strike slip tectonics in the sw barents sea during north atlantic rifting swaen graben northern norway this study uses high quality three dimensional 3 d seismic data to investigate the occurrence of strike slip faults in the swaen graben sw barents sea the swaen graben is divided into two principal sub basins ssb1 and ssb2 the along strike and along dip displacement variations and scale relationships are analyzed for forty two 42 faults the displacement profiles for these faults are complex in the swaen graben showing clear evidence for polycyclic fault growth and marked syn sedimentary activity the observed variations in the displacement profiles indicate complex along strike segmentation linkage and mechanical interactions at distinct structural levels along dip displacement minima indicate fault reactivation by dip linkage importantly geometric evidence for strike slip faulting in the swaen graben includes the presence of extensional horsetail splay faults positive flower structures and minor transfer faults this study shows that the faults in the swaen graben developed under extensional regimes during late jurassic to early cretaceous rifting and were reactivated by regional stresses during the late cretaceous the two principal strike slip faults in the swaen graben reveal sinistral movement and are linked at a shallow depth by minor transfer faults at a relay zone our work further demonstrates the occurrence of late mesozoic strike slip movements in the sw barents sea which were induced by regional tectonics halokinesis and fault block rotation importantly strike slip faulting in the region extends perhaps into the cenozoic interacting with extension during the north atlantic rifting

evolution of faulting and plate boundary deformation in the southern taranaki basin new zealand abstract faulting and folding in the southern taranaki basin constrain the evolution of the new zealand plate boundary since 80 ma sedimentary rocks up to 8 km thick record multiple phases of deformation which have been examined using 2d and 3d seismic reflection data resulting in fault displacement time curves and basin wide isopach maps with temporal resolutions of 5 10 myr and 1 4 myr pre and post 23 ma respectively three main phases of tectonic activity have been recognised late cretaceous and palaeocene extension 80 55 ma mainly oligocene and younger contraction and plio pleistocene 3 7 0 ma extension most of the largest faults e g cape egmont fault accrued displacement during the late cretaceous and were reactivated one or more times during subsequent episodes of deformation the oldest phase of extension occurred during gondwana break up and was ubiquitous throughout the basin contraction along the eastern boundary of the basin associated with the onset of hikurangi margin subduction commenced as early as late eocene the zone of contraction widened and migrated westward during the miocene with reverse faults and folds in westernmost parts of the basin formed in the late miocene 7 5 ma initiation and episodic widening of this zone of contraction may have been partly triggered by changes in the rate of plate convergence contraction is now mainly confined to the northern south island and has been succeeded to the north by plio pleistocene extension the present day transition zone between extension in the north and contraction in the south is defined by a wnw trending line across the basin the extension contraction transition migrated southward during the late miocene and pliocene consistent with steepening of the subducting plate and associated southward movement of the southern termination of the hikurangi subduction system

high resolution fault displacement mapping from three dimensional seismic data evidence for dip linkage during fault growth abstract detailed mapping using high resolution three dimensional seismic data has revealed a number of sub horizontal anomalies in the distribution of vertical displacement throw on the planes of growth faults in the gulf of mexico recognition of these anomalies is highly sensitive to the interval at which the fault displacements are sampled because they represent local decreases in throw which are confined to small discrete parts of the fault planes the distribution of the anomalies is inconsistent with model displacement fields of quasi elliptical concentric contours and is therefore incompatible with models of fault growth by uniform slip distribution and radial tip line propagation an alternative model is proposed whereby the evolution of a fault plane is established by the propagation and linkage of precursor fault segments in the dip direction dip linkage overlap and linkage of fault tips in the dip direction results in relay structures that are sub parallel to fault strike and therefore displacement minima that are sub horizontal on normal and thrust faults however since they are orthogonal to the main slip direction on the fault these structures have a low preservation potential and are therefore unlikely to be well resolved on cross sectional seismic profiles

a simple method of determining sand shale ratios from seismic analysis of growth faults an example from upper oligocene to lower miocene niger delta deposits a plot of fault throw vs depth is a simple geometric tool that graphically represents strata thickness variations in growth fault and growth fold settings and has previously been used to infer fault kinematics in this paper we use it as a prediction tool for lithological change employing only seismic data if growth faulting is a continuous process intervals of shale deposition are recorded by unthickened units while intervals of sand fill in topographic lows the throw vs depth plot easily allows depiction of unthickened and thickened sedimentary intervals from even rough seismic records and can therefore be used to predict sand shale ratios the method is here applied to a growth fault in the niger delta that affects oligocene to lower miocene deltaic deposits most shale intervals are identified and the sand shale ratios are predicted we suggest that the method can be a valuable tool in oil exploration

early cretaceous synrift uplift and tectonic inversion in the loppa high area southwestern barents sea norwegian shelf tectonic inversion of rift basins is most commonly reported in the literature to occur after rifting has ceased in contrast we present evidence for synrift localized tectonic inversion from the loppa high area southwestern barents sea and present a model for the formation of inversion structures as a result of differential uplift the structures are of early barremian to mid albian age c 131 105 ma and are focused in or near pre existing extensional boundary faults along the margins of the loppa high inversion is interpreted to be the result of uplift of the high along its inclined boundary faults leading to space accommodation problems as uplift was not properly compensated by extension in the region the model constrains the initiation of uplift of the loppa high to the early barremian and shows that the asymmetric margin configuration of the high may have led to a bulk clockwise rotation of the high around a vertical axis during uplift the cause of uplift is not fully understood but is suggested to be linked to contemporaneous extreme lithospheric thinning in neighbouring basins to the west processes involved may include isostatic flexure thermal heating lithological phase changes and or far field stresses although these aspects need to be further tested

polygonal mounds in the barents sea reveal sustained organic productivity towards the p t boundary three dimensional 3d seismic reflection data from the barents sea show geometric similarities between permian cool water mounds and older carbonate build ups in detail the samson dome area records the development of polygonal mounds in upper permian strata at the same time a gradual drowning event took place in the barents sea the presence of these polygonal mounds is interpreted to reflect i shallower conditions around the samson dome when compared to other parts of the barents sea ii earlier drowning of upper permian mounds towards the west and northwest into the ottar basin based on the recognition of mounds 20 metres below the permiantriassic stratigraphic boundary this paper proposes for the first time that shallow areas of the barents sea such as the samson dome witnessed sustained organic productivity until the onset of the p t extinction event

southwestern barents sea margin late mesozoic sedimentary basins and crustal extension abstract the deep sedimentary basins of the southwestern barents sea were formed in response to several late mesozoic early cenozoic tectonic events within the north atlantic rift zone which culminated with continental breakup and formation of a mainly sheared margin in early tertiary times due to deteriorating data quality the development of the margin bordering sorvestsnaget basin is not well known to improve on this we use both seismic interpretation and gravity modelling to estimate the depth to the middle jurassic mj sequence boundary which marks the onset of mesozoic rifting the horizon represents a first order contrast in seismic velocity and density and the gravity field correlates well with its depth of burial only one seismic line enables tracing of the mj from surrounding areas into the sorvestsnaget basin down to a depth of at least 17 km in the northeastern part of the basin the deep basin is reflected in a general thinning of the crust from 30 36 km within the barents sea to 20 24 km in the margin area the gravity modelling show that the middle jurassic lower cretaceous sequences are of comparable thicknesses in the tromso and sorvestsnaget basins however adjacent to the rifted margin segment the deep northern part of the sorvestsnaget basin is affected by additional large late cretaceous normal faulting and subsidence these faults also caused additional structuring of the intrabasinal veslemoy high post middle jurassic crustal thinning in the southwestern barents sea shows maximum cumulative values exceeding 4 within the tromso and the northern sorvestsnaget basins the corresponding crustal extension is estimated to 70 85 km in a west to northwest direction there is no uniform increase in crustal thinning toward the continent ocean boundary which we attribute to the transform origin of the margin however there is a gradual migration of tectonic activity toward the incipient margin as the time of continental breakup was approached

mesoscale strike slip faults and damage zones at marsalforn gozo island malta well exposed strike slip faults in limestones in the north western part of gozo show damage zones that can be grouped into three categories based on their location along faults tip damage linking damage and distributed damage the predominant fracture types within damage zones include extension fractures and secondary faults tip damage zones usually show wedge shaped patterns formed by antithetic faults and extension fractures commonly accompanied by block rotation several fractures are combined at linking damage zones typically with the concentration of a high intensity of fractures structures in distributed damage zones are typically similar to the classical riedel shear pattern evolutionary and 3d models are proposed in terms of the geometries of damage zones for small displacement strike slip fault zones different evolutionary routes depend on fault tip modes and locations

kinematic analysis of faults in a physical model of growth faulting above a viscous salt analogue abstract syn sedimentary faults overlying an extended ductile layer within a sand model provide an analogue for studying some aspects of the geometry and kinematics of basin scale extensional listric faults associated with salt rollers the displacement analysis techniques used to examine displacement variations over fault surfaces within the sand model show that displacement varies in a regular and predictable manner deviations from simple fault displacement patterns are due to transfers of displacement onto adjacent synthetic faults aggregation of the displacements on adjacent synthetic faults produces more regular patterns of displacement distribution and demonstrates the geometric coherence of the aggregated faults rapid upward decreases in displacement on the model faults are due to fault growth during sedimentation elsewhere in the model post sedimentary faulting is associated with very low upward displacement gradients and pre and syn faulting sedimentation are readily distinguished on cross sectional fault traces in three dimensions a non horizontal line separating the pre faulting and syn faulting sequences tracks the lateral extent of a fault through time backstripping of fault displacements by subtracting the fault displacement of a sedimentary horizon from the displacements of underlying horizons gives the displacement distribution on a fault surface at the time of deposition of the backstripped horizon backstripped fault displacement distributions also allow examination of the general fault structure through time backstripping of fault displacements on one of the larger faults within the model and on an associated hanging wall synthetic splay shows that the two structures originated as a relay zone which was breached by lateral propagation of one of the overlapping faults which form the relay zone the backstripping technique allows determination of the geometrical changes during growth of a fault system

normal fault 3d geometry and displacement revisited insights from faults in the norwegian barents sea abstract utilizing seismic attributes we image fault 3d geometry for 21 normal faults of different sizes in the norwegian barents sea we revisit the published models of fault shape and growth using the new dataset based on the maximum accumulated length l m a x of faults we have classified them into two classes medium size 1 l m a x 1000 m and long faults l m a x 1000 m the common characteristics of these faults are i the medium size faults show mainly irregular shapes while long faults show a variety of shapes including irregular rectangular and elliptical ii in medium size faults maximum displacement is located close to the fault upper tip line iii no lateral segmentation was observed for most of the medium size faults while long faults contain several internal segments at each depth iv linkage with other faults is less common in medium size faults in comparison to the long ones v long faults with an elliptical shape have several displacement maxima located near the fault centre or close to the upper tip line vi long faults with irregular to rectangular shapes show the displacement maxima close to either upper or lower fault tip line our results show that for many of the analyzed faults the maximum displacement is located on the faults longest segment however this is not the case for some of the faults we found that power law fits well with the displacement length and displacement height relations of the faults furthermore the aspect ratio the ratio between fault maximum accumulated length and height is high for the studied faults and ranges between 1 5 and 16 the results can shed light on the understanding of fault geometry and growth for a variety of applications including geological and mechanical models incorporating faults

displacement geometry in the volume containing a single normal fault fault displacements measured in coal mines and from seismic data are used to develop a model describing the near field displacements associated with an ideal single normal fault displacement on a fault surface ranges from a maximum at the center of the fault to zero at the edge or tip line the tip line is elliptical with the shorter axis of the ellipse parallel to the displacement direction contours of equal displacement form concentric ellipses centered on the point of maximum displacement displacement gradients vary with fault size and with mechanical properties of host rock fault radius to maximum displacement ratios range from 5 to 500 plotting of displacement contour diagrams and knowledge of displacement gradients are useful in interpreting seismic reflectio data both for quality control of interpretations and for quantitative extrapolation of limited data displacements associated with faulting decrease systematically with increasing distance along the normal to the fault surface this decrease is seen as reverse drag in both hanging wall and footwall hanging wall rollover and tilting of the reflectors cannot be used to distinguish listric from planar normal faults even where fault block rotation can be demonstrated neither listric fault geometry nor a flat detachment surface is geometrically necessary because faulting is accommodated by ductile deformation rigid fault bounded blocks cannot exist except in some special circumstances related to a free surface the displacements within the rock volume affected by a single fault are not simply related to regional extension apparent horizontal extension by faulting varies from one layer to another and a significant proportion of the extension in a basin may be due to ductile deformation

fault relays bends and branch lines abstract branch lines between normal faults and their sub parallel splays mapped from 3d seismic reflection data show a range of forms from straight lines to closed loops the different geometries are interpreted as representing stages in the failure of relay zones and in the progressive replacement of fault tip lines with fault branch lines the geometries of these normal fault branch lines are similar to those for thrusts previously inferred from limited two dimensional data the orientation of the axis of a relay and its associated bends relative to a fault slip direction is identified as an important control on the structures developed within the relay neutral restraining and releasing bends can each occur on any fault type normal reverse and strike slip but data bias is a major factor in determining which bend geometry is most often observed with each fault type on normal faults the initial relay zone geometry controls the dominant branch line orientation and the same control is likely on branch lines associated with the other modes of faulting a review of the relay geometries and strains occurring with all three modes of faulting highlights the role of the orientation of the mechanical anisotropy of a bedded sequence relative to the orientations of fault surface and slip directions this relative orientation determines how the relay strain is accommodated and hence the degree of hard linkage and development of branch lines

deep seated faults and hydrocarbon leakage in the snohvit gas field hammerfest basin southwestern barents sea abstract high quality 3d seismic data are used to analyze the history of fault growth and hydrocarbon leakage in the snohvit field southwestern barents sea the aim of this work is to evaluate tectonic fracturing as a mechanism driving hydrocarbon leakage in the study area an integrated approach was used which include seismic interpretation fault modeling displacement analysis and multiple seismic attribute analysis the six major faults in the study area are dip slip normal faults which are characterized by complex lateral and vertical segmentation these faults are affected by three main episodes of fault reactivation in the late jurassic early cretaceous and paleocene fault reactivation in the study area was mainly through dip linkage the throw distance plots of these representative faults also revealed along strike linkage and multi skewed c type profiles the faults evolved through polycyclic activity involving both blind propagation and syn sedimentary activity with their maximum displacements recorded at the reservoir zone the expansion and growth indices provided evidence for the interaction of the faults with sedimentation throughout their growth history soft reflections or hydrocarbon related high amplitude anomalies in the study area have negative amplitude reverse polarity and are generally unconformable with structural reflectors the interpreted fluid accumulations are spatially located at the upper tips of the major faults and gas chimneys four episodes of fluid migration are inferred and are linked to the three phases of fault reactivation and neogene glaciations hydrocarbon leakage in the snohvit gas field is driven by tectonic fracturing uplift and erosion the interpreted deep seated faults are the main conduits for shallow hydrocarbon accumulations observed on seismic profiles

experiments on shortening of a 4 layer model of the continental lithosphere davy ph and cobbold p r 1991 experiments on shortening of a 4layer model of the continental lithosphere in p r cobbold editor experimental and numerical modelling of continental deformation tecronophysics 188 l 25 we present an experimental method for modelhng lithospheric deformation the method is based on a simplified profile of lithosphere rheology where only four layers are considered brittle crust ductile crust brittle mantle and ductile mantle the strengths of the four layers calculated from laboratory determined flow laws depend strongly on geothenns and slightly on strain rates and deformation regimes the rheological profiles of the lithosphere have been recreated in experimental models built with analog materials sand silicone putty and golden syrup which flow under their own weight during lithospheric shortening the style of deformation depends on the relative strengths of the four layers especially those in the mantle of special importance is the existence or non existence of a brittle mantle the initial stages of compression often produce flexures or buckles without local isostatic compensation buckling exerts a strong control on the localisation of thrust faults in later stages the thrusts tend to form at the inflexion points of buckles the style of crustal thickening depends on the relative thicknesses and resistances of the lithospheric layers in 2 layer lithospheric models without resistant mantle shortening was concentrated upon a small number of thrusts widely spaced in 3 layer models shortening was concentrated into a large number of reverse faults more closely spaced and more steeply dipping than before in clayer models a single thrust formed in the brittle mantle motion on this thrust dragged the crustal layers down forming an asymmetric crustal root with steep imbricate slices

analogue modelling of intraplate strike slip tectonics a review and new experimental results abstract intraplate strike slip zones commonly display intricate 3 d geometries with rapid changes in structural style along strike and with depth strike slip deformation typically results in complex vertical and horizontal sections that can be difficult to interpret coherently physical modelling of strike slip fault systems is a powerful and graphic tool to help in providing a unified picture of the evolution of strike slip zones with considerable spatial and temporal detail a large number of experimental studies have investigated different aspects of strike slip tectonics using materials such as dry sand wet clay or silicone the choice of analogue material and experimental design exerts a strong control on the structures that form in the model here we present a review of different experimental setups used to investigate intraplate strike slip tectonics from the classical riedel experiment to more sophisticated setups using brittle and viscous analogue materials we review our current understanding from models of distributed shear transtension transpression pull apart basins formed in releasing stepovers and popups formed in restraining stepovers in addition we present the results of two new experimental series that investigated 1 the effect of crustal weak zones on strike slip fault zone segmentation and 2 strike slip and transpressional reactivation of extensional basins

analogue modelling of orthogonal and oblique rifting abstract the three dimensional progressive development of orthogonal and oblique rift systems has been simulated using scaled analogue sandbox models the orientation of the zone of rifting where angle between the rift axis and the extension direction was varied systematically from 90 orthogonal rifting to 75 60 and 45 oblique rifting completed models were impregnated and sectioned both vertically and horizontally orthogonal rift models are characterized by long straight rift border faults and intra rift faults perpendicular to the extension direction oblique rift models are characterized by shorter segmented rift border faults and intrarift faults in the oblique models the rift border faults formed en echelon arrays parallel to the inderlying zone of basement stretching whereas the intra rift faults formed at a high angle to the extension vector increased extension in the moderately oblique and oblique rift systems 60 and 45 caused the intra rift faults to rotate towards parallelism with the rift border faults no strike slip or oblique slip transfer faults were found in any experiments rift border faults and intra rift faults in the models are segmented along strike with relay ramp structures formed between overlapping fault tips along the strike of the rift variations in half graben polarities and offsets of depocentres are accomplished by accommodation zones formed by interlocking conjugate fault arrays the experimental fault patterns compare well with the fault architectures found in those modern or relatively young rift systems where well defined basement controlled strike slip or oblique slip transfer faults are absent an accommodation zone model consisting of interlocking conjugate extension faults is proposed for the along strike switching of half graben asymmetries and offsetting of depocentres in rift systems the fault geometries in the analogue models can be used as templates for recognition of fault styles in both orthogonal and in oblique rift environments

progressive localisation of strain during the evolution of a normal fault population abstract the evolution of a syn sedimentary normal fault population has been established from the analysis of a high quality 3d seismic reflection survey from the timor sea offshore nw australia growth of the fault population which initiated ca 6 ma ago occurred in three distinct but temporally overlapping stages the initial stage of fault population evolution was characterised by rapid growth of fault length in the first 1 2 ma of extension displacement rates of individual faults were established during this stage and were constant throughout subsequent fault growth the second stage involved amplification of fault displacements on existing fault traces with minimal fault propagation during the third stage shortening of the traces of active faults and high mortality rates for small faults resulted in a net decrease in fault trace length on successively younger horizons this stage was accompanied by a declining extension rate fault throw populations have constant slopes on each syn faulting horizon however an up sequence shallowing of the slope of length and geometric moment populations demonstrates a progressive concentration of strain onto fewer and larger faults through time if extension were to continue beyond the present value of 4 5 this strain localisation might culminate in the formation of a single active through going fault

3 d visualization and isochore analysis of extensional diapirs overprinted by compression palinspastic restorations elucidate geologic and hydrocarbon migration histories in salt provinces however salt dissolution and salt flow in and out of the section plane make it difficult to determine the shape of salt bodies before deformation which hampers accurate restorations three dimensional computer visualization of a physical model and analysis of isochores provide clues to the original shape of allochthonous salt bodies that were emplaced during extension and later compressed

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

latest aspects of earthquake prediction in greece based on seismic electric signals ii abstract since 1983 continuous monitoring of the electrotelluric field has been carried out using an array of measuring stations located at various sites in greece the basic physical properties of the transient changes seismic electric signals ses in the electrotelluric field that are forerunners of earthquakes were first described six years ago since then a large body of data has been collected resulting in new insight into various aspects of the method the present paper reviews the latest developments in ses based earthquake prediction and describes the current procedures used to predict the epicenter and magnitude of an impending earthquake a detailed list of the predictions officially issued in greece during the past 3 years january 1 1987 november 30 1989 is also given public warnings were issued well before the most destructive seismic activity

rapid dike emplacement leads to eruptions and hydrothermal plume release during seafloor spreading events the creation of ocean crust by rapid injection of magma at mid ocean ridges can lead to eruptions of lava onto the seafloor and release of event plumes which are huge volumes of anomalously warm water enriched in reduced chemicals that rise up to 1 km above the seafloor here we use seismic data to show that seafloor eruptions and the release of hydrothermal event plumes correspond to diking episodes with high injection velocities and rapid onset of magma emplacement within the rift zone these attributes result from high excess magma pressure at the dike source likely due to a new influx of melt from the mantle these dynamic magmatic conditions can be detected remotely and may predict the likelihood of event plume release during future seafloor spreading events

long lived fault zones and their influence on the tectonic development of the southwestern barents sea the southwestern barents sea shows a complicated network of fault complexes and systems with various geometrical and genetic characteristics trend relation to basement reactivation fault plane geometry and regional significance using these parameters a classification of the fault complexes has been made and a correlation to onshore faults has been attempted the area is subdivided into several fault blocks separated by deep seated zones of weakness first and second class fault systems these are reactivated in connection with later mesozoic movements in the area and have acted as foci of strain so leaving the central area of the blocks relatively strain free a third class of fault systems is of local significance and reflects deformation limited to the interior of the fault blocks

the three dimensional geometry of relay zones within segmented normal faults abstract individual normal faults are rarely single planar surfaces and often comprise arrays of fault segments arising from the earliest stages of fault propagation current models for the geometry and formation of relay zones between adjacent fault segments have been informed mainly by 2d analysis from either maps or cross sections observed in outcrop and to a lesser extent by the analysis of relay zones from 3d seismic reflection data using high quality 3d seismic reflection datasets from a selection of sedimentary basins we investigate fundamental characteristics of segmentation from the analysis of 67 normal faults with modest displacements

growth and linkage of a complex oblique slip fault zone in the pearl river mouth basin northern south china sea abstract oblique slip faults are ubiquitous in sedimentary basins but have been largely neglected relative to their dip slip counterparts case studies of oblique slip faults are very limited in this study we used 3d seismic data tied to well control to investigate the geometry kinematic characteristics growth and linkage and tempo spatial evolution of a complex oblique slip growth fault zone in the pearl river mouth basin prmb of the northern continental margin south china sea scs the e w oriented 30 5 km long fault zone consists of two superimposed oblique slip fault systems the lower fault system is an integrated zig zag fault consisting of three ene wsw to e w striking right stepping sinistral en echelon fault segments which were hard linked by two nw se trending fault segments while the upper fault system is composed of nine wnw ese striking left stepping dextral en echelon component faults which had overlapping fault tips and were partly hard linked by breaching of the relay zones the lower and upper fault systems were activated in the eocene and the oligocene to pliocene which respectively correspond to the syn rift and post rift stages in the prmb the fault throws up to 288 m and activity rates up to 34 5 m ma of the upper fault system are overall much less than those of its lower counterpart reactivation of the lower syn rift fault system shows clear influence on the development of post rift en echelon fault segments a four stage evolution model of the oblique slip fault zone was presented

normal fault growth and linkage in the whakatane graben new zealand during the last 1 3 myr determination of fault growth rates and fault network evolution at time scales from 104 106 years has been hampered by a lack of a well constrained stratigraphic succession that provides a high fidelity record of fault development over these time periods here we show how seismic reflection data of different spatial resolutions can be used to constrain the linkage history and displacement rate variations of a single major fault we present data collected in the offshore whakatane graben bay of plenty new zealand where intense normal faulting occurs as a result of active back extension the focus of our study is the rangitaiki fault a linked segmented normal fault which is the dominant active structure in the graben the total linked fault length is c 20 km long and has a displacement of up to 830 130 m in the top 1 5 km of sediments the fault has been actively growing for the last 1 34 0 51 ma and has developed from isolated fault segments to a fully linked fault system initially the dominant process of fault growth was tip propagation with an average and maximum displacement rates of 0 52 0 18 mm yr 1 and 0 72 0 23 mm yr 1 respectively interaction and linkage became more significant as the fault segments grew towards each other resulting in the fault network becoming fully linked between 300 and 18 ka following fault segment linkages the average displacement rate of the fault network increased by almost three fold to 1 41 0 31 mm yr 1 while the maximum displacement rate increased to 2 72 0 61 mm yr 1 this is the first time that the growth rate of unlinked fault segments has been resolved and has been shown to be slower than in the subsequent linked fault system

tectonic evolution of the penglai 7 6 structure and its implications for petroleum exploration in a releasing bend of a strike slip fault system tan lu fault zone east china abstract the penglai 7 6 pl7 6 structure is located on the tan lu fault zone a huge fault zone in east asia tectonism of the tan lu fault zone produced complex structural deformation and was an important factor in petroleum accumulation three dimensional seismic data were employed to document the structural geometry and evolutionary process of the pl7 6 structure and implications for petroleum exploration in a releasing bend of a strike slip fault system were discussed systematic analysis of the seismic data indicates that the main fault the bd2 fault of the tan lu fault system slipped right laterally during the cenozoic strike slip movement of the bd2 fault peaked during deposition of e 1 2 k to e 3 d 3 and decreased largely in intensity during e 3 d 1 2 deposition in the neogene and quaternary the bd2 fault was reactivated formation of the bodongnan low uplift is related to the connection between the bodongnan low uplift n and bodongnan low uplift s the bodongnan low uplift n is represented by an anticline produced by strike slip movement of the bd2 fault and the bodongnan low uplift s is represented by the relatively uplifted strata in the vicinity of an extensional fault the bd3 fault the pl7 6 structure developed above a releasing bend formed by the subsequent strike slip movement of the curved bd3 fault orientations of the shallow faults in the pl7 6 structure are not only associated with the lower bd3 fault but also controlled by the basement high unlike traditional releasing bends that are generally disadvantage to petroleum accumulation due to the lower structural elevation in the center the releasing bend in the pl7 6 structure is favorable for petroleum accumulation because of the three reasons 1 adjacent to generative kitchens 2 located on a regional structural high and 3 served by the releasing bend related faults acting as conduits for vertical petroleum migration

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

probability of earthquake occurrence in greece with special reference to the van predictions the van earthquake predictions were made on the basis of seismic electric signals ses but the debate seems to be directed toward the statistical significance of the predictions from seismic data only accordingly applying a logistic regression model to seismicity we present our estimation of the probability of earthquake occurrence in greece the main purpose of our study is to examine whether or not we can find a specific seismicity pattern that can be used to considerably increase probability estimates our estimation of the probability of occurrence of an earthquake of ms 5 0 is less than 0 25 in all the cases that we have examined if we lower the threshold magnitude from 5 0 to 4 3 we can find cases in which the probability becomes as high as 0 75 comparable to the success rate of the van method estimated by hamada 1993 in these cases however such a high probability is due mostly to aftershocks and if aftershocks are removed from the data set the probability falls below 0 5

evolution of a salt related listric growth fault near the d 1 well block 5605 danish north sea displacement history and salt kinematics abstract the top chalk surface and the tertiary sediments of the danish north sea are cut by only a few major faults which are often related to or controlled by the mobile zechstein salt a single listric growth fault the d 1 fault and its adjacent area have been mapped in detail in order to unravel the fault geometry and kinematics the spatial distribution of displacements and lateral dimensions of the fault are used to examine the interaction between salt movements and the evolution of the fault the displacement distribution on the fault is systematic with contours of equal displacement forming concentric semi ellipses centred on the point of maximum displacement with displacement decreasing upwards and laterally approaching the displacement configuration for the upper part of an ideal simple blind fault furthermore within the volume surrounding the fault vertical displacement shows similar contour patterns for the hangingwall and footwall respectively the lateral displacement variation during fault growth and reconstructed displacement geometries indicate that footwall uplift was mainly a result of salt flow despite the complicated nature of salt dynamics the evolution of the d 1 fault resulted in a systematic fault displacement geometry within the rock volume surrounding the fault

new insights into mid ocean ridge volcanic processes from the 2005 2006 eruption of the east pacific rise 9 46 n 9 56 n digital seafloor imagery collected on 37 camera tows and alvin dives in which we identify 186 contacts between new and old lava are used to create the most detailed map of a mid ocean ridge mor eruption to date lava flows erupted in 2005 2006 at the east pacific rise epr covered an area of 14 6 km2 along 18 km of the epr crest between 9 46 and 9 56 n the 2005 2006 lava is characterized by inflated lobate and sheet morphologies in the flow interiors and pillow forms at terminal flow fronts numerous lava channels 10 50 m wide and 1 5 m deep trending approximately east west served as distributory pathways eruptions were sourced from fissures within the epr axial summit trough as well as fissures located on an off axis fissure mound 600 m east of the epr axis between 9 52 and 9 56 n portions of the lava flow reached as far as 2 km east of the axis near 9 51 2 n using a conservative estimate of 1 5 m for the average flow thickness implies that the 2005 2006 eruptions produced 22 106 m3 of lava 4 5 times larger than estimated volumes of 1991 1992 epr lava flows estimated lava volume for the 2005 2006 eruptions represents 15 of the magma available in the axial magma chamber

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

fault development and interaction in distributed strike slip shear zones an experimental approach analogue model experiments using both brittle and viscous materials were performed to investigate the development and interaction of strike slip faults in zones of distributed shear deformation at low strain bulk dextral shear deformation of an initial rectangular model is dominantly accommodated by left stepping en echelon strike slip faults riedel shears r that form in response to the regional bulk stress field push up zones form in the area of interaction between adjacent left stepping riedel shears in cross sections faults bounding push up zones have an arcuate shape or merge at depth adjacent left stepping r shears merge by sideways propagation or link by short synthetic shears that strike subparallel to the bulk shear direction coalescence of en echelon r shears results in major through going faults zones master faults several parallel master faults develop due to the distributed nature of deformation spacing between master faults is related to the thickness of the brittle layers overlying the basal viscous layer master faults control to a large extent the subsequent fault pattern with increasing strain relatively short antithetic and synthetic faults develop mostly between old but still active master faults the orientation and evolution of the new faults indicate local modifications of the stress field in experiments lacking lateral borders closely spaced parallel antithetic faults cross faults define blocks that undergo clockwise rotation about a vertical axis with continuing deformation fault development and fault interaction at different stages of shear strain in our models show similarities with natural examples that have undergone distributed shear

magmatic activity during the breakup of greenland eurasia and fluid flow in stappen high sw barents sea abstract a great deal of magmatic activity was recorded along the northern atlantic margins during the cenozoic opening of the norwegian greenland seas this work uses a recently acquired two dimensional seismic reflection dataset to characterize magmatic rocks and fluid flow features on the western margin of stappen high hard kicks are positive seismic high amplitude anomalies related to igneous rocks in the subsurface while soft kicks are negative high amplitude anomalies interpreted as fluid related anomalies the hard kicks are the most prominent anomalies in the study area and they are distributed in a n s zone that is coincident with the trend of the stappen high the hard kicks include extrusive and intrusive rocks such as lava flows dykes and volcanic sills the sills have saucer bowl transgressive tabular and convex geometries extrusive igneous rocks and other deeply seated volcanic sills are buried to a depth of greater than 3000 ms soft kicks are bright spots and enhanced reflections found close to angular unconformities channels clinoforms and canyons hydrothermal vents and vertical clusters of soft kicks gas charged sediments are evidence of vertically focused fluid flow in the study area this work finds that large scale magmatic edifices recorded in other northern atlantic margins are also present in the study area as volcanoes volcanic plateaus and cascade transgressive sills volcanic rocks in stappen high were emplaced during the late eocene oligocene and early pliocene delimiting the areas into a southern part that is magma rich and a northern hydrocarbon rich province

comparison of dike intrusions in an incipient seafloor spreading segment in afar ethiopia seismicity perspectives 1 oceanic crust is accreted through the emplacement of dikes at spreading ridges but the role of dike intrusion in plate boundary deformation during continental rupture remains poorly understood between 2005 and 2009 the 70 km long dabbahu manda hararo rift segment in ethiopia has experienced 14 large volume dike intrusions 9 of which were recorded on temporary seismic arrays a detailed comparison of the seismic characteristics of the seismically monitored dikes is presented with implications for dike intrusion processes and magmatic plumbing systems all of the migrating swarms of earthquakes started from a 80 of energy is released during the propagation phase with minimal seismic energy release after the dike propagation ceases we interpret that faulting and graben formation above the dikes occurs hours after the passage of the dike tip coincident with the onset of low frequency earthquakes dike lengths show no systematic reduction in length with time suggesting that topographic loading and stress barriers influence dike length as well as changes in tectonic stress the propagation velocities of all the dikes follow a decaying exponential northward propagating dikes had faster average velocities than those that propagated southward suggesting preconditioning by the 2005 megadike or ongoing heating from a subcrustal magma source north of the midsegment

segmentation and growth of an obliquely reactivated normal fault abstract detailed kinematic analysis of a large 1800 m maximum displacement reactivated normal fault in the taranaki basin new zealand has been conducted using high quality 3d seismic data the parihaka fault is approximately north south striking in basement where it accrued late cretaceous to early eocene displacements in response to east west extension and was obliquely reactivated by nw se extension in the pliocene reactivation resulted in upward propagation newly formed segmentation and up dip clockwise rotation of the fault surface by up to 20 from the strike of the basement fault fault segmentation and map view soft linkage by relay zones in post miocene strata was synchronous with the formation of antithetic faults in late miocene strata at bends in the fault surface fault segment lengths antithetic faults and relay zone dimensions were formed geologically instantaneously during initial reactivation of the main fault at 3 7 3 4 ma i e within the first 10 of faulting rapid formation of pliocene fault segments is followed by displacement accumulation without an increase in fault segment length until eventual relay breaching when continued ramp rotation is unsustainable this evolutionary history is consistent with a model in which arrays of fault segments are from inception components of a single coherent structure

what controls relay ramps and transfer faults within rift zones insights from analogue models abstract structures within rift zones exhibit two main types of interaction relevant at the rift scale relay ramps and transfer faults at high angle to the rift analogue experiments have been performed to investigate whether these types of interaction may be affected by differential extension along the rift in these models sand brittle crust analogue overlies two adjacent silicone ductile crust analogue layers with different viscosity in order to simulate different percentage extension rates e along rifts the experiments show a distinct behaviour as a function of e for e e 21 3 the interaction occurs by means of transfer faults striking subparallel to the extension direction experimental data are consistent with the geometries and extension rates of rift zones relay ramps characterize narrow rifts and oceanic ridges where the mean percentage of extension is low e e 39 where the rift more likely achieves differential extension e 21

evolution of shelf margin clinoforms and deep water fans during the middle eocene in the sorvestsnaget basin southwest barents sea interpretation of seismic data from the sorvestsnaget basin southwest barents sea demonstrates gradual middle eocene basin infilling from the north generated by southward prograding shelf margin clinoforms the basin experienced continued accommodation development during the middle eocene because of differential subsidence caused by the onset of early eocene sea floor spreading in the norwegian greenland sea faulting salt movement and different tectonic activity between the sorvestsnaget basin and veslemoy high during this time the margin shows transformation from an initially high relief margin to a progradation in the final stage the early stage of progradation is characterized by the establishment of generally oblique clinoform shifts creating a flat shelf edge trajectory that implies a gentle falling or stable relative sea level and low accommodation to sediment supply ratio 1 in the topsets during the early stage of basin development the high relief margin narrow shelf stable or falling relative sea level seismicity and presumably high sedimentation rate caused accumulation of thick and areally extensive deep water fans seismic scale sandstone injections deform the fans a fully prograding margin developed when the shelf to basin profile lowered apparently because of increased subsidence of the northern part this stage of the basin development is generally characterized by the presence of sigmoid clinoform shifts creating an ascending shelf edge trajectory that is implying steady or rising relative sea level with an accommodation to sediment supply ratio of greater than 1 implying sand accumulation on the shelf this study suggests that some volume of sand was transported into the deep water during relative sea level rise considering the narrow shelf and inferred high rates of sediment supply

the geometry of listric normal faults and deformation in their hangingwalls abstract in cross sections containing listric extensional faults area balancing techniques for depth to decollement are usually based on either bed length conservation or displacement conservation listric fault geometry may be constructed from a hangingwall roll over profile using the chevron construction this construction based on conservation of heave necessitates a reduction in fault displacement with decreasing fault dip a modification of this construction utilizing conservation of fault displacement predicts a listric fault that detaches at a shallower depth a new construction based on slip lines uses fault perpendicular displacement segments to generate listric fault shape fault propagation strain may be responsible for anomalous hangingwall geometries and these can be predicted by forward modelling using either a modified chevron construction or a slip line construction

chronologic modeling of faulted and fractured reservoirs using geomechanically based restoration technique and industry applications we have developed a geomechanically based restoration method to model reservoir deformation the approach founded on the finite element method simulates the physical behavior of the rock mass and considers heterogeneous material properties bedding slip and the mechanical interaction of faults to demonstrate the method s potential we analyze the deformation and fault growth in the hanging wall of a synsedimentary listric normal fault from a sand box model which provides an analog for evaluating complex faulted reservoirs the numerical model results are then analyzed to investigate the chronology of faulting the numerical model corresponds well to the physical model and provides additional insights about reservoir evolution and deformation the approach is also tested on a natural example of folding using outcrop data to study contractional deformation these examples illustrate how undetected faults and fractures reservoir compartmentalization hydrocarbon migration pathways and hydrocarbon traps can be understood in the context of tectonic processes and how this understanding can be exploited in decision making and reducing risk we conclude that the geomechanically based restoration of faulted and fractured reservoirs has significant potential for industry applications compared to common geometric restoration techniques which lack a mechanical basis

theoretical model of block rotation along circular faults abstract the overall structure of rifts is often controlled by normal faults and tilted blocks in several rifts the crests of the blocks have been strongly eroded while the associated half graben has undergone large subsidence the relative movement of the crest of a block can be analysed assuming simple circular geometry of its bounding fault in such a geometric model subsidence of the half graben and relative uplift of the crest are connected and this coupling can be quantified as a function of the fault shape and of the block width knowing the geometry of a fault we can calculate the movements of a rigid block rotating along this fault inversely by knowing the tilting of a block it should be possible to estimate the geometry of the guiding fault i e its detachment depth if we assume the fault to be listric numerical results show that a large block can undergo an absolute uplift the direction of the movement depends on the initial width of the block and is quite independent of the tilt angle except for very low angle faults

electromagnetic precursors to earthquakes in the ulf band a review of observations and mechanisms despite over 2 decades of international and national monitoring of electrical signals with the hope of detecting precursors to earthquakes the scientific community is no closer to understanding why precursors are observed only in some cases laboratory measurements have demonstrated conclusively that self potentials develop owing to fluid flow and that both resistivity and magnetization change when rocks are stressed however field experiments have had much less success many purported observations of low frequency electrical precursors are much larger than expectations based on laboratory results in some cases no precursors occurred prior to earthquakes or precursory signals were reported with no corresponding coseismic signals nonetheless the field experiments are in approximate agreement with laboratory measurements maximum resistivity changes of a few percent have been observed prior to some earthquakes in china but the mechanism causing those changes is still unknown anomalous electric and magnetic fields associated with fluid flow prior to earthquakes may have been observed finally piezomagnetic signals associated with stress release in earthquakes have been documented in measurements of magnetic fields

a new view of the he ar co2 degassing at mid ocean ridges homogeneous composition of magmas from the upper mantle abstract deep sea exploration is rapidly improving our understanding of volatiles geochemistry in mid ocean ridge igneous products it is also placing greater constraints on degassing processes of the earth s mantle with the result that degassing models based on vapour melt equilibrium are no longer able to explain the increasing number of data in fact such models force to postulate an upper mantle strongly heterogeneous at any scale and cannot account for the widespread carbon supersaturation of the recovered igneous products here we review the global he ar co 2 dataset of fluid inclusions in mid ocean ridge glasses using the framework of advanced modelling of multicomponent bubble growth in magmas we display that non equilibrium fractionations among he ar and co 2 driven by their different diffusivities in silicate melts are common in most of the natural conditions of magma decompression and their signature strongly depends on pressure of degassing due to the comparable ar and co 2 diffusivity magma degassing at low pressure fractionates both the he ar and he co 2 ratio by a similar extent while the slower co 2 diffusion at high pressure causes early kinetic effects on ar co 2 ratio and dramatically changes the degassing path on this ground the very different geochemical signatures among suites of data coming from different ridge segments mainly depend on the depth of the magma chamber where the melt was stored besides the variations inside a single suite highlight variable ascent speed and cooling rate of the emplaced lava the large variations in both the he co 2 and ar co 2 ratios at almost constant he ar displayed in glasses coming from the mid atlantic ridge 24 30 n segment and the rodriguez triple junction are therefore interpreted as a high pressure signature in contrast the simultaneous increase in both he co 2 and he ar of the east pacific rise pito seamount and south east indian ridge data sets suggests the dominance of low pressure fractionation implying that the shallow magma chambers are at a lower depth than those of the mid atlantic ridge 24 30 n and rodriguez triple junction our conclusions support the presence of a relationship between spreading rate and depth of high temperature zones below ridges and are consistent with the depth of magma chambers as suggested from seismic studies non equilibrium degassing explains the volatile systematics of mid ocean ridge basalts by starting from a single mantle derived magma dispensing with the supposed need for heterogeneities in abundance ratios of volatiles in the mantle below oceanic ridges

continuation of the caledonides north of norway seismic reflectors within the basement beneath the southern barents sea abstract the offshore continuation of the caledonides to the north of norway is poorly understood and the seismic signature of these rocks is unknown indeed the seismic signature of basement rocks is in general poorly documented from conventional seismic data this paper discusses an area in the southern barents sea the gjesvaer low where inferred caledonian basement rocks have been studied from conventional seismic data the gjesvaer low which has not been described previously as a separate structural element is defined on image processed gravity data the main processing steps were directional filtering and principal component analysis the interpretation of the low as a feature within the inferred basement rocks is based on well data the calculated depth to magnetic basement seismic signature and velocities in addition two dimensional gravity modelling shows that density variations within the basement rocks may explain the observed gravity anomaly although the following model may be simplistic distinct seismic reflectors within the low may be interpreted as originating from tectonic boundaries within a thrust system in the most likely evolutionary scenario the gjesvaer low and the south western part of the nordkapp basin are interpreted as having been formed as continuous caledonian structures whose continuity has survived until the present subsequent late palaeozoic erosion may have removed more than 10 km of caledonian rocks in the area of the low carboniferous rifting reactivated the caledonian structures and the south western nordkapp basin was formed the nordkapp basin which was decoupled from the gjesvaer low in carboniferous times subsided while the low was again eroded

magma dynamics at mid ocean ridges by noble gas kinetic fractionation assessment of magmatic ascent rates abstract despite its impact in understanding oceanic crust formation and eruptive styles of related volcanism magma dynamics at mid ocean ridges are poorly known here we propose a new method to assess ascent rates of mid ocean ridge basalt morb magmas as well as their pre and sin eruptive dynamics it is based on the idea that a rising magma can reach a variable degree of both co2 supersaturation in melt and kinetic fractionation among noble gases in vesicles in relation to its ascent rate through the crust to quantify the relationship we have used a model of multicomponent bubble growth in morb melts developed by extending the single component model of proussevitch and sahagian a a proussevitch d l sahagian dynamics and energetics of bubble growth in magmas analytical formulation and numerical modeling j geophys res 103 1998 18223 18251 to co2 he ar gas mixtures after proper parameterization we have applied it to published suites of data having the required features glasses from pito seamount and mid atlantic ridges our results highlight that the investigated morb magmas display very different ranges of ascent rates slow rises of popping rock forming magmas that cross the crust 0 01 0 5 m s slightly faster rates of energetic effusions 0 1 1 m s up to rates of 1 10 m s which fall on the edge between lava effusion and hawaiian activity inside a single plumbing system very dissimilar magma dynamics highlight the large differences in compressive stress of the oceanic crust on a small scale constraints on how the systems of ridges work as well as the characteristics of the magmatic source can also be obtained our model shows how measurements of both the dissolved gas concentration in melt and the volatile composition of vesicles in the same sample are crucial in recognizing the kinetic effects and definitively assessing magma dynamics an effort should be made to correctly set the studied samples in the sequence of volcanic submarine deposits where they are collected enhanced knowledge of a number of physical properties of gas bearing mor magmas is also required mainly noble gas diffusivities to describe multicomponent bubble growth at a higher confidence level

geometry and segmentation of an evaporite detached normal fault array 3d seismic analysis of the southern bremstein fault complex offshore mid norway abstract the halten terrace offshore mid norway is underlain by a triassic evaporitic package that is rheologically weak and led to decoupling of fault systems during middle jurassic to early cretaceous rifting we use 2d and 3d reflection seismic data constrained by wells from the southern bremstein fault complex of the halten terrace to map faults and key stratigraphic horizons and analyse throw variations along faults allowing us to constrain patterns of fault segmentation and linkage within the complex the bremstein fault complex has an overall tilted monoclinal geometry with localised fault systems at base salt level associated with overlying highly distributed systems of normal faults vertical strain partitioning across the evaporite package means that sub evaporite and supra evaporite fault populations acted as semi independent fault systems supra evaporite faults are partly gravity driven and controlled by sub evaporite faulting and consequent tilting of the evaporitic package this behaviour leads to a wide variety of possible vertical linkage patterns of faults across the evaporite package a greater variety of lateral segment linkage patterns occurs in evaporite detached normal fault systems than in normal fault systems developed in the absence of evaporite units segment boundary styles can also be modified by migration of evaporite some segment boundaries are associated with a footwall anticline and hanging wall syncline in contrast to the footwall synclines and hanging wall anticlines widely described in studies of normal fault systems

offshore prolongation of caledonian structures and basement characterisation in the western barents sea from geophysical modelling this study interprets the potential field of the western barents shelf at a crustal scale and characterises the basement underlying the deep basins in the southwestern barents sea comparing potent

measurements of friction coefficients and cohesion for faulting and fault reactivation in laboratory models using sand and sand mixtures abstract simple laboratory tests have been made on dry quartz sand and on mixtures of sand and clay and sand and cement tests were made on both low and high density specimens of each mixture as determined by physical handling techniques the tests included measurements of density estimates of the coefficient of internal friction based on fault orientation and estimates of the friction coefficients and cohesion values for fault initiation and reactivation in a shear frame apparatus which was also used to test artificial fault zones made from pure clay glass microspheres and wheat flour the results suggest that density is determined more by handling technique than by composition and that friction coefficients and perhaps cohesion both increase with increasing density the shear testing revealed a consistent drop in cohesion for fault reactivation in all densely packed mixtures tested although small this drop may be significant for some types of laboratory models

displacement transfer between intersecting regional strike slip and extensional fault systems interaction and displacement transfer between active intersecting strike slip or transform and extensional fault systems are examined outcrop data from a well preserved strike slip fault and rift intersection in new zealand are compared to a global data set of 13 such intersections in both continental and oceanic crust displacement transfer between strike slip and normal faults is typically accomplished by gradual changes of fault orientations and slip vectors close to the intersection zone for two and three plate configurations these changes result in sub parallelism of the slip vectors of the component faults with their line of intersection the dimensions of the area over which fault strike and slip vectors change are principally controlled by the extent to which displacements on the dominant of the two intersecting fault systems are confined to a single slip surface or distributed across a zone where slip is spatially distributed the region in which the two displacement fields are superimposed produces transtension and associated oblique slip this distributed off fault deformation facilitates the development of a quasi stable configuration of the fault intersection region maintaining both the regional geometry and kinematics of the intersection zone which in many cases would not be possible for rigid block translations the dimensions of the transition zone are larger for continental crust than for oceanic crust because oceanic crust is thinner fault geometries in oceanic crust are simpler two plate configurations and the slip vectors of the component intersecting fault systems are sub parallel

high resolution record of tectonic and sedimentary processes in growth strata growth strata are used to determine the kinematics of synsedimentary structures such as faults classical methods of analysis such as thickness versus throw plot consider that the available space created by fault slip in the hanging wall of faults is instantaneously filled up by sediments this has lead many previous works to identify a cyclic activity for growth faults here we perform a careful analysis of the variation of strata thicknesses on each side of a very well documented normal growth fault in the niger delta we show that these thickness variations are induced by the alternation of sedimentary processes during continuous fault slip suspended load processes induce either uniform or slightly variable thickness of a large majority of mudstone layers bedload processes result in a preferential thickening of sand layers in the hanging wall these high quality data thus provide strong grounds for doubting the polycyclic growth diagnosed for some faults at the scale of sedimentary cycles and supports the notion that fault displacement rates can be very well behaved our study emphasizes the important conclusion that stable fault growth and related displacement rates can appear to be punctuated when viewed at the scale of sedimentary cycles it follows that care should be taken when attempting to derive displacement rates on temporal scales equivalent to those of alternating sedimentological cycles

reply to comment on co2 variability in mid ocean ridge basalts from syn emplacement degassing constraints on eruption dynamics by soule et al earth planet sci lett 2012 327 328 39 49

the late mesozoic and cenozoic evolution of the sorvestsnaget basin a tectonostratigraphic mirror for regional events along the southwestern barents sea margin abstract seismic interpretation and mapping of the sorvestsnaget basin at the southwestern barents sea margin has revealed a complex basin history related to large scale plate tectonic movements in the norwegian greenland sea area the pre cenozoic evolution of the sorvestsnaget basin is poorly understood due to lack of well data and poor seismic data quality regional pre cenozoic geologic models that includes the sorvestsnaget basin should await more and better data prior to break up and sea floor spreading in the norwegian greenland sea late cretaceous and palaeocene shear movements along the senja fracture zone led to structuring and possibly elevation of the southern part of the basin as sea floor spreading took place and propagated northwards along the senja fracture zone the western areas of the basin were uplifted and eroded two large and two smaller intrabasinal features in the southern sorvestsnaget basin are characterised by a low values on the gravimetric anomaly maps b surrounding synforms and c little response on magnetic anomaly maps the features have been interpreted as salt structures the tertiary evolution of intrabasinal salt structures seems to have been governed by extensional faulting and subsidence of the margin during the late palaeocene and eocene periods the oligocene and miocene periods were characterised by local and regional uplift of the sorvestsnaget basin respectively during these periods the area in particular the western part of the basin was subjected to transpressional compressional forces which can be tentatively correlated to contemporaneous large scale plate reorganisations and variations of sea floor spreading rates in the norwegian greenland sea the oligocene and miocene transpressional compressional events influenced the salt structures and is here suggested to be partially responsible for the complex expression of the largest salt structures the late neogene and pleistocene periods are represented by a thick westward prograding wedge indicating subsiden3e with coinciding high sediment input to and minor adjustment of the salt structures in the sorvestsnaget basin

growth of normal faults in multilayer sequences a 3d seismic case study from the egersund basin norwegian north sea abstract we investigate the structural style and evolution of a salt influenced extensional fault array in the egersund basin norwegian north sea through analysis of 3d reflection seismic and well data analysis of fault geometry morphology throw distribution and syn kinematic strata reveal an intricate but systematic style of displacement and growth suggesting an evolution of 1 initial syn sedimentary fault growth contemporaneous with salt mobilization initiated during the late triassic 2 cessation of fault activity and burial of the stagnant fault tips and 3 subsequent nucleation of new faults in the cover above contemporaneous salt re mobilization initiated during the late cretaceous with downward propagation and linkage with faults stage 3 was apparently largely controlled by salt mobilization in response to basin inversion as reactivated faults are located where the underlying salt is thick while the non reactivated faults are found where salt is depleted based on the 3d throw analyses we conclude that a combination of basement faulting and salt re mobilization is the driving mechanisms behind fault activation and reactivation even though the sub and supra salt faults are mainly geometrically decoupled through the salt a kinematic coupling must have existed as sub salt faults still affected nucleation and localization of the cover faults

statistical evaluation of the ses predictions issued in greece alarm and success rates earthquake prediction based on continuous measurements of the electric field of the earth has been systematically carried out by varotsos and co workers in greece predictions were issued by telegrams to greek authorities statistical evaluation of these predictions was made by comparing telegram prediction information with earthquake parameters determined by the us geological survey the space time domain selected for this evaluation was 20 24 e 36 41 n from january 1987 to june 1989 successfully predicted earthquakes are defined here as those that occurred within 22 days of the prediction within 100 km of the predicted epicenter and with a magnitude difference predicted minus true rot greater than 0 7 twelve predictions were issued for earthquakes with expected ms 5 3 following our criteria ten were successful two were not the magnitudes of the predicted earthquakes varied from 4 1 to 5 5 for earthquakes with mb usgs 5 0 the ratio of the predicted to the total number of earthquakes is 6 12 50 and the success rate of the prediction is also 612 50 with a probability gain of a factor of 4 with a confidence level of 99 8 the possibility of this success rate being explained by a random model of earthquake occurrence taking into account a regional factor which includes high seismicity in the prediction area can be rejected for earthquakes with mb usgs 4 5 a statistical significance could not be obtained because of the large number of small earthquakes

an alternative model for the growth of faults conventional growth models suggest that faults become larger due to systematic increases in both maximum displacement and length we propose an alternative growth model where fault lengths are near constant from an early stage and growth is achieved mainly by increase in cumulative displacement the model reconciles the scaling properties of faults and earthquakes and predicts a progressive increase in fault displacement to length ratios as a fault system matures this growth scheme is directly applicable to reactivated fault systems in which fault lengths were inherited from underlying structure and established rapidly the model may also apply to some non reactivated fault systems near constant fault lengths during subsequent growth are attributed to retardation of lateral propagation by interaction between fault tips the model is validated using kinematic constraints from growth strata which are displaced by a system of reactivated normal faults in the timor sea nw australia

estimation of the probability of earthquake occurrence on the basis of logistic models high probability of an earthquake of m 6 5 near the arc junction off northeast japan the probability of the occurrence of an earthquake of m 6 5 is estimated by applying logistic models to seismicity in the hokkaido tohoku region northeast japan it is found that the probability of an earthquake occurrence near the arc junction off northeast japan is high when a specific seismicity pattern appears that is seismic activity increases 7 10 years or decreases 3 6 years before an event of m 6 5 because seismic activity is currently extremely low near the arc junction it is possible that an earthquake of m 6 5 may occur there within a few years specifically the probability estimated on the basis of logistic models is higher than 0 9 for the year of 1988

fault kinematics and localised inversion within the troms finnmark fault complex sw barents sea abstract the areas bounding the troms finnmark fault complex are affected by complex tectonic evolution in this work the history of fault growth reactivation and inversion of major faults in the troms finnmark fault complex and the ringvassoy loppa fault complex is interpreted from three dimensional seismic data structural maps and fault displacement plots our results reveal eight normal faults bounding rotated fault blocks in the troms finnmark fault complex both the throw depth and displacement distance plots show that the faults exhibit complex configurations of lateral and vertical segmentation with varied profiles some of the faults were reactivated by dip linkages during the late jurassic and exhibit polycyclic fault growth including radial syn sedimentary and hybrid propagation localised positive inversion is the main mechanism of fault reactivation occurring at the troms finnmark fault complex the observed structural styles include folds associated with extensional faults folded growth wedges and inverted depocentres localised inversion was intermittent with rifting during the middle jurassic early cretaceous at the boundaries of the troms finnmark fault complex to the finnmark platform additionally tectonic inversion was more intense at the boundaries of the two fault complexes affecting middle triassic to early cretaceous strata our study shows that localised folding is either a product of compressional forces or of lateral movements in the troms finnmark fault complex regional stresses due to the uplift in the loppa high and halokinesis in the tromso basin are likely additional causes of inversion in the troms finnmark fault complex

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

displacement rates of normal faults previous estimates of displacement rates on individual faults have been limited to neotectonic faults and averaged over time intervals of about 200 kyr or less1 2 3 4 5 these estimates have been highly variable which has led to a belief that longer term displacement rates on individual faults are likely to be variable as well here we report estimates of long term normal fault displacement rates averaged over time intervals ranging from 1 to 40 myr and based on observed decreases in displacement of progressively younger horizons intersected by syn sedimentary faults we find that displacement rates are remarkably stable over these longer time periods and within a given fault system the rates are strongly dependent on the relative size of the fault as measured by cumulative vertical displacement taken together these results indicate that faults become large relative to nearby faults by having higher displacement rates even when small rather than as a consequence of having been active for longer our analyses also show that high regional strain rates tend to be accommodated by high fault displacement rates rather than high fault densities

formation of segmented normal faults a 3 d perspective the interpretation of fault kinematics from geometric data is an essential step in developing an understanding of the growth of fault systems constraints on fault geometry are however often restricted to 2 d maps or cross sections in this article we consider the extent to which kinematic interpretations of faulting benefit from a 3 d rather than 2 d geometrical perspective concentrating on relay zones and segmented normal fault arrays we suggest that very different interpretations of their evolution arise from the recognition that the propagation directions of faults and fault segments will rarely be contained within the inspection plane of 2 d data a 3 d perspective favours an interpretation in which the segments of a fault array are kinematically interrelated from their initiation individual segments in such systems may link into a single fault surface out of the plane of inspection or may be unconnected in 3 d we argue that this interpretation which conflicts with the often suggested model of incidental overlap of originally isolated faults should be the preferred model for the generation and growth of segmented normal fault arrays

geometry of thin skinned tectonic systems in relation to detachment layer thickness in sedimentary basins characterizing features of both extensional and compressional thin skinned systems may be controlled by the thickness of the underlying mobile material within extensional fault arrays detachment layer thickness in conjunction with detachment dip controls variations in fault spacing and polarity because rigid fault blocks are only free to rotate as long as there is enough underlying mobile material to redistribute between the fault block keels different styles of extensional fault array range from single polarity arrays with closely spaced faults thin detachment to arrays where the fault blocks rotate until the fault blocks separate from one another thick detachment departure from this relationship depends on the amount of internal deformation that can be sustained by the domino fault blocks within contractional zones detachment folds occur where the amount of mobile material can fill the evolving fold core via redistribution thrusts occur where there is insufficient mobile material to sustain detachment fold growth the variations in extensional and contractional style that are described here in relation to mobile layer thickness can be combined to give an idealized model of regional variation in structural style in relation to regional variation in stratigraphy applying this model to a salt basin an allochthon in the area of thickest salt may be characterized by updip raft tectonics and downdip detachment fold belts this style would be laterally transitional toward areas of thinner or lower net salt to updip domino fault arrays and downdip thrust systems