circulation and transport of water along the western weddell sea margin ocean current temperature and salinity data obtained from the western weddell sea during the austral winter 1992 u s russian drifting ice station experiment ice station weddell 1 isw 1 are used to describe water circulation and transport surface to bottom baroclinic currents were computed by applying the geostrophic approximation to derived density data these were corrected using current measurements obtained from drifting current meter arrays and the resulting total currents were vertically integrated to obtain volume transports transport was found to be northward in the region which encompassed the western boundary current of the cyclonic weddell sea gyre this northward transport increased from south to north by more than a factor of 2 from about 12 106m3 s 1 in the southwestern weddell to about 28 106m3s 1 farther north the increase in northward transport was compensated for by westward flow from the interior of the gyre into the western boundary region about 5 6 106m3s 1 of the northward transport was contained in a 300 500 m thick bottom layer of cold water this layer whose transport increased by about 1 106 m3 s 1 from south to north was identifiable by its water mass characteristics as weddell sea bottom water originating on the southwestern and western shelf regions its north flowing volume was consistent with past estimates of a 1 5 2 106 m3 s 1 production rate coupled with a 300 400 transport increase due to entrainment during downslope flow from the shelves to the deep basin the maximum northernmost northward transport less the bottom water transport is consistent with previous estimates for wind driven transport in the weddell gyre provided that bottom friction and the sea ice influence on wind forcing are taken into consideration

fine structure microstructure and vertical mixing processes in the upper ocean in the western weddell sea the upward flux of heat from the subsurface core of warm deep water wdw to the perennially ice covered sea surface over the continental slope in the western weddell sea is estimated using data obtained during february june 1992 from a drifting ice station through the permanent pycnocline the diapycnal heat flux is estimated to be about 3 w m 2 predominantly because of double diffusive convection there is no evidence that shear driven mixing is important in the pycnocline the estimated mean rate of heat transfer from the mixed layer to the ice is 1 7 w m 2 although peak heat fluxes of up to 15 w m 2 are found during storms it is hypothesized that isopycnal mixing along sloping intrusions also contributes to the loss of heat from the wdw in this region however we are unable to quantify the fluxes associated with this process intrusions occur intermittently throughout this experiment but are most commonly found near the boundary of the warm core current and the shelf modified water to the east these heat fluxes are significantly lower than the basin averaged value of 19 w m 2 fahrbach et al 1994 that is required to balance the heat budget of the weddell gyre other studies suggest that shelf processes to the west of the ice station drift track and more energetic double diffusive convection in the midgyre to the east could account for the difference between our flux estimates for this region and those based on the basin scale heat budget

turbulent mixing near the yermak plateau during the coordinated eastern arctic experiment during the ice camp component of the coordinated eastern arctic experiment cearex in march april 1989 1500 profiles of temperature conductivity and velocity shear microstructure were obtained near the yermak plateau the dominant signal in isopycnal displacements was the diurnal variability near the plateau consistent with the enhanced diurnal currents found in this region previously from the fram iii and fram iv ice camps the dissipation rate of turbulent kinetic energy e reached maximum values of about 10 6 w kg 1 in two distinct regions the surface mixing layer and the pycnocline between 120 and 220 m there was a significant component of diurnal variability in e in each region in the surface layer e was proportional to the cube of the ice relative current speed at 30 m below the ice and it decayed approximately exponentially with increasing depth major mixing events in the pycnocline were correlated with large amplitude short duration isopycnal displacements the lowest dissipation rates were recorded over the deep nansen basin north of the plateau and in the subsurface core of a submesoscale baroclinic eddy in northern fram strait the time averaged vertical eddy diffusivity near the slope of the plateau was about 2 5 10 4 m2 s 1 in the pycnocline above the atlantic layer implying an upward heat flux of 25 w m 2 although only a small fraction of this heat reached the base of the mixed layer the results confirm that current interactions with steep topography are critical to the modification of atlantic water in the eastern arctic ocean

extension during continental convergence with application to the tibetan plateau the tibetan plateau is the product of crustal thickening caused by the collision between india and asia and is the largest active example of extensional tectonics in a zone of continental collision throughout most of the tertiary the tectonics of the plateau were dominated by north south shortening a significant proportion of which took place on east west striking thrust faults for the last 5 m y or so the plateau has been thinning by the mechanism of extension on north south trending normal faults previous investigations of the collision have been able to account for the large scale features of the tertiary deformation but have failed to explain the transition in the late tertiary to quaternary strain rate field of the plateau from north south compression to east west extension the transition could in principle be effected by a reduction in the rate of convergence between india and asia or by a uniform reduction in strength of the whole continental lithosphere of asia it could not however be effected by a reduction in strength of the elevated region alone this produces increased compressional strain rates in the weakened zone an alternative explanation for the transition to extension comes from considering the thermal evolution of thickened continental lithosphere the lower part of the lithosphere consists of a thermal boundary layer which when thickened by horizontal shortening is colder and denser than its surroundings convective instability of the thickened thermal boundary layer and its replacement by hot asthenosphere would rapidly raise the surface elevation and gravitational potential energy of the overlying part of the lithosphere the convective instability would happen in a time brief compared with the collision time scale 50 m y in the case of india and asia but would only occur after there had already been substantial thickening of the lithosphere numerical experiments show that for a range of lithospheric parameters the increase in surface height as much as 2 km and of potential energy 5 to 10 1012 n m 1 resulting from convective instability of the lower lithosphere are sufficient for east west extension to replace north south compression as the dominant feature of the stress field of the tibetan plateau

oil shale sedimentology and geochemistry in cenozoic mae sot basin thailand the intermontane mae sot basin thailand contains carbonate rich oil shales in which oil yield mineralogy and major and trace element geochemistry are related to the rock type higher grade oil shale is significantly enriched in silicate minerals quartz feldspars clays and analcite relative to carbonates and in dolomite relative to calcite couplets of organic rich and mineral rich laminae increase in mean thickness from 0 080 mm to 0 670 mm from high to low grade oil shale the organic material consists mainly of lamalginite and yields up to 341 l of oil mt 81 8 gal ton on retorting fish and vascular plant fragments are the main megafossils mappable oil shale sequences 10 m 33 ft thick are interstratified with marlstone sandstone sequences 70 m 230 ft thick markov chain analysis applied to stratigraphic sequences indicates that low grade oil shale passes gradually into high grade oil shale and vice versa the strata are interpreted as the deposits of extensive fresh to brackish lakes with oil shale sequences formed in perennial stratified lakes and marlstone sandstone sequences formed in shallow perennial lakes and subaerially exposed flats dolomite in the oil shales was authigenic the systematic changes in mineralogy and geochemistry between rock types probably reflect a gradient in redox potential from the center to the margins of the lake sandstone and siltstone beds and some carbonate laminae are interpret d as density flow deposits and form a significant proportion of the sequences the episodic deposition of oil shales reflects changes in lake level within the enclosed basin probably due to climatic fluctuations on a 24 000 to 46 000 year scale

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

heat flux through sea ice in the western weddell sea convective and conductive transfer processes the heat flux through the snow and sea ice cover and at the ice ocean interface were calculated at five sites in the western weddell sea during autumn and early winter 1992 the ocean heat flux averaged 7 2 w m2 from late february to early june and average ice air heat flux in the second year floes depended on the depth of the snow cover and ranged from 9 to 17 0 8 w m2 in late february three of the five sites had an ice surface which was depressed below sea level resulting at two of the sites in a partially flooded snow cover and a slush layer at the snow ice interface as this slush layer froze to form snow ice the dense brine which was rejected flowed out through brine drainage channels and was replaced by lower salinity nutrient rich seawater from the ocean upper layer we estimate that about half of the second year ice in the region was covered with this slush layer early in the winter as the slush layer froze over a 2 to 3 week period the convection within the ice transported salt from the ice to the upper ocean and increased total heat flux through the overlying ice and snow cover on an area wide basis approximately 10 cm of snow ice growth occurred within second year pack ice primarily during a 2 to 3 week period in february and march this ice growth near the surface of the ice provides a salt flux to the upper ocean equivalent to 5 cm of ice growth despite the thick about 1 m ice cover in addition to the ice growth in the small area less than 5 open water regions

diurnal tides near the yermak plateau recent current measurements obtained from drifting platforms over the yermak plateau in the eastern arctic ocean confirm that the plateau is a region of greatly enhanced diurnal tidal currents modulation of the diurnal currents is clearly related to the plateau topography as has been previously proposed we show however that temporal variability due to spring neap modulation must also be considered in interpreting records from drifting platforms we review simple models of tidal current amplification in this region and find that the previous assumption of near resonant barotropic shelf waves propagating around the plateau s entire perimeter is inconsistent with the true topography instead we propose that the diurnal variability is due to topographic shelf waves at the k1 and o1 tidal frequencies that are generated at points on the plateau s perimeter where the waves group velocities are near zero observed cross slope variations in ellipticity orientation and magnitude of tidal oscillations are consistent with the presence of topographic waves generated in this manner the topographic enhancement of the diurnal tide near the yermak plateau has important consequences for the sea ice cover hydrography and general circulation of this region for example the stress divergence applied by the tidal currents at the ice base greatly exceeds the typical divergence of the surface wind stress and tides may therefore be important to local ice deformation the strong cross slope tidal currents also appear to be responsible for the production of high frequency internal wave packets which are associated with energetic diapycnal mixing in the pycnocline we also consider the possibility that tidal rectification is responsible for a mean current transporting atlantic water clockwise around the plateau

calculating tidal current profiles from vertically integrated models near the critical latitude in the barents sea the method of extracting current profiles from vertically integrated hydrodynamic models is extended to incorporate more general boundary conditions and the consistency of the method is investigated using this method the tidal current profiles for semidiurnal and diurnal constituents are studied in high latitudes near the critical latitude where the coriolis frequency equals the tidal frequency for the semidiurnal tide the current profiles are computed at stations in the barents sea where current measurements exist at up to six different depths the observation stations are located close to the critical latitude for the largest semidiurnal constituents and the current profiles are therefore sensitive to variations of magnitude and vertical distribution of the eddy viscosity at this latitude the current is strongly depth dependent and in deep water the tidal ellipse changes direction of rotation near the seabed at four of the stations there are under ice measurements and the effects of an ice covered ocean upon the tidal current profiles are also investigated

turbulent mixing under drifting pack ice in the weddell sea by providing cold dense water that sinks and mixes to fill the abyssal world ocean high latitude air sea ice interaction is the main conduit through which the deep ocean communicates with the rest of the climate system a key element in modeling and predicting oceanic impact on climate is understanding the processes that control the near surface exchange of heat salt and momentum in 1992 the united states russian ice station weddell 1 traversed the western weddell sea during the onset of winter providing a platform for direct measurement of turbulent heat flux and reynolds stress in the upper ocean data from a storm early in the drift indicated i well formed ekman spirals in both velocity and turbulent stress ii high correlation between mixed layer heat flux and temperature gradients iii that eddy viscosity and eddy thermal diffusivity were similar about 0 02 square meters per second and iv that the significant turbulent length scale 2 to 3 meters through most of the boundary layer was proportional to the wavelength at the peak in the weighted vertical velocity spectrum the measurements were consistent with a simple model in which the bulk eddy viscosity in the neutrally buoyant mixed layer is proportional to kinematic boundary stress divided by the coriolis parameter

the red river fault system in the tonkin gulf vietnam abstract the red river fault system in the tonkin gulf offshore haiphong was studied using seismic profiles calibrated by deep wells well characterised left lateral strike slip occurred continuously within a narrow 30 km wide zone southwest of the vinh minh fault between 30 ma and 5 5 ma however the corresponding amount of offset probably does not exceed a few tens of kilometres no sign of post 5 5 ma right lateral motion can be detected prior to 30 ma there is a widespread extension in a wider 100 km wide zone which could be related to a significant amount of left lateral motion the motion of the fault splays to the northeast of the vinh minh fault prior to 30 ma was absorbed in the rifting of the gulf of beibu a 15 5 ma unconformity separates the transtensional regime from a later transpresional regime this 15 5 ma date coincides with the cessation of sea floor spreading in the south china sea

late cenozoic basalt and gabbro in the subsurface in the phetchabun basin thailand implications for the southeast asian volcanic province abstract fragments of basaltic and gabbroic rocks were obtained in cuttings from 15 exploration wells in the na sanun area of the wichian buri sub basin of the phetchabun basin in central thailand the samples represent flows and sills in lacustrine and fluvial sedimentary rocks of the lower to mid miocene wichian buri group mafic igneous units were identified in the sections based on their typically high amplitude seismic reflections confirmed by the examination of several hundred well cuttings and magnetic susceptibility measurements cross sections of the sub basin were constructed on the basis of previously published subsurface interpretations seismic and well data and petrological observations basaltic flows a b e and f have ages of ca 2 ma 16 ma 24 ma and 18 ma based on inferred stratigraphic position gabbroic sill c and dioritic sill g are inferred to be correlative at ca 11 6 ma and differ petrologically from ca 12 8 ma gabbroic sill d major minerals in both basaltic and gabbroic samples are plagioclase ca an50 anorthoclase and augite with pervasive alteration to na and ca zeolite minerals and analcime leucodioritic sill g also contains amphibole and high ti phlogopite overall the rocks show within plate tholeiitic to alkalic characteristics and show similarities to basaltic surface outcrops of similar ages in the wichian buri lop buri area no evidence was seen in the subsurface for the andesitic to rhyolitic rocks of similar ages that occur at surface but their presence cannot be precluded based on our limited data

a stratigraphic case history using three dimensional seismic data in the gulf of thailand a three dimensional marine seismic survey was conducted in the gulf of thailand to aid in the development of a gas field indicated by three wildcat wells the results and interpretation reported previously demonstrated improved fault resolution and better structural definition five successful appraisal wells have now been drilled and these show that most of the sands have limited extent widespread character changes in the seismic data also support stratigraphic variations in many of the sands several new methods of 3d stratigraphic interpretation have been developed while investigating the depositional history of this area anomalous seismic amplitudes tied to sands penetrated by wells and mapped from seiscroptm horizontal sections in time and depth have indicated the distribution of bars and channels horizon seiscrop sections each sliced through a single bed have been used to delineate these depositional features directly g logtm sections displaying seismic logs derived by rigorous wave equation inversion confirm the existence of these features sands greater than 10 m thick have proved mappable

sea level variations in the western mediterranean studied by a numerical tidal model of the strait of gibraltar aspects of the sea level changes in the western mediterranean sea are investigated using a numerical tidal model of the strait of gibraltar as a prerequisite the performance of this model that is a two dimensional nonlinear two layer boundary fitted coordinate numerical model based on the hydrostatic approximation on an f plane is assessed in the simulation of mean and tidal circulation of the strait of gibraltar the model is forced by imposing mean interface and surface displacements as well as m2 s2 o1 and k1 tidal components along the atlantic and mediterranean model open boundaries model results are compared with observations and with results obtained from a tidal inverse model for the eastern entrance of the strait of gibraltar in general good agreement is found a sensitivity study performed by varying different model parameters shows that the model behaves reasonably well in the simulation of the averaged circulation the model is then used to investigate the climatological sensitivity of the simulated dynamics in the strait of gibraltar to changes in the density difference between atlantic and mediterranean waters for this purpose given a certain density difference between atlantic and mediterranean waters the authors iteratively searched for that sea level drop between the atlantic and the mediterranean that fulfills the mass balance of the mediterranean it is found that an increase of the density difference leads to an increase of the exchange flow and to an increase of the sea level drop between the two basins a trend in the sea level drop of o 1 cm yr21 such as the one observed between 1994 and 1997 is explained by the model as the result of a trend of o 10 24 yr21 in the relative density difference between the mediterranean and atlantic waters the observed north south asymmetry in this trend is also captured by the model and it is found to arise from changes in the along strait velocity results suggest that the dynamics within the strait of gibraltar cannot be neglected when sea level changes in the western mediterranean basin are investigated

internal waves in the arctic ocean comparison with lower latitude observations abstract a thermistor chain was moored below the pack ice from 50 150 m in the arctic ocean for five days in 1981 oscillations in temperature are attributed to the vertical dispalcement of internal waves the spectral shape of isotherm dispalcement is consistent with the garrett munk model and other internal wave observations but the spectral level is significantly lower other observations from the arctic ocean also exhibit lower internal wave energy when compared with historical data from lower latitudes the lower energy may be related to the unique generation and dissipation mechanisms present in the ice covered arctic ocean significant peaks in vertical coherence occur at 0 81 and 2 6 cph the peak at 2 6 cph coincides approximately with the high frequency spectral cutoff near the local buoyancy frequency this feature has been observed in many other internal wave experiments the coherent oscillations at 0 81 cph exhibit a node in vertical dispalcement at 75 100 m this is consistent with either

internal tides and baroclinicity in the southern weddell sea 1 model description near the continental shelf break in the southern weddell sea warm deep water and western shelf water meet mixing mechanisms such as internal tides have the potential to mix these water masses and form antarctic bottom water a modified version of the princeton ocean model was utilized to investigate the internal tidal fields generated by the interaction of the m 2 barotropic tide with topography for transects across the continental shelf and slope in the southern weddell sea internal tides were generated over the upper continental slope as predicted by linear internal wave theory although the essentially two dimensional domain resulted in differences between the model elevations and the observations exceeding the observational uncertainties the cross slope velocities agreed well with differences less than the uncertainties for 78 of the existing observations

baroclinic instability of density current along a sloping bottom and the associated transport process numerical experiments with a three dimensional nonhydrostatic ocean model have been carried out to investigate the dynamic processes of downslope density current and associated transport of dense water focusing on the effects of bottom slope for the range of slope inclination s from 0 to 0 04 bottom slope has two effects on baroclinic instability of the flow one is the stabilizing effect due to the topographic effect and to offshoreward increase in water depth the other is the destabilizing effect due to steepened inclination of isopycnal surface which increases available potential energy since the destabilizing effect over the upper slope overcomes the stabilizing one in the early stage unstable waves develop more rapidly with increasing s nonlinear energy conversion due to reynolds stresses also affects the flow stability and then the growth rate of instability increases linearly with s in this stage after the unstable waves have finite amplitudes in the mature stage the stabilizing effect of bottom slope becomes dominant especially over the lower slope thus vigorous unstable eddies are confined to the upper slope region in steep slope cases while they cover the whole slope region in gentle slope cases and this difference in the eddy field causes a drastic change in downslope transport of dense water in gentle slope cases efficiency of the transport becomes higher with increasing s since the destabilizing effect overcomes the stabilizing one as a whole on the contrary the efficiency becomes lower with increasing s in steep slope cases since the stabilizing effect surpasses the destabilizing one as a result the most effective transport is realized in the case with s 0 005 although the transport due to eddies in steep slope cases becomes weak over the lower slope it is still larger than that due to the bottom ekman current since the eddy transport occurs in the bottom layer with a thickness of 100 200 m which is 4 8 times the ekman layer thickness

recent sea level change in the mediterranean sea revealed by topex poseidon satellite altimetry using altimetry data of the topex poseidon satellite available since early 1993 we show that the eastern mediterranean sea level has been continuously rising during 1993 1999 at a rate up to 20 mm yr southeast of crete sea level rise is also observed in the algerian provencal basin as well as in the tyrrhenian and adriatic seas the north ionian sea on the other hand shows an opposite trend i e a sea level drop during the past seven years sea surface temperature trends are strongly correlated to sea level trends indicating that at least part of the observed sea level change has a thermal origin the recent mediterranean sea level rise observed by topex poseidon may be related to the warming trends reported from hydrographic cruises in the intermediate and deep waters of the eastern basin since the early 1990s and of the western basin since the 1960s

cretaceous cenozoic tectonic events in the western myanmar burma assam region correlation of late mesozoic mafic and ophiolitic rocks suggests that in the late lower cretaceous a northeasterly facing mafic arc was emplaced onto southeast borneo western sumatra western myanmar burma then 1100 km south of its present position the mogok belt of myanmar and the denqen bangong co ophiolite zone in tibet all then situated on the southwestern margin of asia reversal in tectonic polarity and eastward subduction generated a late cretaceous magmatic arc in western myanmar and sumatra and its continuation through the mogok belt into the gandise batholith of tibet magmatism interrupted in the latest cretaceous probably resumed in the western myanmar tibet and sumatra arc segments in the early palaeogene it was again interrupted in the mid eocene when an east vergent ophiolite nappe overrode the indo burman ranges deforming lower eocene turbidites derived from the magmatic arc to the east following renewed northward and eastward subduction of ocean floor in the latest eocene india collided with northern myanmar and with tibet along a suture south of the jurassic triassic flysch and adjacent yarlung ophiolite in the mogok segment of the late cretaceous arc crust thickened in the early cretaceous orogeny underwent extension to form a metamorphic core complex as myanmar west of the sagaing fault moved northward more than half of this northward movement preceded the well documented 450 km of post early miocene dextral displacement on the sagaing fault and related spreading in the andaman sea generation of late cretaceous to early eocene i and s type granites in and east of the mogok belt was related either to crustal shortening or more probably to subsequent extension in the mogok belt

coastal sea level rise in southern europe and the nonclimate contribution of vertical land motion 1 in this study we extend the advanced approach of combining tide gauge and satellite altimetry data with supplemental equations from adjacent tide gauge records of at least 30 years of common data to investigate the relative importance of the nonclimate contribution of vertical land movement to the observed rates of sea level change along the coasts of southern europe the sensitivity tests proved that the advanced approach is robust and accurate at the submillimeter per year level of around 0 4 mm yr 1 in estimating rates of vertical land movements it enabled identifying stations displaying large rates of vertical land movements that must be taken into account when predicting future sea level rise and appraising the exposure to its impacts on populations and assets the average rate of coastal climate related sea level rise in the mediterranean sea was consequently revisited to be of 1 7 mm yr 1 over the past century whereas the atlantic northern iberian coast revealed a significant high rate of sea level rise in excess of 3 4 mm yr 1 for the past 70 years future work should consider applying this powerful approach to other geographic contexts as a useful source of supplementary data for geodynamic studies

cenozoic plate reconstruction of southeast asia abstract the india eurasia collision alone set up a series of chain reactions and caused the formation and destruction of sedimentary basins within the domain of the collision belt changes in the rate and angle of convergence between the india and eurasia plates reflect different stages of tectonic development in southeast asia for example extrusion of the indochina block induced the consumption of the pre existing proto south china sea along northeastern kalimantan and led to the eventual opening of the south china sea along the south china margin subsequent motions of the sino burma thailand malay peninsula sumatra and kalimantan blocks have produced a succession of basins stretching from north sumatra to central thailand and on to the natuna area we present reconstructions of the southeast asia region at 60 ma 50 ma 40 ma 30 ma 20 ma 15 ma 10 ma and 5 ma it is clear from the reconstructions that the impact between greater india and southeast asia took place in the northwestern part of southeast asia the duration for the impact was probably from the middle eocene to early miocene this timing is in good agreement with the dating of the main red river fault motion wu et al 1989 scharer et al 1990 since the impact between greater india and southeast asia was basically west of the burma block there is no reason to assume that the sumatra malay peninsula and kalimantan should extrude to the southeast first along the left laterally displaced mae ping and three pagodas fault zones as suggested by peltzer and tapponnier 1988 if the opening of the central thailand basins the gulf of thailand and the malay basin are taken into consideration a dextral megashear zone is required to compensate the relative motion between indochina and the malay peninsula this dextral megashear zone might even extend into western kalimantan and serve as a boundary between the indochina block and kalimantan

right lateral shear along the northwest pacific margin and the india eurasia collision right lateral shear along the eastern margin of asia from the eocene to the present has led to the opening of pull apart basins intracontinental such as the bohai basin or oceanic such as the japan sea we suggest in this paper that this right lateral shear is a consequence of indentation of asia by india as in small scale analog experiments we conclude that antithetic wrench faults accommodate the counterclockwise rotation of large domino blocks between two major left lateral shear zones tien shan baikal stanovoy for the northern one and qin ling for the southern one we discuss the compatibility of this mechanism which involves a rather small amount of extrusion with the fast eastward expulsion described for southeast asia we re emphasize the role played in the opening of marginal basins by the pacific subduction as a free boundary to the east

subduction in the indo burma region is it still active the indo burma region which includes longitude 92 96 e latitude 20 26 n is a subduction zone where the indian plate underthrusts the south eastern asian plate but the nature of subduction is complex i examine here the distribution of the p t and b axes of 37 earthquakes the time period 1977 1995 depths 0 153 km and magnitudes mb 4 8 6 8 with respect to the geometry of the wadati benioif zone the analysis shows that the t axes are clustered close to the down dip direction of the subducting slab implying a predominant down dip tensional stress regime within the slab which is typical of intermediate depth seismicity of active subduction zones these results suggest that the subduction in the indo burma region is possibly active

oblique plate convergence slip vectors and forearc deformation slip vectors from thrust earthquakes at subduction zones where convergence is oblique to the trench often point between the directions of relative plate convergence and normal to the trench axis suggesting that oblique convergence is taken up by partial decoupling decoupling means that a component of arc parallel motion of the leading edge of the upper plate results in less oblique thrusting at the trench partial decoupling is modeled by partitioning of oblique convergence into slip on thrust and strike slip faults that are parallel to the trench and to each other and starting with a force equilibrium condition a relationship between the obliquity and the earthquake slip vector orientation is derived assuming that either fault slips when shear stress on it reaches a yield stress oblique slip parallel to the plate vector should occur on the thrust fault when obliquity is smaller than a critical angle for obliquity at or greater than this angle the stress on the strike slip fault is large enough to start it slipping and when both faults are active the arc parallel motion of the forearc deflects the slip vector back toward the trench normal if we assume that continued slip on either fault occurs at constant stress but the two faults can be at different stresses the slip vector will maintain a constant angle relative to the trench normal even when obliquity is larger than the critical angle this limiting angle of the slip vector called max measured relative to the trench normal is simply the arcsine of the ratio of the shear forces resisting slip on the strike slip and thrust faults a consequence is that when the obliquity exceeds max the slip vectors on the thrust fault are sensitive only to the thrust fault orientation and contain no information about the convergence direction between the plates slip vectors at the java trench southwest of sumatra show the relationship clearly with max 20 5 while slip vectors at the aleutian trench show the relationship less clearly with max 25 to 45 the greater angle at the aleutian trench suggests that the upper plate is stronger in the aleutian arc relative to the thrust fault than in the sumatran arc consistent with the sumatran arc being continental and having a well developed strike slip fault while the aleutian arc is oceanic and without a clear transcurrent fault slip vectors at the philippine trench which like sumatra has a large strike slip fault inboard of it tend to stay within 25 of the trench normal when obliquity is as large as 50 if obliquity exceeds max and continues to increase along a subduction zone the rate of motion of the forearc relative to the upper plate will vary with obliquity in which case the forearc sliver should extend or contract parallel to the arc from the geometry of modern island arcs arc parallel extension should be the more common and has been hypothesized for both sumatra and the aleutians on the basis of earthquake slip vectors and for these and other arcs from geological observations from estimates of max and the arc parallel gradients in obliquity arc parallel strain rates are estimated to be 1 to 3 10 8 yr for the sumatran forearc 2 to 6 10 8 yr for the aleutian forearc and 0 3 to 3 10 8 yr for the philippine forearc oblique convergence and subsequent arc parallel extension if accompanied by crustal thinning may provide an important yet little appreciated mechanism for bringing high grade metamorphic rocks to the surface of subduction complexes

combined escape tectonics and subduction rollback back arc extension a model for the evolution of tertiary rift basins in thailand malaysia and laos the tertiary rift basins of thailand and adjacent countries show considerable variability in the timing of rift initiation termination the timing and magnitude of thermal subsidence and the timing and intensity of inversion episodes the rift basins developed on continental blocks that were extruded southeastwards hence their development must be tied into himalayan extrusion tectonics current tectonic models propose that the tertiary basins opened up as pull apart basins associated with strike slip faults published geochronology of strike slip fault zone rocks mapping of fault patterns in the tertiary basins and mapped releasing restraining bend geometries all indicate that in thailand major sinistral strike slip motion ceased at about 30 ma prior to the formation of most rift basins the thailand the effects of later dextral slip were minor and probably a result of reactivation during episodes of inversion during nw se to ne sw himalayan compression dextral slip was not responsible for opening most of the rift basins in thailand an alternative mechanism to open the rift basins is subduction rollback of the indian plate to the west of thailand it is proposed that subuction rollback can help explain some of the characteristics of the rift basins such as non uniform lithospheric extension deep sag basins and the diachronous onset and termination of rifting

development of cenozoic basins in thailand abstract there are over 60 cenozoic basins distributed in various parts of thailand both onshore and offshore these basins are mainly n s trending half grabens or grabens and most were initiated in the late oligocene the structural framework of the basins is generally governed by n s trending extensional faults which are spatially related to the movement of the nw se and ne sw trending strike slip faults that have been active since the oligocene the nw se faults are the principal dextral strike slip faults whereas the ne sw faults are the conjugate sinistral strike slip faults the collision of the india craton with southern asia since 40 50 ma caused clockwise rotation of southeast asia and movements on the strike slip faults with the associated development of cenozoic basins in this region four major cenozoic basins mergui pattani malay and phitsanulok contain up to 8000 m of sediments generally the cenozoic fills are continental sediments except in the mergui basin in the andaman sea where the sedimentary fill is mainly marine sediments fluviatile with occasional lacustrine deposits were prominent in the gulf of thailand and onshore basins during the oligocene to early miocene from early to middle miocene widespread perennial lake conditions were well developed in the onshore basins and in the western graben area of the gulf of thailand a change in tectonic and or climatic conditions took place in the middle to late miocene times resulting in the cessation of perennial lake conditions and development of a regional unconformity

sea level changes from topex poseidon altimetry and tide gauges and vertical crustal motions from doris sea level difference topex poseidon minus tide gauge time series have been computed over 1993 1997 at 53 selected gauges sites comparison of these sea level differences with vertical crustal motions derived from the doris space geodesy system at 6 colocated sites shows good consistency at one site the socorro volcanic island a striking correlation is reported between sea level differences and doris height time series the observed trend likely reflects a post eruptive deformation associated with a volcanic eruption that occurred in early 1993 at several other gauge sites the sea level differences present large linear trends possibly bearing evidence of land motion this may be the case at rabaul papua new guinea where a volcanic eruption took place in autumn of 1994 the sea level differences at rabaul show a negative trend from this date likely related to the volcanic event

the role of boundary mixing in the deep ocean recent laboratory studies demonstrate that mixing at the boundaries of stratified and rotating fluids can be described by a relatively simple parameterization these results are applied to the deep ocean and by using available field observations it is argued that mixing at the boundaries can lead to an apparent diapycnal diffusivity in the interior of the deep ocean whose magnitude has an upper bound of 3 10 5 m2 s 1

main differences between thrust belts it is useful to differentiate between thrust belts that are related to east e dipping or west w dipping subduction more precisely these either follow or resist the overall eastward mantle flow detected by the hot spot reference frame because of the overall westward drift of the lithosphere we find in e dipping subduction that the basal decollement underlying the eastern plate reaches the surface and involves deep crustal rocks with w dipping subduction however we find that the basal decollement of the eastern plate is warped as well as subducted consequently thrust belts related to e or ne dipping subduction show conspicuous structural and morphologic relief involve deep crustal rocks and are associated with shallow foredeeps on the other hand thrust belts related to w or sw dipping subduction show relatively low structural and morphological relief involve only shallow upper crustal rocks and are associated with deep foredeeps as well as back arc extension the accretionary wedge foredeep back arc basin association is visualized as an overall eastward propagating tectonic wave the accretionary wedge forms in the frontal parts and generally below sea level this is followed by forward migrating extension that cuts the earlier accretionary wedge typically such a system occurs in the context of overall w dipping subduction and is characterized by an arcuate shape e g carpathians apennines barbados etc along the branches of the arc external transpression and internal transtension co exist but with different sense i e sinistral transpression contrasting with dextral transtension we also observe that with w dipping subduction the tangent to a pre deformation marker is descending into the foredeep at an angle in the range of 1 10 while with e or ne dipping subduction the same marker would rise towards the hinterland with typical angles of about 5 10 foredeep subsidence is mainly controlled by the load of the thrust sheets in thrust belts due to e or ne dipping subduction and by the roll back of the subduction hinge in accretionary wedges due to w dipping subduction subsidence or uplift rates in the foredeeps and accretionary wedges related to the two different types of subduction are very different providing different p t t paths in the two geodynamic realms the present shape and structure of the thrust belts belonging to one of these two general types may help us in reconstructing the location of thinned lithosphere and basin evolution in the past

structural evolution of the li basin northern thailand exposures in the oligocene to miocene section of coal mines in the li basin of northern thailand show a complex structural evolution the basins formed under approximately east west extension nw to north south striking normal faults are dominant with some east west normal faults also being present but much less frequently episodically compressional and or strike slip events affected the basin creating new east west to ne sw striking thrusts and folds and inverting some normal faults the latest episode of compression formed nw se to north south striking thrusts and folds cross cutting structures reactivation of structures syn sedimentary deformation and unconformites help to constrain the relative timing of structural events at least five episodes of predominantly nnw sse to ne sw oriented compression interrupted the extensional development of the basin the compression was probably related to the escape tectonics of the himalayan orogeny the episodic nature of the compression and extension is inconsistent with either simple strike slip related opening of the rift basins or simple extension the data from the li basin indicate a reappraisal of current tectonic models for the region is necessary

trends and interannual oscillations in the main sea level surface pressure patterns over the mediterranean 1955 1990 the evolution of the main sea level pressure patterns built from rotated principal component analysis rpca over a domain centered on the mediterranean for the period 1955 1990 is examined the annual cycle and the interannual variations are analyzed using singular spectrum analysis ssa and three methods of spectral analysis to detect trends and oscillations in the main patterns the dominant patterns show oscillations characteristic of nao and so this paper shows that nao and so seem to be correlated in a band centered in 6 8 years and that slp behaviour over the region is dominated by qbo which controls the oscillation frequency while nao modulates the amplitudes

modelling the plate driving mechanism this paper demonstrates how sub lithospheric loading gives rise to plate interior stresses and plate boundary forces the stressing of the lithosphere resulting from plume heads in the upper mantle hot spots from low density asthenospheric upwelling beneath ocean ridges and from dense subducting slabs has been modelled by finite element analysis it is first demonstrated how a sub lithospheric load exemplified by a sub continental plume head produces local deviatoric stress in the strong upper lithosphere within a plate interior region it is shown that a 500 km wide region of anomalous density averaging 8 kg m 3 between 100 km and 400 km depths gives rise to a deviatoric tension of 75 mpa in a 20 km thick strong layer forming the upper lithosphere above the deep buoyant load the large stresses in the strong layer are caused by the shear drag and excess pressure exerted by the buoyant load when such a stress system is cut across by a zone or plane of weakness then plate boundary forces and distant plate interior stresses are produced a weak zone beneath the crest is incorporated in a model of a normal ocean ridge and this yields a ridge push force of 2 5 10 12 nm 1 referenced to old ocean floor and deviatoric compression of about 40 mpa in old ocean floor a model of a ridge underlain by an anomalously low density upper mantle plume head yields a much larger ridge push force and large deviatoric compressions of nearly 100 mpa extend into the bordering continents subduction pull slab pull and trench suction of about 4 5 10 12 nm 1 is modelled for a 300 km deep slab separated from the overriding plate by a weak fault and collision pull is shown to result from downbulging lower lithosphere beneath collision mountain ranges

on the characteristics of internal tides and coastal upwelling behaviour in marguerite bay west antarctic peninsula abstract internal waves and coastal upwelling have important roles in both physical oceanography and marine ecosystems via processes such as mixing of water masses and transfer of heat and nutrients to biologically active layers in this paper we use quasi weekly hydrographic profiles and moored records of temperature salinity and water velocity to investigate the nature of internal tides and coastal upwelling behaviour in northern marguerite bay at the western antarctic peninsula within ryder bay a near coastal site in northern marguerite bay atmospherically forced oscillations of the water column with periods around 2 7 days are observed associated with wind induced coastal upwelling and downwelling sea ice cover is seen to play a role in the seasonal suppression of these oscillations significant internal tides also are observed at this site a range of processes are seen to be important in controlling internal tide variability including changes in local stratification and sea ice conditions both diurnal and semidiurnal internal tidal species are observed despite the study region being poleward of the critical latitude for diurnal internal tides this suggests that at least the diurnal internal tides are generated close to the study location and we investigate likely sources

tertiary diachronic extrusion and deformation of western indochina structural and 40ar 39ar evidence from nw thailand the wang chao and three pagodas fault zones cut the western part of the indochina block and run parallel to the red river fault evidence of intense ductile left lateral shear is found in the lansang gneisses which form a 5 km wide elongated core along the wang chao fault zone dating by 40 ar 39 ar shows that such deformation probably terminated around 30 5 ma the wang chao and three pagodas faults offset the north striking lower mesozoic metamorphic and magmatic belt of northern thailand 40 ar 39 ar results suggest that this belt suffered rapid cooling in the tertiary probably around 23 ma these results imply that the extrusion of the southwestern part of indochina occurred in the upper eocene lower oligocene it probably induced rifting in some basins of the gulf of thailand and in the malay and mekong basins in the oligo miocene the continuing penetration of india into asia culminated with the extrusion of all of indochina along the ailao shan red river fault this occurred concurrently with the onset of e w extension more to the south plotting in a geographical reference frame the diachronic time spans of movement on left lateral faults east and southeast of tibet implies that the northward movement of the indian indenter successively initiated new strike slip faults located farther and farther north along its path

shear and strain in santa monica basin by injecting a cloud of sf6 into santa monica basin at a depth of 790 m and observing its vertical spread ledwell and watson 1991 estimate the average diapycnal diffusivity between 750 and 850 m as kp 2 5 10 5 m2 m 1 this diffusivity is higher than inferred from microstructure measurements in the open ocean thermocline for typical internal wave levels gregg and sanford 1988 to examine shear and strain in the basin we dropped expendable current profilers xcps and calculated strain from conductivity temperature and depth ctd casts shear and strain are above the gm76 model spectrum garrett and munk 1975 cairns and williams 1976 and comparisons with published parameterizations indicate more than enough shear variance to account for the high diffusivity reported by ledwell and watson thus the eddy diffusivity in santa monica basin is not at odds with lower values estimated from microstructure measurements in the open ocean but is due to an elevated internal wave field the spectral shapes however differ from typical open ocean spectra

western mediterranean sea level rise changing exchange flow through the strait of gibraltar sea level data from tide gauges and satellite altimetry show a decrease of nearly 40 in the sea level drop between the atlantic and the mediterranean from 1994 to 1997 coming mainly from a rapid rise of western mediterranean sea level by more than 10 mm year a decrease in the sea level difference across the strait coincident with this mediterranean rise indicates that the surface inflow is reduced by an amount dynamically consistent with the change along the strait these secular changes are accompanied by a seasonal cycle in the sea level drop between the atlantic and the mediterranean which indicates a seasonal flipping of hydraulic exchange states in the strait of gibraltar thus we suggest the sea level rise in the mediterranean is a consequence of a changing exchange flow through the strait of gibraltar driven indirectly by changing conditions in the mediterranean

indochina peninsula and the collision of india and eurasia the collision of india with asia results in a rapidly changing stress pattern around both himalayan syntaxes the maximum compressive stress which is north south north of the indenter fans radially through nearly 180 around the syntaxes to accommodate the necessary strike slip motion on the edges of the indenter thus the whole indochina peninsula was swept by the migrating stress and associated strain pattern as the eastern syntaxis moved to the north as a result the maximum horizontal component of the stress field is predicted to have been first oriented east west then north south we propose that this changing stress field controlled the opening of the sedimentary basins and of the south china sea as well as the direction of motion of the major strike slip faults

variability of the large scale general circulation of the mediterranean sea from observations and modelling a review abstract in this paper we present an overview of the most recent findings about the mediterranean sea present day circulation structure both historical observations and numerical model simulations are presented outlining the differences and agreement the model simulations are presented for both an eddy resolving and a coarse resolution numerical model and the results are intercompared the importance of the mesoscales in modifying the large scale flow field is elucidated the critical point is the discovery of the large amplitude interannual variability of the circulation and water mass structure associated with the anomalies of atmospheric forcing over the basin the seasonal variability can be strictly related to changes in heat and momentum fluxes while the interannual variability has a component which is related to the mesoscale field the latter is very intense in the algerian current region and levantine basin but different in structure in the two regions results are shown which confirm the importance of wind driving in establishing the kinetic energy of the flow field by comparing the current transport at the strait of corsica with observations in conclusion the essential characteristics of the present day circulation are associated with the atmospheric forcing and the basin topographic structure results from palaeoceanographic simulations for the last 20 000 years show that changing the atmospheric forcing can cause large changes in the circulation structure which may have affected sapropel formation

observations of internal gravity waves under the arctic pack ice internal gravity waves measured under the arctic pack ice were strikingly different from measurements at lower latitudes the total wave energy integrated over the internal wave frequency band was lower by a factor of 0 03 0 07 and the spectral slope at high frequency was nearly 1 in contrast to the 2 observed at lower latitudes this result has implications for theoretical investigations of the generation evolution and destruction of internal waves and is also important for other processes such as the propagation of sound and the wave induced turbulent diffusion of heat plankton and chemical tracers

paleomagnetism of borneo abstract the paleomagnetism of borneo remains controversial although the preponderance of results both from the island itself and from the surrounding regions suggest that counterclockwise ccw rotation has taken place ccw rotations are seen in minor intrusions in sarawak sabah and kalimantan which increase systematically with the age of the intrusion to a maximum value of 51 8 3 7 the rotation can be no older than 25 ma which is the age of the intrusion showing the maximum rotation the rotation appears to have neared completion by 10 ma similar ccw rotations are seen in sites from peninsular malaysia through borneo to sulawesi the celebes sea and palawan in the philippines but the ages of these rotations are for the most part unknown in mesozoic rocks in kalimantan and sarawak a stronger declination rotation of nearly 90 ccw is recorded at seven sites including sites which pass fold and reversal tests this strong rotation is no older than youngest cretaceous and although seen over a wide region in borneo it is not seen in peninsular malaysia nor in the celebes sea or palawan where only the weaker ccw rotation is seen the widespread occurrence of this strong rotation in western borneo suggests that it is essentially a rigid plate or microplate rotation and not a series of local rotations caused by distributed shear in limited deformation zones the rotation of borneo appears to be a consequence of convergence between the australian and eurasian plates which is accommodated by subduction along the northwest margin of borneo

early summer thermohaline characteristics and mixing in the western weddell sea abstract the ice station polarstern ispol cruise revisited the western weddell sea in late 2004 and obtained a comprehensive set of conductivity temperature depth ctd data this study describes the thermohaline structure and diapycnal mixing environment observed in 2004 and compares them with conditions observed more than a decade earlier hydrographic conditions on the central western weddell sea continental slope off larsen c ice shelf in late winter early spring of 2004 2005 can be described as a well stratified environment with upper layers evidencing relict structures from intense winter near surface vertical fluxes an intermediate depth temperature maximum and a cold near bottom layer marked by patchy property distributions a well developed surface mixed layer isolated from the underlying warm deep water wdw by a pronounced pycnocline and characterized by lack of warming and by minimal sea ice basal melting supports the assumption that upper ocean winter conditions persisted during most of the ispol experiment much of the western weddell sea water column has remained essentially unchanged since 1992 however significant differences were observed in two of the regional water masses the first modified weddell deep water mwdw comprises the permanent pycnocline and was less saline than a decade earlier whereas weddell sea bottom water wsbw was horizontally patchier and colder near bottom temperatures observed in 2004 were the coldest on record for the western weddell sea over the continental slope minimum temperatures were 0 4 and 0 3 c colder than during 1992 1993 respectively the 2004 near bottom temperature salinity characteristics revealed the presence of two different wsbw types whereby a warm fresh layer overlays a colder saltier layer both formed in the western weddell sea the deeper layer may have formed locally as high salinity shelf water hssw that flowed intermittently down the continental slope which is consistent with the observed horizontal patchiness the latter can be associated with the near bottom variability found in powell basin with consequences for the deep water outflow from the weddell sea

sunda java trench kinematics slab window formation and overriding plate deformation since the cretaceous the kinematics and time dependence of back arc extension or compression is one of the most poorly understood aspects of plate tectonics and has nearly exclusively been studied from snapshots of present day observations here we combine absolute and relative plate motions with reconstructions of now subducted ocean floor to analyse subduction kinematics and upper plate strain from geological observations since 80 ma along the 3200 km long sunda java trench one of the largest subduction systems on earth combining plate motions and slab geometries enables us to reconstruct a time dependent slab window beneath sundaland formed through wharton spreading ridge subduction we find that upper plate advance and retreat is the main influence on upper plate strain but subduction of large bathymetric ridges and slab window effects also play a significant and at times dominant role compression in the sundaland back arc region can be linked to advance of the upper plate extension of the sundaland backarc region correlates with two patterns of upper plate motion a retreat of the upper plate and b advance of the upper plate combined with more rapid advance of the sundaland margin due to hinge rollback subduction of large bathymetric ridges causes compression in the upper plate especially wharton ridge subduction underneath sumatra over the period 15 0 ma our reconstructions unravel the evolving geometry of a slab window underlying the java south sumatra region and we propose that decreased mantle wedge viscosities associated with this slab window exacerbated palaeogene extension in the java sea region via active rifting and enabled sumatran continental extension to continue at 50 35 ma when upper plate advance would otherwise have led to compression

bathymetry depth to magnetic basement and sediment thickness estimates from aerogeophysical data over the western weddell basin we estimated the bathymetry and sediment thickness of a remote and difficult to access portion of the antarctic continental margin using aerogeophysical surveying techniques the u s argentina chile aerogeophysical survey collected magnetic and gravity data over the basins surrounding the antarctic peninsula thirty seven of these flight lines were used to estimate bathymetry and depth to magnetic basement for the western weddell basin a wavenumber technique was applied to individual magnetic anomaly profiles in an automated fashion to obtain estimates of the depth to magnetic basement the bathymetric estimates were obtained by admittance inversions of the gravity field the results were then gridded at a 40 km interval for the region 64 w 44 w 73 s and 62 s bathymetric estimates and depth to magnetic basement estimates were differenced at each grid point to obtain a regional estimate of the thickness of nonmagnetic overburden assumed to be sediment subsequent spot measurements of topography in the estimated region of the continental margin generally agree to about 52 m the estimated magnetic basement deepens from the antarctic peninsula margin eastward to a maximum of 10 12 km near 54 w we also postulate the existence of two moderately large basins flanking the eastward continuation of the jason peninsula farther east the basement steps upward with a correspondent thinning of the sedimentary layer along the east coast of the peninsula results agree well with seismic studies on james ross island and magnetotelluric studies on marambio island and the larsen nunatak as well as the british antarctic survey basement estimates from aeromagnetic data this study further demonstrates the utility of combined application of airborne and satellite geophysical techniques in the study of structure and tectonic evolution of continental margins and marine basins

toward an understanding of deep water renewal in the eastern mediterranean abstract this paper presents a scenario for understanding the unexpectedly large changes of deep waters and thermohaline circulation in the eastern mediterranean during the past decade it is demonstrated as a possible deep water renewal mechanism in the eastern mediterranean in a numerical simulation with a high resolution model which has successfully reproduced the observed 1987 and 1995 regimes as shown by the two meteor cruises a budget study of the model simulation has shown that more than 75 of the salt added to the deep layers of the eastern mediterranean could have come from the top 1000 m by a salinity redistribution process triggered by intensive cooling over the aegean sea a water transformation process analysis is carried out in the model simulation to reveal how colder and fresher dense deep water formed in the aegean is turned into the eastern mediterranean deep water emdw as observed surface heat and freshwater fluxes are diagnosed to show the roles of each component during the trans

internal waves and mixing near the kerguelen plateau abstractin the stratified ocean turbulent mixing is primarily attributed to the breaking of internal waves as such internal waves provide a link between large scale forcing and small scale mixing the internal wave field north of the kerguelen plateau is characterized using 914 high resolution hydrographic profiles from novel electromagnetic autonomous profiling explorer em apex floats altogether 46 coherent features are identified in the em apex velocity profiles and interpreted in terms of internal wave kinematics the large number of internal waves analyzed provides a quantitative framework for characterizing spatial variations in the internal wave field and for resolving generation versus propagation dynamics internal waves observed near the kerguelen plateau have a mean vertical wavelength of 200 m a mean horizontal wavelength of 15 km a mean period of 16 h and a mean horizontal group velocity of 3 cm s 1 the internal wave characteristics are dependent on regional dynamics suggesting tha

deep and bottom water of the weddell sea s western rim oceanographic observations from the ice station weddell 1 show that the western rim of the weddell gyre contributes to weddell sea bottom water a thin 300 meters highly oxygenated benthic layer is composed of a low salinity type of bottom water overlying a high salinity component this complex layering disappears near 66 s because of vertical mixing and further inflow from the continental margin the bottom water flowing out of the western rim is a blend of the two types additionally the data show that a narrow band of warmer weddell deep water hugged the continental margin as it flowed into the western rim providing the continental margin with the salt required for bottom water production

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

phanerozoic plate boundaries in mainland se asia the himalayas and tibet recently available geological data on tibet yunnan and burma facilitate recognition of phanerozoic subduction systems and two continental fragments of gondwanaland which extend through mainland se asia a cambrian subduction system and 5 mesozoic early caenozoic collision belts are identified in the region indochina eastern thailand and central tibet accreted to china in the early triassic western se asia and s tibet separated from gondwanaland in the permian or early triassic and collided with asia in the late triassic and the western burma island arc system collided with asia in the jurassic upper triassic flysch and schist in the eastern indoburman ranges were accreted to western burma in the jurassic early cretaceous during eastward subduction and formation of a back arc thrust belt following collision of greater india with arc complexes to the n in the cretaceous and with tibet in the early eocene western burma moved northwards about 450 km along the sagaing namyin ridge thrust transform fault formation of the 3 major belts of tin granites and the porphyry copper deposits in the region took place in specific tectonic settings within the subduction systems and collision belts

ocean heat flux in the central weddell sea during winter abstract seasonal sea ice which plays a pivotal role in air sea interaction in the weddell sea a region of large deep water formation with potential impact on climate depends critically on heat flux from the deep ocean during the austral winter of 1994 an intensive process oriented field program named the antarctic zone flux experiment measured upper ocean turbulent fluxes during two short manned ice drift station experiments near the maud rise seamount region of the weddell sea unmanned data buoys left at the site of the first manned drift provided a season long time series of ice motion mixed layer temperature and salinity plus a truncated high resolution record of temperature within the ice column direct turbulence flux measurements made in the ocean boundary layer during the manned drift stations were extended to the ice ocean interface with a mixing length model and were used to evaluate parameters in bulk expressions for interfacial stress a rossby similarity drag law and ocean to

late cretaceous extension and exhumation of the stong and taku magmatic and metamorphic complexes ne peninsular malaysia fragmentation of large continental areas by post orogenic extension requires favourable geodynamic conditions and frequently occurs along pre existing suture zones or nappe contacts as exemplified by the stong and taku magmatic and metamorphic complexes of northern peninsular malaysia for this case we have employed a field and microstructural kinematic study combined with low temperature thermo chronology to analyse the tectonic and exhumation history the results show that the late palaeozoic triassic indosinian orogeny created successive phases of burial related metamorphism shearing and contractional deformation this orogenic structure was subsequently dismembered during a cretaceous thermal event that culminated in the formation of a large scale late santonian early maastrichtian extensional detachment genetically associated with crustal melting the emplacement of syn kinematic plutons and widespread migmatisation the emplacement of these magmatic rocks led to an array of simultaneously formed structures that document deformation conditions over a wide temperature range represented by amphibolite and greenschist facies mylonites and as well as brittle structures such as cataclastic zones and normal faults that formed during exhumation in the footwall of the detachment the formation of this detachment and a first phase of late cretaceous cooling was followed by renewed eocene oligocene exhumation as evidenced from our fission track ages we infer that an initial cretaceous thermal anomaly was responsible for the formation of an extensional gneiss dome associated with simple shear and rotation of normal faults these cretaceous processes played a critical role in the establishment of the presently observed crustal structure of peninsular malaysia

internal waves in the upper ocean during mile abstract we describe the spectral analysis of temperature and velocity measurements made in the northeast pacific as part of the mixed layer experiment mile and attempt to relate the observed fluctuations to internal wave models of the upper ocean from the inertial frequency to 1 cph there is good agreement between these upper ocean data and typical deep ocean observations as described by the wkb scaled garrett munk model the largest deviations from the garrett munk model occur in the vertical displacement field at high frequency 1 5 cph where there is a spectral peak or shoulder and high vertical coherence these high frequency features in vertical displacement are successfully modeled using a few standing modes and un correlated noise though the velocity spectra are poorly modeled probably because of contamination by mooring motion there are significant temporal fluctuations of the high frequency energy that are not correlated with the local winds but are perhaps associated with the advection of

cenozoic metamorphism along the shan scarp myanmar evidences for ductile shear along the sagaing fault or the northward migration of the eastern himalayan syntaxis the mogok metamorphic belt exposed along the n s trending shan scarp and sagaing fault in the eastern part of myanmar has been regarded as paleozoic to precambrian for a long time new observations in the shan scarp area close to the sagaing fault from thaton in the south to mandalay in the north allowed us to collect samples of high grade metamorphic and intrusive rocks that have been analyzed by 40ar 39ar step heating method the 13 samples we analyzed provide oligocene to lower miocene ages for this metamorphism oriented thin sections and field observations suggest that this metamorphism was caused by a nnw sse to n s ductile extension therefore we suggest that this metamorphism is not directly related to the sagaing fault but could be instead related to the northward migration of the eastern himalayan syntaxis characterized by crustal thinning resulting from the india asia oblique collision

observation of sub inertial internal tides in mcmurdo sound antarctica 1 mcmurdo sound antarctica at 78 s is poleward of the critical latitudes for both diurnal and semi diurnal internal tides which are respectively 30 s and 75 s yet fieldwork during april 2003 and november 2004 observed energy at both frequencies high temporal resolution density profiles in april 2003 and mooring observations at 240 m depth in november 2004 show a diurnal internal tide with displacements of up to 12 m the horizontal decay length scales for diurnal evanescent internal tides indicate that they were locally generated the november 2004 mooring observations also show a semi diurnal tide with displacements up to 12 m although some of the energy in these waves could be baroclinic inertial motion which has a similar frequency at this latitude the semi diurnal internal waves have a larger decay length scale than the diurnal internal waves so are not necessarily locally generated

mixing in the stratified interface of the faroe bank channel overflow the role of transverse circulation and internal waves mixing in the stratified interface of the faroe bank channel overflow the role of transverse circulationand internal waves

diurnal shelf waves in the southern weddell sea abstract strong evidence is presented for the existence of barotropic shelf waves at diurnal frequencies in the shelf break region of the southern weddell sea rotary spectra from long term current meter records on the slope at the shelf break and on the shelf show the same rotational sense as that predicted by a barotropic model phase speeds of the zero mode shelf waves calculated from tidal analysis and rotary coherencies of current meter pairs oriented in an along shelf direction are in the same range as that predicted by barotropic theory except for the o1 constituents the weak stratisfication of the weddell sea in the region of the slope results in nearly barotropic motion at diurnal frequencies the anomalous behavior of the o1 constituent could not be explained

aspects of reservoir geology and production behavior of sirikit oil field thailand an integrated study using well and 3 d seismic data the sirikit oil field lies in the phitsanulok basin one of a series of tertiary rift related structures in central and northern thailand the tectonic history of the area is complex the original extensional half graben was deformed during deposition of the upper reservoir sequence by left lateral strike slip faulting careful interpretation of a three dimensional seismic data set has resulted in the reliable mapping of seismic markers detailed correlation of well logs based on field wide acoustically soft lacustrine claystone markers confirmed a lacustrine deltaic reservoir geologic model derived from core analyses the sirikit deltas are of constructive lobate type with sheetlike mouth bar bay mouth bar reservoir sandstone geometries interpretation of seismic horizon seiscrops amplitude maps of mapped seismic horizons has refined the understanding of the complex local reservoir structure subtle amplitude anomalies interpreted as small displacement faults are visible on horizon seiscrop maps these faults may reduce the drainage area inferred from log correlations the resolution of small dislocations and flexures by seiscrop analysis may apply to well targeting production decline rates are variable in the sirikit wells showing no simple relationship to the perforated reservoir thickness the geologic model explains this behavior in terms of effective drainage area wells perforated in thin sheet sandstones commonly have lower decline rates than those completed in thicker better reservoir quality but isolated channel sandstones

a statistical description of temperature finestructure in the presence of internal waves abstract we have developed a statistical model describing a random field of internal waves passively oscillating a random locally horizontally uniform temperature finestructure here we define finestructure to be non internal wavelike temperature fluctuations of any vertical scale caused by phenomena such as horizontal intrusions or geostrophic eddies the model allows one to examine the effects of finestructure upon all relevant measurable statistical quantities of the temperature field as a function of the vertical scale of the finestructure also the effects of the time variation of the finestructure itself are considered the model was fit to data obtained during the 3 week mid ocean acoustic transmission experiment mate in summer 1977 new cobb seamount in the northeastern pacific various spectra and coherences estimated from temperature time series and vertical profiles were used to make an assessment of the finestructure as well as establish the consistency of the model temperature variance me

on the importance of leads in sea ice to the energy balance and ice formation in the weddell sea for a considerable coverage the energy balance of and ice formation by leads in sea ice in the weddell sea are evaluated on the basis of data obtained from drifting buoys for the winter periods from 1986 to 1994 and by using a kinematic thermodynamic sea ice model the net heat flux is defined as the sum total of radiative and turbulent fluxes for thin ice the net turbulent flux is 3 4 times the net radiative flux the contribution of the net heat flux through open and refrozen leads to the total net heat flux through sea ice is twice as large as the area contribution of open and refrozen leads to the total area covered with sea ice in the eastern and central parts of the weddell sea leads contribute some 30 to the total energy flux from the ocean to the atmosphere this flux increases from 10 15 mbox w m 2 in the eastern and central weddell sea regions to 30 mbox w m 2 in the western part of the weddell sea where leads contribute more than 80 of the total net energy transfer the increase is mainly due to the colder and windier atmosphere in connection with the higher variability of the ice motion in the diurnal andsemidiurnal band in the western weddell sea the contribution of leads in winter ice formation exceeds 50 in the whole of the weddell sea monthly area weighted ice growth is 10 15 cm in the east and up to 30 mbox cm over the western continental shelf region in the western part of the weddell sea tidal and inertial motions in the diurnal and semidiurnal bands enhance lead formation and thus contribute 7 to total net heat flux 12 to ice formation and 23 to the salt mass released during ice growth the results are used to assess quantitatively the importance of leads to the interaction of the ocean the sea ice and the atmosphere

internal waves and tides in the western weddell sea observations from ice station weddell the upper ocean current and temperature fields in the western weddell sea were measured from the drifting pack ice at ice station weddell 1 isw and nearby sites using a vertical profiler and an array of moored sensors in january june 1992 these data document the structure and variability of the internal gravity wave field and tidal currents in this remote region the variance of the internal wave continuum frequency n at isw was 0 2 0 6 of the garrett munk gm universal level for the first 60 days increasing to near gm levels during the final 10 days of the deployment in contrast the energy density at site c 50 km west of isw and farther up the continental slope was always near gm levels variations may be due to a combination of spatial and temporal gradients of the internal wave field at isw coherence between vertically separated sensors was used to estimate vertical wave number bandwidth energy and bandwidth estimates are compared with previous studies in both ice covered and temperate oceans using our measurements of the internal wave field and existing parameterizations of mixing we estimate the vertical heat flux from the warm deep water toward the surface at isw the upward heat flux due to mixing associated with the internal waves was about 1 w m 2 much less than the 20 w m 2 average flux required to balance the heat budget for the weddell gyre tidal currents contributed significantly to the total measured horizontal velocity variance the tides were primarily barotropic and increased toward the west in both the semidiurnal and diurnal frequency bands it is suggested that the stronger tidal currents to the west over the shallower water of the upper continental slope are indirectly responsible for the higher internal wave energy at site c relative to isw

late oligocene recent stress evolution in rift basins of northern and central thailand implications for escape tectonics abstract the tertiary rift basins of thailand are known through sub surface seismic and borehole data collected for hydrocarbon and coal exploration outcrops in open cast coal mines and a few natural outcrops these data provide mixed perspectives on how the basins evolved some providing data on ages and structural geometries others palaeostress data in general the region evolved under approximately e w extension although the extension direction probably changed periodically within basins extension was episodically interrupted by inversion events associated with sub horizontal nw se to ne sw 1 direction there is no evidence to suggest that the string of rift basins running from n thailand and laos into the gulf of thailand evolved in a similar way on the contrary the evolution of each basin seems different although certain regional trends along the rift system are apparent as follows 1 oligocene lower miocene extension is widespread in the region 2 in central and northern thailand middle miocene extension is also important and extension persisted into the upper miocene pliocene 3 in the extreme south of the area w natuna basin penyu basin malay basin extension ceased in the earliest miocene 4 in the northern gulf of thailand extension ceased in the middle miocene 5 thermal subsidence is greatest up to 4 km in the south malay pattani w natuna and penyu basins and least in northern thailand a few tens to hundreds of metres 6 inversion in the southern gulf of thailand was intense and occurred during the lower and middle miocene in the northern gulf of thailand inversion is very mild and occurred during the lower and middle miocene onshore inversion is patchy during the miocene but is strongest in the northwestern rift basins particularly the li basin the most widespread inversion event that affects the north occurred during the plio pleistocene it might be associated with the change from left to right lateral motion on the red river fault the relationship between strike slip faults and rift basins in terms of timing of extensional and inversion events and palaeostress orientation and evolution is more complex than can be explained by simple escape tectonic models

zircon and monazite upb dating of the doi inthanon core complex northern thailand implications for extension within the indosinian orogen abstract the doi inthanon metamorphic core complex occupies a prominent central position within the northwestern thai gneiss belt which has been inferred to be as old as precambrian and as young as permo triassic u pb dating of zircon from core orthogneisses of the complex suggests that the orthogneisses were derived from granitic protoliths with essentially the same late triassic early jurassic age as the mae cham pluton 205 3 4 ma to the west of the doi inthanon complex monazite ages from the orthogneisses indicate that low pressure and high temperature metamorphism and migmatitization occurred in the late cretaceous 84 72 ma limited published radiometric age data from elsewhere in the migmatitic gneiss belt suggest that widespread minor plutonism accompanied this thermal event a younger u pb data of 26 8 0 5 ma for zircon and monazite from the mae klang granite which intruded mylonitic gneisses on the eastern side of the doi inthanon complex indicates that there was also significant plutonism in the late oligocene these u pb ages constrain the development of the complex and hence of the migmatitic gneiss belt as a whole to an interval between late cretaceous and early miocene ductile shearing uplift and tectonic denudation via detachment faulting chronologically overlap the initiation of extensional basin development to the east and southeast of the gneiss belt and imply a genetic connection thus oligocene early miocene thermal rifting from the gulf of thailand northward into mainland thailand may have been the direct product of crustal extension rather than the transtensional product of regional strike slip faulting

generation of internal waves by sea ice observations in the greenland sea marginal ice zone suggest that when strong stratification occurs near the surface momentum flux into the internal wave field of the upper ocean can be a major component of the force balance that governs ice drift since energy is radiated away by the internal waves turbulent mixing and heat flux are also affected we investigate the downward flux of momentum and energy by internal waves in an ice covered ocean with an idealized model comprising a mixed layer overlying a deep uniformly stratified layer a buoyancy jump separates the mixed layer from the pycnocline drag from a single wave number component of the under ice roughness spectrum is derived as the product of a drag coefficient based on ice speed under ice roughness wave number and amplitude and uniform stratification to the ice ocean interface times an attenuation factor that depends additionally on mixed layer depth and the buoyancy jump at the base of the mixed layer the model is extended to a plausible spectrum of under ice roughness by integration over wave number space internal wave effects are parameterized in terms of the drag coefficient from the integrated spectrum and incorporated into an upper ocean turbulence model model calculations show that plausible values for the peak wave number of the idealized spectrum and roughness variance can account for 1 decreased ice velocity relative to the wind 2 decreased heat exchange coefficient between the ice and ocean and 3 lack of mixed layer deepening all of which were observed during the last week of the 1984 marginal ice zone experiment

internal wave observations from the arctic environmental drifting buoy a free drifting buoy serving as an ice anchor and flotation sphere for a 125 m instrumented mooring line was deployed in the arctic pack ice by the r v polarstern in august 1987 at the northernmost point achieved by the arktis iv expedition current measurements were made from this arctic environmental drifting buoy aedb using a 150 khz acoustic doppler current profiler adcp attached to the mooring line at a depth of 16 m below the flotation sphere with the transducers facing downward velocity profiles spanning depths between 35 and 327 m with 15 m resolution were collected at half hour intervals over a period of 216 days while the buoy drifted from its starting point near 86 n 22 e to about 70 n 16 w the full experimental record was separated into three sections corresponding to periods of the drift spent in the nansen basin over the yermak plateau and in the greenland sea velocity time series and spectra were computed and results for the three analysis sections were compared spectra in the nansen basin were found to have energy levels significantly less than those typical for mid latitudes roughly one third of the canonical garrett munk gm level and a spectral slope between and 2 5 that was significantly flatter than that expected from the gm model between 83 n and 81 n as the buoy passed over the yermak plateau internal wave energy increased to levels comparable to gm isolated energetic near inertial wave packets with upward group velocity were observed in this portion of the record presumably generated by interaction of the barotropic tide with the bottom topography of the plateau estimates of the upward energy flux from these near inertial packets were comparable to the downward fluxes from typical surface sources interpretation of the greenland sea section was complicated by adcp sampling problems and a lack of argos fixes but the available data showed internal wave spectral levels that were intermediate between those of the nansen basin and yermak plateau and no evidence of upward propagating near inertial energy

notes on southern ocean hydrography sea ice and bottom water formation abstract the southern ocean circulation and sea ice distribution is briefly described the formation of extremely cold bottom water in the weddell sea and its relation to the floating ronne filchner ice shelves is discussed it is shown that a concentrated swift eroding bottom current with anomalous low 18 o ratio transports the cold and dense ice shelf water from the shelf towards large depths comments are made on possible implications of this process for the large scale deep water circulation and for the interpretation of sediment cores

high frequency ice motion and divergence in the weddell sea we describe the spatial variability of high frequency ice velocity in the weddell sea using satellite tracked ice mounted buoys ice motion is analyzed separately for diurnal 1 36 1 18 cph and semidiurnal 1 18 1 6 cph bands ice motion in both bands is caused by a combination of ocean tidal currents and wind stress monthly mean diurnal band ice speeds over the deep basin range from 2 to 4 cm s 1 depending on wind stress variance and ice concentration cice higher speeds 10 cm s 1 are found in the semidiurnal band in regions of low cice notably the northern weddell sea where the ice velocity is dominated by the inertial response to wind stress variations monthly mean tidal band ice speeds over the continental slope and shelves often exceed 10 cm s 1 we use comparisons between buoy velocities moored current meter data and an ocean tidal model to demonstrate that ice motion is frequently a good indicator of ocean tidal currents in strongly tidal regions the standard deviation of the divergence of ocean tidal currents estimated from an ocean only tidal model is small 0 1 10 6 s 1 over most of the weddell sea but has values of 1 5 10 6 s 1 along the ronne ice front and the continental shelf break high frequency ice divergence is dominated by ice response to wind stress rather than by tides except along the shelf break and ice fronts in these tidally dominated regions the periodic divergence maintains a mean lead open water area of 2 5 this increased lead fraction implies an increase in area averaged winter ocean to atmosphere heat exchange rate of 4 10 w m 2 and an increase in salt flux into the upper ocean as new ice forms in the leads

a possible influence of the north atlantic oscillation on the circulation of the western mediterranean sea a current time series spanning from 1985 to 1996 in the corsica channel shows that seasonal and interannual variabilities are stable components of the circulation of the northern part of the western mediterranean sea for the first time these characteristics are related to the state of the north atlantic oscillation during winter we have found that this large scale control is mainly maintained through the air sea interaction processes which take place in the northern basin these results provide new elements for a consistent explanation of the major features of the basin circulation such as the seasonal increase of the boundary current and deep water formation

coincident buoy and sar derived surface fluxes in the western weddell sea during ice station weddell 1992 propagation shows lower agreement for divergence 47 4 rmse 7 46 10 8 s 1 but we find these results sufficient for integrated surface flux comparisons using a toy model we test the effects of aliasing in surface flux determination the results show that variability associated with storms ocean tides inertial oscillations and other highfrequency forcing affects integrated sea ice growth rates along this continental slope location integrated salt and new ice production rates computed from buoys are found to be two times larger than those computed from ers 1 sar motion products we show that these differences in salt and ice production rates result primarily from inadequate temporal resolution of heat flux variability and sea ice divergence comparison with other studies shows that the problem is widespread thereby impacting the modeling of sea ice mass balance and variability the small scale processes cited here have significant ramifications for larger scales and the global thermohaline circulation

coastal sea level trends from topex poseidon satellite altimetry and tide gauge data in the mediterranean sea during the 1990s a joint analysis of topex poseidon satellite altimetry and tide gauge data is used to estimate sea level trends along the mediterranean sea coast from 1993 january to 2002 february a generalized least squares gls method allows us to take into account the space time distribution of the data and their respective error budgets nearly optimal parameters of the covariance functions involved in the gls method are estimated at different scales of analysis using a trial and error method combined data time series are then reconstructed at 153 locations along the coast the basin wide averaged linear trend for the coastal area shows a sea level rise of 4 54 0 30 mm yr 1 compared to 4 28 0 30 mm yr 1 for the open ocean only i e a 0 26 0 16 mm yr 1 difference the error is smaller because the systematic error does not take part in the error budget which is quite significant at local scales the coastal linear trends ranges from 8 5 to 13 5 mm yr 1 which is much narrower than ranges found by other open sea studies 24 0 to 10 0 16 0 to 29 0 mm yr 1 however a detailed error budget shows that the largest estimation errors come from the spatial extrapolation of the sea level signal required when tide gauge and altimeter data are merged the second error source is the instrumental noise and the random noise generated by the littoral contamination on altimeter measurements and from the crustal motions that are contaminating the tide gauge signal at local scale it is estimated that 85 percent of the error on linear trends does not exceed 2 mm yr 1

seismotectonics of the 2014 chiang rai thailand earthquake sequence on 5 may 2014 a mw 6 2 strike slip earthquake occurred in the mae lao region of chiang rai province in thailand this earthquake took place in a region of known faults and caused substantial damage and injuries although the region had been previously identified as having a relatively low earthquake hazard detailed field reconnaissance and deployment of a dense temporary network of broadband seismometers allowed details of the damage and its relationship to seismicity to be analyzed the aftershock sequence associated with this main shock occurs on two well defined trends reflecting the two potential fault planes in earthquake mechanisms for the main shock and the majority of the aftershocks the damage area was relatively large for an event of this magnitude but building damage was largely limited to the primary rupture region while liquefaction and other ground failure is spatially associated with the rupture area and along regional rivers stress modeling combined with the time series and pattern of aftershock activity lead us to propose that slip near the northern termination of the main shock rupture continued slightly onto a conjugate fault helping to trigger the distinct pattern of two discrete conjugate trends of aftershock activity that mirror the kinematics of the main shock fault mechanism

climatic changes in the aegean sea influence the eastern mediterranean thermohaline circulation 1986 1997 recent changes of water mass characteristics in the south aegean sea have considerably influenced the eastern mediterranean thermohaline circulation a combination of salinity increase 1987 92 and temperature drop 1992 94 caused massive dense water formation and strong outflow towards the deep and bottom parts of the eastern mediterranean this climatic shift the most important since the existence of observations in the basin is a combined effect of extreme meteorological events superimposed on large scale trends it has initiated a series of modifications in the hydrology and dynamics of the entire eastern mediterranean with possible influence on the mediterranean outflow in the north atlantic ocean