does not seem to have moved much since the mid pliocene collision that emplaced the nappes on timor however microearthquake data suggest some activity is continuing

quaternary hinterland evolution of the active banda arc surface uplift and neotectonic deformation recorded by coral terraces at kisar indonesia abstract coral terrace surveys and u series ages of coral yield a surface uplift rate of 0 5 m ka for kisar island which is an emergent island in the hinterland of the active banda arc continent collision based on this rate kisar first emerged from the ocean as recently as 450 ka these uplifted terraces are gently warped in a pattern of east west striking folds these folds are strike parallel to more developed thrust related folds of similar wavelength imaged by a seismic reflection profile just offshore this deformation shows that the emergence of kisar is influenced by forearc closure along the south dipping kisar thrust however the pinnacle shape of kisar and the protrusion of its metamorphic rocks through the forearc basin sediments also suggest a component of extrusion along shear zones or active doming coral encrusts the island coast in many locations over 100 m above sea level terrace morphology and coral ages are best explained by recognizing major surfaces as mostly growth terraces and minor terraces as mostly erosional into older terraces all reliable and referable coral u series ages determined by mc icp ms correlate with marine isotope stage mis 5e 118 128 ka the only unaltered coral samples are found below 6 m elevation however an unaltered tridacna giant clam shell in growth position at 95 m elevation yields a u series age of 195 31 ka which corresponds to mis 7 this age agrees with the best fit uplift model for the island loose deposits of unaltered coral fragments found at elevations between 8 and 20 m yield u series ages of

active deformation in eastern indonesia and the philippines from gps and seismicity data in this study we combine global positioning system gps velocities with information on the style of regional seismicity to obtain a self consistent model velocity and strain rate field for the entire eastern indonesia and philippines region in the process of interpolating 93 previously published gps velocities the style and direction of the seismic strain rate field inferred from earthquakes with m0 1 1020 n m from the harvard centroid moment tensor catalog are used as constraints on the style and direction of model strain rates within the plate boundary zones the style and direction of the seismic strain rate field are found to be self similar for earthquakes up to m0 1 1020 n m equivalent to mw 7 3 our inversion result shows the following the java trench which lacks any significant historic seismicity delineates the australian plate au sunda block sunda plate boundary west of the island of sumba east of sumba convergence is distributed over the back arc and banda sea and there is no subduction at the timor trough suggesting that the northern boundary of the au plate runs north of this part of the banda arc through the banda sea in new guinea most motion is taken up as strike slip deformation in the northern part of the island delineating the pacific plate pa au boundary however some trench normal convergence is occurring at the new guinea trench evidence that the strain is partitioned in order to accommodate oblique pa au motion pa au motion is consistent with nuvel 1a direction but 8 mm yr 1 slower than the nuvel 1a estimate for pa au motion the sulawesi trench and molucca sea delineate zones of high strain rates consistent with high levels of active seismicity the sulawesi trench may take up some of the au sunda motion philippine sea plate motion is in a direction slightly northward of the nuvel ia estimate and is partitioned in some strike slip strain rates along the philippine fault and relatively larger trench normal convergence along the philippine trench and on the philippine mainland in the southern philippines and along the manila trench in the northern philippine islands the high level of strain rate along the manila trench is not released by any significant historic seismic activity for the entire eastern indonesia philippines region seismicity since 1963 has taken up 40 of the total moment rate inferred from our model

active tectonics of the eastern sunda and banda arcs the tectonics of the eastern sunda and banda arcs of eastern indonesia are inferred from the centroid depths seismic moments and fault plane solutions of 63 large earthquakes that occurred between 1962 and 1984 source parameters are estimated by inverting long period teleseismic p and sh waves earthquakes show that the collision of the australian continent with the banda arc shortens the upper plate beneath the forearc and back arc basin over the broad area between the timor and seram troughs along the eastern end of the sunda arc and along the southern banda arc earthquakes reveal that the arc and forearc respond to collision by shortening in the direction of convergence by elongating in the direction perpendicular to convergence and by thrusting over the back arc basin shallow thrust and strike slip earthquakes beneath the banda basin the back arc basin demonstrate that deformation within the back arc accommodates some of the northward motion of the australian continent the rate of north south shortening of the entire upper plate at the longitude of timor calculated from the seismic moments of the earthquakes over the 22 year period is roughly 20 of the predicted convergence rate between australia and southeast asia strike slip faulting within the banda basin results also in eastward motion of the banda arc with respect to western indonesia and australia eastward extrusion of the banda arc results in thrusting at the aru trough earthquakes due to thrusting of the back arc basin beneath the volcanic arc are too shallow to corroborate that the arc s polarity has reversed although the wetar back arc thrust zone at present has a high seismic slip rate earthquakes and their mechanisms provide evidence that the lithosphere of the weber basin a 7500 m deep forearc basin rests on the subducting lithosphere without intervening asthenosphere so that the weber basin subsides in response to sinking of the subducting lithosphere closure of the banda basin is geometrically incompatible with the australian plate subducting simultaneously beneath both the timor and seram troughs instead the bird s head which subducts beneath seram is decoupled from the australian plate in western new guinea and probably moves west or southwest with respect to australia in the eastern indonesian example strike slip faulting plays a major role in the evolution of the collision zone and clearly demonstrates the complexity in three dimensions of continental accretion and mountain building by arc continent collision

multi data type source estimation for the 1992 flores earthquake and tsunami we revisit the source of the 1992 flores earthquake and tsunami using finite fault inversion we simultaneously invert teleseismic body and surface waves together with coseismic uplift subsidence datasets we then verify the inverted source against tsunami run up heights along the northern coast of flores island and the only tide gauge recording of the tsunami our preferred source model provides a good fit to all the datasets whereas previous models only explained a subset of the available data we show that the fault geometry implies segmentation of the back arc thrust system in the eastern sunda arc

crustal motion in indonesia from global positioning system measurements terrestrial reference frame 2000 we compute poles of rotation for the australia eurasia and pacific plates based on our analysis of the global gps data we find that regional tectonics is dominated by the interaction of four discrete rotating blocks spanning significant areas of the sunda shelf the south banda arc the bird s head region of new guinea and east sulawesi the largest the sunda shelf block ssh is estimated to be moving 6 3 mm yr se relative to eurasia the south banda block sbb rotates clockwise relative to both the ssh and australia plate resulting in 15 8 mm yr of motion across the timor trough and 60 3 mm yr of shortening across the flores sea southern new guinea forms part of the australia plate from which the bird s head block bhb moves rapidly wsw subducting beneath the seram trough the east sulawesi block rotates clockwise about a nearby axis with respect to the sunda shelf thereby transferring east west shortening between the pacific and eurasia plates into north south shortening across the north sulawesi trench except for the sunda shelf the crustal blocks are all experiencing significant internal deformation in this respect crustal motion in those regions does not fit the microplate tectonics model index terms 1206 geodesy and gravity crustal movements interplate 8155 1243 geodesy and gravity space geodetic surveys 8150 tectonophysics plate boundary general 3040 8158 tectonophysics plate motions present and recent 3040 9320 information related to geographic region asia keywords crustal motion indonesia tectonics gps current plate motions southeast asia

late cretaceous miocene diachronous onset of back thrusting along the south caribbean deformed belt and its importance for understanding processes of arc collision and crustal growth 1 the venezuelan basin is obliquely subducted to the east southeast beneath the continental south american plate at the east west trending south caribbean deformed belt scdb a 50 100 km wide wedge of accreted sedimentary rocks derived both from offscraping of the 0 5 to 1 km thick sedimentary cover of the subducting venezuelan basin and from incorporation of clastic sediments derived from the continental margin of south america in this paper we describe the structure and sequence stratigraphy of five late cretaceous to recent sedimentary sequences overlying a 230 000 km2 area of the southern venezuelan basin and beata ridge the data set includes 5900 km of 2d seismic reflection data that are tied to lithologic and age data taken from dsdp sites 146 149 and 150 in the central part of the venezuelan basin we use observed patterns of wedging in mapped and dated sedimentary sequences adjacent to the scdb to determine the age of the diachronous west to east initiation of thrusting and subduction at the scdb the onset of subduction in the scdb corresponds with the cessation of thrusting from west to east along the zone of collision between the intraoceanic caribbean arc and the south american continent this correlation in the age of deformation indicates that collision between the caribbean arc and the south american continent led to subduction polarity reversal a process that is commonly observed at various stages of tectonic evolution in other areas of active arc continent collision including japan and sunda

geodynamic patterns of ophiolites and marginal basins in the indonesian and new guinea regions analysis of spatial temporal geological and geochemical patterns of ophiolites in the indonesian and new guinea region indicates a strong correlation with marginal basin development and closure the spatial distribution of ophiolites is mostly linked with marginal basin producing zones of oblique convergence and collision strain partitioning in these zones creates a series of ephemeral plate boundaries between several independently moving lithospheric blocks repeated disruption of the diffuse boundaries between the blocks by changes in plate motion and collision induced mantle extrusion creates space that is rapidly filled by new ocean basins in the upper plate of subduction zones suprasubduction zone ssz spreading of these basins is enhanced by episodic extrusion of asthenosphere escaping collisional suture zones various closure events and global plate motion changes are reflected in the temporal distribution of marginal basin and ophiolite ages most ophiolite slabs in the indonesian and new guinea region represent fragments of oceanic lithosphere with a subduction zone component as indicated by the common refractory petrochemistry of the mantle sequence and occurrence of boninite age and compositional heterogeneity may indicate that some ophiolite bodies are composite terranes collisions with buoyant lithosphere transfo parts of these ocean basins into ophiolites the connection between ophiolites and marginal basins is strongest where parts of actively spreading ssz basins are partially represented as ophiolites in collision zones many of the various tectonic models proposed for the origin and tectonic evolution of ophiolites are supported by plate interactions in the indonesian and new guinea region dewey bird 1970 silver smith 1983 moores et al 1984 searle stevens 1984 dilek moores 1990 harris 1992 dickinson et at 1996 however the geolo gical associations of these interactions remain poorly resolved allowing different parts of the region to be used as modern analogues for almost any tectonic scenario simple explanations based on plate kinematics alone fail to account for the increasing levels of complexity observed in the indonesian and new guinea region new ideas and supporting evidence for mantle extrusion mechanisms e g flower et at 2001 also rely heavily on descriptions of plate interactions in this region doglioni et at 1999 and raise new questions about how these processes may relate to the spatial and temporal pattern of ophiolites this paper provides a synthesis of the temporal and spatial patterns and tectonic associations of marginal basins and ophiolites throughout the indonesian and new guinea region it explores the relations between various plate boundary processes and ophiolite genesis and emplacement such as the role of strain partitioning trench rollback subduction polarity asymmetry astheno spheric flow and plate kinematics

new insights into regional tectonics of the sunda banda arcs region from integrated magnetic and gravity modelling abstract the lombok island indonesia situated along the sunda banda arcs transition region lies between zones characterized by very large intensity magnetic anomalies these anomalies have been noted as being part of the eight most important ones seen on the 1st edition of the world digital magnetic anomaly map unfortunately only marine magnetic data of surroundings are available and no regional high resolution magnetic surveys of this island had been done since 2004 we have carried out several geomagnetic ground surveys in this region here we present modelling results for a new geological and tectonic interpretation of the magnetic anomalies the new results confirm the general pattern of contiguous negative positive anomalies revealing two active quaternary normal faults and a magmatic arc related to a subduction region this outcome agrees with earlier results in surrounding areas obtained by satellite aeromagnetic and marine platforms and provides a more detailed picture of strong anomalies on this island considering both magnetic anomalies and gravity models it is possible to suggest an extension of the flores thrust zone reaching the northwest off the lombok island the flores thrust zone may be considered as a mature subduction in the back arc region showing a tendency of progressive subduction during last decades

plate boundary reorganization in the active banda arc continent collision insights from new gps measurements abstract new gps measurements reveal that large sections of the se asian plate are progressively accreting to the edge of the australian continent by distribution of strain away from the deformation front to forearc and backarc plate boundary segments the study was designed to investigate relative motions across suspected plate boundary segments in the transition from subduction to collision the oblique nature of the collision provides a way to quantify the spatial and temporal distribution of strain from the deformation front to the back arc the 12 sites we measured from bali to timor included some from an earlier study and 7 additional stations which extended the epoch of observation to ten years at many sites the resulting gps velocity field delineates at least three sunda arc forearc regions around 500 km in strike length that shows different amounts of coupling to the australian plate movement of these regions relative to se asia increases from 21 to 41 to 63 eastward toward the most advanced stages of collision the regions are bounded by the deformation front to the south the flores wetar backarc thrust system to the north and poorly defined structures on the sides the suture zone between the nw australian continental margin and the sunda banda arcs is still evolving with more than 20 mm yr of movement measured across the timor trough deformation front between timor and australia

historical tsunamis and present tsunami hazard in eastern indonesia and the southern philippines 1 eastern indonesia and the southern philippines comprise a huge and seismically highly active region that has received less than the deserved attention in tsunami research compared with the surrounding areas exposed to the major subduction zones in an effort to redress the balance the tsunami hazard in this region is studied by establishing a tsunami event database which in combination with seismological and tectonic information from the region has allowed us to define and justify a number of credible worst case tsunami scenarios these scenarios have been used in numerical simulations of tsunami generation and propagation to study maximum water level along potentially affected shorelines the scenarios have in turn been combined to provide regional tsunami hazard maps in many cases the simulations indicate that the maximum water level may exceed 10 m locally and even reach above 20 m in the vicinity of the source which is of the same order as what is forecasted along the sumatra and java trenches for comparable return periods for sections of coastlines close to a source a tsunami may strike only a few minutes after it is generated providing little time for warning moreover several of the affected areas are highly populated and are therefore also high risk areas the combination of high maximum water levels short warning times dense populations and relatively short return periods suggests strongly that the tsunami hazard and risk in these regions are alarmingly high

microblock rotations and fault coupling in se asia triple junction sulawesi indonesia from gps and earthquake slip vector data the island of sulawesi eastern indonesia is located within the triple junction of the australian philippine and sunda plates and accommodates the convergence of continental fragments with the sunda margin we quantify the kinematics of sulawesi by modeling gps velocities and earthquake slip vectors as a combination of rigid block rotations and elastic deformation around faults we find that the deformation can be reasonably described by a small number of rapidly rotating crustal blocks relative to the sunda plate the southwestern part of sulawesi makassar block rotates anticlockwise at 1 4 myr the northeastern part of sulawesi the bangai sula domain comprises three blocks the central north sula block moves toward the nnw and rotates clockwise at 2 5 myr the northeastern manado block rotates clockwise at 3 myr about a nearby axis and east sulawesi is pinched between the north sula and makassar blocks along the boundary between the makassar block and the sunda plate gps measurements suggest that the trench accommodates 15 mm yr of slip within the makassar strait with current elastic strain accumulation the tectonic boundary between north sula and manado blocks is the gorontalo fault moving right laterally at about 11 mm yr and accumulating elastic strain the 42 mm yr relative motion between north sula and makassar blocks is accommodated on the palu koro left lateral strike slip fault zone the data also indicate a pull apart structure in palu area where the fault shows a transtensive motion and may have a complex geometry involving several active strands sulawesi provides a primary example of how collision can be accommodated by crustal block rotation instead of mountain building