late cenozoic geodynamic evolution of eastern indonesia this paper presents an internally and globally consistent model of plate evolution in eastern indonesia from middle miocene to present time it is centered on the banda sea region located in the triple junction area between the pacific philippine australia and south east asia plates the geological and geophysical data available from indonesia were until recently insufficient to define a unique plate tectonic model in this paper the new data taken into account clearly restrict the possible interpretations owing to a great number of geological geophysical and geochemical studies the major plate boundaries the sunda banda subduction zone to the south the tarera aiduna fault zone and the seram thrust to the east and the sorong fault zone and molucca sea collision zone to the north are now clearly identified the age of the major tectonic structures is also better known geodetic measurements well constrain the present time plate kinematics we also consider the deformation history within eastern indonesia where numerous short lived microplates and their related microcontinents successively accreted to the asiatic margin moreover magnetic anomalies identification of the north and south banda sea basins allows a precise kinematic reconstruction of the back arc opening we used the plates software to test the coherency of our model presented as a series of 4 plate reconstruction maps from 13 ma to the present finally the origin of oceanic domains restored by our reconstruction is discussed

mantle flow in regions of complex tectonics insights from indonesia 1 indonesia is arguably one of the tectonically most complex regions on earth today due to its location at the junction of several major tectonic plates and its long history of collision and accretion it is thus an ideal location to study the interaction between subducting plates and mantle convection seismic anisotropy can serve as a diagnostic tool for identifying various subsurface deformational processes such as mantle flow for example here we present novel shear wave splitting results across the indonesian region using three different shear phases local s sks and downgoing s to improve spatial resolution of anisotropic fabrics allows us to distinguish several deformational features for example the block rotation history of borneo is reflected in coast parallel fast directions which we attribute to fossil anisotropy furthermore we are able to unravel the mantle flow pattern in the sulawesi and banda region we detect toroidal flow around the celebes sea slab oblique corner flow in the banda wedge and sub slab mantle flow around the arcuate banda slab we present evidence for deep sub 520 km anisotropy at the java subduction zone in the sumatran backarc we measure trench perpendicular fast orientations which we assume to be due to mantle flow beneath the overriding eurasian plate these observations will allow to test ideas of for example slab mantle coupling in subduction regions

geodetic observations of the 2018 mw 7 5 sulawesi earthquake and its implications for the kinematics of the palu fault

india and sunda plates motion and deformation along their boundary in myanmar determined by gps using a regional gps data set including 190 stations in asia from nepal to eastern indonesia and spanning 11 years we update the present day relative motion between the indian and sundaland plates and discuss the deformation taking place between them in myanmar revisiting measurements acquired on the main boundary thrust in nepal it appears that points in southern nepal exhibit negligible deformation with respect to mainland india including these points using a longer time span than previous studies and making an accurate geodetic mapping in the newest reference frame allows us to refine the present day indian motion our results confirm that the current motion of india is slower than predicted by the nuvel 1a model and in addition our india eurasia motion is significantly 5 mm yr slower than previous geodetic determinations this new indian motion combined with a refined determination of the sundaland motion gives way to a relative india sunda angular velocity of 20 2 n 26 1 e 0 370 myr in itrf2000 predicting a relative motion of 35 mm yr oriented n10 at the latitude of myanmar there the sagaing fault accommodates only 18 mm yr of right lateral strike slip only half of the shear component of motion we present two models addressing how and where the remaining deformation may occur a first model of distributed deformation implies convergence on the arakan subduction the northern continuation of the now famous sumatra andaman trench and wrench faulting in the arakan wedge the second model uses localized deformation where deformation observed west of the sagaing fault is entirely due to elastic loading on a faster and oblique arakan subduction 23 mm yr this latter model predicts that a major earthquake of mw 8 5 may occur every century on this segment of the subduction

the 1996 earthquakes in sulawesi indonesia we study the rupture process of the 1 january mw 7 9 16 july mw 6 6 and 22 mw 7 july 1996 earthquakes in sulawesi indonesia a teleseismic body waveform inversion of very broadband records shows that these events occurred beneath the accretionary prism the main shock was due to a well determined fault with a strike of 53 n and a very shallow dip of 7 from its source time function duration 30 sec and the aftershock distribution we estimate a rupture area of 90 60 km2 and an average slip of 1 80 m the surface displacement computed with our best model fits well the displacement vector at the only available gps station at tomini the tsunami generated by the mainshock had an approximate source radius of 45 km which roughly agrees with the rupture size estimated above the earthquakes took place in a relay zone between the trench and the palu koro transcurrent fault they ruptured a shallow dipping thrust fault which corresponds to the subduction interface under the north sulawesi arm the slip vectors of all the events have a nnw orientation parallel to the direction of convergence between the north sulawesi arm and the celebes sea among the peculiarities of the rupture process we found that the july 22 aftershock was the only event to have a well defined precursor 1 8 sec before the main p wave onset

basement character and basin formation in gorontalo bay sulawesi indonesia new observations from the togian islands we present a new stratigraphy for the togian islands sulawesi and interpret the age character and evolution of gorontalo bay at its western end the bay is underlain by continental crust the central part is underlain by eocene to miocene oceanic and arc rocks although the area south of the togian islands could have continental crust of the banggai sula microcontinent thrust beneath this and the east arm ophiolite gorontalo bay was not a significant deep bathymetric feature before the miocene field relationships indicate a latest miocene to pliocene age for inception of the basin medium k to shoshonitic volcanism in the togian islands is not due to subduction but reflects crustal thinning and extension in the pliocene and pleistocene causing the underlying mantle to rise decompress and melt extension is continuing today and is probably the cause of volcanism at una una volcanic activity migrated west with time and volcanic products have been offset by dextral strike slip displacement along the balantak fault extension and subsidence was driven by rollback of the subduction hinge at the north sulawesi trench with a possible contribution due to flow of the lower crust 2011 the geological society of london

stratigraphy and tectonic setting of the cretaceous and paleogene volcanic sedimentary successions in northwest sulawesi indonesia implications for the cenozoic evolution of western and northern sulawesi abstract new field and laboratory data from nw sulawesi indonesia integrated with existing information provide a tectonostratigraphic framework for the cretaceous and paleogene of this region the study area straddles two distinct provinces referred to as western and northern sulawesi western sulawesi forms the rifted continental margin of eastern sundaland it consists of a metamorphic basement partly of australian origin overlain by late cretaceous turbidites that were deposited in a fore arc setting latimojong formation these are in turn covered by volcanic sedimentary successions that were deposited during the early middle eocene to earliest miocene they represent a transgressive cycle from syn rift siliciclastics through nummulitic limestone and associated shelf sediments to deeper marine mudstones and turbidites budungbudung and tinombo formations during the same period northern sulawesi developed as an oceanic island arc characterized by bimodal volcanism papayato volcanics founded on back arc oceanic crust the cretaceous and paleogene volcanic and sedimentary suites show lithological and geochemical characteristics that reflect the contrasting tectonic setting of the two provinces the tectonic relationship between the two domains is not clear they probably formed a more or less continuous belt throughout the cenozoic but were definitely connected not later than the early miocene strong deformation in the paleogene formations in the northern part of nw sulawesi and their unconformable relationship with the overlying formations may be the result of the collision of the north arm of sulawesi with a continental fragment of australian derivation during the early miocene or it may be related to the formation of a metamorphic core complex in a mid miocene extensional tectonic setting a second major tectonic event which commenced in the pliocene and is still ongoing affected the entire region

collisional model for rapid fore arc block rotations arc curvature and episodic back arc rifting in subduction settings 1 we review geophysical and geological data from 23 active and ancient plate boundaries to document a compelling spatial and temporal relationship between collision plate boundary curvature rapid tectonic rotations and the occurrence of back arc rifting our observations support a conceptual model where the change from subduction to collision causes rapid fore arc rotation when viewed in a reference frame relative to the bounding tectonic plates leading to marked plate boundary curvature our global compilation reveals that most active back arc rifts are associated with rapidly rotating fore arcs and nearby collisions thus we propose that collision and rapid fore arc rotations play a major role in the evolution and kinematics of back arc basins we conduct numerical modeling to better understand the physical processes behind these observed rapid tectonic rotations at convergent margins our results suggest that the presence of an indentor or choke point in the subduction system e g collision can generate rapid rotation of the fore arc about a nearby pole and lead to back arc rifting the rate of fore arc rotation and back arc rifting depends on the incoming indentor velocity and can be greatly enhanced by slab rollback and the presence of a low viscosity back arc where viscosity of the back arc is low fore arc rotation dominates where back arc viscosity is high the formation of strike slip faults and tectonic escape dominates our observational and model derived results illustrate that shallow crustal forces produced by the entry of buoyant features into subduction zones are a fundamental mechanism for the generation of fore arc block rotations plate boundary curvature back arc rift evolution and tectonic escape in subduction systems rollback of the subducting slab within the mantle will certainly enhance the processes we describe but it is not the only driving force

new paleomagnetic constraints on the cenozoic tectonic evolution of the north arm of sulawesi indonesia abstract extensive paleomagnetic sampling 34 sites was carried out in cenozoic formations of the north arm of sulawesi between 120 and 124 e consistent results obtained between 120 and 122 e suggest the existence of a unique post miocene clockwise rotation of about 20 25 of the western part of the north arm this rotation probably occurred during the northward drift of the north arm along the palu matano sinistral transcurrent fault between 122 5 and 124 e both clockwise and counterclockwise rotations with various amplitudes from 6 to 85 are encountered and these very likely correspond to individual microblock rotations due to pervasive deformation along shear zones this result is consistent with the complex fault system of the gorontalo and kotamobagu shear zones that have been recognized on radar imagery and by spot image analyses

petrologic isotopic and radiometric age constraints on the origin and tectonic history of the malino metamorphic complex nw sulawesi indonesia the malino metamorphic complex mmc is located at the western end of the north arm of sulawesi it consists of mica schists and gneisses derived from proximal turbidite and granitoid protoliths with intercalations of greenschist amphibolite marble and quartzite forming an e w elongated dome like structure bounded on all sides by faults the age of the mmc is constrained between devonian and early carboniferous this paleozoic age the presence of archean and proterozoic inherited zircons and the isotopic signature of the mica schists and gneisses indicate that the terrane was derived from the new guinea australian margin of gondwana similarities with basement rocks in the bird s head suggests a common origin greenschists forming a discontinuous selvage metamorphic carapace around the complex were derived from adjacent autochthonous paleogene formations the rocks of the mmc show a barrovian type progression from greenschist through epidote amphibolite to amphibolite facies p t estimations suggest a depth of burial of up to 27 30 km k ar and 40ar 39ar cooling ages of 23 11 ma and a 7 ma age for unconformably overlying volcanic rocks indicate that the complex was exhumed during the miocene two tectonic scenarios are considered 1 the continental fragment docked with sulawesi during the mesozoic and was exhumed as a metamorphic core complex during the miocene 2 it was subducted beneath the north arm during the late oligocene and then rapidly returned back to the surface

fission track and fault kinematics analyses for new insight into the late cenozoic tectonic regime changes in west central sulawesi indonesia abstract the left lateral strike slip central sulawesi fault system csfs composed of the nnw palu koro pkf and the ese matano faults is located within the eastern indonesian triple junction between the pacific indo australian and eurasian plates fault kinematic and fission track analyses show that the late cenozoic central sulawesi deformation results from three successive tectonic regimes 1 a late miocene early pliocene 5 ma wnw trending shortening characterized by transpressional deformation along the pkf and compressional in the poso area this tectonics resulted from the collision between the banggai sula block with sulawesi it produced locally a transpressional regime as a consequence of the northward extrusion of the central sulawesi block limited by the pkf 2 a pliocene collapse tectonic regime associated with w trending extension coeval with these events regional cooling and exhumation took place 3 a quaternary transtensional regime resulting from the combined effects of the central sulawesi block northward motion and extension related to back arc spreading behind the north sulawesi subduction tomini gulf

plate convergence measured by gps across the sundaland philippine sea plate deformed boundary the philippines and eastern indonesia summary the western boundary of the philippine sea ph plate in the philippines and eastern indonesia corresponds to a wide deformation zone that includes the stretched continental margin of sundaland the philippine mobile belt pmb extending from luzon to the molucca sea and a mosaic of continental blocks around the ph australia sunda triple junction the gps geodyssea data are used to decipher the present kinematics of this complex area in the philippines the overall scheme is quite simple two opposing rotations on either side of the left lateral philippine fault clockwise to the southwest and counterclockwise to the northeast transfer 55 per cent of the ph sundaland convergence from the manila trench to the northwest to the philippine trench to the southeast further south 80 per cent of the ph sunda convergence is absorbed in the double subduction system of the molucca sea and less than 20 per cent along both continental margins of northern borneo finally within the triple junction area between the sundaland ph and australia plates from sulawesi to irian jaya preferential subduction of the celebes sea induces clockwise rotation of the sulu block which is escaping toward the diminishing celebes sea oceanic space from the eastwardadvancing ph plate to the south we identify an undeformed banda block that rotates counterclockwise with respect to australia and clockwise with respect to sundaland the kinematics of this block can be defined and enable us to compute the rates of southward subduction of the banda block within the flores trench and of eastward convergence of the makassar straits with the banda block the analysis made in this paper confirms that this deformation is compatible with the eastward motion of sundaland with respect to eurasia determined by the geodyssea programme but is not compatible with the assumption that sundaland belongs to eurasia as was often assumed prior to this study

energetic bubble plumes in arbitrary stratification field and laboratory experiments were performed to investigate the mixing induced by energetic point source bubble plumes in water columns of arbitrary stable stratification published data from various sources were also used in the present study to increase the parameter range it was found that the bubble plume surface signatures were marked by a central unsteady core consisting of an air water mixture surrounded by an annular up thrusting flow consisting of water only outside this the rising plume water spread radially plunged below the surface and then flowed outward as an intrusive gravity current at a level of neutral buoyancy by equating the observed arbitrary stratification to a linear profile of equal potential energy the radial extent of the plunge point and the net detrainment rate could be parameterized using natural scales of the problem these formulas were verified using field and laboratory data and may thus be used in air diffuser design procedures

the blue angel i the mineralogy and petrogenesis of a hibonite inclusion from the murchison meteorite a detailed mineralogie chemical and petrologic study of the blue angel a relatively large 1 5 mm hibonite containing inclusion from the murchison meteorite was performed in an attempt to understand the mechanisms of formation and modification of hibonite rich inclusions the blue angel inclusion is composed of roughly equal amounts of hibonite and calcite with minor amounts of spinel perovskite diopside and an fe rich silicate the inclusion can be divided into three roughly concentric zones a hibonite rich core a calcite rich mantle and a spinel rich layered rim the mineral chemistry and petrography of the blue angel are consistent with a three stage formation history 1 an early stage of nebular condensation which produced the hibonite perovskite and spinel 2 a moderate temperature stage of aqueous alteration and metamorphism occurring on a small planetary body containing co 2 and h 2o during which calcite was formed in the inclusion and 3 the final emplacement of the blue angel into its present position in murchison the study of the blue angel indicates that extensive alteration of ca al rich inclusions cai may have occurred by aqueous alteration and thermal metamorphism followed by explosive mixing processes on a parent body such metamorphic reactions may involve formation and destruction of phases such as melilite and diopside which have been previously thought to be primary condensates the mechanisms proposed for the formation and modification of the blue angel help to explain the secondary phases and oxygen isotope anomalies found in many cai and eliminate the need for invoking kinetically complicated back reactions at very low pressures with a cool part of the solar nebula the contribution of planetary metamorphism in the formation and alteration of cai must be considered along with nebular processes in order to understand the formation of carbonaceous chondrites

collision rotation and the initiation of subduction in the evolution of sulawesi indonesia the island of sulawesi indonesia has been shaped and deformed as a result of collision with the sula platform a sliver of continental material from the northern margin of australia new guinea the collision has resulted in rotation of the north volcanic arm of sulawesi and the development of the accretionary wedge of the north sulawesi trench the north sulawesi trench changes laterally from a zone of no active deformation in the eastern part to a wide accretionary wedge in the west early stages of thrusting produce a steep frontal slope 8 16 indicative of relatively high basal shear stress whereas the more advanced western zone of thrusting produces a gentle 2 slope consistent with low basal shear stress reported paleomagnetic data suggest post late eocene counter clockwise rotation of the north arm and the offshore geophysics are explained by a pivot of the north arm with respect to the celebes basin about the eastern end of the arc convergence between the north banda basin and southeast sulawesi is documented by the presence of the tolo thrust its outcrop is strongly arcuate and its accretionary wedge varies in width from a minimum of a few kilometers at each end to a maximum of 30 40 km in the central part the northern end transforms to the leftlateral matano fault with a reported offset of 20 km the southern end of the thrust projects toward the deformed rocks of buton but the structural relations there are not clear the matano fault zone appears to connect westward with the palu fault which forms the western transform of the north sulawesi trench the palu matano fault system acts as a trench trench transform between the north sulawesi trench and the tolo thrust and this system is described by the same rotation pole as that for the sulawesi north arm

determining the sula block kinematics in the triple junction area in indonesia by gps summary the point of convergence of the eurasian philippine and australian plates is situated adjacent to the island of sulawesi indonesia the relative plate velocities are estimated by nuvel1 to be 7 to 9 cm yr 1 the complex tectonic mechanism of the triple junction has been studied over a two year period in the course of the geodyssea southeast asian project the gps investigations concentrate on measurements of both the sulawesi eastern indonesia part of the inter regional geodyssea network and a local subnetwork on sulawesi motions derived using data from the subnetwork con rm what the results of the inter regional geodyssea network have suggested that is that current deformation is high and there are distinct deformation domains in the study area on sulawesi the tectonic mechanism of the triple junction has been analysed using a rigid microblock model the triple junction area can best be interpreted as a headland of the australian plate de ected by its collision with the philippine plate thereby identifying the driving forces of the current deformation the northern part is dominated by the sula domain which shows clockwise rotation to the south it is connected to the australian plate by an ensemble of microblocks undergoing counterclockwise rotation in addition to the above our tectonic model permits the determination of the local in uence of two large earthquakes m 7 8 1996 january 1 and m 7 0 1996 july 22 on the motion of the station tomini north sulawesi more observations and a denser gps network are planned in order to study the behaviour of the palu koro fault the main fault on the western limit of the sula block

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

unstable forearc stress in the eastern nankai subduction zone for the last 2 million years abstract transpressional tectonics characterizes the sw japan arc however we will show in this article that offshore seismic profiles and onshore mesoscale faults indicate that the eastern part of the forearc was subject to transtensional tectonics since ca 2 0 ma offshore normal faults imaged on the profiles run parallel to the nankai trough and started activity at 1 0 ma but transtensional tectonics commenced the onshore area earlier in order to understand the stress history in the forearc region we collected fault slip data from onshore mesoscale faults in plio pleistocene sedimentary rocks in the kakegawa area at the northeastern extension of the offshore normal faults most of the mesoscale faults are oblique normal indicating that the area was subject to transtensional tectonics the faults suggest that the compressional tectonic regime was followed by the transtensional one at 2 0 ma in agreement with regional tectonostratigraphic data which indicate that folding ceased at that time present compressional stress followed the transtensional tectonic regime sometime in the late pleistocene transtensional or extensional tectonic zone shifted from the kakegawa area to the offshore region these observations indicate that the state of stress just behind the accretionary prism of the eastern nankai subduction zone has been unstable in the last 2 million years suggesting that the forearc wedge has been at critical state in that gravitational force and basal shear traction on the wedge have been balanced but the forearc tectonics has been susceptible to small perturbations possible factors compatible with the observed stress history include the change of subduction direction of the plate at 1 0 ma and the rapid uplift of central japan thereafter

source parameters and slip distribution of the 2018 mw 7 5 palu indonesia earthquake estimated from space based geodesy abstract the 2018 mw 7 5 palu earthquake is one of the most geometrically complex events ever recorded on central sulawesi island it caused devastating tsunamis and landslides after the mainshock resulting in great casualties and damages to the infrastructures in palu city and surrounding areas in this study we combined far field insar near field sar and optical sub pixel correlation data to determine the fault geometry source parameters and fault slip distribution of this event along the palu koro fault zone our best fitting fault model contains three fault segments with variable strike angles showing that the coseismic rupture is dominated by a left lateral strike slip motion accompanied by minor normal slip and reverse slip components on the onshore segments the maximum slip is up to 8 4 m with a left lateral strike slip component of 6 8 m at a depth of 4 km on the central segment near palu city a normal slip component of 4 3 m in the left releasing step over and a reverse slip component of 3 2 m in the offshore area near the palu bay on the offshore segment the maximum slip is up to 4 2 m with a normal slip component of 1 8 m we argue that the offshore reverse slip motion might have played a key role in the generation of the palu tsunami we also suggest that the linking normal segment contributed to the rupture propagation across the left releasing step over from the central segment to the southern segment while the linking reverse segment arrested the rupture propagation across the right restraining step over to north the coulomb stress change reveals that there is possibility of future great earthquakes occurring on several major faults in the northeast of palu city our results have great significance to qualitatively assess the risk of future seismic hazards in such a geometrically complex fault system

analysis and direct numerical simulation of the flow at a gravity current head part 1 flow topology and front speed for slip and no slip boundaries direct numerical simulations are performed of gravity current fronts in the lock exchange configuration the case of small density differences is considered where the boussinesq approximations can be adopted the key objective of the investigation is a detailed analysis of the flow structure at the foremost part of the front where no previous high resolution data were available for the simulations high order numerical methods are used based on spectral and spectral element discretizations and compact finite differences a three dimensional simulation is conducted of a front spreading along a no slip boundary at a reynolds number of about 750 the simulation exhibits all features typically observed in experimental flows near the gravity current head including the lobe and cleft structure at the leading edge the results reveal that the flow topology at the head differs from what has been assumed previously in that the foremost point is not a stagnation point in a translating system rather the stagnation point is located below and slightly behind the foremost point in the vicinity of the wall the relevance of this finding for the mechanism behind the lobe and cleft instability is discussed in order to explore the high reynolds number regime and to assess potential reynolds number effects two dimensional simulations are conducted for reynolds numbers up to about 30 000 for both no slip and slip i e shear stress free boundaries it is shown that although quantitative reynolds number effects persist over the whole range examined no qualitative changes in the flow structure at the head can be observed a comparison of the two dimensional results with laboratory data and the three dimensional simulation provides evidence that a two dimensional model is able to capture essential features of the flow at the head the simulations also show that for the free slip case the shape of the head agrees closely with the classical inviscid theory of benjamin

a laboratory study of the velocity structure in an intrusive gravity current laboratory experiments were performed in which an intrusive gravity current was observed using shadowgraph and particle tracking methods the intrusion was generated in a two layer fluid with a sharp interface by mixing the fluid behind a vertical lock gate and then suddenly withdrawing the gate from the tank the purpose of the experiments was to determine the structure of the velocity field inside the intrusion and the stability characteristics of the interface soon after the removal of the lock gate the front of the intrusive gravity current travelled at a constant speed close to the value predicted by theory for an energy conserving gravity current the observed structure of the flow inside the intrusion can be divided into three regions at the front of the intrusion there is an energy conserving head region in which the fluid velocity is nearly uniform with speed equal to the front speed this is followed by a dissipative wake region in which large billows are present with their associated mixing and in which the fluid velocity is observed to be non uniform and have a maximum speed approximately 50 greater than the front speed behind the wake region is a tail region in which there is very little mixing and the velocity field is nearly uniform with a speed slightly faster than the front speed

neogene sutures in eastern indonesia five suture zones are described from the zone of collision between the eurasian indian australian and pacific philippine sea plates within the eastern indonesia region these are the molucca sorong sulawesi banda and borneo sutures each of these sutures has a relatively short history compared to most pre neogene orogenic belts but each preserves a record of major changes in tectonics including subduction polarity reversals elimination of volcanic arcs changing plate boundaries and important extension within an overall contractional setting rapid tectonic changes have occurred within periods of less than 5 ma many of these events although important would be overlooked in older orogenic belts because the age resolution required to identify them even when the evidence is preserved is simply not possible q 2000 elsevier science ltd all rights reserved

three dimensional numerical simulation for tidal motion in singapore s coastal waters abstract this paper describes the development and application of a three dimensional 3 d multi level hydrodynamic model to tidal motions in singapore s coastal waters in this model a two step euler predictor corrector algorithm is introduced to predict and correct the free surface water elevation the governing equations are explicitly and implicitly discretized into finite difference forms in a non uniform staggered grid system the velocity components in the x y and z directions are directly obtained the 3 d model is tested against analytical solutions for two standard cases in rectangular basins the model results for the velocities and the free surface water elevations coincide with analytical results the model is applied to the singapore coastal region and its surrounding waters in the first simulation the tidal current behavior including current circulation time history of sea levels currents and discharges as well as patterns of residual currents without wind effects is predicted the numerically predicted results show good agreement with field measurements in the second simulation the response of velocity fields to seasonal wind forcing is investigated

numerical and hydraulic simulations of the effect of density current generator in a semi enclosed tidal bay a large dyke built in 1997 in isahaya bay the spatial scale of about 10 km in ariake bay about 80 km raises huge scientific and social discussions in japan it is said that since the construction of the dyke physical and ecosystem environments have changed and fishery has been damaged enormously on the other hand it is known that the density current generator is successfully enhancing water quality in hazama inlet the spatial scale of 3 km of gokasho bay in this study we conducted numerical and physical model simulations on the hydrodynamics to investigate whether the apparatus is also applicable to isahaya bay in ariake bay a laboratory scale rotating hydraulic model and a three dimensional numerical code called the mec ocean model were adopted for the physical and numerical simulations respectively the mec ocean model has a special feature which is a hybrid of hydrostatic and nonhydrostatic models tests in a simple bay elucidated the importance of the nonhydrostatic model nested in the hydrostatic model i e the former can simulate the appropriate intrusion depth of the mid density water discharged in stratification the numerical results for ariake bay suggested that the water discharged from the apparatus spreads in the head of the bay within a couple of weeks with nontrivial concentration of nutrients this was also confirmed by the physical model test by using the luminance measurement of dye spread

global trench migration velocities and slab migration induced upper mantle volume fluxes constraints to find an earth reference frame based on minimizing viscous dissipation sincetheadventofplatetectonicsdifferentglobalreferenceframeshavebeenusedtodescribethemotionofplatesandtrenches thedifferencein plate motion and trench migration between different reference frames can be substantial up to 4 cm yr this study presents an overview of trench migration velocities for all the mature and incipient subduction zones on earth as calculated in eight different global reference frames calculations show that irrespective of the reference frame 1 trench retreat always dominates over trench advance with 62 78 of the 244 trench segments retreating 2 the mean and median trench velocity are always positive retreating and within the range 1 3 1 5 cm yr and 0 9 1 3 cm yr respectively 3 rapid trench retreat is only observed close to lateral slab edges b1500 km and 4 trench retreat is always slow far from slab edges n2000km thesecalculationsarepredictedbygeodynamicmodelswithavaryingslabwidth inwhichplatemotion trenchmotionandmantleflow result from subduction ofdense slabs suggesting that trenchmotion is indeedprimarily drivenby slab buoyancyforces andthat proximity to alateral slab edge exerts a dominant control on the trench migration velocity despite these four general conclusions significant differences in velocities between such reference frames remain it is therefore important to determine which reference frame most likely describes the true absolute velocities togetanunderstandingoftheforcesdrivingplatetectonicsandmantleconvection itishereproposedthat basedonfluiddynamicconsiderationsand predictions from geodynamic modelling the best candidate is the one which optimises the number of trench segments that retreat minimizes the trench perpendicular trench migration velocity vt in the centre of wide n4000 km subduction zones maximizes the number of retreating trench segments located within 2000 km of the closest lateral slab edge minimizes the average of the absolute of the trench perpendicular trench migration velocity vt forallsubductionzonesonearth andminimizestheglobaluppermantletoroidalvolumeflux to thatresultsfromtrenchmigration and associated lateral slab migration i e slab rollback or slab roll forward calculations show that these conditions are best met in one particular indo atlantic hotspot reference frame where 75 of the subduction zones retreat vt in the centre of wide subduction zones ranges between 3 5 and 1 8 cm yr 83 of the trench segments located within 2000 km of the closest lateral slab edge retreat the average of vt is 2 1 cm yr and to 456 km 3 yr lower limit and 539 km 3 yr upper limit inclusion of all the incipient subduction zones on earth results in slightly greater fluxes of 465 km 3 yr lower limit and 569 km 3 yr upper limit it is also found that this reference frame is close to minimizing the total sub lithospheric uppermantlevolumeflux k associatedwithmotionofcontinentalkeelslocatedbelowthemajorcratons itisstressed however that kisanorder of magnitude smaller than to and thus of subordinate importance in conclusion the indo atlantic hotspot reference frame appears preferable for calculating plate velocities and plate boundary velocities

the sulu sea a back arc basin setting within a neogene collision zone abstract the southeast sulu sea is a small oceanic basin that opened in middle miocene time in a back arc setting along the sundaland margin during subduction of the celebes sea plate beneath the sulu arc this back arc extension post dates compressive tectonism present in this back arc area in early middle miocene time progressive and still incomplete closing of this basin initiated in late miocene time is the result of collision of exotic terranes with the sundaland margin this collision also induced flipping of the sulu subduction zone the neogene geodynamic evolution of the sulu sea provides a modern example of how young oceanic crust can be incorporated within an orogenic belt

deformation and mantle flow beneath the sangihe subduction zone from seismic anisotropy abstract subduction of oceanic lithosphere is the most direct feedback between the earth s surface and deep interior however the detail of its interaction with the broader convecting mantle is still unclear mantle flow around subduction zones can be constrained using seismic anisotropy but despite many such studies a simple global picture is lacking the sangihe subduction zone where the molucca sea microplate is subducting westward beneath the eurasian plate is part of the tectonically complex sulawesi philippine region and an ideal natural laboratory to study complex subduction processes we investigate the anisotropic structure of the sangihe subduction zone with shear wave splitting measurements of local s and sks phases at two stations mni in sulawesi dav in the philippines as well as downgoing s phases at five stations at teleseismic distances combining different phases allows a better vertical resolution of anisotropic fabrics than is possible with a single phase the broad depth distribution of local events 60 630 km allows us to observe a change in splitting behaviour at 380 km depth above fast directions are trench parallel and delay times t are 0 34 0 53 s with no increase with depth we suggest this anisotropy is caused by aligned cracks possibly melt filled beneath the volcanic arc and fossil anisotropy in the overriding plate below 380 km is predominantly trench normal and t are slightly higher 0 53 0 65 s as no correlation is observed with inferred distance travelled inside the slab we attribute this anisotropy to shear layers atop the slab which are coherent from 200 to 400 km depth and perhaps extend into the transition zone sks and source side measurements show larger t 1 53 and 1 33 s respectively and trench parallel since these phases predominantly sample sub slab mantle we consider along strike lateral flow associated with the double sided subduction of the molucca sea microplate to be the most likely explanation we thus infer three dominant regions of anisotropy at the sangihe subduction zone one within the overriding lithosphere one along the slab wedge interface and one below the subducting molucca sea slab the mantle wedge above 200 km depth and the slab itself do not seem to contribute notably to the measured anisotropy this study demonstrates the insight seismic anisotropy can provide into mantle dynamics even in tectonically complex subduction systems

high slip rate for a low seismicity along the palu koro active fault in central sulawesi indonesia accurate chronological records are critical for understanding the landformsevolution and in particular of alluvial fan sequences emplaced during glocal global climatic changes toward this end we measured in situ produced 10be in quartz boulders exposed on top surfaces of sulawesian late quaternary alluvial fans combined geomorphic study spot image and field analyses indicate that this site is composed of twoalluvial fan units in situ produced 10be concentrations suggest that they were emplaced during two successive major climatic events the calculated minimum exposure ages date the younger unit abandonment at 11 000 2 000 years and seem consistent with a late interglacial abandonment age 120 000years for the older unit this study demonstrates that using both the neutron and muon components implicated in the production of in situ10be surficial erosion rates can be estimated 6 m ma in sulawesi and alluvial fan surfaces dated in particular it shows that10be may be used to date fan surface emplacement during the last 120 ka under humid tropical conditions significantly helping to constrain continental paleo climatology in these regions

monitoring of the palu koro fault sulawesi by gps years of gps measurements across the palu koro fault sulawesi indonesia state left lateral strike slip 3 4 cm yr with a small normal component 0 4 cm yr the measurements on intermediate points of the transect show that the fault is locked at a depth estimated around 8 16 km by a very simple model the best measured baseline linking the two most separate sites watatu and toboli shows very interestingly a constant rate of 2 6 cm yr from 1992 to 1995 and an increased rate of 6 3 cm yr since then this increase is due to an earthquake on january 1 1996 in the minahasa trench presumably affecting station toboli s position by 2 cm of co seismic and 2 cm of post seismic displacement which is added to its long term velocity we interpret this phenomenon as additional stress loading on the palu fault driven by the slip during the earthquake 100 km to the north east

magmatic evolution of sulawesi indonesia constraints on the cenozoic geodynamic history of the sundaland active margin abstract tertiary and quaternary magmatic rocks from west sulawesi record the complex history of part of the sundaland margin where subduction and collision have been and are still active the present study based on petrographic data major and trace element chemistry and 40 k 40 ar dating aims to document the age and chemical characteristics of the magmatic formations from west sulawesi and to determine the corresponding constraints on the geodynamic evolution of the sundaland border the west sulawesi magmatic province includes the south arm of sulawesi ujung pandang area the western part of central sulawesi with the toraja and palu areas and finally the north arm extending from palu to manado which includes the tolitoli and manado areas paleocene magmatic activity seems to be restricted to an episode of calc alkaline magmatism in the ujung pandang area 61 59 ma the major eocene 50 40 ma magmatic event is tholeiitic and is documented in all areas except in ujung pandang it led to the emplacement of tholeiitic pillow lavas and basaltic dykes of back arc basin bab affinity these rocks are potential equivalents to the celebes sea basaltic basement from oligocene to miocene magmatic eruptions produced successively island arc tholeiitic iat and calc alkaline ca rock series the youngest iat activity occurred around 18 ma in the central part palu area and around 14 ma in the north arm tolitoli area while ca magmas were emplaced in the north arm at ca 18 ma tolitoli and manado areas typical calc alkaline activity resumed only in the north arm tolitoli and manado areas during the late miocene 9 ma and is still active in the manado region in other areas palu toraja and ujung pandang areas an important and widespread magmatic event occurred between 13 and 10 ma and emplaced k rich magmas either silica undersaturated alkali potassic basalts ak ultrapotassic basanites uk or shoshonites sh k rich activity continued in the south until the pleistocene 0 77 ma with alkali potassic ultrapotassic and shoshonitic magmas in central sulawesi toraja and palu areas the most recent magmatic event occurred between 6 5 and 0 6 ma the corresponding products are granitic rocks and widely distributed rhyolitic pyroclastic flow deposits all these rocks are acidic in character sio 2 60 with trace element and isotopic signatures sr nd pb typical of a strong continental imprint the most striking tectonic implication of this magmatic evolution is that west sulawesi can no longer be considered as a typical magmatic arc as previously assumed with the exception of the manado area beneath which subduction is still active calc alkaline and island arc tholeiitic lavas and plutonics are volumetrically minor with respect to k rich magmas their occurrence through time is also fairly restricted mostly to the period between 30 and 15 ma another important feature is the occurrence of island arc tholeiitic and calc alkaline magmas crosscutting an older terrane of bab affinity the tinombo formation manado tolitoli and palu areas as this formation is being regarded as an equivalent to the celebes sea floor the most likely explanation for this feature is the hypothesis of tectonic erosion linked to the nw dipping subduction beneath the north arm the late miocene high k magmatic activity in central and south sulawesi reflects the prevalence of a post collisional tectonic regime following the docking of microcontinents of australian origin to central sulawesi during neogene times the incompatible element enriched character of these high k rocks might reflect their derivation from a mantle source enriched through metasomatism related to a previous subduction event such a model cannot account for the plio pleistocene cak magmatism of central sulawesi the acidic composition of which does not support a derivation from an ultrabasic source the trace element patterns of the cak rocks are very similar to those of the high grade metamorphics of central sulawesi suggesting that the latter might represent their possible source such an anatectic model implies a collisional to post collisional tectonic regime limited to central sulawesi while a post subduction regime prevailed in the south

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

paleomagnetic evidence for clockwise rotation of the northern arm of sulawesi indonesia abstract paleomagnetic results from the northern arm of sulawesi show that the arm has been subjected to a clockwise rotation of more than 90 and that its rotational motion began no later than the middle miocene the mean direction showing a normal polarity at the eocene to the early miocene is d 98 0 and i 6 9 a declination value of d 50 1 obtained from miocene rocks indicates a transition stage of the rotational motion the datum from plio pleistocene volcanics is d 4 6 and i 9 3 this suggests that the rotational motion terminated before the initiation of volcanic activity during the plio pleistocene

miocene to recent extension in nw sulawesi indonesia the malino metamorphic complex mmc in the western part of the north arm of sulawesi indonesia has previously been suggested to be a metamorphic complex exhumed in the early middle miocene this idea was based on limited k ar and 40ar 39ar age data but no structural data were presented to provide evidence for the mechanism of exhumation here we present new field observations micro structural analyses and a revised stratigraphy of nw sulawesi based on new age data to provide better constraints on the timing and mechanism of exhumation the data presented here suggest that the mmc is a metamorphic core complex which underwent lithospheric extension during the early middle miocene although the mmc experienced significant extension there is no evidence that it was exhumed during this time there is no contact between the mmc and the pliocene ongka volcanics contradicting a previously inferred unconformable contact pliocene undeformed granitoids intruding the mmc indicate the complex was still at depth during their emplacement furthermore pliocene and pleistocene cover sequences do not contain metamorphic detritus a second phase of extensional uplift was accommodated by brittle faulting from the late miocene pliocene onwards during which the mmc was exhumed this extension is widespread as indicated by synchronous exhumation of the adjacent palu metamorphic complex in west sulawesi and rapid subsidence offshore in gorontalo bay it is linked to northward slab rollback of the southward subducting celebes sea since the pliocene gps data show rapid northward motion of the north arm of sulawesi with respect to the celebes sea indicating that this process is ongoing at present day

rapid rotations about a vertical axis in a collisional setting revealed by the palu fault sulawesi indonesia global positioning system gps measurements from 1992 to 1995 indicate that the left lateral palu fault in central sulawesi slips at a rate of 38 8 mm a with a locking depth between 2 and 8 km from the measured slip rate and the historic seismicity of the fault we estimate that the palu fault currently has stored enough strain to produce a mw 7 earthquake the palu and other nearby faults accommodate rapid clockwise rotation of nearly 4 ma of e sulawesi relative to eastern sunda the rotation of east sulawesi transfers e w shortening between the pacific and eurasian plates to n s subduction of the celebes basin beneath sulawesi

cenozoic tectonic and depth age evolution of the indonesian gateway and associated back arc basins abstract we reconstruct the tectonic and paleo age and depth history of the indonesian seaway and associated southeast asian back arc basins to create a comprehensive paleogeographic framework for the region during the cenozoic we combine published tectonic models with revised models of the evolution of back arc basins based on available marine magnetic anomaly data and a recently published high resolution 1 min marine gravity anomaly grid which reveals many fine scale tectonic features previously not resolved reconstructions of the now subducted ceno tethys ocean floor are integrated with a revised absolute plate motion reference frame for the indian ocean based on moving hotspots all marginal seas north of australia formed in a back arc setting with the caroline and celebes seas opening north of a northward dipping subduction zone and the solomon sea south of a southward dipping subduction zone north of australia we suggest that the evolution of the two sub basins of the caroline sea from 36 to 25 ma followed different seafloor spreading patterns with the western sub basin being influenced by the manus hotspot our model suggests that collision between the melanesian and the caroline arcs led to cessation of oceanic crustal production in the caroline basin shortly before 25 ma combined geophysical and geological observations suggest that several major tectonic events occurred north of australia at around 45 ma roughly at the time when australia started moving northwards at fast rates similar to the present we suggest that this event is related to a relocation of the subduction zone nw of australia under the philippine sea plate due to a collision and subsequent accretion of old pacific plate material to the northward subducting australian plate our gridded oceanic paleo depth maps capture the history of marginal seas north of australia and the stepwise destruction of the ceno tethys ocean floor in the northern wharton basin and the west pacific providing boundary conditions for both paleoceanograpic and geodynamic models a regional analysis of basement depth anomalies reveals that median negative anomalous depth of several back arc basins is of the order of 650 800 m with a range of 300 1100 m accompanied by negative regional heatflow anomalies suggesting that mantle driven dynamic topography plays a larger role in modulating regional basement depth than previously suggested regional shear wave mantle tomography cross sections highlight that all marginal basins that exhibit large negative dynamic topography are underlain by massive buried slab material in the lower portion of the upper mantle and or below the transition zone supporting the notion that the observed paired negative dynamic topography and heatflow anomalies are due to basin formation above slab burial grounds

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

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

geodetic measurement of tectonic deformation in the santa maria fold and thrust belt california we have analyzed geodetic observations to resolve tectonic deformation across the santa maria fold and thrust belt northwest of santa barbara california the geodetic network forms a braced quadrilateral with 40 km sides whose southwest corner is the vandenberg very long baseline interferometry station the data include 1 historical triangulation from the 1880s 1920s and 1950s 2 electronic distance measurement trilateration from 1971 and 1985 and 3 global positioning system observations from 1986 and 1987 we combine the three different types of data to estimate two dimensional station positions and strain rate parameters simultaneously using a model which constrains the relative velocity field to be linear in space and constant in time we find significant strain rates the maximum compressive strain is oriented n17 e 5 e and the compressive strain rate in this direction is 0 13 0 03 strain yr under the assumption that the unresolved rotational component of the velocity field is zero we estimate that the integrated rate of deformation across the basin is 7 1 mm yr oriented at n03 e 13 this vector can be decomposed into 6 2 mm yr of crustal shortening on the general structural trend of n30 e and 3 1 mm yr of right lateral shear across this axis on the basis of these values and earthquake focal mechanisms in the area we infer that the deformation occurs on northwest trending folds and thrusts within the belt these results are consistent with the rate and direction of deformation across the central california coast ranges inferred by balancing pacific north america plate motion against san andreas slip and basin and range extension they imply that the santa maria fold and thrust belt is the primary active element in transforming motion from the coast ranges to the western transverse ranges and the santa barbara channel