wellen radar wera a new ground wave hf radar for ocean remote sensing hf radars can be used to measure surface currents and wave spectra the coastal radar codar used by the university of hamburg was designed for current mapping only it has been operated for 15 field experiments during the past 15 years recently a new hf radar called wellen radar wera has been developed at the university of hamburg one main advantage of the system is the possibility of connecting different configurations of receive antennas when operated with a linear array information on the sea state can be obtained via second order spectral bands a further advantage is the flexibility in range resolution between 0 3 and 1 2 km instead of the fixed resolution of about 2 km of codar this is achieved by transmitting frequency modulated continuous wave fmcw chirps instead of continuous wave cw pulses in addition this technique avoids the blind range of about 3 km in front of the codar the technical design of wera is described and first experimental results are presented

basin superposition on the northern margin of the south china sea abstract basin superposition on the northern margin of the south china sea is a product of pulsed basin development with geometries which changed through space and time of changing strain fields and of tectonically inherited pre existing zones of crustal weakness this region of the south china sea was welded together or assembled prior to the cretaceous three distinct episodes of continental disassembly and accompanying basin evolution ensued each episode commencing with rifting and the formation of grabens or half grabens and each terminating with a gentle subsidence phase the major trends of the faults and basins varied from predominantly ne for the first episode through ne ew for the second to ew nw for the third the first episode occurred during the late cretaceous to paleocene as a back arc extensional domain induced by the dip steepening of a subducted oceanic slab the second basin episode of the late eocene to early oligocene was initiated by the collision of the indian plate with the eurasian plate the continued penetration of the former into the latter led to the tectonic escape and subsequent clockwise rotation of the indochina block creating regional transtension and left lateral motion along the red river fault the third episode of basin development occurred during the middle miocene as a reactivated product of this collision owing to the clockwise rotation of indochina the approximately e w trend of the simple shear principal displacement zone changed to northwest by the pliocene the eastward extrusion of south china had exceeded that of indochina reversing the sense of red river fault displacement to right lateral a clockwise rotation of the red river geosuture together with considerations of the influence of zones of inherited crustal weakness provides a model for the observed episodic changes in regional strain such a model best explains the post cretaceous evolution of superimposed basins on the northern margin of the south china sea

kinematics of cenozoic extension on the south china sea continental margin and its implications for the tectonic evolution of the region abstract in the northern south china sea several large sedimentary basins developed during the cenozoic characterized by episodic rifting clockwise rotation of the rifts an eastward aging breakup unconformity and intensifying crustal extension to the east these features may be summarized by a scissors model the maximum rifting occurred north of the maximum thermal subsidence which was in turn north of the seafloor opening in contrast the nansha microcontinent south of the south china sea basin was dominated by compressional deformation during the cenozoic extension was of subordinate significance and manifested mainly by block faulting and tilting in the late early oligocene maximum tilting occurred in the southern part of the nansha microcontinent at distance from the deep sea basin of the south china sea the asymmetric development of extensional structures around the south china sea basin may be explained by the simple shear model proposed by wernicke 1981 the tectonic development of the south china sea was the consequence of various interactions of three major plates and may be summarized into three stages with dominating influences of respectively the retreat of the west pacific subduction zone in the late cretaceous the hard collision and impinging of india to tibet since the late eocene and the fast northward subduction of the indian ocean australian plate since the late early miocene

the mechanical relationship between strike slip faults and salt diapirs in the zagros fold thrust belt analogue models are used to study the mechanical relationship between basement strike slip faults and salt diapirs displacement along a strike slip fault in 1 g models resulted in extension along pre existing jogs and the formation of oblique extensional faults where reactive diapirs were triggered in some models in the centrifuge models prescribed cuts simulating pre existing structures were reactivated during simple shear deformation of the models resulting in formation of pull apart basins which were intruded by diapirs the models show that because of the low ratio of salt to overburden thickness in the zagros 0 15 0 35 it is unlikely that diapirs have formed solely if at all as a result of movement along basement strike slip faults two mechanisms are suggested first pre kinematic thin overburden and continuous movement along a releasing bend in the cover units may have triggered some of the diapirs in the zagros which were later downbuilt to their current geometry by additional sedimentation second movement along the strike slip faults e g the kazerun and mangarak faults induced oblique movement along nw se zagros structures folds or thrusts resulting in the formation of pull apart basins where diapirs were eventually intruded fault plane solution of shallow earthquakes supports the second scenario which is also in agreement with previous interpretations that some of the salt diapirs associated with basement faults are younger than zagros shortening and young southwestwards

modeling the influence of sinking anhydrite blocks on salt diapirs targeted for hazardous waste disposal due to the low permeability and high ductility of rock salt many salt diapirs such as those in germany and the netherlands are targeted as long term repositories for disposal of high level radioactive and chemical wastes geophysical and subsurface data show that the gorleben salt diapir which is one of the most extensively investigated diapirs in the world and other salt diapirs of the zechstein formation in germany contain large blocks 80 m thick of high density anhydrite inclusions these blocks which were carried upward by the rising salt are considered to be detached segments of intercalated layers that initially were deposited with the salt results of physical and numerical models presented here show that such detached high density blocks which were entrained and carried upward by the diapir at an earlier stage tend to sink in the late stages of diapiric evolution when the rate of diapiric rise slows down during their descent these high density competent blocks deform by folding and create shear zones at the immediate contact with the less competent salt the descending blocks initiate a secondary internal flow within the salt diapirs they descend and they may deform any repository built within such diapirs which would otherwise be considered as tectonically inactive

evolution of the hourglass structures in the laminaria high timor sea implications for hydrocarbon traps abstract in cross section an hourglass structure can be visualized as an older horst block and superimposed younger graben bounding faults of the horst and graben blocks represent separate conjugate fault systems formed by two distinct episodes of extension in the timor sea during late jurassic early cretaceous 1st phase and middle miocene pliocene 2nd phase with an 120 my hiatus of limited or no fault activity in between horst blocks were formed by the 1st phase of extension and buried post deformation with the onset of the 2nd phase of extension the hourglass geometry began to form by nucleation of the graben bounding faults in the shallow sedimentary section in isolation from the horst bounding faults location of the graben is biased by the buried horst block and graben bounding faults grew down dip from the shallow locus of nucleation toward the underlying horst block on which only minor reactivation occurred detachment of the two systems in this way was predominantly controlled by the first order mechanical layering a thick shale rich ductile layer separates the horst and graben bounding fault systems and acts as a barrier to vertical fault propagation confinement of the graben bounding faults into the shallow section was also facilitated by outer arc style extension due to lithospheric flexure controlling the 2nd phase strain in the region the complex evolution history and the composite nature of the hourglass structures resulted in systematic along dip variation of displacement this variation predominantly relates to syn kinematic deposition and location of fault tips that are controlled by the ductile layer the presented evolution model of the hourglass structures concentrates fault tips and related stress perturbation onto the top seal and is likely to be detrimental to top seal integrity

three dimensional geometry and kinematics of experimental piggyback thrusting the three dimensional geometry and kinematics of piggyback stacks of imbricate thrust sheets are illustrated and discussed using a single model shortened in a squeeze box strike parallel geometric elements simulated include lateral ramps eyed sheath folds splays and thrust thrust interference fine details of these structures were exposed by eroding a shortened wedge of sand using a newly developed vacuum eroding technique a kinematic analysis of the model shows a stepwise increase in imbricate thrust spacing and or a decrease in rate of nucleation of imbricate thrusts in the direction of thrust transport despite the steady forward advance of a rear wall the piggyback wedge accreted episodically recording different strain domains in longitudinal cross sections strain partitioning in single layers by bed length balancing showed an increase in layer shortening with volume loss and a corresponding decrease in imbricate thrusting and ramp folding with depth

how normal faulting and sedimentation interact to produce listric fault profiles and stratigraphic wedges abstract in a series of scale experiments we generated listric normal faults by extending models composed of colored sand layers deposited at regular time intervals throughout deformation during syntectonic sedimentation progressive bulk extension along a single set of faults caused domino type tilting of fault blocks underlying tilted faults propagated upwards with constant dips into newly sedimented layers hence fault profiles become progressively more listric tilting of the free surface resulted in asymmetrical depressions and in fan shaped deposits stepwise or continuous geometric models of domino tilting and synchronous sedimentation yield the same structural and stratigraphic features as observed in the sand models the continuous geometric model shows that a critical parameter governing fault curvature is the ratio r between rates of bulk strain and sedimentation both types of models reveal that synchronous sedimentation and bulk extension are capable by themselves of generating listric normal faults

remote sensing of wind speed at sea surface level using hf skywave echoes from decametric waves using an hf skywave radar to study the decametric sea waves it appears that their amplitudes do not saturate as the wind speed increases a measurement method based on the kahma sea wave spectrum is proposed and radar estimations of the wind speed are compared with in situ measurements performed on board a ship the rms difference between the two measurements is 2 5m s and is probably mainly due to the spatial variability in the wind speed

the origin and evolution of complex transfer zones graben shifts in conjugate fault systems around the funan field pattani basin gulf of thailand abstract changes in dip province associated with conjugate fault sets produce complex transfer zones locally known as graben shifts between sets of convergent conjugate faults in the pattani basin 3d seismic data over a well developed graben shift geometry in the funan field area of the pattani basin has revealed details of the transfer zone development in map view the graben shift is seen as west dipping faults forming a wedge shaped incursion into a zone of east dipping faults the wedge boundaries trend ne sw and nw se at a high angle to the n s striking normal faults within the transfer zones faults only slightly overlap with their neighbours with individual faults tending to widen upwards the narrow regions of overlap indicate displacement transfer must occur between more widely separated faults not neighbouring faults the initial oligocene early miocene syn rift fault pattern appears to have been strongly influenced by pre existing basement trends as indicated by 1 the restriction of west dipping secondary faults to the present day area of the graben shift 2 the line of the ne sw boundary to the graben shift coinciding with fault segment linkage geometries in two major syn rift faults and 3 curvature of minor fault tips into the transfer zone the subsequent conjugate fault system developed during thermal subsidence shows that the dip asymmetry and map boundaries of the fault dip panels are strongly influenced by the syn rift fault geometry there is no indication of active strike slip faulting affecting the graben shift geometry fault displacement diagrams commonly show linkage between deeper and shallower displacement maxima indicating early late oligocene early miocene minor west dipping normal faults influenced the location and width of higher middle late miocene conjugate faults hence two stages of structural inheritance led to the middle late miocene graben shift geometry

petroleum generation migration and entrapment in the zhu 1 depression pearl river mouth basin south china sea abstract analysis of crude oils from several fields in and near the huizhou sag zhu 1 depression pearl river mouth basin provides an excellent demonstration of inferring petroleum generation migration and entrapment in areas where drilling encounters hydrocarbons but fails to penetrate the effective generative sequence this paper illustrates the integration of geochemical geophysical and geological interpretations to develop a model of petroleum generation migration and entrapment the zhu 1 depression is one of three subbasins in the pearl river mouth basin sediment fill within the subbasin consists of paleogene synrift units and miocene to recent postrift deposits although drilling in the zhu 1 s huizhou sag and on the adjacent dongsha massif has netted numerous oil discoveries since the early 1980 s it has not encountered any effective or potential source rocks within the penetrated sections however interpretation of the systematic variations in crude oil chemistry within the regional geologic and structural framework has been invaluable in inferring source attributes and delineating location and distribution of the unpenetrated probable source the signatures resulting from genetic and alteration processes suggest that high wax oils were generated in mature lacustrine source facies of the synrift sequence and were expelled into a tightly sealed massive sandstone carrier system they migrated south southeast toward the dongsha massif were entrapped to spill point in traps along the migration route and were altered increasingly within the successively shallower and cooler reservoirs on the massif

the depositional characteristics and oil potential of paleo pearl river delta systems in the pearl river mouth basin south china sea abstract delta systems in the zhuhai zhujiang and hanjiang formations are interpreted as having formed during periods of sea level rise from the late oligocene to mid miocene 30 10 5 my b p deltas in the zhuhai formation were developed in a shallow water environment on a sandy wave or fluvial dominated coasts thick and blanket like sandstones are common but mudstones are infrequent oil bearing zones have been found only in the upper part of the systems overlain by mudstone of the zhujiang formation deltas in the zhujiang formation are interpreted as having formed in a deeper water environment on sandy wave or fluvial dominated coasts carbonate platforms started growing on the dongsha massif as the sea level slowly rose the moderate sandstone mudstone ratio in the delta systems and a zone of secondary porosity in the carbonate rocks provide an excellent reservoir rock and seal rock for the basin deltas in the lower hanjiang formation are similar to those of the zhujiang formation but the upper part of the formation is interpreted as having formed in a shelf environment the thick shelf mudstone interbedded with offshore bar sandstones would be one of the better regional seal rocks in the study area no carbonate rock developed on the dongsha massif due to the rapid rise in sea level all delta systems from the zhuhai to the zhujiang formation are stacked in an onlap pattern indicating a more and more expanding marine transgression which was caused by eustatic sea level rise this marine transgression is almost unique and contrasts to the progradational offlap pattern of cenozoic delta systems in the gulf of mexico it resulted in thick sandstone deposits immature or poorly mature source rock and no ductile mudstones with no growth faults or rollover structures hydrocarbons generated from eocene oligocene lacustrine source rocks are trapped by drape structures related to local basement highs or by carbonate rock with secondary porosity most of the remaining undiscovered reserves in the basin will be found in non structural subtle traps especially stratigraphic traps

three dimensional geometry and growth of conjugate normal faults abstract good quality 2 d and 3 d seismic reflection data from the timor sea are used to determine the threedimensional geometry displacement patterns and development of intersecting conjugate normal faults these data are supplemented by data from previous physical modelling studies conjugate structures which comprise two intersecting opposed dipping normal faults or fault sets form synchronously on a geological time scale and develop due to the incidental intersection of the faults factors which affect both the formation and imaging of these structures include the fault density the spatial distribution of opposed dipping faults the seismic resolution and the vertical extent of the imaged fault data large conjugate structures grow from smaller ones larger conjugates are associated with more numerous and larger faults than small structures on the scale of the seismic data fault throws range from ca 10 400 m synchronous fault movements are accommodated by a reduction of displacements on discrete fault surfaces towards the fault intersection zone and a corresponding increase in ductile strain of this region high strains in the volume proximal to the fault intersection zone are expressed as thinning of stratigraphic units between the conjugate faults and are believed to be accommodated by numerous small sub seismic faults intersection of two opposed dipping faults does not prevent their continued synchronous movement and does not result in mechanical locking of the system

rheological and tectonic modeling of salt provinces abstract technological improvements and a more rigorous research approach have led the petroleum industry to renew and expand its interest in physical modeling of faulting associated with halokinesis salt tectonics and the formation of structural hydrocarbon traps can be reproduced in models using viscous polymers for the substratum and frictional plastic granular materials for the overburden the fault patterns simulated in these dynamically scaled models are remarkably similar to those in depth converted seismic sections scale models are therefore useful for generating new concepts and for reconstructing the structural evolution of hydrocarbon traps although even unsealed models may help generating ideas the full transfer of quantitative data requires that models be dynamically scaled to their natural prototypes previously published scaling theory for salt tectonics has erroneously assumed fluid behaviour of the overburden this paper provides a sound scaling approach for geological deformations involving brittle overburdens on ductile substrata rheological data from overburden rocks and salt are compiled and compared to model rheologies using dimensions of laboratory analogs and other intrinsic material properties scaling approaches are compared and rules are formulated for achieving dynamic similarity in models of salt tectonics including those with synkinematic sedimentation

cenozoic tectonic subsidence in deepwater sags in the pearl river mouth basin northern south china sea the cenozoic tectonic subsidence of the deepwater area in the pearl river mouth basin northern south china sea is studied by subsidence analysis via backstripping calculations based on data of newly interpreted sequence boundaries in the subsidence analysis local porosity depth parameters were estimated based on well data the paleo water depth parameters and lithology were estimated for all grid nodes based on well data and sedimentary system maps and ages of sequence boundaries were adjusted according to the international chronostratigraphic chart v2013 01 sensitivity analysis shows that these are essential to ensure the quality of the subsidence analysis in the slope areas maps of tectonic subsidence rates of 18 cenozoic sequences were constructed and spatial temporal variations of the tectonic subsidence were discussed the subsidence was restricted in the baiyun and liwan sags before 30 ma and extended to uplifts after 30 ma this indicates that the 30 ma unconformity is the breakup unconformity that separated the syn rift and post rift sequences four substages of post rift subsidence were identified by cyclic changes in the rate and pattern of tectonic subsidence at boundaries of 23 3 ma 17 2 ma and 11 9 ma respectively anomalous post rifting tectonic subsidence was significant and totaled to similar to 1200 m at the center of the baiyun sag and punctuated by rapid subsidence and uplift events the baiyun event was manifested in the study area by a short lived uplift event in 23 9 23 3 ma followed by a short lived rapid subsidence in 23 3 19 8 ma in the central study area this localized rapid subsidence caused northward jump and anti clockwise rotation of the shelf break two order teeterboard seesaw like subsidence was observed in the study area in the post rifting stage suggesting elastic deformations of the crust and lithosphere c 2014 elsevier b v all rights reserved

experiments on faulting in a two layer cover sequence overlying a reactivated basement fault with oblique slip abstract two series of experiments were undertaken to investigate the development of faults in a cover sequence overlying a reactivated basement fault with oblique slip the experiments represent physical models properly scaled to account for gravitational forces brittle behaviour of the upper cover and ductile behaviour of evaporites in the lower cover models were made with a coulomb layer sand overlying a newtonian ductile layer silicone putty in each series the thickness of the silicone layer was varied from each experiment to the next in all normal wrench experiments a domain of faults appeared in the brittle layer vertical offsets were mostly of normal sense but some reverse faults occurred in experiments with thick silicone layers the thicker the silicone the wider the fault domain the deformation zone was in all cases limited to the faulted domain in the reverse wrench experiments discrete reverse riedel faults appeared without a silicone layer as the silicone layer became thicker the importance of the reverse faults diminished with the thickest layer of silicone 3 cm no faults appeared in the overburden but a monoclinal flexure accommodated the dip slip component in the presence of silicone the deformation zone was not limited to a faulted domain and the strike slip component was accommodated by a bulk shearing of the overburden in the uplifted compartment these experiments demonstrate that in basins deformed in oblique slip mode any deformation that is localized along discrete faults at the basement level becomes distributed over a much wider zone of overburden when this overlies an interval of evaporites

thrust dip and thrust refraction in fault bend folds analogue models and theoretical predictions analogue models made of two layers of loose sand separated by a thin layer of micro glass beads were shortened by a rigid emerging ramp dipping at either 30 or 45 and possessing a high intermediate or null surface friction shortening resulted in formation of closely spaced back thrusts in the sand layers the dips of the back thrusts vary within a range of 30 depending on the ramp friction and 7 depending on its dip an increase in ramp friction or to a lesser extent in ramp dip decreases the thrust dips in the model the second important observation is that when friction is greater along the ramp than along the layer of glass beads then the glass beads layer acts as a separate upper ramp above which the back thrusts steepen the theory proposed to explain these observations predicts the thrust dips through a two step procedure first global equilibrium of forces in the two layers is required to yield the mean forces at stake along the ramps and thrusts second the total dissipation is minimized with respect to the dips of the back thrusts the relevant frictional properties of our analogue materials have been measured in stress conditions as close as possible to the experimental ones below 1 kpa and used with the theory to yield optimal back thrust dips that are all within 3 of the measured dips this is a surprisingly good fit when considering that we did not take into account geometric changes strain softening and dilatancy or compaction due to slip on the thrusts we conclude that this general two step theoretical procedure is validated in the context of analogue frictional materials we also propose a possible mechanism for thrust refraction and top to the foreland sense of shear observed in the hanging walls of lower flat to ramp transition in sedimentary piles that is based on the triggering of secondary upper ramps finally this mechanical approach can also be seen as complementary to the kinematic models of fold thrust structures which by definition cannot grasp the strong effects of friction on the kinematics

experimental models of hangingwall deformation in ramp flat listric extensional fault systems abstract the results of three experimental models of ramp flat extensional fault systems are presented the experiments were constructed from sand and mica layers to form an anisotropic sequence that would respond to the imposed deformation by both faulting and folding the geometry of the underlying detachment controls the deformation in the hangingwall sequence ramp flat detachment geometries produce an upper roll over with a crestal collapse graben system a ramp syncline and fold reverse fault zone and a lower roll over with a crestal collapse graben system short ramp geometries produce only minor perturbations in a larger roll over structure as extension progresses the crestal collapse systems migrate and superimpose earlier systems the models of ramp flat extensional structures produce templates for the interpretation of natural ramp flat listric fault systems

pattern of normal faulting in the gediz graben sw turkey hanging wall deformation of the fault systems controlling the southern margin of the gediz graben were investigated separately within the plio quaternary and neogene predominantly miocene deposits of the graben fill fault styles observed in both packages share many similarities in terms of geometry and comprise conjugate fault sets that show clustering of strike orientations predominantly around wnw ese but also sw ne and nw se directions the main difference between the two units is observable in terms of fault dips and rake of the slickenside lineations measured on the exposed fault planes both measurements show a uni modal distribution for the plio quaternary deposits but a tri modal distribution for the neogene deposits this variation is probably related to the geometrical modification of the older faults by the process of domino style back rotation in the hanging wall of higher order faults similarities among the two units are not limited to geometrical aspects of the fault systems but also counts for the orientation of the principal stress axes that controlled the deformation during the deposition of each sedimentary package inversion of the fault slip data showed that approximately n s oriented extension which varies in the range of nnw sse and nne ssw controlled the faulting during the accumulation of the entire graben fill with almost no evidence of change in the state of stress during the graben evolution however some heterogeneity in terms of stress field is observable among the fault systems formed within the same time frame this heterogeneity is probably related to poorly defined direction of extension in the graben indeed low ratio in the order of 0 25 suggests that 2 and 3 are close in magnitudes and the direction of extension is not well constraint with a potential of 2 3 axes permutations local stress field anomalies related to fault segment interaction could also contribute to the observed heterogeneity

the mechanism of post rift fault activities in baiyun sag pearl river mouth basin post rift fault activities were often observed in deepwater basins which have great contributions to oil and gas migration and accumulation the main causes for post rift fault activities include tectonic events mud or salt diapirs and gravitational collapse in the south china sea continental margin post rift fault activities are widely distributed especially in baiyun sag one of the largest deepwater sag with its main body located beneath present continental slope during the post rift stage large population of faults kept active for a long time from 32 ma t70 till 5 5 ma t10 seismic interpretation fault analysis and analogue modeling experiments indicate that the post rift fault activities in baiyun sag between 32 ma 170 and 13 8 ma t30 was mainly controlled by gravity pointing to the main baiyun sag which caused the faults extensive on the side facing main baiyun sag and the back side compressive around 32 ma t70 the breakup of the continental margin and the spreading of the south china sea shed a combined effect of weak compression toward baiyun sag the gravity during post rift stage might be caused by discrepant subsidence and sedimentation between strongly thinned sag center and wing areas this is supported by positive relationship between sedimentation rate and fault growth index after 13 8 ma t30 fault activity shows negative relationship with sedimentation rate compressive uplift and erosion in seismic profiles as well as negative tectonic subsiding rates suggest that the fault activity from 13 8 ma t30 to 5 5 ma t10 might be controlled by the subductive compression from the philippine plate in the east c 2014 published by elsevier ltd

an inversion method for extraction of wind speed from high frequency ground wave radar oceanic backscatter a new approach to extracting sea surface wind speed from high frequency radar doppler spectra is presented based on certain appropriate approximations associated with the doppler region close to the first order bragg peaks the second order radar cross section equation is differentiated once doppler shifts due to ocean currents are removed from the data an expression that relates the wind speed to the frequency position of the second order peak is derived the method is applied to simulated noisy data as well as to field data obtained from a seasonde a product of codar oceans sensors in breezy point ny in the latter case the retrieved wind speeds are then compared to ground truth data measured by an anemometer from a national oceanic and atmospheric administration weather station located in the vicinity of the illuminated patch of ocean subject to certain constraints as detailed in the manuscript the algorithm shows significant promise

determining dislocation love number of vertical displacement using gps observations case study of 2011 tohoku oki earthquake mw 9 0

petroleum migration and mixing in the pearl river mouth basin south china sea abstract two oil groups have been investigated in the pearl river mouth basin using their geochemical characteristics in combination with source data the two oil groups may be extrapolated into two end member oils petroleum populations a and b the oil population a with abundant 4 methylsteranes derived from the deeper wenchang source rocks migrated and accumulated earlier the oil population b with absent 4 methylsteranes was expelled from the enping source rocks and is associated with a relatively later phase of migration and accumulation the two distinctive oil populations migrated updip through the marine blanket like sandstone carriers within the zhuhai formation to accumulate in a series of traps along the main migration pathways at different times most of the accumulations are mixtures of the two end member oils the variations of 4 methylsterane concentrations in the accumulations can be related to the contributions from the two sources the oils which migrated furthest contain greater contributions from the wenchang source rocks whereas those with shorter migration paths have greater contributions from the enping sources the later migrated oils closer to the depression areas are highly mature and the former oils in the liuhua oil fields are of relatively low maturity which may indicate the main migration direction along the hui liu structure ridge hlsr oils with abnormally high maturity in the middle of the hlsr may suggest oil filling points from which branch conduits connected the source kitchens to the main migration pathway oils with abnormally low maturities may reveal minor contributions from some small sags in the dongsha massif in a latest phase

the role of pre existing discontinuities in the development of extensional faults an analog modeling perspective abstract several mountainous regions are currently affected by syn or post orogenic active extension we investigate how a newly formed normal fault interacts with structures inherited from a previous contractional phase to this end we use analog models that adopt an innovative technique for performing a precut that mimics such inherited structures into a clay layer this clay layer is laid on top of a master fault simulated by two rigid blocks sliding along an inclined plane we carry out six experiments with variously oriented precuts and compare the results with those obtained in a reference isotropic experiment all other conditions are identical for all seven realizations fault evolution is monitored by taking closely spaced snapshots analyzed through the digital image correlation method we find that the upward propagation of the normal fault can be either accelerated or decelerated depending on the presence of a precut and its orientation such precuts can also promote or inhibit the formation of bending moment faults these interactions between master fault and precut also affect the shape of the fault related syncline anticline pair

hf radar wave and wind measurement over the eastern china sea high frequency hf radar can be employed to measure sea surface state parameters such as waveheight wind field and surface current velocity this paper describes the application of the hf ground wave radar in remote sensing the surface conditions over the eastern china sea in october 2000 the radar referred to as the osmar2000 was developed by wuhan university preliminary wave spectra waveheights and wind fields estimated from the collected data are presented and compared with ship recorded measurements where such are available the range for wind direction sensing is up to 200 km wave information and wind speed can be provided up to a range of 120 km the mean difference between radar and ship measured significant waveheight is 0 323 m wind direction is measured within 20 spl deg and wind speed to within 0 6 m s with such agreement being fairly reasonable the feasibility of the inversion algorithm and the ocean state real time sensing capability of osmar2000 are demonstrated

a crustal structure profile across the northern continental margin of the south china sea an ocean bottom seismometer obs geophysical experiment was carried out across the northern continental margin of the south china sea two dimension kinematic ray tracing was used to construct synthetic records and to define the geological model along the obs profile according to the calculation and interpretation of refracted p wave phases the crustal thickness decreases from 22 km obs 1 in littoral area to 8 km obs 15 in deep sea the lower slope structured by volcanism changes sharply in moho depth from 22 to 9 km the volcanoes over the lower slope were markers of ocean continental transition zone a high velocity layer hvl with an average thickness of 4 km was found in the base of the lower crust over the shelf and slope the south china sea was originated by the passive rifting of south china continent and seafloor spreading however geological and geophysical data collected in the northern margin of the south china sea show a small amount of magma intruded into or erupted onto the crust during pull apart and breakup further analysis shows that the hvz in the base of the thinned continental crust was related to magmatism that occurred after the cessation of seafloor spreading of the south china sea magmatism during the crustal extension and breakup is very weak therefore the northern continental margin of the scs is classified as non volcanic passive margin the southern margin of the south china sea has a crust with a steady thickness of 18 24 km which is different from the nor them margin of the south china sea with a gradually thinned crust they constitute an asymmetrically conjugated pair of passive margins c 2001 elsevier science b v all rights reserved

modeling of thrust fronts above ductile and frictional detachments application to structures in the salt range and potwar plateau pakistan series of scaled sandbox models are used to simulate the development of thin skinned simultaneous shortening above adjacent ductile and frictional substrates these models simulate the evolution of the potwar plateau and salt range in pakistan where pale

the effect of cover composition on extensional faulting above re activated basement faults results from analogue modelling abstract analogue models were used to investigate differences in deformation between sedimentary cover sequences of contrasting composition above reactivated basement faults during extension two types of model arrangements were used the first represented clastic sediments directly overlying faulted basement and the second represented a basal ductile layer in an overburden overlying the same faulted basement the basement configuration consisted of faults both oblique and orthogonal to the bulk extension direction particular attention was paid to the resulting map view fault patterns in experiments without a basal ductile layer in the overburden grabens only developed in areas directly above basement faults in section cover faults above oblique basement faults curved in profile and in places exhibited reverse movement at shallow depth in experiments involving a ductile layer at the base of the overburden faults developed oblique to both the bulk extension direction and the basement faults the resulting fault pattern was influenced by both bulk extension and basement fault reactivation the results indicate that cover sequences that include thick basal ductile layers above reactivated basement faults are more likely to develop faults with strikes perpendicular to the regional extension direction compared to those without faulting in an overburden lacking a basal ductile sequence is more likely to be directly influenced by the underlying reactivated basement faults

3d analogue modeling of the south china sea a discussion on breakup pattern the opening of the south china sea is one of the most important cenozoic events in se asia in order to investigate its tectonic evolution three analogue modeling experiments were compared the modeling results suggest that rifting pattern and orientation change of the rift zone were related to initial theological stratification affected by the ductile flow of silicone lower crust and honey asthenosphere the faults became flattened especially close to the breakup area we conjecture that the slope area may bear relatively hotter and thinner lithosphere than the shelf area from the beginning of rifting due to stretching and mantle upwelling associated with this regional extension which in turn lead to the change in initial rheological stratification and therefore the rifting pattern from shelf to slope in the experiments breakup developed first at isolated points which grew and coalesced to become a single spreading area the conjugate boundaries were either all concave or all convex where a rigid massif was located at the divergent boundary stretching history was different in this case the northern and southern areas thinned rapidly and developed into two deep troughs which may finally evolve into spreading centers the shape of the massif controls the orientation and boundary shape of the spreading area it is interpreted that crustal breakup was more viscous in style and the nw sub sea basin developed along the northern trough of the zhongsha xisha massif macclesfield bank c 2008 elsevier ltd all rights reserved

analogue and numerical modeling of normal fault patterns produced due to slip along a detachment zone abstract in this paper we investigate normal fault patterns produced by the sliding motion along a gently dipping normal fault by using analogue model tests and numerical modeling the motivation for this study was offered by microseismic test data that indicate the existence of an active low angle shear zone at a depth of 9 11 km in the extensional region of high seismic activity of the gulf of corinth greece both modeling techniques seem to support the hypothesis that the system of high angle normal faults that are responsible for the final asymmetrical graben formation initiate at the tip of the active basal detachment nearest to the free surface the normal faults propagate upwards with progressive sliding of the inclined basal plane resulting in a first phase of symmetrical graben configuration that is delimited by a main synthetic fault and an antithetic fault forming a rankine zone subsequent sliding on the inclined base induces a family of secondary antithetic normal faults which are responsible for the asymmetry of the failure pattern and the diffusive character of deformation in that area shear deformation is more intense and localized along the synthetic normal fault than along the antithetic faults elaboration on the analogue test results has led to the phenomenological relations among four main parameters that describe the geometry of grabens namely i the width and ii the maximum subsidence of the graben iii the dip angles of the conjugate normal faults and iv the amount of sliding along the low angle normal fault however analogue models do not produce the system of synthetic faults that is observed in the gulf of corinth the effects of both friction angle variation along the detachment base and of the constitutive behavior of the model material on the configuration of the final structural pattern were also studied with a series of numerical continuum models it was found that a the fault pattern of the gulf of corinth may be reproduced with either a strain softening material with low elastic modulus or a constant strength material and b two consecutive grabens such as those of gulfs of corinth and evia may also be reproduced by an appropriate combination of variation of dip and frictional properties along the hypothesized detachment zone

the influence of pre existing thrust faults on normal fault geometry in nature and in experiments relations between normal faults and pre existing thrust faults are classically described in terms of three basic situations normal faults can cross cut thrust faults they can branch out from thrust faults at depth on a de collement level or they can entirely reactivate thrust planes the mechanical aspects of these types of interaction were studied by analogue modelling in which sand simulates the brittle rocks and silicone putty an interlayered de collement the models underwent compression producing thrust faults with variable dips followed by extension three possible ways of interaction are described here a no interaction occurs in the case of low dip thrust faults 32 1 and normal faults are developed independently displaying a listric geometry b branching at depth on the de collement level occurs when dip of the thrust faults reaches 32 1 in this case the dip of the normal faults whose geometry becomes planar decreases with increasing thrust dip we suggest that this change in dip of normal faults depends upon the rotation of stress tensor axes along the pre existing fault zone where a drop in the friction coefficient is likely to occur c reactivation occurs in brittle material when dip of the pre existing fault exceeds 41 1

tectonic characteristics and evolution history of the pearl river mouth basin abstract on the basis of the new understandings from tens of thousand of kilometres of geophysical material and over 60 exploration and evaluation wells providing data on the pearl river mouth basin prmb this paper analyses the special tectonic position of the prmb where three major plates i e the eurasian the pacific and the indo australian plates meet and interact the characteristics of the basin geological structure and its tectonic evolution are also discussed situated on continental and transitional crust the prmb is a mesozoic cenozoic oil and gas bearing basin developed on caledonian folding basement which was reformed during the mesozoic in the process of its formation and evolution the prmb underwent extension slight compression and re extension with the eruption of intermediate acid and basic magma meanwhile it formed double structural layers with faulting below and depression above and sediments were laid down with marine facies following continental facies hydrocarbons accumulated from continental source rocks in the marine reservoir rocks by using a fracture structure model of the uplift and depression the mechanism of the prmb and its evolution history have been interpreted

strains at the intersections of synchronous conjugate normal faults abstract processes accommodating the mutual offsetting of intersecting conjugate faults are investigated by outcrop examination of three pairs of conjugate normal faults with maximum throws from 5 mm to 10 cm in two cases resolved fault throws decrease sharply towards the intersection zones which on the scale of observation are zones of ductile thinning of inter fault layers that accommodate the throw reductions strain within the intersection zone of conjugate faults in fluvio glacial sands is accommodated by inter grain slip and layer thinning is complemented by layer parallel extension at constant volume in a second example strain within the intersection zone of conjugate faults in inter layered chalk and marl is accommodated by volume reduction without layer extension in a third example also in fluvio glacial sands strain in the intersection zone is accommodated by small faults throws 1 mm when throws on all resolvable faults are aggregated there is no decrease in throw towards the conjugate intersection the presence or absence of a decrease in resolved throw towards conjugate intersections and of a complementary ductile zone accommodating the change in throw is a function not only of the resolution limit of the observations but also of the scale of the deformation process within the conjugate zone

evolution of the south china sea revised ages for breakup and seafloor spreading abstract the continental breakup which gave way to the formation of the oceanic south china sea scs basin began in the latest cretaceous in the northeastern scs and propagated in southern and western direction over a long period of time possibly more than 40 m y the seafloor spreading history of the south china sea has been interpreted in different ways in the past and the debate over the correct timing of the major tectonic events continues we review the different models that have been published and present a revised interpretation of seafloor spreading anomalies based on three datasets with documented high quality which cover all of the scs but the northernmost and southernmost parts we can precisely date the onset of seafloor spreading in the central part of the scs at 32 ma after a ridge jump at 25 ma spreading also began in the southwestern sub basin and spreading ended at 20 5 ma in the entire basin followed by a phase of magmatic seamount formation mainly along the abandoned spreading ridge spreading rates vary from 56 mm yr in the early stages to 72 mm yr after the ridge jump to 80 mm yr in the southwestern sub basin we find indications for a stepwise propagation of the seafloor spreading from northeast to southwest in segments bounded by major fracture zones seafloor spreading ended abruptly probably because the subduction zone along the eastern and southern boundary of the scs of which today the manila trench remains was blocked by collision with a continental fragment possibly the northern part of palawan or a part of the dangerous grounds

the pearl river mouth basin a rift basin and its geodynamic relationship with the southeastern eurasian margin abstract based on multichannel seismic reflection profiles exploration well data and gravity studies the tectonic development of the pearl river mouth basin is discussed in terms of the geodynamic evolution of the southeastern eurasian margin the area around the pearl river mouth basin has been dominated by two episodes of rifting of the attenuated continental crust along the south china margin from the late cretaceous to the early oligocene the rifting brought about ruptures of various magnitudes in various segments of the basin regional normal faults have been produced and resulted in the formation of three major subbasins zhu 1 zhu 2 and zhu 3 which are separated by local uplifts and are characterized by horst and graben structures regional subsidence prevailed throughout the late oligocene recent period and resulted in a tilted continental shelf upon which rests a unified rift basin the pearl river mouth basin a three stage model involving doming rifting and drifting is proposed for the tectonic evolution of the pearl river mouth basin the uplifting and rifting of the continental crust along the south china margin are related to the late episodes of the yanshan orogeny during the late cretaceous early oligocene period when the intensity of rifting decreased the thermal subsidence of the continental margin of south china prevailed during the late oligocene recent period of the himalaya orogeny

effect of ductile and frictional decollements on style of extension abstract scaled analogue models were used to study the effect of frictional and ductile detachments on thin skinned extension models consisted of two halves one half is the ductile and the other has a frictional detachment extension occurred above two different basal configurations a stretchable rubber sheet and a folded banded sheet intended to produce homogeneous and heterogeneous extension respectively model parameters varied systematically and included the brittle ductile thickness ratio rheologies and bulk strain structures in the two halves are compared in profiles and plan views a series of graben developed above both halves of models extended above a banded sheet although there were differences in style propagation rate and width of the deformation zone between the two halves different rates of propagation of structures in the two halves led to the formation of an accommodation or transfer zone parallel to the extension direction most relay ramps and inflection of normal faults in this zone indicate differential extension between the two halves in contrast in models extended above a stretchable rubber sheet extensional structures such as horst and graben developed only above the ductile detachment model results indicate that heterogeneous mechanical stratigraphy and displacement rate have no effect on extensional structure above a rubber sheet however above 20 bulk extension deformation becomes heterogeneous along multiple sets of conjugate faults oblique to the extension direction

measurement of sea surface wind direction using bistatic high frequency radar a method for extracting sea surface wind direction information from bistatic high frequency hf radar doppler spectra is presented by analogy to the monostatic case the ratio of the intensities of the positive and negative bistatic bragg peaks is used to derive the ambiguous wind direction for bistatic operation the reference is taken with respect to the scattering ellipse normal rather than the radar beam direction the method is shown to be valid based on simulated bistatic hf radar doppler spectra wind direction is also extracted from the bistatic radar data collected on the southern china coast comparison between the radar measured wind directions and those obtained from the advanced scatterometer shows good agreement

intersection patterns of normal faults in the lufeng sag of pearl river mouth basin china insights from 4d physical simulations abstract interpretation of seismic data from the lufeng sag of the pearl river mouth basin prmb in the northern part of south china sea shows that different intersection patterns developed in the cover units above basement normal faults a series of analogue models are used to investigate the intersection patterns and deformation in the sedimentary cover sequences above a basement horst bounded by two non parallel faults modelling results show that during their upward propagation the basement faults may intersect within the cover sequences and form a graben above the basement horst length and width of the graben increase with cover thickness the strike and dip intersection points are controlled directly by the thickness of the cover sequences dip and strike of the basement faults and width of the basement horst the intersection point migrates along the axis of the graben toward the wide end of the basement horst when the cover sequence thickens in contrast it migrates toward the narrow end of the basement horst where both fault dip and angle of strike difference increase the intersection point moves upward with increasing width of the basement horst crest model profiles also indicate that in the presence of a ductile layer between the cover and basement such intersection patterns do not form interpretation of seismic data and model results show that the intersection pattern developed in the lufeng sag is a result of propagation of basement faults into cover units during different extension stages of the basin results of this study can be applied to many other sedimentary basins where such fault intersection patterns are likely to form when non parallel conjugate basement faults are active during sedimentation