seismic characteristics and strontium isotope ages of the middle miocene ngrayong formation in the madura strait basin implications for the paleogeographic reconstruction of east java abstract east java on the southeastern margin of the sundaland shelf is an ideal and pilot location to study paleogeographic changes due to the interactions of the eurasian and the indian australia plates many studies have been conducted however some issues remain poorly understood such as the initial compression stage and associated paleogeography of east java here we report newly acquired high resolution seismic data and drilling wells in the area of the madura strait we systematically reconstruct a three dimensional model on the paleogeography of east java in the middle miocene in combination with others results different depositional environments and characteristics of the related lithofacies observed on both sides of the middle miocene volcanic arc imply that weak subaerial and subaqueous volcanism existed in east java the extensive ngrayong fining in the southward clastic sequences located north of the mentioned volcanic arc were deposited in a bathyal marine environment which showed an oversteepening slope and basinal characteristics with outer neritic to bathyal facies within the present day kendeng zone and madura strait area this differs from the northern region of the present day rembang madura inversion zone and the northern offshore region of east java which were deposited in a transitional and neritic marine environment we identified two new turbidite fans showing opposite source directions based on 3d seismic data within the madura strait area four controlling factors contributed to the formation of the ngrayong turbidite fans including the paleotopography of the underlying kujung formation short term intense regional tectonic events high rates of sediment supply and occasional volcanic activity

synchronous compressional pulses in extensional basins abstract such paradoxes as synchronous compression and tension in extensional sedimentary basins and synchronous deformation of intractonic basins and eustatic sea level falls can each be related to pulsed changes in curvature of the earth s surface australia is everywhere in a state of significant relatively uniform upper crustal horizontal compression approximately perpendicular to the continental margins and generally directed towards its centre the compression commenced in the pliocene but was absent in the late miocene during the evolution of the gippsland and bass basins under extensional stress from the late jurassic to recent seven pulses of similarly directed compression have been identified from the campanian to recent time equivalent compressional pulses can also be demonstrated in such widely separated areas as northwest and northeast australia northwest europe and central america nine earlier pulses of early triassic to albian age are similarly synchronous global events and another twenty three pulses inferred since the neoproterozoic 800 ma are probably similarly globally synchronous earth expansion with subduction can explain these observations since it causes the surface curvature to decrease resulting in flattening of the semi rigid crust flattening results in lower crustal extension which generates sedimentary basins while contemporaneous upper crustal compression inverts and folds the sediments since globally synchronous compressional pulses may reflect expansion in the ocean basins there is a correlation of such pulses with major eustatic sea level lowstands any site of expansion within the earth is transmitted to the semi rigid crust as a volume increase by the whole gravitating fluid oblate spheroid this results in ubiquitous synchronous compressional pulses in the upper crust detectable on seismic reflection data not only at basin scale but also in individual petroleum producing structures

controls on back arc basin formation the relationship between subduction and back arc spreading has been well known since the early days of plate tectonics however the reasons why back arc basins are associated with some subduction systems but not all has remained elusive we examine the kinematic controls on subduction and back arc basins for both the present day and cenozoic to differentiate between the major competing hypotheses for back arc basin formation and to explain their temporal and spatial distribution our new data set of subduction and back arc basin parameters uses a new set of paleo oceanic age grids muller et al 2005 associated with a moving atlantic indian ocean hot spot reference frame o neill et al 2005 the plate model includes detailed reconstructed spreading histories of back arc basins based on marine geophysical and satellite gravity data our combined rotation and oceanic paleo age model provides the age distribution of subducting lithosphere through space and time convergence rates and the absolute motion of the downgoing and overriding plates we find that back arc basins develop when the age of subducting normal oceanic lithosphere is greater than 55 million years additionally we establish an age dip relationship showing that the intermediate dip angle of the subducting slab is always greater than 30 with back arc spreading our results suggest that back arc basin formation is always preceded by an absolute motion of the overriding plate away from the subduction hinge thereby creating accommodation space between the overriding and subducting plates once back arc extension is established it continues regardless of overriding plate motion indicating back arc spreading is not a simple consequence of overriding plate behaviour the landward migration of the overriding plate as a precursor to back arc extension may indicate that extension on the overriding plate is influenced by the oceanward lateral flow of the mantle however once back arc extension is established rollback of the subduction hinge appears to be the primary force responsible for the continued creation of accommodation space our analysis indicates the driving mechanism for back arc extension is a combination of surface kinematics properties of the downgoing slab the effect of lateral mantle flow on the slab and mantle wedge dynamics

crustal deformation of the eastern tibetan plateau revealed by magnetotelluric imaging the ongoing collision of the indian and asian continents has created the himalaya and tibetan plateau through a range of deformation processes these include crustal thickening detachment of the lower lithosphere from the plate delamination and flow in a weakened lower crust 1 6 debate continues as to which of these processes are most significant 7 in eastern tibet large scale motion of the surface occurs but the nature of deformation at depth remains unresolved a large scale crustal flow channel has been proposed as an explanation for regional uplift in eastern tibet 6 8 9 but existing geophysical data 10 11 do not constrain the pattern of flow magnetotellurics uses naturally occurring electromagnetic waves to image the earth s subsurface here we present magnetotelluric data that image two major zones or channels of high electrical conductivity at a depth of 20 40 km the channels extend horizontally more than 800 km from the tibetan plateau into southwest china the electrical properties of the channels imply an elevated fluid content consistent with a weak crust 12 13 that permits flow on a geological timescale these findings support the hypothesis that crustal flow can occur in orogenic belts and contribute to uplift of plateaux our results reveal the previously unknown complexities of these patterns of crustal flow many previous studies of the indiaasia

impact of india asia collision on se asia the record in borneo abstract borneo occupies a central position in the sundaland promontory of se asia it has a complex cenozoic geological history of sedimentation and deformation which began at about the same time that india is commonly suggested to have started to collide with asia some tectonic reconstructions of east and se asia interpret a large se asian block with borneo at its centre which has been rotated clockwise and displaced southwards along major strike slip faults during the cenozoic due to the indentation of asia by india however the geological history of borneo is not consistent with the island simply forming part of a large block extruded from asia the large clockwise rotations and displacements predicted by the indentor model for borneo are incompatible with palaeomagnetic evidence and there is no evidence that the major strike slip faults of the asian mainland reach borneo seismic tomography shows there is a deep high velocity anomaly in the lower mantle beneath se asia interpreted as subducted lithosphere but it can be explained just as well by alternative tectonic models as by the indentor model very great thicknesses of cenozoic sediments are present in borneo and circum borneo basins and large amounts of sediment were transported to the crocker turbidite fan of north borneo from the eocene to the early miocene but all evidence indicates that these sediments were derived from local sources and not from distant sources in asia elevated by india asia collision the cenozoic geological history of borneo records subduction of the proto south china sea and miocene collision after this ocean lithosphere was eliminated and a variety of effects resulting from long term subduction beneath se asia there is little to indicate that india asia collision has influenced the cenozoic geological record in borneo

extensional collapse of the tibetan plateau results of three dimensional finite element modeling 1 following their initial collision 50 70 myr ago the indian and eurasian plates have been continuously converging toward each other whereas the regional stress field is predominately compressive the late cenozoic tectonics within the tibetan plateau features widespread crustal extension numerous causes of the extension have been proposed but their relative roles remain in debate we have investigated the major factors contributing to the tibetan extension in a three dimensional viscoelastic model that includes both lateral and vertical variations of lithospheric rheology and relevant boundary conditions constrained by the present topography and gps velocity field the model predicted predominately extensional stress states within the plateau crust resulting from mechanical balance between the gravitational buoyancy force of the plateau and the tectonic compressive stresses the predicted stress pattern is consistent with the earthquake data that indicate roughly e w extension in most of tibet and nearly n s extension near the eastern margin of the tibetan plateau we explored the parameter space and boundary conditions to examine the stress evolution during the uplift of the tibetan plateau when the plateau was lower than 50 of its present elevation strike slip and reverse faults were predominate over the entire plateau and no e w crustal extension was predicted significant crustal extension occurs only when the plateau has reached 75 of its present elevation basal shear associated with underthrusting of the indian plate beneath tibet may have enhanced crustal extension in southern tibet and the himalayas and a stronger basal shear during the miocene may help to explain the development of the south tibetan detachment system

fault reactivation and structural inversion backarc and intraplate compressive deformations example of the eastern sunda shelf indonesia the tectonic evolution of the eastern sunda platform in indonesia is revealed by the study of seismic profiles and comprises three general tectonic periods during the cenozoic extension with graben infill from the paleogene to the early miocene a tectonically quiet period with only broad subsidence and a middle miocene recent period of folding inversion and thrusting these structures reveal changes in the intraplate stress field which was controlled by the changes in the boundary conditions of the plates collisions on the northern and eastern sides and interplate coupling southward along the java subduction zone inversions often occurred without reactivation of pre existing normal fault planes at the upper levels of these faults the factors controlling these deformations are discussed with special interest placed on the conditions for the potential reactivation of cohesionless normal faults inversion and reactivations were mostly controlled by the orientation of the pre existing fault planes in relation with the regional stress field and by the tectonic stress regime in a strike slip regime effective principal stresses 1 and 3 horizontal with 1 2 3 the optimum conditions for reactivation in isotropic rocks are pre existing faults that strike close to the potential two vertical conjugate failure planes the same mechanical properties as for pre existing fault prevail in such conditions strike slip movements and reverse strike slip movements and associated en echelon folds were generally observed in a compressive regime 1 and 2 horizontal with 1 2 3 typical steeply dipping normal faults are difficult to reactivate by slip movements we suggest that reverse slip movements occurred in the deeper levels of faults and were accommodated by flexure above the pre existing fault planes and the inversion of grabens the strongly inverted grabens are those whose orientation is perpendicular to the regional compression nevertheless with strong regional shortening large uplifts and thrust faults were observed with reactivation in the form of reverse or reverse strike slip movements along pre existing steeply dipping normal fault planes

kinematic model of active deformation in central asia the velocity field of present day deformation in central asia is modelled using a set of four rotating blocks siberia tarim tibet india on a spherical earth a best fit is inverted on the basis of estimated shortening rates across the main thrust zones himalayas tien shan and measured slip rates along the principal strike slip faults altyn tagh and karakorum separating those blocks the fit to the data implies that nearly all the present convergence between india and asia can be accounted for by slip partitioning on these four zones with as much as 50 absorbed by northeastwards extrusion of tibet this suggests that localised deformation governs the present mechanical behaviour of the central asian lithosphere

dynamics of the india eurasia collision zone we present simple new dynamic calculations of a vertically averaged deviatoric stress field over a depth average of 100 km for asia from geodetic geologic topographic and seismic data a first estimate of the minimum absolute magnitudes and directions of vertically averaged deviatoric stress is obtained by solving force balance equations for deviatoric stresses associated with gravitational potential energy differences within the lithosphere plus a first order contribution of deviatoric stresses associated with stress boundary conditions this initial estimate of the vertically averaged deviatoric stress field is obtained independent of assumptions about the rheology of the lithosphere absolute magnitudes of vertically averaged deviatoric stresses vary between 5 and 40 mpa assuming bulk viscous behavior for the lithosphere the magnitudes of deviatoric stresses together with the magnitudes of strain rates inferred from quaternary fault slip rate and gps data yield vertically averaged effective viscosities for tibet of 0 5 5 1022 pa s compared with 1 2 5 1023 pa s in more rigid areas elsewhere in the region a forward modeling method that solves force balance equations using velocity boundary conditions allows us to refine our estimates of the vertically averaged effective viscosity distribution and deviatoric stress field the total vertically averaged deviatoric stress and effective viscosity field are consistent with a weak lower crust in tibet they are consistent with some eastward motion of tibet and south china lithosphere relative to eurasia and they confirm that gravitational potential energy differences have a profound effect on the spatially varying style and magnitude of strain rate around the tibetan plateau our results for the vertically averaged deviatoric stress argue for a large portion of the strength of the lithosphere to reside within the seismogenic upper crust to get deviatoric stress magnitudes there to be as high as 100 300 mpa in accord with laboratory and theoretical friction experiments indicating that stress drops in earthquakes are small fractions of the total deviatoric stress

evidence for mechanically coupled lithosphere in central asia and resulting implications the recent dramatic increase in seismic anisotropy and surface global positioning system gps data for central asia permits a comprehensive examination of the mantle s role in mountain building a joint analysis of 178 shear wave splitting and 2000 gps observations using a new technique reveals that the crust and lithospheric mantle deform coherently arguing for crust mantle mechanical coupling during deformation the observed spatial variations in anisotropy refl ect the large scale pattern of lithospheric deformation as well as a change in deformational style from simple shear on the tibetan plateau transitioning to pure shear in surrounding regions

hydrocarbon charge of a bacterial gas field by prolonged methanogenesis an example from the east java sea indonesia abstract the terang sirasun field in the east java sea of indonesia contains 1 0 trillion cubic feet tcf of dry gas reserves which are made up of over 99 5 methane with 13c of 65 and d of 185 the methane was formed exclusively by methanogenic bacteria via the co2 reduction pathway the primary source sediments for the methane were identified based on bulk geochemical and absolute biomarker concentrations specifically the c25 acyclic isoprenoid 2 6 10 15 19 pentamethyleicosane pme and related isoprenyl glyceryl ethers which are well known markers for methanogenic archaebacteria were used as indicators for sediment layers thought to have had the most abundant methanogen activity burial history analysis and precise biostratigraphic age control provided the framework for assessing the timing of hydrocarbon fill our findings show that methanogenic activity was highest in marine shelfal claystones mid outer neritic ranging in age from 8 ma late miocene to present the gas is reservoired in limestones and sands of the paciran member which are dated from 6 5 to 1 3 ma late miocene pliocene the top seal for the present accumulation was deposited less than 0 5 ma ago quaternary although there is strong geological evidence that older seals existed these older seals were catastrophically removed by submarine slumping resulting in the loss of earlier accumulated gas methanogenesis from older source beds continued and the trap was recharged after deposition of the current top seal the information obtained from this field study provides evidence that large accumulations of bacterial methane do not necessarily require early entrapment of methane from freshly deposited marine sediments traps may be filled with bacterial gas long after the deposition of source beds provided that the required conditions for active methanogenesis are maintained throughout this period

structural and stratigraphic evolution of the east java sea indonesia abstract the east java sea displays excellent examples of miocene to present day structural inversion of a palaeogene extensional transtensional basin system the structural geometry of these inversions has been analysed by a series of regional cross sections which demonstrate significant lateral variation in structural style this variation is interpreted to be a function of the fault shape and linkage which evolved during the extensional phase of basin development prediction of fault geometry has been aided by analogue modelling of inverted extensional basins driving mechanisms of structural inversion have been assessed by modelling the motion of the eurasian indian ocean australian and pacific plates during the neogene the evolution of inversion within the east java sea is interpreted to be a function of the propagating collision of the australian plate with the sunda arc and the resultant variation in relative convergence rate and direction of the subducting indian ocean plate and the s e eurasian plate stratigraphic evolution is strongly influenced by relative sea level fluctuations principally eustatic within overall control of tectonic processes particularly inversion the sediment fill is mainly fine grained with alternating carbonate dominated and clastics dominated cycles the use of wireline logs seismic data and biostratigraphic data allows a detailed sequence stratigraphy to be developed with both regionally and locally recognisable highstand lowstand and transgressive systems a well imaged progradational carbonate platform margin exhibits late stage growth and subsequent inundation which are used to calibrate locally derived relative sea level curves

two crustal low velocity channels beneath se tibet revealed by joint inversion of rayleigh wave dispersion and receiver functions abstract competing geodynamic models such as rigid block extrusion continuous deformation and the mid lower crustal flow have been proposed to describe the growth and expansion of eastern tibet however the dynamic processes responsible for plateau evolution and deformation remain poorly understood partly due to resolution limitations of previous models of lithospheric structure on the basis of joint inversion of rayleigh wave dispersion and receiver functions using data from a newly deployed seismic array we have obtained a high resolution 3d image that reveals the distribution of low velocity zones lvzs with unprecedented clarity the prominent feature of our model is two low velocity channels that bound major strike slip faults in se tibet and wrap around the eastern himalaya syntaxis consistent with the clockwise movement of crustal material in this region most large earthquakes in this region occurred in the boundaries of the lvzs we propose that ductile flow within these channels in addition to shear motion along strike slip faults played a significant role in accommodating intensive lithospheric deformation during the eastward expansion of tibet in the cenozoic

contemporary crustal deformation around the southeast borderland of the tibetan plateau 1 we derive a detailed horizontal velocity field for the southeast borderland of the tibetan plateau using gps data collected from the crustal motion observation network of china between 1998 and 2004 our results reveal a complex deformation field that indicates that the crust is fragmented into tectonic blocks of various sizes separated by strike slip and transtensional faults most notably the regional deformation includes 10 11 mm yr left slip across the xianshuihe fault 7 mm yr left slip across the anninghe zemuhe xiaojiang fault zone 2 mm yr right slip across a shear zone trending northwest near the southern segment of the lancang river fault and 3 mm yr left slip across the lijiang fault deformation along the southern segment of the red river fault appears not significant at present time the region south and west of the xianshuihexiaojiang fault system whose eastward motion is resisted by the stable south china block to the east turns from eastward to southward motion with respect to south china resulting in clockwise rotation of its internal subblocks active deformation is detected across two previously unknown deformation zones one is located 150 km northwest of and in parallel with the longmenshan fault with 4 6 mm yr right slip and another is continued south southwestward from the xiaojiang fault abutting the red river fault with 7 mm yr left slip while both of these zones are seismically active the exact locations of faults responsible for such deformation are yet to be mapped by field geology comparing our gps results with predictions of various models proposed for tibetan plateau deformation we find that the relatively small sizes of the inferred microblocks and their rotation pattern lend support to a model with a mechanically weak lower crust experiencing distributed deformation underlying a stronger highly fragmented upper crust

late quaternary activity of the zemuhe and xiaojiang faults in southwest china from geomorphological mapping abstract there has been limited detailed geomorphological research on the kangding fault system located along the eastern margin of the tibetan plateau despite the system containing active faults with high slip rates fault related landforms such as offset streams were mapped at selected sites along the zemuhe and xiaojiang faults in the central and southern sections of the kangding fault system the results permitted assessment of the mode and rate of late quaternary fault movement based on more comprehensive information than used in previous studies the left lateral strike slip of these faults reflects the large scale clockwise rotation of the southern tibetan plateau the estimated strike slip rate of the zemuhe fault is ca 5 9 mm yr 1 whereas that of the xiaojiang fault is ca 14 22 mm yr 1 these rates and the known slip rates of the adjacent faults indicate that in the northern and southern sections of the kangding fault system the regional tectonic stress from the clockwise rotation has been released mainly along the major faults whereas the stress in the central section has been released by both fault movement and deformation in surrounding areas the latter mechanism reflects a more complex geological structure in the central system of distinct thrusts and folds late quaternary vertical deformation along the zemuhe and xiaojiang faults has mostly resulted from local stresses associated with strike slip movement although the zemuhe fault has also undergone slow but consistent normal faulting since the early quaternary due to its orientation oblique to the direction of the clockwise rotation

structural styles of an accretionary wedge south of the island of sumba indonesia revealed by seamarc ii side scan sonar the accretionary wedge south of sumba island indonesia is in the early stages of continent island arc collision australian continental shelf sediments are being actively accreted to the sunda arc at the timor trough we have correlated seamarc ii side scan images and bathymetry with 3 5 khz and seismic reflection profiles to construct a structural interpretation of this zone deformation is concentrated on the lower slope of the accretionary wedge within 15 to 25 km of the thrust front above which the strain rate appears to decrease abruptly three distinct structural styles are developed in the survey area the characteristics of the easternmost region are 1 deformation in a fold and thrust geometry 2 presence of mud volcanoes and mud ridges parallel to the thrust front indicating elevated fluid pressure and 3 the development of a long decollement extending 10 to 15 km from the thrust front in contrast the central region shows a more homogeneous thickening resulting mainly from closely spaced faulting seaward verging thrust faults and conjugate strike slip faults are the main structures in this segment of the accretionary wedge mud volcanoes and a very long decollement are absent in the central region we present a hypothesis in which structural style is controlled by the length of the decollement developed in front of the thrust front short thick thrust sheets may favor uniform shortening whereas long thin sheets may be unstable to buckling and deform by folding high fluid pressure may facilitate propagation of the decollement in contrast to the accretion occurring in the other two regions the western part of the accretionary wedge is in the process of being indented and redeformed by a basement ridge

sandbox experiments of inverted listric and planar fault systems abstract the kinematic and geometric evolution of basement controlled inversion structures has been analyzed using a plane strain sandbox apparatus the results of two representative scaled analogue models comprising rigid listric and planar detachment faults that both have cut off angles of 60 to the horizontal are described in detail the hangingwall above these detachment geometries was constructed from alternate layers of sand and mica in order to simulate an anisotropic sedimentary sequence in both experiments initial shortening at the onset of inversion was accommodated by bulk strain this was followed by reactivation of the basal detachment together with the main basin controlling planar and listric faults which propagate upwards through the post rift sequence at approximately the same angle as the upper part of the detachment fault i e 60 reactivation of relatively steep intra basinal extensional faults within the cover was restricted to nucleation of reserve faults and thrusts in the region of the tips during approximately the first 10 to 15 contraction this resulted in gently dipping thrusts that propagated upwards through the post rift sequence to produce harpoon shaped structures later in the inversion phase after approximately 15 contraction backthrusts cut through and displaced the original antithetic extensional graben faults producing downward tapering wedge shaped structures at the margins of the basin although deformation in these experiments was limited to purely dip slip displacement the nature of the original extensional faults and their reactivated tip regions resulted in cross sectional geometries that have a marked resemblance to strike slip induced flower structures uplift was asymmetric and centred above the upper part of the main detachment above the listric fault but was more symmetrical and centred above the soling out point of the detachment in the case of the planar fault geometry the results of these experiments show distinct similarities to structures seen on seismic sections form the southern north sea and other inverted sedimentary basins

present day crustal motion within the tibetan plateau inferred from gps measurements 1 using the measurements of 726 gps stations around the tibetan plateau we determine the rigid rotation of the entire plateau in a eurasia fixed reference frame which can be best described by an euler vector of 24 38 0 42 n 102 37 0 42 e 0 7096 0 0206 ma the rigid rotational component accommodates at least 50 of the northeastward thrust from india and dominates the eastward extrusion of the northern plateau after removing the rigid rotation to highlight the interior deformation within the plateau we find that the most remarkable interior deformation of the plateau is a glacier like flow zone which starts at somewhere between the middle and western plateau goes clockwise around the eastern himalayan syntaxis ehs and ends at the southeast corner of the plateau with a fan like front the deformation feature of the southern plateau especially the emergence of the flow zone could be attributed to an eastward escape of highly plastic upper crustal material driven by a lower crust viscous channel flow generated by lateral compression and gravitational buoyancy at the later developmental stage of the plateau the first order feature of crustal deformation of the northeastern plateau can be well explained by a three dimensional elastic half space dislocation model with rates of dislocation segments comparable to the ones from geological observations in the eastern plateau although gps data show no significant convergence between the eastern margin of the plateau and the sichuan basin a small but significant compressional strain rate component of 10 5 2 8 nstrain yr exists in a relatively narrow region around the eastern margin in addition a large part of the eastern plateau northeast of the ehs is not undergoing shortening along the northeastward convergence direction of the ehs but is stretching

on the effect of the water body geometry on landslide tsunamis physical insight from laboratory tests and 2d to 3d wave parameter transformation preliminary landslide tsunami hazard assessment is commonly based on empirical equations derived from wave channel 2d or wave basin 3d experiments the far field wave in 2d can easily be an order of magnitude larger than in 3d the present study systematically investigates the effect of the water body geometry on the wave characteristics in the near and far field subaerial landslide tsunami tests were conducted relying upon both a 2d and a 3d physical model undertaken with identical boundary conditions the test parameters included two water depths three rigid slides as well as various slide release positions empirical equations for 3d offshore and laterally onshore wave properties are presented and compared with previous work a direct comparison of the wave features reveals that the waves decay in 2d 3d onshore and 3d offshore with x 0 30 r 0 67 and r 1 0 where x 2d and r 3d describe the distance from the impact zone in 2d four wave types are observed whereas only the two least non linear types were observed in 3d this finding is further analysed with wavelet spectra for a large slide froude number f relative slide thickness s and relative slide mass m the 3d wave heights in the slide impact zone can be as large as in 2d however for small f s and m the 3d waves are considerably smaller both in the near and far field a novel method is presented and validated to transform data from 2d studies to 3d this method may have favourable implications on preliminary landslide tsunami hazard assessment

the origin of the east java sea basins deduced from sequence stratigraphy abstract a study of facies distribution through time shows there are at least six different basinal areas which are usually described as a single entity called the east java basin each of these different depositional lows plus the transgressed platforms between them have a unique stratigraphic history and distinct sets of petroleum systems with different exploration risks the development of the main phases of sedimentation indicate that the east java basinal system was formed as a continuation of extension around the makassar straits and not as a back arc basin this interpretation is based on a tectonically pulsed east to west trend in crustal thinning subsidence and transgression in addition there were elongate and anastomosing faults along the southern edge of this extending crust creating a unique stratigraphic zone south of the rembang line fault periodic changes in strain strongly affected this faulted southern margin including a mid oligocene tectonic event that also created a new depocentre the sibaru trough a poorly defined lithostratigraphic term the ngimbang formation is recommended to be abandoned its historical usage for a series of highly diverse lithofacies spanning four or five major unconformity bounded sequences renders it meaningless its long standing and inconsistent use is one of the factors that has prevented a clearer stratigraphic history from emerging an alternative nomenclature based on facies and natural sequences of deposition is recommended instead

active deformation of asia from kinematics to dynamics using estimated strain rates across the actively deforming region of asia to infer variations in viscous stress it is shown that gradients of stress point uphill toward the center of tibet where gravitational potential energy per unit surface area reaches a maximum thus the dynamics of the deformation seem to obey the equation of creeping flow which expresses a balance between gradients in stress and the gravitational body force this balance in the region of the tibetan plateau yields an estimate of 10 22 pascal second for the average viscosity of the tibetan lithosphere which is only about 10 to 100 times greater than the viscosity of the convecting upper mantle

evaluating the role of preexisting weaknesses and topographic distributions in the indo asian collision by use of a thin shell numerical model thin viscous sheet models have proved to be very useful in exploring the interaction between plate boundary and gravitational forces during continental collision however simplifications of these models e g absence of faults planar geometry of the collision zone limit their use in making specific predictions regarding tectonic evolution such as the role of eastward extrusion along major strike slip faults during the indo asian collision this deficiency is overcome by a thin shell finite element model with faults that can assess the effects of preexisting fault configurations and topographic distributions on velocity fields numerical simulations of a palinspastically restored asia at ca 50 ma suggest that preexisting lithospheric weaknesses favor north south shortening during initial collision whereas preexisting high topography in southern asia promotes eastward extrusion these results underscore the first order importance of initial topography and the distribution of preexisting faults in the outcome of geodynamic modeling

what drives short and long term crustal deformation in the southwestern united states 1 the driving forces for crustal deformation are often inferred from the crustal kinematics in the southwestern united states however crustal kinematics delineated by the global positioning system gps measurements differs significantly from that reconstructed from the geological records this discrepancy is likely due to the different timescales reflected in these datasets here we explore the geodynamic links between the short and long term crustal deformation in the southwestern us using regional scale three dimensional elastic and viscous finite element models we show that the gps measured short term crustal deformation results mainly from interseismic traction along the san andreas fault saf much of the short term strain is transient that does not contribute to permanent deformation the long term traction on the saf is 10 mpa lower than that constrained by the gps data which together with gravitational spreading can reproduce the geologically reconstructed long term crustal deformation

reconstruction of the deformed collision zone between india and asia by backward motion of lithospheric blocks 1 on the basis of a synthesis of tectonic data available on the india asia collision we present a first attempt to reconstruct the evolution of the collision zone assuming that the deformation of the lithosphere is localized along narrow shear zones and that the interiors of mantle blocks in between remain relatively undeformed we define block contours from the fault pattern and move back the blocks along their boundary faults along convergent or extensional boundaries the crust is assumed to shorten or stretch coherently step by step we go backward in time to finally reach the collision onset for each time step we find a solution compatible with the data set available and the position of the adjacent blocks for each block the search for compatibility at the scale of the entire collision zone allows for solving the kinematics of regions with fewer data and suggests plausible scenarios for regions where data is lacking for each step we calculate large scale displacement maps and determine euler poles for each block for the most recent time step the map proposed is compared to gps motions the deformation budget implies that extrusion absorbed 30 of the convergence between india and siberia during the entire collision span but varied with time accounting for as little as 3 or as much as 60 of this convergence at different epochs

rayleigh wave tomography of the northeastern margin of the tibetan plateau abstract the convergence between the indian continent and the southern margin of eurasia has eventually led to the growth of the tibetan plateau eastward various models have suggested that a large scale flow in the lower crust or and the asthenosphere is responsible for the uplift of eastern tibet it has also been suggested that the continental flow may move around the thick lithosphere of the ordos plateau and the sichuan basin in order to investigate the validity of the crust mantle flow and its possible path we have used rayleigh wave tomography with sensitivity kernels to estimate both the phase velocity structure 20 143 s and the shear wave velocity structure 0 200 km across the northeastern margin of the tibetan plateau from the surface to 100 km our shear wave velocity model shows a prominent low velocity anomaly beneath northeastern tibet suggestive of a warm lithosphere its boundary lies at 105 e longitude which borders the western ordos plateau and sichuan basin from 125 km to 200 km our shear wave velocity model shows a low velocity channel beneath the qilian qinling orogen that lies between the ordos and sichuan blocks this channel may represent the asthenosphere given the fact that the lithosphere is 120 150 km thick in northeastern tibet and the qinling orogen we also inverted for the anisotropy parameters in the study area simultaneously with the velocity parameters the dominant fast direction is nww see generally consistent with the sks splitting results the calculated shear strain from gps and the fault slip rate measurements furthermore the fast directions in our anisotropic model vary only slightly with periods and the anisotropy magnitudes at long periods 100 143 s are large and exceed those at short medium periods 20 80 s indicating potentially although not necessarily vertically coherent deformation from the crust to the asthenosphere and possibly large deformation in the asthenosphere the deformation seems to be linked to the southeastward extrusion tectonics caused by the collision boundary force

identification of wrench faults using subsurface structural data criteria and pitfalls 1 many structures imaged with reflection seismic can resemble a wrench fault system because of the great structural diversity of strike slip faults and the wide range of contractional and extensional features associated with these faults because of these resemblances numerous faults are misidentified as wrench faults by workers using subsurface structural data credible identification requires combinations of profile and map criteria 1 narrow long straight throughgoing solitary master fault or zone of deformation 2 steep to moderate dip of the master fault at depth 3 offset of the top of basement 4 changes in relative upthrown side separation sense and or fault dip direction at depth or along the strike of the master fault 5 narrow fault slices within the master fault zone that steepen and join at depth negative and positive flower structures 6 different separation sense and orientation of relative upthrown side at these fault slices and 7 coeval en echelon flanking structures the identification should be confirmed with other criteria that refute alternative interpretations the main pitfalls to a reliable identification are not considering alternative structural styles and the misinterpretation of features or patterns that superficially resemble wrench systems the profile geometries of basement involved reverse or normal faults particularly those with structural inversion can resemble the single strand of convergent or divergent wrench faults profile geometries of flower structures can be mimicked by narrow contractional horsts or narrow extensional grabens complexly faulted anticlines or synclines splay faults fault zones intruded by salt or shale and overprinted structures pitfalls in interpreting map relationships are possible when structural patterns combine several tectonic influences are controlled by rock anisotropy or include elements hat are not coeval and if the patterns characteristic of other styles are misinterpreted many erroneous identifications of wrench faults can be eliminated by demonstrating that the investigated fault or feature lacks a straight trace lateral length or throughgoing continuity

the indo asian continental collision a 3 d viscous model abstract the large scale physical process of the indo asian continental collision and the formation of the himalayan tibetan plateau have been simulated in various viscous thin sheet models but the thin sheet simplification also kept some important issues from being fully explored among these issues are the role of strike slip fault zones in facilitating large scale lateral translation of lithospheric blocks the escaping tectonics during the collision and the speculated lateral flow of the ductile middle lower crust under the tibetan plateau here we present a fully three dimensional finite element model to simulate the indo asian continental collision the model includes major boundary faults to simulate the escaping tectonics and vertically variable rheological structures to model lower crustal flow the collisional process is constrained by the history of the indo eurasian plate convergence and the present crustal thickness and topography of the tibetan plateau our results indicate that the restrictive boundaries of the tibetan plateau including the rigid tarim and south china blocks largely control the spatiotemporal patterns of crustal deformation in the collision zone as the indian indenter moves toward the tarim block higher strain rates and topography developed in the western part of the collision zone than in the eastern part causing the northward migration of the deformation front to gradually change to eastward migration in the past 10 20 myr broadly consistent with the initiation of widespread e w extension in the plateau these restrictive boundary blocks also force the crustal and mantle materials in the collision zone to flow coherently hence providing an alternative explanation for the apparently vertically coherent deformation in tibet assuming that the crust weakens as it thickens our model predicts the lateral expansion of the tibetan plateau an important feature of the tibetan tectonics that is missing in previous models with constant rheology

a thin viscous sheet model for continental deformation summary for the purposes of describing its large scale and long term deformation the continental lithosphere is regarded as a continuum obeying a newtonian or a power law rheology the flow of a thin sheet of power law material overlying an inviscid substrate is studied under the assumption that vertical gradients of the horizontal velocity are negligible a numerical model is used to investigate the deformation of such a sheet under conditions approximating those of continent continent collision the material flows in response to forces applied to its boundaries for example the indenting of one continent by another and to forces in its interior arising from gradients in crustal thickness the horizontal divergence of the flow produces changes in the crustal thickness and hence a time dependent form to the flow itself for a given set of boundary conditions the flow depends on the stress exponent in the power law rheology n and on the argand number which is a measure of the ratio between the stress arising from crustal thickness contrasts and the stress required to deform the material at the ambient strain rates when the effective viscosity of the medium is very high ar o crustal thickness variations do not influence the flow if the material is newtonian n l the deformation associated with an influx of material approximating an indenter is of much greater lateral dimension than the width of the indenter whereas when material has a power law rheology n 3 5 are used the deformation is confined to a region of lateral extent comparable to that of the indenter as ar increases the forces arising from crustal thickness contrasts exert more influence on the flow and the maximum crustal thickness that can be sustained by a given influx of material is related by a simple expression to the effective viscosity of the medium at the ambient strain rates in the limit of a very weak medium ar 10 the lithosphere is unable to sustain appreciable crustal elevation contrasts the results of these numerical experiments show that systems in which the effective viscosities are such that the maximum deviatoric stresses are between 1 kbar

continuous deformation of the tibetan plateau from global positioning system data global positioning system velocities from 553 control points within the tibetan plateau and on its margins show that the present day tectonics in the plateau is best described as deformation of a continuous medium at least when averaged over distances of 100 km deformation occurs throughout the plateau interior by ese wnw extension and slightly slower nne ssw shortening relative to eurasia material within the plateau interior moves roughly eastward with speeds that increase toward the east and then flows southward around the eastern end of the himalaya crustal thickening on the northeast ern and eastern margins of the plateau occurs over a zone 400 km wide and cannot be the result of elastic strain on a single major thrust fault shortening there accommodates much of india s penetration into eurasia a description in terms of movements of rigid blocks with elastic strain associated with slip on faults between them cannot match the velocity field

active crustal deformation in southeastern tibetan plateau the kinematics and dynamics abstract crustal deformation in southeastern tibetan plateau has been attributed to tectonic extrusion and gravitational spreading here we analyzed the present day strain partitioning in this region using gps data the results show highly localized shear strain along the xianshuihe anninghe xiaojiang strike slip faults as expected by the model of tectonic extrusion however the localized shear strain along strike slip faults ends in southern yunnan and transfers to crustal extension in yunnan and contraction in myanmar we developed three dimensional visco elastoplastic finite element models to investigate the causes of the observed crustal deformation our results indicate that the present day crustal deformation in southeastern tibetan plateau can be largely explained by gravitational spreading

origin and age of carbonate clasts from the lusi eruption java indonesia abstract deep stratigraphic constrains below the indonesian lusi mud eruption are currently lacking due to the absence of deep wells and good quality seismic data a collection of carbonate clasts has been sampled from the lusi site active since its birth in 2006 these specimens are part of a large variety of lithotypes erupted from the main crater the carbonates analysed comprise scleractinian coral and bivalve shell fragments probably shallow water in origin and clasts consisting of planktonic foraminifera bearing mudstone from pelagic deposits selected rocks were analysed using planktonic foraminifera and 87sr 86sr dating with the aim to constrain their age and to improve the understanding of the so far unknown sequence of limestone deposits inferred at this site based on biostratigraphy using planktonic foraminifera one group of samples reveal to belong to the planktonic foraminifera zone m5b with an age comprised between 16 29 and 15 10 ma miocene latest burdighalian to langhian the sr isotope based ages of clasts analysed for 87sr 86sr cover a larger time window spanning from pliocene zanclean and piacenzian miocene messinian down to eocene priabonian the pliocene and messinian ages are unreasonably young from what is known of the local geology and one sample provided an 87sr 86sr age that is 8 my younger compared to that obtained from the planktonic foraminifera assemblage occurring in that sample the discrepancy suggests that this and the other unduly young samples have possibly been contaminated by geological materials with radiogenic sr isotope composition the minimum age of 37 18 ma obtained by 87sr 86sr from a well preserved oyster shell indicates that some of the clasts can be attributed to the deep seated ngimbang formation the dating has been combined with the interpretation of seismic profiles to investigate the stratigraphy of inferred carbonates below lusi and the prg 1 well located some kilometres to the north east prg 1 borehole data are also integrated and discussed in this study the obtained results reveal multiple implications a the tuban and kujung formations are overlapping at lusi site b the lusi feeder conduit brecciated and mobilized to the surface carbonate lithologies buried as deep as possibly 3 8 km as well as even older and deeper seated lithotypes from the ngimbang formation c since the deeper carbonate samples erupted in 2006 belong to the typically not overpressured kujung formation an additional overpressure generated from deeper units ngimbang formation would be required to force these fragments to surface

characteristics of the active xiaojiang fault zone in yunnan china a slip boundary for the southeastward escaping sichuan yunnan block of the tibetan plateau abstract the xiaojiang fault zone within the yunnan province china is one of the most active fault zones of the southeastern edge of the tibetan plateau this n s trending 400 km long fault zone defines the southern part of the eastern boundary of the sichuan yunnan block which is escaping southeastward from the tibet plateau and rotating around the eastern himalayan syntaxis the middle section of the fault zone splits into two branches each branch fault consists of several en echelon faults basins of various ages have developed on the step overs between the secondary faults the left lateral strike slip rate along the eastern branch is up to 9 mm a and that on the western branch is 7 mm a more than 10 m 6 historic earthquakes have occurred along the fault zone the largest was the 1833 songming earthquake of m 8 four earthquake rupture zones were discovered along the fault zone 15 trenches have been excavated along every major segment of the fault zone and 4 5 paleoearthquakes have been distinguished along the xiaojiang fault zone the average strong earthquake recurrence interval is 2000 2500 years

significant and vertically coherent seismic anisotropy beneath eastern tibet 1 shear wave splitting measurements using teleseismic sks and skks phases recorded by the indepth iv arrays has revealed a strong upper mantle anisotropic fabric in northeastern tibet with large delay times of up to 2 2 s suggesting that anisotropy exists in both the lithospheric and asthenospheric mantle the coherence among fast polarization orientations of split core phases and the left lateral slip on eastern striking southern striking faults in eastern tibet and the surface deformation fields calculated from both gps observations and quaternary fault slip rates support the idea that left lateral shear strain is the predominant cause of the orientation of the upper mantle petrofabrics we suggest the bending of the eastern himalayan syntaxis around the foundering burma andaman sumatra slab also contributes to the observed seismic anisotropy in the eastern himalayan syntaxis region two plausible competing processes are proposed for the flow of asthenosphere in eastern tibet in the first the deforming lithosphere glides over the passive asthenosphere inducing flow in the asthenospheric mantle in the second the asthenosphere beneath northeastern tibet is squeezed between the advancing indian continental lithosphere and the thick tarim and qaidam lithospheric blocks to the north a westward retreat of the burma slab from eurasia may induce flow that is toroidal and located exclusively around the northern edge of the slab the rotation of fast orientations for stations in the eastern himalayan syntaxis region are consistent with the toroidal flow pattern as well as the rotational deformation of the overlying lithosphere

carbonate shelf evolution during the oligocene to early miocene insights from shelf architecture lithofacies and depositional models of the kujung formation offshore east java indonesia

cenozoic tectonic evolution of asia a preliminary synthesis abstract asia has been a major testing ground for various competing models of continental deformation due to its relatively well understood plate boundary conditions in the cenozoic exceptional exposure of active structures and strain distribution and widespread syn collisional igneous activity as a proxy for the thermal state of the mantle and crust two cenozoic orogens dominate the continent the himalayan tibetan orogen in the east induced by the india asia collision and the turkish iranian caucasus orogen in the west induced by the arabia asia collision the development of the two orogens was accomplished by shortening in the early stage followed by strike slip faulting and extension in the late stage in the himalayan tibetan orogen shortening across two discrete thrust belts at 55 30 ma in southern and northern tibet created a large intracontinental basin the paleo qaidam basin in between subsequent crustal thickening and a possible thermal event in the mantle e g convective removal of central tibetan mantle lithosphere may have raised the elevation of this early intra plateau basin up to 2 3 km to its current height collision between india and asia also caused lateral extrusion of southeast asia between 32 ma and 17 ma the latest stage of the india asia collision was expressed by north trending rifting and the development of trench facing v shaped conjugate strike slip faults in central mongolia central tibet eastern afghanistan and southeast asia in the turkish iranian caucasus orogen early crustal thickening in the orogenic interior began at or prior to 30 20 ma this style of deformation was replaced by strike slip faulting at 15 5 ma associated with further northward penetration of arabia into asia westward extrusion of the anatolia turkey block and rapid extension across the sea of crete and sea of aegean the late stage extension in both orogens was locally related to extensional core complex development the continental margin extension of east asia was developed in two stages initially in a widely distributed zone that has an east west width of 500 800 km during 65 35 ma which was followed by localized extension and opening of back arc basins associated with the development of spreading centers at 32 17 ma e g japan sea or east korea sea bohai bay and south china sea opening of the back arc basins could be induced by 1 rapid eastward migration of the western pacific trench system or 2 oblique subduction of pacific plate beneath asia that had produced a series of en echelon right slip primary shear zones linking with back arc spreading centers oriented obliquely to the strike of the nearby trench since 15 ma the eastern margin of asia became contractional in the east west direction as indicated by the collapse of back arc basins in the western pacific and the development of fold thrust belts along the eastern continental margin coeval with the contraction is widespread east west extension in siberia north china and the tibetan plateau the above observations can be explained by a change in boundary condition along the eastern margin of asia that allowed the thickened asian continent to spread eastward causing east west extension in its trailing edge and east west compression in its leading edge in west asia continental margin extension started at about 25 20 ma in the aegean and cretan regions which was associated with a rapid southward retreat of the hellenic arc the complex evolution of cenozoic deformation in asia may be explained by a combined effect of temporal changes in plate boundary conditions thermal evolution of the upper mantle perturbed by collisional tectonics and the built up of gravitational energy through crustal thickening and thermal heating although the past research in asia has treated the india asia and arabia asia convergence as separate collisional processes their interaction may have controlled the far field cenozoic deformation in asia the most pronounced result of this interaction is the creation of a northeast trending 300 400 km wide and 1500 km long zone of northwest striking right slip faults which extends from the zagros thrust belt in the south to western mongolia in the north and links with the active tian shan and altai shan intracontinental orogens cenozoic deformation and coeval igneous activity spatially overlap with one another in the himalayan tibetan and turkish iranian caucasus orogens a large cenozoic magmatic gap exists between tibet in the south and mongolia in the north where cenozoic deformation has not been associated with any coeval igneous activity finally cenozoic igneous activity is always associated with jurassic cretaceous magmatic arcs suggesting a causal relationship between the early arc magmatism and later syn collisional magmatism

the geological evolution of the tibetan plateau the geological evolution of the tibetan plateau is best viewed in a context broader than the india eurasia collision zone after collision about 50 million years ago crust was shortened in western and central tibet while large fragments of lithosphere moved from the collision zone toward areas of trench rollback in the western pacific and indonesia cessation of rapid pacific trench migration 15 to 20 million years ago coincided with a slowing of fragment extrusion beyond the plateau and probably contributed to the onset of rapid surface uplift and crustal thickening in eastern tibet the latter appear to result from rapid eastward flow of the deep crust probably within crustal channels imaged seismically beneath eastern tibet these events mark a transition to the modern structural system that currently accommodates deformation within tibet

a tectonic model for the tertiary evolution of strike slip faults and rift basins in se asia abstract models for the tertiary evolution of se asia fall into two main types a pure escape tectonics model with no proto south china sea and subduction of proto south china sea oceanic crust beneath borneo a related problem is which if any of the main strike slip faults mae ping three pagodas and aliao shan red river asrr cross sundaland to the nw borneo margin to facilitate continental extrusion recent results investigating strike slip faults rift basins and metamorphic core complexes are reviewed and a revised tectonic model for se asia proposed key points of the new model include 1 the asrr shear zone was mainly active in the eocene oligocene in order to link with extension in the south china sea the asrr was less active during the miocene tens of kilometres of sinistral displacement with minor amounts of south china sea spreading centre extension transferred to the asrr shear zone 2 at least three important regions of metamorphic core complex development affected indochina from the oligocene miocene mogok gneiss belt doi inthanon and doi suthep around the asrr shear zone hence paleogene crustal thickening buoyancy driven crustal collapse and lower crustal flow are important elements of the tertiary evolution of indochina 3 subduction of a proto south china sea oceanic crust during the eocene early miocene is necessary to explain the geological evolution of nw borneo and must be built into any model for the region 4 the eocene oligocene collision of ne india with burma activated extrusion tectonics along the three pagodas mae ping ranong and klong marui faults and right lateral motion along the sumatran subduction zone 5 the only strike slip fault link to the nw borneo margin occurred along the trend of the asrr fault system which passes along strike into a right lateral transform system including the baram line

the basins of sundaland se asia evolution and boundary conditions abstract most of the basins developed in the continental core of se asia sundaland evolved since the late cretaceous in a manner that may be correlated to the conditions of the subduction in the sunda trench by the end of mesozoic times sundaland was an elevated area composed of granite and metamorphic basement on the rims which suffered collapse and incipient extension whereas the central part was stable this promontory was surrounded by a large subduction zone except in the north and was a free boundary in the early cenozoic starting from the palaeogene and following fractures initiated during the india eurasia collision rifting began along large faults mostly n s and nnw sse strike slip which crosscut the whole region the basins remained in a continental fluvio lacustrine or shallow marine environment for a long time and some are marked by extremely stretched crust phu khanh natuna n makassar or even reached the ocean floor spreading stage celebes flores western sundaland was a combination of basin opening and strike slip transpressional deformation the configuration suggests a free boundary particularly to the east trench pull associated with the proto south china sea subduction java sulawesi trench subduction rollback in the early miocene australian blocks reached the sunda subduction zone and imposed local shortening in the south and southeast whereas the western part was free from compression after the indian continent had moved away to the north this suggests an important coupling of the sunda plate with the indo australian plate both to se and nw possibly further west rollback had ceased in the java sumatra subduction zone and compressional stress was being transferred northwards across the plate boundary the internal compression is expressed to the south by shortening which is transmitted as far as the malay basin in the late miocene most of the sunda plate was under compression except the tectonically isolated andaman sea and the damar basins in the pliocene collision north of australia propagated toward the north and west causing subduction reversal and compression in the short lived damar basin docking of the philippine plate confined the eastern side of sundaland and created local compression and uplift such as in nw borneo palawan and taiwan transpressional deformation created extensive folding strike slip faulting and uplift of the central basin and arakan yoma in myanmar minor inversion affected many thailand rift basins all the other basins record subsidence the uplift is responsible for gravity tectonics where thick sediments were accumulated sarawak ne luconia bangladesh wedge

late cretaceous and cenozoic tectono stratigraphic development of the east java sea basin indonesia abstract the east java sea basin is underlain by a metamorphic basement complex subsidence of this basement during the late cretaceous resulted in accumulation of up to 3 km of marine upper cretaceous sediments megasequence 1 contraction and near peneplanation of the upper cretaceous sediments and underlying basement occurred before the middle early eocene producing a regional unconformity which defines the base of megasequence 2 the cenozoic east java sea basin started to form during the early eocene by crustal extension on both planar normal faults and extensionally reactivated cretaceous thrusts normal faulting was pulsed from the early eocene to early oligocene and affected a progressively larger area with time complex structural geometries evolved in response to local extensional reactivation of obliquely orientated pre existing structures the resultant palaeogene fault controlled sub basins were filled with fluvial coastal plain and shelf clastic and carbonate sediments recording an overall transgressive evolution regional subsidence became dominant over fault controlled subsidence during the early oligocene basin fill during this time was dominated by deep marine fine grained clastic sediments a regional unconformity of intra oligocene age is recognized and is overlain by oligocene to lowermost miocene deep water calcareous mudrocks and limestones which locally onlap erosionally truncated eocene rocks the lower eocene to lowermost miocene sediment package comprises megasequence 2 regional inversion of palaeogene sub basins commenced in the early miocene and continues to the present day the syn inversion lower miocene to recent sediments comprise megasequence 3 inversion has resulted from regional contraction and resultant reverse reactivation of palaeogene normal faults and cretaceous thrusts regional subsidence has been continuous during the inversion history resulting in a gradual reversal of depocentre location palaeogene depocentres became neogene highs whereas palaeogene platforms became neogene depocentres miocene deposition during inversion was dominated by the alternation of fine grained carbonate dominated and clastic dominated cycles subsequent pliocene sandstone deposition followed fluvial incision during an early pliocene lowstand the depositional history during the pleistocene to recent records rapid relative sea level changes progradation of clastic and carbonate sediments erosional truncation channelling and slumping the tertiary structural geometrical evolution and preserved sediment distribution can be explained by dominantly dip slip fault movement during the extensional and contractional phases of basin development and deformation basin scale cross sectional geometries similar to classical positive flower structures have evolved by the reverse reactivation of a geometrically complex extensional fault system

field study of a highly active fault zone the xianshuihe fault of southwestern china the xianshuihe fault of western sichuan province china is one of the world s most active faults having produced 4 earthquakes during this century of magnitude 7 along a 350 km length of the fault at least 8 such events have occurred since 1725 in the more limited 150 km long segment including luhuo and daofu major earthquakes in 1904 1923 1973 and 1981 m 7 7 7 6 6 9 were associated with overlapping surficial fault ruptures and with individual left lateral displacements as large as 3 6 m field studies indicate that this high degree of activity is typical of the fault s longer term history the holocene left lateral slip rate on the north western segment of the fault has been 15 5 mm yr decreasing to about 5 mm yr on its southeastern segment based on radiometrically dated offset stream channel and terrace deposits and on offset glacial moraines physiographic features of active faulting are fully as diagrammatic as those of california s san andreas fault mainly because of high altitude preservation and the absence of cultural modification on this eastern margin of the tibetan plateau detailed en echelon tensional and pushup features resulting from surface ruptures in 1973 1955 1923 and 1893 can still be recognized today and new data have been collected bearing on the offsets and fault rupture lengths during these and other events the locations and magnitudes of historic earthquakes suggest that the characteristic earthquake model may apply to the xianshuihe fault obvious geometric segmentation of the fault has controlled the initiation and termination of ruptures in some events whereas segmentation control for others remains obscure based on the historic record repeat times estimated from slip rates and current seismic gaps two segments are particularly likely sites for m 7 earthquakes in the near future the 65 km long segment between daofu and qianning and the 135 km long segment bracketing kangding continuing creep has been documented along some segments of the fault and this together with the high degree of activity and other unique attributes makes the xianshuihe fault one of the most promising sites in the world for earthquake prediction and hazard evaluation studies

subsidence and uplift of sidoarjo east java due to the eruption of the lusi mud volcano 2006 present global positioning system gps and satellite based insar interferometric synthetic aperture radar measurements of the subsidence and uplift of a populated area of sidoarjo east java are due to the eruption of the lusi mud volcano 2006 present these data are the first direct quantitative measurements of deformation due to the growth of a mud volcano edifice the gps data were recorded over periods of a few hours to several months and show that between june 2006 and september 2007 the earth s surface has been subsiding at rates of 0 1 4 cm day maximum rates of subsidence occurred in an area 300 400 m to the northwest of the main mud volcano vent horizontal displacements were 0 03 0 9 cm day and were also towards this area in general uplifts of up to 0 09 cm day were recorded in areas outside of the edifice changes in elevation measured using satellite imagery insar technique provide regional datasets of subsidence and uplift they confirm that during the first year a roughly circular area was undergoing sag like subsidence centered to the northwest of the main vent and that uplift was occurring 3 4 months after the initiation of the eruption due to the movement watukosek fault system subsidence occurred due to the weight of mud and man made dams and the collapse of the overburden due to removal of mud from the subsurface assuming constant rates of subsidence of 4 cm day then in the centre of the edifice there would be up to 44 m of subsidence in 3 years and up to 16 m in 10 years the mud volcano is now in a self organizing state with new fluid conduits forming as a result of the collapse

multiscale estimation of gps velocity fields we present a spherical wavelet based multiscale approach for estimating a spatial velocity field on the sphere from a set of irregularly spaced geodetic displacement observations because the adopted spherical wavelets are analytically differentiable spatial gradient tensor quantities such as dilatation rate strain rate and rotation rate can be directly computed using the same coefficients in a series of synthetic and real examples we illustrate the benefit of themultiscale approach in particular the inherent ability of the method to localize a given deformation field in space and scale as well as to detect outliers in the set of observations this approach has the added benefit of being able to locally match the smallest resolved process to the local spatial density of observations thereby both maximizing the amount of derived information while also allowing the comparison of derived quantities at the same scale but in different regions we also consider the vertical component of the velocity field in our synthetic and real examples showing that in some cases the spatial gradients of the vertical velocity field may constitute a significant part of the deformation this formulation may be easily applied either regionally or globally and is ideally suited as the spatial parametrization used in any automatic time dependent geodetic transient detector

the east java mud volcano 2006 to present an earthquake or drilling trigger abstract on may 29th 2006 a mud volcano later to be named lusi started to form in east java it is still active and has displaced 30 000 people the trigger mechanism for this the world s largest and best known active mud volcano is still the subject of debate trigger mechanisms considered here are a the may 27th 2006 yogyakarta earthquake b the drilling of the nearby banjar panji 1 gas exploration well 150 m away and c a combination of the earthquake and drilling operations we compare the distance and magnitude of the earthquake with the relationship between the distance and magnitude of historical earthquakes that have caused sediment liquefaction or triggered the eruption of mud volcanoes or caused other hydrological responses based on this comparison an earthquake trigger is not expected the static stress changes caused by the rupture of the fault that created the yogyakarta earthquake are a few tens of pascals much smaller than changes in stress caused by tides or variations in barometric pressure at least 22 earthquakes and possibly hundreds likely caused stronger ground shaking at the site of lusi in the past 30 years without causing an eruption the period immediately preceding the eruption was seismically quieter than average and thus there is no evidence that lusi was primed by previous earthquakes we thus rule out an earthquake only trigger the day before the eruption started may 28th 2006 as a result of pulling the drill bit and drill pipe out of the hole there was a significant influx of formation fluid and gas the monitored pressure after the influx in the drill pipe and annulus showed variations typical of the leakage of drilling fluid into the surrounding sedimentary rock strata furthermore we calculate that the pressure at a depth of 1091 m the shallowest depth without any protective steel casing exceeded a critical level after the influx occurred fractures formed due to the excess pressure allowing a fluid gas mud mix to flow to the surface with detailed data from the exploration well we can now identify the specific drilling induced phenomena that caused this man made disaster

the role of the east asian active margin in widespread extensional and strike slip deformation in east asia east asia is a region of widespread deformation dominated by normal and strike slip faults deformation has been interpreted to result from extrusion tectonics related to the india eurasia collision which started in the early eocene in east and se china however deformation started earlier than the collision latest cretaceous to palaeocene suggesting that extrusion tectonics is not the only driving mechanism for east asia deformation it is suggested that the east asian active margin has influenced deformation in east asia significantly along the margin cenozoic back arc extension took place behind several adjoining arcs implying eastward rollback of the subducting slab and collapse of the overriding plate towards the retreating hinge line we show that extension took place along a c 7400 km long stretch of the east asian margin during most of the cenozoic physical models are presented simulating overriding plate collapse and back arc extension the models reproduce important aspects of the strain field in east asia for geometrical and rheological conditions scaled to represent east asia modelling shows that the active margin can be held responsible for deformation in east asia as far west as the baikal rift zone located c 3300 km from the margin

extensional fault systems in sedimentary basins a review of analogue model studies abstract scaled analogue models have provided graphic new insights into the progressive development of extensional fault systems this paper reviews recent results of an on going analogue modelling programme and compares the structural styles in the models with examples of natural extensional fault systems four fundamental model styles scaled to simulate deformation in brittle sedimentary rocks in the upper 10 km of the crust are reviewed extension above a basal detachment which undergoes stretching over a limited are produces an asymmetric rift graben bounded by planar faults and in which the internal deformation is accommodated by rotational domino faults these experimental results are directly comparable to structures found in intracontinental rifts extension above a basal detechment which undergoes extension under the whole model and which has no constraints at the ends produces domino style fault arrays in the pre rift sequence and listric growth faults in the syn rift sequence these results compare with highly extended rift basins and terranes such as the basin and range province usa extension above a simple listric fault produces a characteristic hangingwall roll over and crestal collapse graben system at high values of extension superposed crestal collapse grabens occur and a fan of listric growth faults is developed these structures bear striking similarities to growth faults in progradational delta systems ramp flat listric extensional fault systems using sand mica models produce a characteristic family of structures with an upper roll over crestal collapse system a ramp syncline and reverse fault fold zone and a lower roll over crestal collapse system an example of a ramp flat fault system from the gulf coast usa is presented as a comparison with the analogue model results preliminary results of three dimensional extensional model experiments are presented to illustrate the complexities in such fault systems in all of the experimental models it is found that the geometry of the underlying detachment system exerts fundamental control on structures produced in the hangingwall the analogue models illustrated in this review provide valid geometric and kinematic templates for the progressive evolution of extensional fault systems in sedimentary basins

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

burma plate motion 1 plate motion in the indo burmese arc andaman sumatra region of burma plate is poorly resolved this is mainly due to lack of relevant data and complex tectonics of the region we analyze 1 azimuths of coseismic displacements due to the 2004 sumatra andaman and 2005 nias earthquakes 2 estimates of interseismic deformation in the indo burmese arc andaman sumatra and sagaing fault regions all based on gps measurements 3 long term plate motion rates across sumatra fault system sagaing fault and andaman sea from geomorphological and other geophysical studies and 4 the earthquake focal mechanisms in the region we suggest that the ssw motion of sunda plate with respect to indian plate may be partitioned into the dextral strike slip motion across the sagaing fault in the north and sumatra fault system in south in the back arc region and the arc normal motion across the sumatra subduction zone which becomes oblique in andaman and southern indo burmese arc region and dextral in the northern indo burmese arc region of the fore arc under the rigid plate approximation we estimate a pole for india burma plate pair at 27 1 n 82 1 1 e with an angular velocity of 0 845 0 12 ma and for burma sunda at 22 3 1 1 n 109 3 2 5 e with an angular velocity of 0 67 0 12 ma thus the plate motion in the northern and southern regions of burma plate namely the indo burmese arc and andaman sumatra arc may be explained by a single pole and does not require a boundary between the two

eastward expansion of the tibetan plateau by crustal flow and strain partitioning across faults the tibetan plateau is expanding eastwards but the modes of deformation are poorly understood high resolution seismic images from the region identify localized zones of weak crustal rocks as well as deep faults implying that deformation occurs through a combination of crustal flow and movement of rigid blocks of crust