relay zone geometry and displacement transfer between normal faults recorded in coal mine plans abstract overlap lengths separations and throw gradients were measured on 132 relay zones recorded on coal mine plans throws on the relay bounding fault traces are usually 2 m and individual structures are recorded on only one seam throw gradients associated with relay zones are not always higher than on single faults but asymmetry of throw profiles is diagnostic of relay zones bed geometries around larger faults in opencast mines are used to assess the displacement accommodated by shear in the vertical plane normal to the faults and displacement transfer accommodated by shear in the fault parallel plane three dimensional structure is defined for two relay zones each recorded on five seam plans these relay zones are effectively holes through the fault surfaces and overlap occurs between salients or lobes of the parent fault surfaces lobes initially terminated at tip lines but as the faults grew gradually rejoined the main fault surfaces along branch lines this type of relay zone originates by bifurcation of a single fault surface at a locally retarded tip line and is an almost inevitable result of a tip line irregularity

architecture and growth of normal fault zones in multilayer systems a 3d field analysis in the south eastern basin france abstract 3d field data on mesoscale normal faults were collected to examine the geometries and growth of faults in multilayer systems observation and analysis of the fractures include the collection of geometric attributes such as fault dips and fault zone thicknesses detailed mapping in cross sections and plan views and the construction of individual and cumulative displacement profiles fault zone growth is consistent with a coherent model and is strongly influenced by the multilayer system in the limestone layers faults grew in several steps including opening and frictional sliding on 80 dipping segments faulting in clay layers was in the form of 40 dipping faults and sub horizontal faults the latter being mostly early features developed under the same extensional regime as normal faults and disturbing the fault architecture the fault zone thickness increases with the limestone thickness and the presence of sub horizontal faults in clay beds numerous connections occur in clay units the moderate 0 08 and low

an evaluation of criteria to deduce the sense of movement in sheared rocks some of the most useful criteria for the deduction of the sense of shear are summarized for use in areas where unequivocal field evidence is lacking apparently conflicting evidence from rotated pressure shadow regions around porphyroclasts and porphyroblasts is clarified the use of quartz crystallographic fabric asymmetry to deduce the shear sense in the bulk rock should be treated with caution and used only together with detailed microstructural observations

sequence stratigraphy of the upper oligocene lower miocene of eastern jylland denmark role of structural relief and variable sediment supply in controlling sequence development the upper oligocene lower miocene succession in eastern jylland can be subdivided into three sequences a c from older to younger deposited on and around the ringkobing fyn high the development of the sequences reflects a complex interaction between eustatic sea level changes physiography and variable sediment supply superimposed on this frequent storms promoted longshore sediment transport and the development of spit systems adjacent to structural highs as a consequence sequence boundaries and flooding surfaces are not always expressed as portrayed in conventional sequence models sequence boundaries or flooding surfaces may only be marked by subtle changes in depositional environment that can only be revealed by careful integration of sedimentological observations with palynological data the influence of the topography resulted in the development of brackish water basins that were sufficiently large to permit the deposition of hummocky cross stratified sands with muds these deposits are overlain by clean hummocky and swaley cross stratified sands that were deposited in a fully marine high energy environment this evolution from mud rich storm influenced sediments to sand dominated shoreface sediments resulted from a rise in sea level and was not the result of shoreface progradation and downstepping during a sea level fall in addition to the topographic control on sequence development sediment supply to the study area changed significantly during the deposition of the three sequences initially the basin was sediment starved favouring the formation of glaucony rich sediments the sediment input gradually increased and the influence of structural highs and lows became less significant with time consequently both sequence boundaries and flooding surfaces are characterized by more conventional features in the younger part of the succession where a basinward displacement of the shoreline resulted in thick lowstand delta deposits

strain compatibility and fault linkage in relay zones on normal faults relay zones on normal faults are unlikely to have tabular geometries as depicted in idealised models rotation of a relay ramp between non parallel and non planar relay bounding faults will inevitably lead to strain compatibility problems causing open gaps or overlaps within the relay zone linkage of relay bounding faults does not evolve from a single branch point rather linkage occurs at multiple points along the fault tip lines giving rise to initially discontinuous branch lines where linkage occurs along a discontinuous slip aligned branch line displacement at different levels within the relay zone is partitioned between variable amounts of ramp rotation and slip across the branch line the linking fault propagates when strain compatibility can no longer be maintained by continuous deformation processes such as thickening or thinning of incompetent layers within the relay ramp step like changes in vertical displacement vs distance d x profiles on horizons containing apparently intact relay ramps are probably indicative of incipient breaching and can be used predict the presence of a slip aligned branch line in the sub surface despite the complexity of the strain distribution within relay zones the total vertical displacement across the relay remains geometrically coherent at all levels

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

a model for the structure and development of fault zones cross sections of fault zones commonly show two sub parallel slip surfaces which bound more or less deformed rock this characteristic geometry can be explained by a combination of 9tip line9 and 9asperity9 bifurcation processes fault tip line bifurcation is due to irregular tip line propagation resulting in leading edge segmentation fault overlap and eventual duplex formation asperity bifurcation removes a fault surface irregularity by the generation of a new slip surface which by passes the original slip surface repetitions of either or both bifurcation processes give rise to a fault zone with a complex and unpredictable internal geometry these processes are described mainly on the basis of observation of normal faults hut can be applied to other fault types fault zone thickening by bifurcation is intermittent rather than progressive and localised fault zone thinning may occur

the role of coseismic coulomb stress changes in shaping the hard link between normal fault segments the mechanism and evolution of fault linkage is important in the growth and development of large faults here we investigate the role of coseismic stress changes in shaping the hard links between parallel normal fault segments or faults by comparing numerical models of the coulomb stress change from simulated earthquakes on two en echelon fault segments to natural observations of hard linked fault geometry we consider three simplified linking fault geometries 1 fault bend 2 breached relay ramp and 3 strike slip transform fault we consider scenarios where either one or both segments rupture and vary the distance between segment tips fault bends and breached relay ramps are favoured where segments underlap or when the strike perpendicular distance between overlapping segments is less than 20 of their total length matching all documented examples transform fault linkage geometries are preferred when overlapping segments are laterally offset at larger distances few transform faults exist in continental extensional settings and our model suggests that propagating faults or fault segments may first link through fault bends or breached ramps before reaching sufficient overlap for a transform fault to develop our results suggest that coulomb stresses arising from multi segment ruptures or repeated earthquakes are consistent with natural observations of the geometry of hard links between parallel normal fault segments

evidence from high resolution topography for multiple earthquakes on high slip to length fault scarps the bilila mtakataka fault malawi geomorphological features such as fault scarps and stream knickpoints are indicators of recent fault activity determining whether these features formed during a single earthquake or over multiple earthquakes cycles has important implications for the interpretation of the size and frequency of past events here we focus on the bilila mtakataka fault malawi where the 20 m high fault scarps exceed the height expected from a single earthquake rupture we use a high resolution digital elevation model 1 m to identify complexity in the fault scarp and knickpoints in river profiles of 39 selected scarp profiles 20 showed evidence of either multi scarps or composite scarps and of the seven selected river and stream profiles five showed evidence for multiple knickpoints a near uniform distribution of vertical offsets on the sub scarps suggests they were formed by separate earthquakes these independent methods agree that at least two earthquakes have occurred with an average vertical offset per event of 10 and 12 m this contrasts earlier studies which proposed that this scarp formed during a single event and demonstrates the importance of high resolution topographic data for understanding tectonic geomorphology we use a one dimensional diffusion model of scarp degradation to demonstrate how fault splays form multi scarps and estimate the diffusion age t of the bilila mtakataka fault scarp to be 48 m25 m2 corresponding to 6400 4000 years since formation we calculate that a continuous rupture would equate to a mw 7 8 0 3 earthquake greater than the largest seismic event previously recorded in east africa

geometry and development of relay ramps in normal fault systems relay ramps occur between normal fault segments that overstep in map view the geometry and evolution of exposure scale relay ramps are described from the somerset coast england and are compared with larger scale ramps from elsewhere relay ramps can be classified into four groups based on the degree of interaction and linkage between the overstepping segments these groups are interpreted as being evolutionary stages in stage 1 the segments do not interact stage 2 involves the reorientation of bedding between two interacting faults to produce a relay ramp in stage 3 connecting fractures start to break the relay ramp stage 4 is when the relay ramp is destroyed to produce a single fault that has an along strike bend these evolutionary stages can develop through ti e but they can also be seen spatially a branch line between normal faults or an along strike bend may represent a stage 4 relay with progressively earlier stages occurring updip or downdip characteristic variability in displacement distance profiles for fault segments and linked faults accompanies the interaction and linkage processes displacement transfer by relay ramps is accompanied by steep displacement gradients along fault segments at oversteps relay ramps often contribute to a minimum in total fault displacement at a linkage point

tectonic inversion in the santa barbara system of the central andean foreland thrust belt northwestern argentina 1 the santa barbara system sbs of northern argentina is a 400 km long segment of the subandean foreland thrust belt it is characterized by predominantly west verging relatively high angle thrust faults many of these faults are reactivated normal faults from one branch of a complex cretaceous to paleogene rift system heteroaxial folding in parts of the sbs is probably due to a slight component of range parallel dextral strike slip motion acting on preexisting faults striking north and ne during inversion regional balanced cross sections along two transects across the northern sbs indicate that the major faults flatten into a detachment in the basement at about 10 km depth neogene e w contraction in the sbs is of the order of 21 26 km rift extension is not very well constrained but was probably less than 10 km the structural style of the sbs differs from the thin skinned subandean thrust belt to the north and from the large wavelength sierras pampeanas basement uplifts to the south the changes between the different styles are sharp and coincide with the northern and southern boundaries of the rift in the foreland suggesting that crustal or lithospheric heterogeneities exert an overriding control on foreland structural style

estimation of average to maximum displacement ratio by using fault displacement distance profiles abstract fault displacement is an important factor in the study of discontinuous deformation considering that the values of average displacement dav and maximum displacement dmx are linearly related by dav dmx we calculate the values of estimated from 205 published displacement distance profiles the following results are obtained a the value of is largest for the mesa type or flat topped m type profiles b the value of increases when ductile continuous deformation is added to the displacement profile c generally the value of for a linked fault array is smaller than that for segmented faults in the array i e the value of changes with fault evolution and at the stage where linkage occurs the value of becomes smaller d the simulation results indicate that for an ellipse function the value of varies from 0 667 to 0 785 for trapezoid m type profiles the value of is from 0 5 to 1 depending on the ratio of the upper base to the lower base for best fit polynomial curves the value of can be less than 0 5 e the values of more frequently observed in the published profiles are between 0 6 and 0 7 the average value is 0 6023 and the standard deviation 0 1123 these data indicate that the displacement distance profiles are hybrids from the triangular profile to the elliptical or mesa profile the average value 0 6023 would be useful to determine the average displacement in cases where not enough displacement data can be obtained finally the value change of with fault evolution can be used to quantitatively evaluate the level of interaction between segmented faults

alternative model of thrust fault propagation a widely accepted explanation for the geometry of thrust faults is that initial failures occur on deeply buried planes of weak rock and that thrust faults propagate toward the surface along a staircase trajectory we propose an alternative model that applies gretener s beam failure mechanism to a multilayered sequence invoking compatibility conditions which demand that a thrust propagate both upsection and downsection we suggest that ramps form first at shallow levels and are subsequently connected by flat faults this hypothesis also explains the formation of many minor structures associated with thrusts such as backthrusts wedge structures pop ups and duplexes and provides a unified conceptual framework in which to evaluate field observations

constraints on deformation conditions and the origin of oceanic detachments the mid atlantic ridge core complex at 15 45 n 1 deformed rocks sampled from a corrugated detachment fault surface near the mid atlantic ridge 15 45 n constrain the conditions of deformation and strain localization samples recovered in situ record deformation restricted to the cold shallow lithosphere greenschist facies with no evidence for significant high temperature deformation either at the fault zone or in the footwall near it high temperature deformation 720 750 c is observed only at two sites and cannot be directly linked to the detachment detachment faulting was coeval with dyke intrusions that cross cut it as demonstrated by the presence of undeformed and highly deformed diabase found in shear zones and by the presence of chill margins in diabase against fault rock basalts are very scarce and restricted to clasts in breccias with no evidence of pillows or extrusive structures gabbros crop out along mass wasted and fault scarps structurally below the detachment footwall rocks show little or no deformation due to strain localization along a narrow shear zone 200 m with fluid flow as required to form talc and amphibole schists after an ultramafic protolith we speculate that the alteration front in a heterogeneous lithosphere may be a rheological boundary that may localize deformation during long periods of time our observations and other geological evidence elsewhere suggest that this detachment model limited to the cold shallow lithosphere is applicable to other corrugated surfaces along slow and intermediate spreading ridges these observations preclude detachment models rooting in melt rich zones i e atlantis bank southwest indian ridge or recording high temperature deformation we infer that oceanic detachment faults 1 localize strain at t 500 300 c 2 persist during active magmatism and 3 root at shallow rheological boundaries such as a melt rich zone or magma chamber hot detachments or an alteration front cold detachments

the frictional behavior of serpentinite implications for aseismic creep on shallow crustal faults serpentine is common in many active faults and may be responsible for aseismic creep along segments of these faults to test this we have conducted a series of velocity stepping experiments to determine the frictional velocity dependence of serpentinite we slid initially bare rough surfaces of antigorite serpentinite at room temperature with velocities from 0 0032 to 10 0 m s 1 0 102 to 3 2 105 mm yr and normal stresses from 25 to 125 mpa we find that the velocity dependence of serpentinite undergoes a transition from velocity weakening at fast loading velocities to velocity strengthening at slow velocities and that this change is accompanied by other changes in the constitutive behavior these results suggest that serpentinite should not be the site of instability initiation during sliding at plate velocities but may permit propagation of unstable slip initiated elsewhere

3d seismic analysis of the ak fault orange basin south africa implications for hydrocarbon leakage and offshore neotectonics abstract a high resolution 3d reflection seismic dataset was used to achieve a detailed description of the half graben bounded ak fault in the ibhubesi gas field of the offshore orange basin seismic analysis of the fault involved the combination of both the conventional seismic interpretation and seismic attributes the main objective of the study was to provide insights into hydrocarbon leakage and neotectonic activity along the west coast shelf of south africa the ak fault is among the several half graben bounded faults that formed in the late jurassic to early cretaceous during the separation of the south american and the african continents the ak fault consists of five seismically detectable segments whose evolution reflects characteristics of both the coherent and the isolated end members model of segmented fault origin diapiric structures that are direct indicators of vertical fluid movement were also observed along the ak fault system providing evidence of significant roles that the fault plays in promoting the vertical migration of hydrocarbon in the orange basin recent reactivation of the fault has also occurred along an oblique extensional regime that is dominated by normal dip slip faulting with minor shear components along the tips

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

talc friction in the temperature range 25 400 c relevance for fault zone weakening abstract talc is one of the weakest minerals that is associated with fault zones triaxial friction experiments conducted on water saturated talc gouge at room temperature yield values of the coefficient of friction shear stress effective normal stress n in the range 0 16 0 23 and increases with increasing n talc gouge heated to temperatures of 100 400 c is consistently weaker than at room temperature and talc has a temperature pressure range of stability that extends from surficial to eclogite facies conditions making it of potential significance in a variety of faulting environments talc has been identified in exhumed subduction zone thrusts in fault gouge collected from oceanic transform and detachment faults associated with rift systems and recently in serpentinite from the central creeping section of the san andreas fault typically talc crystallized in the active fault zones as a result of the reaction of ultramafic rocks with silica saturated hydrothermal fluids this mode of formation of talc is a prime example of a fault zone weakening process because of its velocity strengthening behavior talc may play a role in stabilizing slip at depth in subduction zones and in the creeping faults of central and northern california that are associated with ophiolitic rocks

talc bearing serpentinite and the creeping section of the san andreas fault the section of the san andreas fault located between cholame valley and san juan bautista in central california creeps at a rate as high as 28 mm yr 1 ref 1 and it is also the segment that yields the best evidence for being a weak fault embedded in a strong crust serpentinized ultramafic rocks have been associated with creeping faults in central and northern california and serpentinite is commonly invoked as the cause of the creep and the low strength of this section of the san andreas fault however the frictional strengths of serpentine minerals are too high to satisfy the limitations on fault strength and these minerals also have the potential for unstable slip under some conditions here we report the discovery of talc in cuttings of serpentinite collected from the probable active trace of the san andreas fault that was intersected during drilling of the san andreas fault observatory at depth safod main hole in 2005 we infer that the talc is forming as a result of the reaction of serpentine minerals with silica saturated hydrothermal fluids that migrate up the fault zone and the talc commonly occurs in sheared serpentinite this discovery is significant as the frictional strength of talc at elevated temperatures is sufficiently low to meet the constraints on the shear strength of the fault and its inherently stable sliding behaviour is consistent with fault creep talc may therefore provide the connection between serpentinite and creep in the san andreas fault if shear at depth can become localized along a talc rich principal slip surface within serpentinite entrained in the fault zone

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

numerical modelling of syntectonic subaqueous sedimentation the effect of normal faulting and a relay ramp on sediment dispersal abstract relay ramps are common in extensional settings and play a significant role in sediment dispersal as they control sedimentary pathways unlike for subaerial settings the impact of subaqueous relay ramps on sediment dispersal and clastic sedimentation is less studied in these subaqueous cases numerical approximations could be a good approach to understand syntectonic sedimentation considering this a numerical model is used to study the sedimentary infill in an extensional basin specifically related to a relay ramp system the study is carried out using a novel program that merges a discrete element code for tectonic deformation and a stratigraphic modelling code for sedimentation to perform a test study two configurations are designed with one normal fault and with two overlapping normal faults linked by a relay ramp to these initial configurations three different deformation velocities 10 5 and 2 cm y are applied in dip slip direction these scenarios are considered as initially submerged the same incoming amount of three different terrigenous sediments is considered in all the experiments these sediments are transported basinward in suspension by processes of advection dispersion and diffusion finally these examples also include four different boundary conditions for the sedimentary model which define the source area location for the incoming water and sediment results show that the source area location in relation to the available accommodation space plays the major role in the distribution of different sediment types into the basin nonetheless when the source area for water and sediment is defined as regional and parallel to the fault the grain size distribution obtained by the two overlapping faults configuration has clear asymmetries when compared with the ones obtained by one fault configurations therefore the different extensional experiments allow concluding that the relay ramp configuration can play an important role in the distribution of the sediments into the basin

the 3d geometry of small scale relay zones between normal faults in soft sediments serial cross sections of faults within soft sediments of miocene age on the east coast of denmark were collated to provide 3d data sets with which to study the geometry of minor faults displacements 10 cm from the wide variety of geometrical complexities displayed by these faults many due to mutually cross cutting relationships between opposed dipping faults we present relatively simple structures considered to demonstrate stages in the evolution of relay zones between overlapping fault segments the structures described are 1 initial embayments in fault tip lines 2 established relay zones displaying transfer of displacement between overlapping fault segments 3 breached relay zones and 4 fault bound lenses an individual relay zone may display more than one of these structures along its length and relay zones that are intact on one cross section may be breached along strike on another examples of relay zones that are isolated from the fault tip line and are effectively holes within a continuous fault are also observed the observed relay zones breach by propagation of the initial parent fault through the relay zone rather than by the formation of a new breaching fault

inhibition of subduction thrust earthquakes by low temperature plastic flow in serpentine abstract serpentine is considered a candidate hydrous mineral in explaining aseismic zones along faults however recent frictional experiments have shown a marked increase in its shear strength with increasing depth implying its deformation via unstable sliding at a plate interface in subduction zones here we report the results of a series of simple shear experiments designed to determine the dominant deformation style of low temperature serpentine species under p t conditions that correspond to the mantle wedge corner in cool subduction zones ca p 1 gpa and t 200 c we found that with increasing shear strain the dominant flow mechanism of the serpentinite evolves from 1 inhomogeneous semi brittle flow by strain localization into sample scale shear bands to 2 homogeneous ductile flow by intracrystalline deformation within individual serpentine grains with the development of a planar shape fabric and a strong crystallographic preferred orientation tem observations revealed that grain size reduction in lizardite crystals occurs due to 001 interlayer glide represented by the occurrence of tiny sheet like sectors oriented parallel to 001 liz lattice fringes which evolved from large elongated sectors with long axes oriented normal to 001 liz given that a low viscosity serpentinized layer upon a subducting plate interface produces strain localization within the layer and subsequent large bulk shear strains the above results indicate that the presence of low temperature serpentine species at the plate interface in cool subduction zones inhibits the initiation of subduction thrust earthquakes as stress is preferentially accommodated by plastic flow this hypothesis explains the occurrence of an anomalous non seismic region devoid of large thrust earthquakes in locally hydrated forearc mantle within northeast japan

field examples and numerical modelling of oversteps and bends along normal faults in cross section abstract oversteps and bends along cross sections through small scale numerical modelling distinct element analysis has been carried out to simulate the patterns of deformation at oversteps and bends area increase pull apart development and localised stress concentration occur at extensional oversteps and bends stress concentration and a tendency for compaction are typical of contractional oversteps and bends such results are compatible with the structures observed in the field a sensitivity analysis of the modelling has been carried out to investigate the effects of variations in mechanical parameters on deformation although models with weaker properties are more deformable the overall geometry of deformation varies little with variations in mechanical parameters

impacts of small scale faults on continental to coastal plain deposition evidence from the realgrunnen subgroup in the goliat field southwest barents sea norway abstract in this study we synthesise sedimentological fault and amplitude versus angle ava analysis and propose that the fruholmen and tubaen formations realgrunnen subgroup are syn kinematic deposits that record a previously undocumented early phase of mesozoic rifting on the troms finnmark fault complex and within the hammerfest basin the realgrunnen subgroup hosts one of two triassic reservoirs currently being produced in the goliat field here the subgroup sits unconformably on top of the storfjorden subgroup carnian snadd formation away from the goliat field which is characterised by a periclinal anticline the realgrunnen subgroup also comprises the lower middle jurassic nordmela and sto formations sedimentological analysis of six exploration wells reveals that the fruholmen formation was deposited in a prodelta to delta plain environment where tide influenced and fluvial dominated distributary channels are represented by clay siltstones and very fine grained sandstones the overlying tubaen formation is characterised by medium to very coarse grained deposits locally conglomeratic and represents a widespread braid plain with localised alluvial fans displacement profiles of faults and along fault thickness variations demonstrate that an immature fault system was active during deposition of the realgrunnen subgroup a series of unconnected fault segments hosted isolated sub basins and erosional catchment areas in their hanging and footwalls respectively an ava attribute map generated from a 10 ms interval of the uppermost part of the subgroup reveals gross sand prone depositional bodies i e individual and amalgamated channels some of which show meandering geometries ox bow lakes and alluvial fans sand bodies frequently show elongate geometries parallel to faults indicative of syn depositional fault related subsidence driving mechanisms responsible for the norian to rhaetian event may relate to contemporaneous rejuvenation of the fennoscandian hinterland development of the novaya zemlya fold and thrust belt and or the early cimmerian tectonic phase in northern europe

integrating 3 d seismic data field analogs and mechanical models in the analysis of segmented normal faults in the wytch farm oil field southern england united kingdom we propose a methodology for the analysis of normal fault geometries in three dimensional 3 d seismic data sets to provide insights into the evolution of segmented normal fault systems and to improve recovery efforts in fault controlled oil fields limited seismic resolution can obscure subtle fault characteristics such as segmentation and gaps in fault continuity that are significant for oil migration and thus accurate reservoir characterization detailed seismic data analyses that incorporate principles of normal fault mechanics however can reveal evidence of fault segmentation we integrate seismic attribute analyses outcrop analog observations and numerical models of fault slip and displacement fields to augment the use of 3 d seismic data for fault interpretation we applied these techniques to the wytch farm oil field in southern england resulting in the recognition of significant lateral and to a lesser extent vertical segmentation of reservoir scale faults slip maxima on fault surfaces indicate two unambiguous segment nucleation depths controlled by the lithological heterogeneity of the faulted section faults initiated preferentially in brittle sandstone and limestone units subsequent growth and linkage of segments predominantly in the lateral direction resulted in composite fault surfaces that have long lateral dimensions and multiple slip maxima reservoir compartmentalization is greatest at the level of prevalent segment linkages which corresponds at wytch farm with the predominant hydrocarbon producing unit the sherwood sandstone at relatively shallower depths fault segments are younger and less evolved resulting in a greater degree of segmentation with intact relay zones

3d geometries of normal faults in a brittle ductile sedimentary cover analogue modelling abstract it is well known that ductile layers play a major role in the style and location of deformation however at the scale of a single normal fault the impact of rheological layering is poorly constrained and badly understood and there is a lack of information regarding the influence of several decollement levels within a sedimentary cover on the single fault geometry under purely extensive deformation we present small scale experiments that were built with interbedded layers of brittle and ductile materials and with minimum initial constraints only a velocity discontinuity at the base of the experiment on the normal fault geometry in order to investigate the influence of controlled parameters such as extension velocity rate of extension ductile thickness and varying stratigraphy on the 3d fault geometry these experiments showed a broad spectrum of tectonic features such as grabens ramp flat ramp normal faults and reverse faults forced folds are associated with fault flats that develop in the decollement levels refraction of the fault angle one of the key points is that the normal fault geometry displays large variations in both direction and dip despite the imposed homogeneous extension this result is exclusively related to the presence of decollement levels and is not associated with any global regional variation in extension direction and or inversion

contrasting origins of breached relay zone geometries abstract relay zones accommodate transfer of displacement between pairs of adjacent segments of a fault array that become linked to form a through going fault as displacement increases 3d geometric and kinematic analysis of two vertically aligned relay zones that form a complex boundary between two fault segments generally support this model of relay zone growth but they also highlight some departures from this scheme the two seismically mapped relay zones although separated vertically by 100 m were synchronously active over most of their development history a causal relationship between them is proposed with the geometric complexity arising from the formation of the lower relay zone triggering the formation of the upper the lower relay zone is now breached but originally formed a hole within the fault surface up to throws of ca 50 m the upper relay zone displays both breached and intact relay zone geometries at different structural levels demonstrating that relay zone breaching is a protracted rather than geologically instantaneous process geometrically the lower part of this structure resembles a breached relay zone but it formed by propagation of a splay fault from a pre existing bend to enclose an intervening and steepening ramp a growth scheme which is the opposite of conventional relay zone models

fault growth by linkage observations and implications from analogue models abstract using time sequence analyses of extensional fault models we demonstrate the pivotal role played by fault segmentation in the accumulation of displacement and length during the growth of faults experiments are described in which incremental steps during the development of individual faults have been reconstructed from time lapse photographs taken during model deformation these records confirm the composite segment hierarchy of fault structure a pattern that is frequently recognised in many natural arrays they reveal the progressive enlargement of individual faults to be the product of a repetitive cycle of tip line propagation overlap and linkage between nearest neighbours by contrasting the displacement patterns of successive increments during growth convincing evidence is also presented to suggest that individual segments of faults may remain kinematically independent once they are physically linked this behaviour is shown to be responsible for the characteristic saw tooth patterns often recognised in strike parallel fault displacement profiles such patterns are believed to arise where relict segment boundaries remain preserved as asperities to slip so that displacement is confined to discrete parts of a fault plane surface growth in this way also causes the maximum displacement d and surface length l of faults to continually change by different proportions incremental displacement records presented here corroborate field evidence which shows that linkage between fault segments during growth is responsible for a significant component of the spread of values often recorded in d versus l compilations finally we speculate that linkage between fault segments also accounts for transient irregularities recorded in the frequency distribution of the fault length populations of each model

sandbox models of relay ramp structure and evolution relay ramps are a common feature formed during the growth of normal fault systems we performed analogue experiments to investigate the structure and evolution of relay ramps an extending rubber sheet induces extension at the base of a sand pack brittle crust analogue silicone bars between the rubber and the sand control the location of fault nucleation we tested the role of fault spacing fault length overlap length and fault strike in the evolution of relay ramps the modelled relay ramps evolved in three stages characterized by the growth of the normal faults their interaction and linkage interaction and linkage occurred only when the combined length of the two interacting faults was larger than eight times their spacing the length to width ratio of the relay ramps during the interaction stage showed preferred geometries clustering around three the propagation of the fault tips was observed both before and after the linkage stage overlap length and spacing relations of the modelled relay ramps are similar to those in nature at different scales and can be explained using existing mechanical models nevertheless the further propagation of the fault tips after linkage has not been described previously

the updip and downdip limits to great subduction earthquakes thermal and structural models of cascadia south alaska sw japan and chile this study examines thermal and structural controls of the updip and downdip rupture limits of great subduction thrust earthquakes data on past great earthquake seismic limits have been compiled for four continental subduction zones cascadia sw japan south alaska and chile these limits have then been compared to the predictions of several models for what constrains great earthquake rupture temperatures on the subduction thrusts have been estimated by finite element numerical models the landward limits of the observed updip aseismic zones correspond to the position where the thrust temperature reaches about 100 c that is depths of about 2 to 10 km for the subduction zones studied this temperature agrees with the dehydration of stable sliding smectite clays to illite chlorite the temperatures in this region are controlled mainly by the thickness of sediment on the incoming crust and by the crustal age and thus heat flow the downdip limits correspond to the depth on the thrust where either 1 the temperature reaches about 350 c which corresponds to thermally activated stable sliding behavior for crustal rocks with a transition to 450 c or 2 about 40 km depth if 350 c is reached at greater depth depths of about 40 km approximately correspond to the intersection of the thrust with the continental forearc moho and this downdip limit may be a consequence of stable sliding serpentinite or talc and other hydrated forearc mantle rocks the primary temperature controls on the downdip region are the age of the subducting oceanic plate and the thrust dip profile secondary control comes from the thickness of incoming sediment the convergence rate and the radioactive heat generation in the overlying forearc the 100 c updip limit occurs near the trench for young subducting plates with a thick sediment section such as cascadia 6 8 ma and up to 80 km landward for older oceanic crust such as south alaska 50 ma the 350 c downdip thermal limit is applicable for young oceanic plates e g cascadia and nankai whereas the forearc mantle limit applies for older plates e g south alaska and chile except near the chile rise for the margins studied that have experienced great earthquakes there is generally good agreement between the postulated thermal and moho limits and the rupture or seismogenic zone as defined by the distribution of aftershocks and by waveform tsunami and dislocation modeling the downdip limit of the interseismic locked zone from dislocation modeling is also in agreement with these limits

interpretation of the rupture history of a low slip rate active fault by analysis of progressive displacement accumulation an example from the quaternary eupcheon fault se korea abstract the eupcheon fault one of more than 20 identified quaternary faults recently reported in the area around the yangsan and ulsan faults se korean peninsula was discovered during the construction of a primary school in an area close to a nuclear power plant we analysed a trench excavated across the eupcheon fault with the aim of understanding its movement history and kinematics the eupcheon fault is a reverse fault strike dip n20 e 40 se that records 6 7 m of displacement 3 4 m vertical separation the fault consists of a series of branch faults associated fault related folds and rotated pebbles a previous study reported that the fault originally recorded normal slip but was reactivated during the quaternary as a reverse fault we identified four or five quaternary faulting events upon the fault based on an interpretation of the trench logs including an analysis of colluvial wedges and measurements of displacement distance d x relationships along the fault we used a quantitative analysis of d x relationships commonly used for consolidated sedimentary rocks to interpret the deformation history of the fault from this we estimated the amount of slip in the range of 0 7 1 8 m for each of the five identified faulting events and the earthquake magnitude in the range of m w 5 4 7 4 we propose two ideal d x profiles for syndepositional and post depositional faulting and a tectonic evolution model for the area around this fault this approach may be applicable to analyses of earthquake hazards and studies of fault evolution elsewhere

geometrically coherent continuous deformation in the volume surrounding a seismically imaged normal fault array abstract we calculated an apparent dip attribute which was used to ascertain the spatial distribution of fault related continuous deformation the vertical component of displacement calculated from the continuous deformation acts to fill in missing displacement in the fault throw profile this result shows that apparently complex 3d patterns of continuous strain in the volumes surrounding the fault array developed as part of a single geometrically coherent fault array however if this component of continuous deformation was not added to the throw profile the fault array could have been misinterpreted as a series of isolated fault segments with coincidental overlaps this technique permits the analysis of continuous deformation structures which are up to an order of magnitude smaller than previously described in the study area these structures are interpreted as small fault propagation folds forming in a shale dominated cover sequence the fault propagation folds above the upper tip line of the mapped fault array bifurcate upwards from the fault surface into three coherent lobes and resemble secondary fault segments the near constant along strike length of the region of continuous deformation throughout the syn rift sequence implies that the length of the fault array was established at an early stage in its growth prior to the establishment of a seismically visible fault surface

identifying fault segments from 3d fault drag analysis vienna basin austria abstract the segmented growth of the markgrafneusiedl normal fault in the late miocene clastic sediments of the central vienna basin austria was investigated by construction of a detailed three dimensional 3d structural model using high resolution 3d seismic data the fault surface and marker horizons in the hanging wall and the footwall of the markgrafneusiedl fault were mapped and orientation displacement and morphology of the fault surface were quantified individual fault segments were identified by direct mapping of the deflection of the marker horizons close to the fault surface correlating the size of the identified segments with the magnitude of fault drag and displacement distribution showed that fault evolution progressed in several stages the proposed method allows the detection of segments that are not recorded by the magnitude of displacement or fault morphology most importantly detailed mapping of marker deflections in the hanging wall could help to constrain equivalent structures in the footwall which may represent potential hydrocarbon traps

unique deformation processes involving the recrystallization of chrysotile within serpentinite implications for aseismic slip events within subduction zones serpentinite bodies within the franciscan complex a mesozoic accretionary prism located in california usa display a unique form of deformation that involves the recrystallization of chrysotile and the formation of a block in matrix structure the phacoidal shaped blocks have a preferred orientation and result from the local replacement of serpentine minerals by chrysotile grains that are aligned parallel to ductile shear planes such as s c foliation ultimately some of the rocks evolved into chrysotile schist the relic blocks are also fragmented into multiple parts with the spaces between fragments being infilled by recrystallized chrysotile the low coefficient of friction of chrysotile means that this deformation process acts to suppress the frictional properties of the entire serpentinite body within the forearc mantle this phenomenon can be attributed to the slip style that occurs in aseismic regions of subduction zones in areas shallower than the stability field of antigorite

3d mechanical stratigraphy of a deformed multi layer linking sedimentary architecture and strain partitioning abstract stratigraphic influence on structural style and strain distribution in deformed sedimentary sequences is well established in models of 2d mechanical stratigraphy in this study we attempt to refine existing models of stratigraphic structure interaction by examining outcrop scale 3d variations in sedimentary architecture and the effects on subsequent deformation at monkstone point pembrokeshire sw wales digital mapping and virtual scanline data from a high resolution virtual outcrop have been combined with field observations sedimentary logs and thin section analysis results show that significant variation in strain partitioning is controlled by changes at a scale of tens of metres in sedimentary architecture within upper carboniferous fluvio deltaic deposits coupled vs uncoupled deformation of the sequence is defined by the composition and lateral continuity of mechanical units and unit interfaces where the sedimentary sequence is characterized by gradational changes in composition and grain size we find that deformation structures are best characterized by patterns of distributed strain in contrast distinct compositional changes vertically and in laterally equivalent deposits results in highly partitioned deformation and strain the mechanical stratigraphy of the study area is inherently 3d in nature due to lateral and vertical compositional variability consideration should be given to 3d variations in mechanical stratigraphy such as those outlined here when predicting subsurface deformation in multi layers

structural controls on orogenic au mineralization during transpression lupa goldfield southwestern tanzania au mineralization in the western lupa goldfield southwestern tanzania was associated with transpression and reverse sinistral slip along a network of steeply s dipping shear zones with non andersonian geometries slip was accommodated by 1 frictional failure and sliding during emplacement of quartz au bearing veins and 2 crystal plasticity and fluid assisted diffusive mass transfer the kenge mineral system is situated along a nw se trending shear zone and is characterized by 10 m thick au bearing fault fill veins hosted by well developed phyllosilicate rich mylonites the broadly contemporaneous porcupine mineral system is situated along an ene wsw to e w trending shear zone which is characterized by narrow discontinuous mylonitic shear zone within a silicified and nonfoliated granitoid protolith au mineralization at porcupine occurs within steeply dipping fault fill and subhorizontal extension oblique extension veins three dimensional frictional reactivation theory provides a self consistent explanation for the different vein styles at kenge and porcupine and extends the classic fault valve model to the general case of oblique slip along multiple arbitrarily oriented shear zones analysis of the differential stress required for frictional reactivation suggests the following 1 the kenge shear zone was intrinsically weaker than the porcupine shear zone consistent with the lack of well developed mylonites at porcupine and 2 frictional reactivation of the kenge shear zone occurred under suprahydrostatic but sublithostatic pore fluid pressures whereas frictional reactivation of the porcupine shear zone occurred under near lithostatic fluid pressures we hypothesize that near lithostatic pore fluid pressures relieved effective normal stresses at grain grain contacts helping to preserve intragranular and fracture porosity at the porcupine orebody as such these pore spaces may be important microstructural sites for au mineralization low effective normal stresses can also explain the poorly developed phyllosilicate rich mylonites and limited degree of shear zone weakening at porcupine

3d seismic analysis of the structure and evolution of a salt influenced normal fault zone a test of competing fault growth models abstract in this paper we determine the structure and evolution of a normal fault system by applying qualitative and quantitative fault analysis techniques to a 3d seismic reflection dataset from the suez rift egypt our analysis indicates that the october fault zone is composed of two fault systems that are locally decoupled across a salt bearing interval of late miocene messinian age the sub salt system offsets pre rift crystalline basement and was active during the late oligocene early middle miocene it is composed of four planar nw se striking segments that are hard linked by n s striking segments and up to 2 km of displacement occurs at top basement suggesting that this fault system nucleated at or more likely below this structural level the supra salt system was active during the pliocene holocene and is composed of four nw se striking listric fault segments which are soft linked by unbreached relay zones segments in the supra salt fault system nucleated within pliocene strata and have maximum throws of up to 482 m locally the segments of the supra salt fault system breach the messinian salt to hard link downwards with the underlying sub salt fault system thus forming the upper part of a fault zone composed of i a single amalgamated fault system below the salt and ii a fault system composed of multiple soft linked segments above the salt analysis of throw distance t x and throw depth t z plots for the supra salt fault system isopach maps of the associated growth strata and backstripping of intervening relay zones indicates that these faults rapidly established their lengths during the early stages of their slip history the fault tips were then effectively pinned and the faults accumulated displacement via predominantly downward propagation we interpret that the october fault zone had the following evolutionary trend i growth of the sub salt fault system during the oligocene to early middle miocene ii cessation of activity on the sub salt fault system during the middle miocene to early pliocene iii stretching of the sub and supra salt intervals during pliocene regional extension which resulted in mild reactivation of the sub salt fault system and nucleation of the segmented supra salt fault system which at this time was geometrically decoupled from the sub salt fault system and iv pliocene to holocene growth of the supra salt fault system by downwards vertical tip line propagation which resulted in downward breaching of the salt and dip linkage with the sub salt fault system the structure of the october fault zone and the rapid establishment of supra salt fault lengths are compatible with the predictions of the coherent fault model although we note that individual segments in the supra salt array grew in accordance with the isolated fault model our study thereby indicates that both coherent and isolated fault models may be applicable to the growth of kilometre scale basin bounding faults furthermore we highlight the role that fault reactivation and dip linkage in mechanically layered sequences can play in controlling the three dimensional geometry of normal faults

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

seismic consequences of warm versus cool subduction metamorphism examples from southwest and northeast japan warm and cool subduction zones exhibit differences in seismicity seismic structure and arc magmatism which reflect differences in metamorphic reactions occurring in subducting oceanic crust in southwest japan arc volcanism is sparse and intraslab earthquakes extend to 65 kilometers depth in northeast japan arc volcanism is more common and intraslab earthquakes reach 200 kilometers depth thermal petrologic models predict that oceanic crust subducting beneath southwest japan is 300 to 500 c warmer than beneath northeast japan resulting in shallower eclogite transformation and slab dehydration reactions and possible slab melting