kinematic analyses of brittle roto translational planar and listric faults based on various rotational to translational velocities of the faulted blocks abstract research on rotational roto translational faults have been relatively less than translational faults this is despite perfect translational faults seldom occur in mega scale this work models slickenside lineation patterns on planar and listric fault planes for different ratios of rates of rotation to the uniform speed towards a specific geographic direction v of faulted blocks curves simulated for the planar fault planes are fitted with natural examples of such roto translational faults in our 10 chosen examples the v ratio ranges between 0 2 fault at san miguelito range central mexico and as high as 2 4 fault at hyogoken nambu japan knowing the v ratios from terrains can better interpret its tectonics for example if v and the total time of duration of the deformation are known from some other studies even the total amount of rotation can be estimated the far reaching implication of this study is that as several hydrocarbon reserves and terrains with landslides are related to roto translational faults this work will be a stepping stone in petroleum geosciences e g stability of hydercarbon reserve and engineering geology e g stability of slope

hydraulic stability of rock armors in breaking wave conditions abstract armor layers of mound breakwaters are usually designed with empirical formulas based on small scale tests in non breaking wave conditions however most rubble mound breakwaters are constructed in the depth induced breaking zone where they must withstand design storms having some percentage of large waves breaking before reaching the structure in these cases the design formulas for non breaking wave conditions are not fully valid to characterize double layer rock armor damage in breaking wave conditions 2d physical model tests were carried out with a bottom slope m 1 50 in order to develop a simple method to determine the wave parameters in the depth induced breaking zone experimental wave measurements were compared to the numerical estimations given by the swanone model an analysis was conducted to select the best characteristic wave height to estimate rock armor damage when dealing with depth induced breaking waves the spectral significant wave height h m0 estimated at a distance of 3h s seaward from the structure toe was found to be the most adequate a new hydraulic stability formula is proposed for double layer rock armors in breaking wave conditions considering the observed potential 6 power relationship between the equivalent dimensionless armor damage and the h m0 at 3h s seaward distance from the structure toe

brevard fault zone southern appalachians a medium angle dextral alleghanian shear zone the record of alleghanian movements in the rocks of the brevard fault zone has been studied by using modern techniques of kinematic analysis mylonitic and phyllonitic fabric involves 1 strong subhorizontal stretching lineation trending northeast southwest parallel to the fault 2 mylonitic foliation dipping moderately to the southeast and 3 a great variety of kinematic indicators suggesting a dextral sense of shear both palmetto and ben hill granites georgia ca 325 ma were sheared during this event the age of which should be younger probably ca 310 ma the brevard zone is usually regarded as a listric thrust fault along which the piedmont terrains have been displaced toward the northwest onto the blue ridge by contrast the movement picture resulting from our analysis is compatible only with right lateral strike slip faulting along a moderately dipping shear zone several kilometres wide causing southwestward displacement of the piedmont relative to the blue ridge province parallel to the appalachian trend

geomorphic constraints on listric thrust faulting implications for active deformation in the mackenzie basin south island new zealand 1 deformed fluvial terraces preserved over active thrust related folds record the kinematics of folding as fault slip accumulates on the underlying thrust in the mackenzie basin of southern new zealand the kinematics revealed by folded fluvial terraces along the active ostler and irishman creek fault zones are inconsistent with traditional models for thrust related folding in which spatially uniform rock uplift typically occurs over planar fault ramps instead warped and tilted terraces in the mackenzie are characterized by broad continuous backlimbs and abrupt forelimbs and suggest folding through progressive limb rotation by relating this pattern of surface deformation to the underlying thrust with a newly developed simple geometric and kinematic model we interpret both faults as listric thrusts rooted at depth into gently dipping planar fault ramps constraints on the model from detailed topographic surveying of deformed terraces ground penetrating radar over active fault scarps and luminescence dating of terrace surfaces suggest slip rates for the ostler and irishman creek faults of 1 1 1 7 mm yr and 0 5 0 7 mm yr respectively the predicted depth of listric faulting for the ostler fault 0 7 0 2 0 1 km and the irishman creek fault 1 3 0 5 0 1 km generally agrees with geophysical estimates of basin depth in the mackenzie and suggests control of preexisting basin architecture on the geometry of active thrusting despite the potential effects of changes in fault curvature and hanging wall internal deformation the methodology presented here provides a simple tool for approximating the kinematics of surface deformation associated with slip along listric or curviplanar thrust faults

fault scarps and deformation rates in lazio abruzzo central italy comparison between geological fault slip rate and gps data abstract we compare new and literature data concerning the integrated deformation rate since 18 ka for the central apennines with deformation rate data derived from a 6 year gps campaign we constructed topographic profiles across the majority of the active faults in the area we derived deformation rate data from displaced post glacial sediments and slopes associated with the last major glacial retreat that occurred in the region about 18 kyr ago paleoseismic investigations in this region clearly show that offset of these features is the cumulative effect of repeated surface faulting earthquakes with magnitudes in the range 5 5 ms 7 0 a cumulative throw rate diagram incorporating both our values and the values extracted from the literature i e previously published trenching studies scarp profiles and offset terraces is presented providing a regional picture of the spatial deformation rate distribution in the central apennines during the latest pleistocene and holocene by converting cumulative throw rates into heave rates we calculate maximum extension rates of ca 2 mm year at the location of the same transect where 6 2 mm year has been measured with gps over 6 years this discrepancy between geodetic and geological fault slip rate data implies that we have to be cautious whenever we use gps data for seismic hazard assessment purposes or when attempting to reconstruct the tectonic processes in an area because geodetic data may be unrepresentative of the longer term deformation rates on the other hand this discrepancy may provide insights into the mechanics of the seismic cycle we discuss various scenarios that may explain the mis match between long term and short term measurements

types and kinematic stability of triple junctions a triple junction is kinematically stable if the orientation of each plate boundary remains constant relative to other boundaries in the triple junction during a finite time interval instantaneous relative velocity vectors have been used elsewhere to indicate the relative motion of plates during a finite time interval a technique that is not generally valid where finite relative plate motion is not circular in the typical case in which all three plates have non zero velocities around different plate specific poles of rotation the direction and magnitude of relative plate velocity varies systematically with time five plate boundary types are considered in evaluating triple junction stability ridges r right lateral and left lateral transform faults fr and fl and trenches in which the overriding plate is clockwise tc or anticlockwise ta from the trench judged by a rotation around the triple junction one hundred twenty five triplet combinations of boundary types are possible some combinations display symmetry with other combinations grouping all similar configurations 25 types of triple junctions can be distinguished of which 19 types may be stable when finite relative motion is circular vectorial descriptors of the geometry of ridges transform faults and trenches permit the listing of general conditions for the kinematic stability of triple junctions under conditions of both circular and non circular relative motion the tj1 model for the evolution of rrr triple junctions provides estimates of the variation in the geometry of triple junctions in which spreading is orthogonal and near symmetric rrr triple junctions at which spreading is orthogonal and symmetric are always stable when the finite relative motion of all corresponding plates is circular however tj1 indicates that rrr triple junctions are not generally stable when relative motion is non circular in general triple junctions are not kinematically stable but evolve with changes in the finite relative motion of plates

evolution of a fault surface from 3d attribute analysis and displacement measurements abstract a large fault surface evolves by growth and coalescence of numerous segments through time which results in strong undulations of the principal fault surface we interpreted a strongly segmented 13 km long fault using 3d seismic data and studied the morphology in terms of fault linkage using curvature azimuth and dip attributes displacement profiles of two horizons were measured to analyse the different displacement relations and to quantify their variation and dependence on fault morphology we identified four orders of fault segments over a scale range from a few hundred metres to several kilometres which evolved during fault growth the strong changes in orientation of the several segments might result in a heterogeneous small scale fracture distribution and different fault drag geometries displacement measurements on the undulated fault surface indicate a strong variation between real vertical and horizontal displacement values however the commonly used throw values lead to a smoothing of the real displacement curves and to an underrepresentation of their values and therefore cannot show a triangular shape that is typically identified from ruptures fault surfaces of earthquake processes therefore for any kind of fault analysis care should be taken when using throw as approximation for the real displacement

east pacific rise from siqueiros to orozco fracture zones along strike continuity of axial neovolcanic zone and structure and evolution of overlapping spreading centers we have used the sea beam multibeam echo sounding system to survey the east pacific rise epr from 8 20 n to 18 30 n obtaining complete coverage of the epr axial neovolcanic zone and all intervening transform faults here we focus on the epr neovolcanic zone and the definition of overlapping spreading centers ocs s between the orozco and siqueiros transform faults the neovolcanic zone is narrow 0 5 2 0 km and continuous along strike and occurs within and near a strike continuous axial summit graben the neovolcanic zone and summit graben reside along the crest of a volcanic axial high which is 2 10 km wide and which continues uninterrupted along strike for 40 140 km within 20 50 km of an intersection with a transform fault the axial neovolcanic zone narrows and deepens and within only 3 6 km of the intersection the neovolcanic zone turns sharply into the transform valley at seven locations between the siqueiros and orozco transform faults the axial neovolcanic zone is discontinuous and is laterally offset a short distance 1 15 km in contrast with a classic ridge transform ridge plate boundary however offset rise terminations overlap each other by a distance approximately 3 times greater than their offset they curve toward each other and often one merges into the other along strike separating the osc s is an elliptical overlap basin up to 600 m deep whose long axis is subparallel to the adjacent spreading centers the overlap basin is characterized by volcanic constructional edifices a key difference between these offsets and small transform faults in the atlantic is that there are no transform fault structures in the overlap basin which link the offset rise axes a continuous axial depth profile reveals a long wavelength 20 60 km undulation of the rise axis which may be associated with variations in the magmatic budget along strike the lowest points in the axial depth profile occur near transform faults and at osc s suggesting that these features are associated with along strike minima in the magmatic budget we suggest that major phases of volcanic activity propagate episodically along the axis away from centers of magmatic inflation and that osc s develop where magmatic pulses fail to meet due to misalignment of fracture systems sinuous bends in the rise axis or other heterogeneities transform faults fail to develop on fast spreading centers where the lateral offsets are small 15 km because the lithosphere is too thin and weak to maintain a classic rigid plate ridge transform fault pattern the osc geometry is unstable and evolves rapidly and the overlapping rises may propagate at rates faster than the local spreading rate one of the two osc s prevails while the other is abandoned while the locations of osc s may not be fixed relative to the rise axis they may tend to recur near the same place creating scars in older lithosphere which resemble fracture zones but whose fine scale structure is quite different there is excellent agreement between the observed structure of osc s and laboratory studies of osc s using wax models photoelastic studies of overlapping cracks and boundary element modeling of overlapping cracks seismic refraction and reflection near two osc s suggests that large offset osc s have separate magma chambers beneath the offset rise axes while small offset osc s may share a single axial magma chamber three dimensional inversion of magnetic anomalies suggests that significant petrologic anomalies may occur near some osc tips waxing and waning of overlapping magma chambers may give rise to the eruption of highly fractionated feti basalts and associated magnetic anomalies

block rotation by strike slip faulting structural and paleomagnetic evidence geometric analysis shows that motion of sets of strike slip faults should cause block rotation otherwise the distorted fault domain would not fit with its surrounding the sense of the block rotation depends on the sense of fault slip and the spacing and orientation of the faults all of which can be obtained from structural data the predictions of the geometric model can then be independently tested by paleomagnetic measurements the model was tested in northern israel structural data reveal several domains of contemporaneous right and left lateral strike slip faults paleomagnetic measurements show that in a domain of nnw trending left lateral faults blocks rotated 23 3 8 2 clockwise and in a domain of right lateral faults blocks rotated 22 4 9 0 anticlockwise these results are in agreement with the prediction of the geometric analysis of the structure the combined results of the heterogenous deformation of the area resembles a pure shear which allows n s extension by about 1 3 in other domains rotations of 34 6 9 1 and 53 1 11 0 were found in their original orientation the left and right lateral faults intersected at angles of 60 70 enclosing the principal axis of shortening in accordance with theories of brittle failure as a result of block rotations this angle is now larger and may reach 110 the results demonstrate large block rotations in different senses in domains of strike slip faults the independent structural and paleomagnetic data can be interpreted within the framework of a simple geometric model northern israel is considered to be a good model for this efficient mechanism of intraplate deformation which is expected to occur in similar tectonic settings elsewhere

slickenside and fault surface kinematic indicators on active normal faults of the alpine betic cordilleras granada southern spain abstract twenty four mesoscopic slickenside kinematic indicators are described here for the pliocene quaternary active normal faults of the alpine betic cordilleras granada southern spain the indicators are classified into twelve groups depending on the down or up slope asymmetric orientation of features such as concavities damaged versus sharp grain borders or step edges v shaped markings fractures and trailed material seventeen of the indicators were not previously described in the literature the new kinematic indicators include two types of asymmetric grains a carrot shaped marking six substructures of congruous and incongruous steps trailed fault material a drop shaped figure a v shaped marking three types of synthetic hybrid fractures with congruous steps and two varieties of pluck holes we think that some of these kinematic indicators provide information on the amount of displacement aseismic versus seismic slip rates cataclastic flow frictional wear or surface polishing

structure and kinematics of oblique continental convergence in northern fiordland new zealand abstract southeast of the alpine fault in fiordland new zealand late tertiary faults envelope exposures of early cretaceous high p 12 16 kbar granulite facies orthogneisses these exposures allowed us to examine how pre cenozoic structures influenced variations in the degree and style of kinematic partitioning within a zone of oblique continental convergence fault slip data and kinematic modelling show that oblique slip and reverse displacements preferentially were partitioned east of the alpine fault onto curved ne striking surfaces and moderately dipping 30 52 n and nw striking surfaces respectively approximately 3 0 5 5 km of exhumation and 6 5 7 0 km of oblique dextral displacement occurred on faults that display palm tree style geometries and subhorizontal detachments in profile this heterogeneous style contrasts with the near horizontal slip on subvertical surfaces that define the alpine fault north of milford sound the principal axes of instantaneous strain we determined using faults are compatible with principal stress axes derived from earthquakes our data indicate that mechanical anisotropies created by inherited structures controlled the locations and highly variable geometries of faulting since 7 9 ma the effects of these pre existing structures and a focusing of contractional deformation along the northeast margin of fiordland resulted in an unusually high degree of strike slip partitioning across the southernmost onshore segment of the alpine fault

current plate velocities relative to the hotspots incorporating the nuvel 1 global plate motion model nuvel 1 is a new global model of current relative plate velocities demets et al 1990 which differ significantly from those of prior models here we incorporate nuvel 1 into hs2 nuvel1 a new global model of plate velocities relative to the hotspots hs2 nuvel1 was determined from the hotspot data and errors used by minster and jordan 1978 to determine am1 2 which is their model of plate velocities relative to the hotspots am1 2 is consistent with minster and jordan s relative plate velocity model rm2 here we compare hs2 nuvel1 with am1 2 and examine how their differences relate to differences between nuvel 1 and rm2 hs2 nuvel1 plate velocities relative to the hotspots are mainly similar to those of am1 2 minor differences between the two models include the following 1 in hs2 nuvel1 the speed of the partly continental apparently non subducting indian plate is greater than that of the purely oceanic subducting nazca plate 2 in places the direction of motion of the african antarctic arabian australian caribbean cocos eurasian north american and south american plates differs between models by more than 10 3 in places the speed of the australian caribbean cocos indian and nazca plates differs between models by more than 8 mm yr although 27 of the 30 rm2 euler vectors differ with 95 confidence from those of nuvel 1 only the am1 2 arabia hotspot and india hotspot euler vectors differ with 95 confidence from those of hs2 nuvel1 thus substituting nuvel 1 for rm2 in the inversion for plate velocities relative to the hotspots changes few euler vectors significantly presumably because the uncertainty in the velocity of a plate relative to the hotspots is much greater than the uncertainty in its velocity relative to other plates

curved slickenfibers a new brittle shear sense indicator with application to a sheared serpentinite abstract brittle fault zones are commonly characterized by penetrative fracturing of the rock to form an aggregate of blocks so that the rock becomes in essence like a granular material composed of rigid grains the surfaces of the blocks or grains have a wide distribution of orientations and shearing of the blocks past one another on these planes accommodates the large scale motion i e the macromotion in the fault zone during a macromotion that is a non coaxial deformation the rigid blocks and their surfaces may undergo a progressive rigid rotation that is distinct from the macromotion and is described by the microspin if a macroscopic non coaxial deformation has monoclinic symmetry this symmetry should be reflected in the sense of rigid rotation of the blocks and their surfaces on the surfaces of the blocks which are local shear planes the history of displacement may be recorded by mineral fibers that grow progessively with displacement because of the rigid rotation of the local shear planes slickenfiber lineations commonly are curved the sense of curvature from the youngest to the oldest part of the fiber looking down the normal to the local shear plane is different for those planes whose normals are on opposite sides of the unique monoclinic symmetry plane for the macroscopic shearing the intersection of the symmetry plane with the plane of the fault zone defines the macroscopic slip direction and the sense of rigid rotation of the local shear planes determined from the lineations defines the shear sense application of this technique to the disrupted and sheared margins of the feather river peridotite in the northern sierra nevada of california indicates that late deformation involved dextral normal oblique slip along the melones fault zone

hotspot tracks and the early rifting of the atlantic abstract many hotspot tracks appear to become the locus of later rifting as though the heat of the hotspot weakens the lithosphere and tens of millions of years later the continents are split along these weakened lines examples are the west coast of greenland east coast of labrador madeira hotspot the south coast of mexico north coast of honduras guyana hotspot and the south coast of west africa north coast of brazil st helena hotspot a modern day analog of a possible future rift is the snake river plain where the north american continent is being pre weakened by the yellowstone hotspot track this conclusion is based on reconstructions of the motions of the continents over hotspots for the past 200 million years the relative motions of the plates are determined from magnetic anomaly isochrons in the oceans and the motion of one plate is chosen ad hoc to best fit the motions of the plates over the hotspots however once the motion of this one plate is chosen the motions of all the other plates are prescribed by the relative motion constraints in addition to the correlation between the predicted tracks and sites of later continental breakup exposed continental shields correlate with the tracks their exposure may be the result of hotspot induced uplift which has led to erosion of their former platform sediment cover

cycloid kinematics of relative plate motion the trajectory of a point on one plate as observed from another plate is generally a complex curve and not a small circle around a single axis of relative motion as is commonly assumed the shape of the relative motion path is given the general name spherical cycloid because of its morphological similarity to cycloid planetary trajectories described by early astronomers the cycloid relative motion model predicts that the following phenomena occur during finite displacements 1 the relative velocity and the curvature of the trajectory of a point on one plate relative to another plate varies systematically 2 plates wobble relative to one another and 3 the angle of convergence and or divergence varies systematically along the length of any given transform fault the small circle relative motion model whereby transform faults have been considered lines of pure slip along which crust is conserved is not generally valid for finite relative displacements

rotational velocity for oblique structures boltana anticline southern pyrenees abstract despite the large amount of paleomagnetic and structural studies on fold and thrust belts many key questions about rotational kinematics remain unsolved pace of rotation subsequent accommodation of the hanging wall etc excellent exposure conditions and syntectonic sedimentation related to the growth of oblique structures in the southern pyrenees allow an accurate investigation that sheds light on the rotational kinematics of thrust systems fifty nine paleomagnetic sites 819 specimens are homogeneously distributed in both limbs along the marine and continental sedimentary sequences contemporary with the uplift of the boltana anticline and its post folding evolution they indicate a clockwise rotation of about 52 during ypresian to priabonian times primary stable 350 580 c pre folding magnetization in the eocene rocks is attested by a positive fold test and the antipodality proof with magnetite and iron sulphide traces as magnetic carriers rotation velocity fits a logarithmic model and shows a low rate during the ilerdian middle lutetian interval ca 1 m y and much higher up to 10 m y in the late lutetian priabonian interval most of the clockwise rotation of the boltana anticline can therefore be constrained within the 42 35 m a interval partially post folding indicating a period of strong differential displacement in the southern pyrenean zone probably related to the emplacement of the underlying external sierras thrust sheets tozal alcanadre

rupture process of the wenchuan earthquake mw 7 9 from surface ruptures and fault striations characteristics abstract on 12 may 2008 the wenchuan earthquake mw 7 9 produced complicated thrust type co seismic surface rupture zones which encompass the dextral slip thrust of the yingxiu beichuan fault the approximately pure thrust of the guanxian anxian fault and the sinistral slip thrust of the xiaoyudong rupture zone located between the former two in order to understand the faulting mechanism we discuss the rupture process by examining the segmentation and kinematics of the surface rupture zones together with the co seismic fault striations at various sites based on the two along strike main displacement peaks 6 6 5 m and 11 12 m and on the different geometric and kinematic patterns for the southern and northern segments of the surface rupture zones we find that the wenchuan earthquake might have consisted of two rupture stages which is in agreement with seismic wave inversion results by comparing the kinematics of fault striations occurring in the bajiaomiao and beichuan areas it suggests that during the first stage thrusting along both the yingxiu beichuan fault and guanxian anxian fault produced the 80 100 km long yingxiu qingping surface rupture segment and the 80 km long guanxian anxian surface rupture zone respectively then faulting was triggered along the yingxiu beichuan fault by the first rupture process yielding the second rupture stage which was characterized by dextral strike slip or dextral oblique thrusting due to the overlap between the two rupture stages the southern segment yingxiu qingping of the yingxiu beichuan rupture zone comprises two different processes while the northern segment gaochuan beichuan shikan only suggests one rupture phase

slip heterogeneity on a corrugated fault abstract slip heterogeneity reflects the fundamental physics of earthquake rupture and has been attributed to strong fault patches termed asperities or barriers we propose that variations in fault surface orientation due to slip parallel corrugations may act as geometric asperities and barriers generating variations in incremental i e due to a single earthquake slip across a fault surface we evaluate this hypothesis using observations from the arkitsa normal fault exposure in central greece a scan of the arkitsa fault surface with 1 m spatial resolution and mm scale precision reveals corrugations made up of 1 5 m wide synforms antiforms and nearly planar fault sections with long axes that extend in the slip direction across the entire exposed surface the surface is thus more than an order of magnitude smoother in the direction of slip than in the perpendicular direction slip perpendicular profiles exhibit nearly self similar scaling across the range of observed wavelengths 2 50 m whereas slip parallel profiles are significantly smoother at shorter wavelengths

a new angle on the tectonic evolution of the ridge basin a strike slip basin in southern california the ridge basin located in southern california between the san andreas and san gabriel faults contains as much as 14 km of mio pliocene marine and nonmarine sedimentary fill these strata are exposed as a northwest dipping homoclinal sequence that becomes increasingly younger to the northwest pliocene to holocene deformation uplift and dissection of this basin provide an opportunity to study stratal geometry and sedimentary facies in what is commonly cited as a classic strike slip basin newly acquired seismic data from the northern ridge basin provide new evidence for the subsurface basin geometry these data lead us to conclude that the principal northern strand of the san gabriel fault is a listric east southeast dipping oblique slip fault rather than a subvertical strike slip fault the principal san gabriel fault appears to become subhorizontal at the southeastern end of the seismic line at a present day sub surface depth of 4 km this interpretation is consistent with preliminary two dimensional gravity models across the basin and with the homoclinal structure of basin fill subsidence within the ridge basin is explained as the result of northwest southeast extension locally accommodated along the listric right lateral san gabriel and associated late miocene strike slip faults as a consequence of oblique normal slip on the gently dipping san gabriel fault sedimentary strata were continuously tilted and moved southeastward in the hanging wall away from the depocenter this mechanism of basin formation allowed 14 km of sediment to accumulate without deep burial the geometry and displacement history of the san gabriel fault controlled sediment accommodation and resultant stratal geometries within the basin slip along the san gabriel fault and associated subsidence of the ridge basin correspond temporally with regional tectonic events in southern california reflecting both changes in the relative motion of pacific and north american plates and the evolution of strain partitioning across this plate boundary

the transition from large magnitude extension to distributed dextral faulting in the buckskin rawhide metamorphic core complex west central arizona brittle fault data from the buckskin rawhide metamorphic core complex west central arizona document the miocene transition from large magnitude ne directed extension to distributed e w extension and dextral faulting the buckskin rawhide detachment fault locally records a clockwise rotation of the slip direction from dominant top ne directed slip to ene and e directed slip during the last stages of activity postmylonitic brittle deformation is dominated by normal and dextral slip along moderately to steeply ne dipping faults relative timing relationships indicate that most postmylonitic normal faulting was coeval with middle miocene detachment fault slip whereas dextral and oblique dextral faulting postdates detachment fault slip post 11 ma based on the persistent sw dip of lower plate fabrics and ne dip of abundant normal faults the amount of ne sw brittle extension across the mylonitic lower plate is estimated to be 20 30 in several areas the end of detachment faulting in the buckskin rawhide metamorphic core complex was marked by a transition to dominantly e w extension and associated dextral normal faulting at least 10 ne dipping postdetachment faults record 0 1 1 km dextral or oblique dextral displacement the cumulative amount of dextral shear across the core complex is probably 7 9 km which is the amount needed to restore the topographic trend of lower plate corrugations into alignment with the dominant extension direction postdetachment dextral transtensional faulting across the core complex reflects the increasing influence of the diffuse pacific north america transform plate boundary toward the end of the middle miocene

morphotectonic fabric of the orozco transform fault results from a sea beam investigation we have used data collected with the sea beam system to produce a detailed regional bathymetric map of the medium to fast slipping 90 mm yr orozco transform fault the morphotectonic fabric of the 90 50 km transform domain is spatially heterogeneous and is composed of relatively shallow areas 3200 m the plate boundary geometry is clearly identified morphologically and is characterized by a series of linked basins and troughs that approximate a zed pattern in plan view east west trending basins define the northern and southern boundaries of the transform domain and these troughs are thought to mark the location of strike slip tectonism a central north south trending ridge with an axial valley called here the mid orozco spreading center is thought to represent a short 30 km ridge segment that links two transform faults morphotectonic relationships developed along the southeastern flank of the survey area suggest that this plate boundary geometry has recently become unstable and is presently undergoing a transformation as the tip of the east pacific rise axis propagates northward across the transform domain bypassing the mid orozco spreading center if the southern ridge axis continues to propagate northward it will link with the aseismic extension of the northern strike slip strand and the present day plate boundary will evolve into a simple ridge transform ridge r t r geometry with an offset of approximately 70 km

a sea beam investigation of the clipperton transform fault the morphotectonic expression of a fast slipping transform boundary a regional scale bathymetric map of the fast slipping 11 0 cm yr clipperton transform boundary and adjoining east pacific rise segments has been constructed using the high resolution capabilities of sea beam the transform domain is 85 km long varies in width from 10 to 20 km and is defined by an assemblage of transform parallel ridges and troughs the largest of which is a 40 km long median ridge that stands up to 700 m above the surrounding seafloor these major topographic elements of the transform domain are bisected by a very narrow 1 km swath of strongly lineated terrain composed of elongate depressions narrow lozenge shaped ridges and gullies that integrate spatially to create a narrow zone of disturbed topography this zone trends 082 and cuts like a knife across the grain of the clipperton transform domain linking one truncated ridge tip with the other we interpret this swath of disturbed terrain to be the product of strike slip tectonism thereby fixing the location of the present day plate boundary the present day structural geometry of the clipperton transform appears relatively simple and characterized by a narrow strike slip plate boundary linking two offset ridge axes

rotational basement kinematics deduced from remagnetized cover rocks internal sierras southwestern pyrenees 1 paleomagnetic data from the internal sierras unravel the kinematic relationship between basement guarga gavarnie bielsa and cover thrusts larra monte perdido the new data come from an area of 100 km along strike and 5 15 km across strike of the southwestern pyrenees the area covers a variety of structural positions that range from cover to basement thrusts from 84 sites located in upper cretaceous two meaningful magnetic components are found 1 the higher temperature c component unblocks at 575 c presents two polarities is prefolding has a mean declination and inclination d i of 010 44 95 8 k 15 and is considered primary and 2 the intermediate b component unblocks between 250 c and 450 c has a mean d i of 198 43 95 4 k 18 and has always reverse polarity and postfolding the nine sites located in the eocene flysch south of the upper cretaceous show the same postfolding component b the acquisition of this intermediate component alludes to a widespread tectonic related remagnetization event affecting the internal sierras this event must be younger than the folding of the flysch deposits middle upper eocene the tilting induced by the basement thrust gavarnie bielsa in the axial zone does not alter the inclination of the b so that the sediments acquire the b component later than priabonian emplacement age of the gavarnie thrust the b component is rotated clockwise with respect to the tertiary reference this means that the rotation takes place after the remagnetization event the position of the c component before the rotation of the b component is negligibly rotated d i of 002 44 95 7 k 94 with respect to the cretaceous reference therefore the b component records the last and only rotational event in the region the rotation is related to the latest basement deformation guarga thrust during upper oligocene times and it reflects the regional shortening gradient in the southwestern pyrenees the emplacement of the larra monte perdido cover thrust system that took place prior to basement thrusts mentioned above did not undergo any significant rotation

fault block rotations at the edge of a zone of continental extension southwest turkey the ne sw trending burdur acigol and baklan basins of southwest turkey are bounded by normal faults which became active in quaternary times prior to this a more widely spaced system of pliocene basins had existed each of the quaternary basins has a half graben geometry with a major nw dipping fault on its southeast side previous studies of the 1971 burdur earthquake caused by movement on the fault bounding the burdur basin have shown this fault to flatten slightly at depth deformation in the hangingwall of the fault controlling the pliocene basin in the burdur region suggests a planar fault geometry it is suggested that the pliocene fault rotated to its present shallow orientation then became inactive and acted as a detachment at depth for the more recent quaternary fault quaternary faults bounding the burdur acigol and baklan basins have a sinistral strike slip component with slip vectors indicating extension in an nw se direction this is at variance with regional n s extension in western turkey a solution for this contrast is found by invoking block rotations about vertical axes in a deforming zone between the rapidly extending aegean region to the west and the stable unstretched anatolian plateau to the east

instantaneous velocity of mid ocean ridges abstract intuition suggests that all points on the same mid ocean ridge should rotate around the relative pole of the two plate system at the same instantaneous angular velocity contrary to intuition the instantaneous angular velocity of a ridge varies from one point to another along the ridge given the general case in which two plates move around different plate specific poles of rotation the variation in the instantaneous angular velocity of a ridge is a function of the motion characteristics of the plates and the position of the ridge relative to the poles of plate motion the length or orientation of individual ridge segments is predicted to vary over time leading to local changes in the shape of the ridge the gradient in instantaneous angular velocity for the fast spreading east pacific ridge between the cocos and pacific plates is an order of magnitude greater than the gradient along the mid atlantic ridge between the north american and african plates this great contrast in ridge instantaneous velocity gradients may be reflected in the contrasting ridge geometries of the east pacific and mid atlantic ridges

3 d numerical modelling of the influence of pre existing faults and boundary conditions on the distribution of deformation example of north western ghana abstract high strain zones bound and separate the high grade tectono metamorphic terranes from low grade greenstone belts in the north western parts of ghana these belts are bounded by granitoid domains characterized by two main episodic pulses of magmatic intrusive events which occurred between 2213 ma and 2086 ma high strain zones are thought to play a significant role in creating fluid pathways particularly for partially molten material from lower crustal sources to the upper crust in this study a three dimensional thermo mechanical model has been used to explore the evolution of high strain zones and relief under compressional and simple shear boundary conditions different orientations of a system of branched strike slip faults were tested the effects of the frictional angle and density contrast on the evolution of relief were also compared in this study the resulting model indicates domains of tensile vs compressional strain as well as shear zones this shows that the internal fault zones as well as the host rock in between the faults behave as relatively weaker domains than the external regions under both applied compressive and simple shear boundary conditions these weakened domains constitute preferential zones of tensile and shear strain accommodations in the upper crust which may favour infilling by deeper partially molten rocks this processes is suggested by the authors as the most likely processes to have occurred in pre existing branched shear zones systems in north western ghana during the eburnean orogeny around 2 20 2 10 ga the orientations of faults in these models play an important role in controlling the evolution of relief and localized deformation in particular greatest the largest relief is obtained when faults dip parallel to each other and when they are inclined at depth as they thus facilitate strain rotation and material transfer from depth the host rock density does not play a primary role in producing relief compared to variations in friction angle at crustal scale of our model relief increases by 200 300 m when the host rock density is increased by 200 kg m3 whereas relief reduces by about 1200 m when decreasing the host rock friction from 20 to 10 this study suggests a model for interpreting the evolution and locus of exhumation of partially molten rocks in north western ghana

the cycloid relative motion model and the kinematics of transform faulting abstract adequate models of instantaneous plate tectonics currently exist however a model to describe the continuous relative motion of lithospheric plates during a finite time interval has been necessary the small circle relative motion model suggests that a particle on a given plate follows a circular path around a pole of relative motion as viewed from another plate during finite relative displacement it can be shown that the small circle model is not generally valid in describing the finite relative motion of plates so this motion must trace a curve that is more complex than a circle a new approach has been developed that permits improved modeling of finite relative plate motion the first order cycloid relative motion model cyc1 is based upon the idea that each plate is in motion around a plate specific pole elsewhere termed an absolute or no net torque pole the observed relative motion between two plates is the result of the two plate specific motions combining the two rotations a point on one plate moves along a cycloid figure of rotation around two axes as viewed from another plate a cycloid a two axis curve is the simplest spherical curve that is more complex than a circle a one axis curve the mathematical expression of cycloid relative motion involves a series of coordinate transformations the small circle model is a subset of the cycloid model cyc1 indicates that significant variations in the direction and velocity of relative motion can occur even when the governing axial positions and angular velocities are constant hence a variety of boundary interactions are possible during finite relative displacements that would not have been predicted by a small circle model of finite relative plate motion the cycloid model indicates that transform faults are not simply lines of pure slip along which crust is conserved systematic changes in the amount of convergence or divergence along the length of a given transform fault are predicted this gradient is probably reflected in local boundary deformation and is predicted to be a factor controlling the length of a given fault segment transform faults are generally in motion relative to the corresponding relative pole and plate specific poles the relative velocity along a given transform fault and the spreading rate across the adjacent ridge segments vary as the radius from the fault to its relative pole changes the curvature of a given transform fault is also predicted to change with finite displacement as the fault moves with respect to its relative pole motion of a given transform fault with respect to its relative pole and to the plates that it bounds suggests that the traces of the resulting fracture zones should be complex curves that are not symmetrical across the ridge axis improved modeling of finite relative plate motion should enhance understanding of the structural stratigraphic magmatic and metamorphic evolution of plate margins

theory of slickenline patterns based on the velocity gradient tensor and microrotation abstract brittle fault zones commonly are characterized by a multitude of lineated shear planes having a wide distribution of orientations in our model we assume the faulted rock comprises an aggregate of rigid blocks whose surfaces are the shear planes we define two independent scales of motion to distinguish the local rigid rotation of the blocks with their shear planes the micromotion from the average deformation of the material on a macroscopic scale the macromotion the macromotion is defined by the macrovelocity gradient tensor which is separated into symmetric and antisymmetric parts the deformation rate and the macrospin tensors respectively the micromotion is defined by a microspin tensor on any shear plane slickenlines form parallel to the direction of the maximum rate of shear which we assume is determined by the direction of the maximum component of the macrovelocity gradient tensor tangent to the shear plane and by a component of the microspin in the shear plane for a restricted kinematic model patterns of slickenline orientations are defined on a uniform distribution of shear plane orientations by the values of d and w d is a ratio of differences in the principal values of the deformation rate tensor and w is a ratio of the net spin to the maximum rate of macroshear we distinguish between instantaneous slickenline patterns and finite deformation patterns the two are different if the shear planes rotate relative to the principal deformation rate axes in which case finite deformation slickenlines form curved or crossing lineations if w 0 the instantaneous slickenline patterns have orthorhombic symmetry 0 d d 1 or 0 if w 0 the instantaneous slickenline patterns have monoclinic symmetry for pure shear in an isotropic body instantaneous slickenline patterns have orthorhombic symmetry w 0 d 0 5 whereas for pure shear accommodated by shear on a planar anisotropy w 1 d 0 5 the pattern is monoclinic for simple shear with the rigid rotation of local shear planes defined by the shear induced spin w 0 d 0 5 the instantaneous slickenline pattern is orthorhombic but the finite deformation pattern is monoclinic for simple shear with no shear plane rotation w 1 d 0 5 the instantaneous pattern is monoclinic special cases of our hypothesis are equivalent to the hypothesis that slickenlines are parallel to the direction of maximum resolved shear stress e g angelier 1979 1984 the slickenline patterns predicted for this case are always of orthorhombic or higher symmetry and are equivalent to our instantaneous patterns for which w 0 and to our finite deformation patterns for which in addition there is no microspin

fault motion and curved slickenlines a theoretical analysis slickenlines record on a fault surface the nature of relative movement of the faulted blocks an assemblage of straight slickenlines indicates linear translational fault motion curved slickenlines on the other hand may arise either due to rotational translational fault motion or due to fault motions where the translation direction changes continuously curvilinear translational fault motion the analysis of roto translational fault motion involves the ratio of relative rate of rotation vs translation whereas that of curvilinear translational fault motion involves the ratio of rate of change of translation direction to the rate of translation the analyses reveal that an assemblage of curved slickenlines where each slickenline differs in shape from the other is indicative of roto translational fault motion whereas an assemblage where the slickenlines are of similar shape is the consequence of curvilinear translational fault motion