le bassin de tizi n test haut atlas maroc exemple d evolution d un segment oblique au rift de l atlantique central au trias detailed mapping completed by a microtectonic study of the tizi n test triassic basin located along the tizi n test fault zone in the moroccan high atlas has allowed us to improve the knowledge on the geometry of the structures and the activity of faults during the triassic extensional events related to the rifting of the central atlantic the latter are reflected by the development of a rift at present inverted and deformed by the collision of africa and europe comprising kilometric scale grabens and half grabens bounded by major faults trending ene wsw with a dip towards the nnw and a dip slip syndepositional motion inverse analysis of fault slickenside populations shows a heterogeneous triassic state of stress however in the most significant measurement sites the maximum horizontal stress 1 is vertical while the minimum stress 3 is horizontal with a nw se trend the strike slip component appears to be very small during the triassic a noticeable fact because of the obliquity of the basin w

release fault a variety of cross fault in linked extensional fault systems in the sergipe alagoas basin ne brazil abstract two types of cross faults are herein recognized transfer faults and the newly termed release faults transfer faults form where cross faults connect distinct normal faults and horizontal displacements predominate over vertical ones in contrast release faults form where cross faults associated with individual normal faults die out within the hangingwall before connecting to other normal faults and have predominantly vertical displacements release faults are geometrically required to accommodate variable displacements along the strike of a normal fault thus they form to release the bending stresses in the hangingwall and do not cut normal fault planes nor detachment surfaces at depth release faults have maximum throws adjacent to normal faults and may be nearly perpendicular or obliquely oriented to the strike of the latter such geometry appears not to depend upon pre existing weaknesses but such variable orientation to normal faults is an inherent property of release faults release faults commonly appear as simple normal faults in seismic sections without implying extension along the strike of rift and basins three dimensional strain deformation occurs in the hangingwall only between the terminations of an individual normal fault but regionally release faulting is associated with plane strain deformation in linked extensional fault systems

release faults associated structures and their control on petroleum trends in the reconcavo rift northeast brazil release faults are rift cross faults which develop to accommodate the variable displacements of the hanging wall block along the strike of normal faults release faults are nearly perpendicular or obliquely oriented to the strike of the normal fault they are related to they have maximum throws adjacent to the parent normal fault and die out in the hanging wall away from it they form to release the bending stresses in the hanging wall and do not reflect the orientation of the regional stress field in a basin commonly they show normal oblique displacements and are preferentially located along the strike ramps release faults may also act at the scale of an entire basin reaching displacements of thousands of meters joints shale and salt diapirs may develop in association with release faults because all these structures represent domains of stress release they may work as conduits for oil migration and oil traps in extensional basins this is the case of the reconcavo basin in northeastern brazil a cretaceous failed rift connected to the eastern brazilian continental margin basins in the reconcavo basin two large scale release faults with displacements in the order of 3 km developed in the hanging wall of the rift border faults and control the location of the main oil fields

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

normal fault development during two phases of non coaxial extension an experimental study we use scaled experimental analog models to study the effect of a pre existing fault fabric on fault development during extension in our models a homogeneous layer of wet clay undergoes two noncoaxial phases of extension whose directions differ by up to 45 the normal faults that develop during the first phase create a pronounced fault fabric that influences normal fault development during the second phase in all models the pre existing faults are reactivated during the second phase of extension their sense of slip depends on the angle between the first and second phase extension directions specifically the component of dip slip relative to strike slip decreases as the angle between the first and second phase extension directions increases new normal faults also form during the second phase of extension in all models the number of new fault segments increases as the angle between the first and second phase extension directions increases the orientations of the new normal fault segments are both orthogonal and oblique to the second phase extension direction indicating that both the secondphase extension direction and the pre existing fault fabric control the orientation of new fault segments some of the new normal faults cut and offset the pre existing faults whereas others terminate against them producing complex fault patterns and interactions the modeling results explain fault interactions observed in the jeanne d arc rift basin of offshore newfoundland canada and the reactivation of abyssal hill normal faults at outer highs near subduction zones

transverse versus longitudinal extension in the foredeep peripheral bulge system role of cretaceous structural inheritances during early miocene extensional faulting in inner central apennines belt this study reports on the rocca di cave extensional fault system which is located in the prenestini mountains central italy of the apennines fold and thrust belt and presently represents the oldest exposure of early orogenic foreland fault system of the apennines this fault system was oriented perpendicular to the strike of the foredeep peripheral bulge system indicating that the onset of convergence was marked by a foredeep parallel extension instead of the commonly observed foredeep perpendicular stretching associated with lithosphere flexuring the studied fault system is formed by a 10 km long and 2 km wide e w elongated area that includes two mutually orthogonal sets of faults oriented about e w and n s respectively e w and mainly n s striking faults developed during a preorogenic santonian to campanian in age e w oriented extension kinematics which caused first uplift and erosion and then drowning of the cretaceous carbonate platform and the onset of a pelagic environment both fault sets were later reactivated in the early miocene when the area was forming part of the foreland region ahead of the eastward migrating apennines fold and thrust belt and was undergoing local n s oriented i e foredeep parallel stretching this extensional stage implied the sedimentation of hundreds of meters of synkinematic strata in the northern block of the rocca di cave fault system coevally with episodes of subaerial erosion in areas of the southern block further extensional and right lateral reactivation of inherited faults occurred in the late miocene during the progressive incorporation of the area into the apennines belt

a variation of the collapsing method to delineate structures inside a microseismic cloud we describe a modification to the collapsing method a technique that aims to find the simplest structures in a cloud of microearthquakes by utilizing the statistical uncertainties in the data in the modified collapsing method the movements of the locations are dependent on the shape of the distribution of the locations within the confidence ellipsoid and not just the position of the center of gravity as is the case in the original method additionally whereas the original collapsing method implicitly assumes that all locations belong to point structures in this modified version three types of structure are considered point line and plane principal component analysis of the locations is used to evaluate to which type of structure each location most probably belongs the modified technique has been applied to microseismic events associated with hydraulic stimulation at the fenton hill hdr field new mexico and known small scale structures were imaged

tectonic evolution of the sergipano fold belt ne brazil during the brasiliano orogeny abstract the sergipano fold belt sfb represents the southern segment of a brasiliano age 600 ma continental collision zone which extends over ne brazil and continues into central africa as the north equatorial fold belt major sinistral transcurrent fault shear zones and thrusts separate domains with individual lithological tectonometamorphic and magmatic characteristics the principal steeply dipping strike slip zones trend east west to wnw ese lithological correlations across the shears have not proved possible which suggests that displacements were probably large but as yet are unquantified major folding and thrusting affected all the domains folds have a southerly vergence with nw se to wnw ese trends consistent with a ne sw to nne ssw shortening direction although small differences in shortening trends exist between individual domains the southernmost allochthonous domain of carbonate to clastic shelf slope sediments was subject to a single phase of folding and thrusting onto the sao francisco craton accompanied by greenschist facies metamorphism north of this domain lies the macurure domain which is separated from the southernmost allochthonous domain by the major sao miguel do aleixo transpressive shear zone polyphase deformation amphibolite facies metamorphism and massive granitic intrusion characterize this domain north of the macurure domain lie the migmatites and granites of the poco redondo domain which represent a deeper crustal level they are separated from the macurure domain by the belo monte shear a late tectonic leucogranite in the poco redondo domain yields a 600 ma rb sr isochron finally the poco redondo domain was overthrust from the north by the caninde gabbroic complex associated with carbonates pelites and amphibolites metamorphosed to greenschist and upper amphibolite facies this has previously been interpreted as an ophiolite sequence although the relative movements or absolute ages of the domains are unknown their distinct geological differences suggest that they are separate crustal blocks which underwent large lateral movement during the brasiliano collision

scaling properties of normal fault populations in the western corinth graben greece implications for fault growth in large strain settings abstract a variety of one dimensional and two dimensional map techniques of fractal analysis have been employed to investigate the scaling properties of the dominant wnw trending normal fault population of the western corinth graben in central greece to assess possible constraints on fault geometry during fault growth the data have been compiled separately from the northern and southern domains of the graben which have experienced differing amounts of finite strain based on power law distributions of the fault throw the applied extension is estimated at 30 and 22 for the northern and southern domains respectively however the fault spacing and fault length populations in both domains obey similar power law relationships these conclusions are also supported by maximum throw vs trace length data which demonstrate that the faults in the northern domain have systematically higher values for the slip to length ratios than those in the southern domain it is proposed that the corinth graben has reached fracture saturation that is the fault spacing stops evolving and displacement increases rather than faults lengthening to accommodate the increasing extension this growth process consistent with throw distributions along individual faults may be explained either in terms of a stress feedback mechanism or by the mechanical interaction between the wnw trending normal faults with a set of nne trending transverse faults

mesozoic rifting in the basque cantabrian basin spain inherited faults transversal structures and stress perturbation terra nova 24 70 76 2012 abstract in the basque cantabrian basin northern iberian margin inherited wnw ese striking faults were reactivated during the mesozoic extensional stage associated with the opening of the bay of biscay syn rift structures in the area include different sets apparently indicating multiple extensional stages in particular abundant ne sw striking extensional elements have been interpreted in the past as having developed during a late rifting left lateral transtensional stage however the development of these structures also fits well with an analytical model of ridge perpendicular extension along strike stretching imposed by displacement variations along inherited faults locally produced an additional stress field oriented obliquely to the regional one this caused rotation of the local minimum stress and development of anomalously oriented transversal structures a single extensional stage is thus inferred during mesozoic rifting with a stretching direction oriented approximately perpendicular to the trend of the bay of biscay oceanic ridge

extensional fault control on the sedimentation patterns in a continental rift basin el castellar formation galve sub basin spain in the galve sub basin the sedimentary record of the upper hauterivian lower barremian el castellar formation is divided into two stages by a marlstone interval with gypsum stage 1 shows a great variety of subenvironments and facies alluvial palustrine and lacustrine whereas in stage 2 an extensive shallow carbonate lake developed sedimentation was controlled by a system of south dipping ene wsw listric normal faults laterally bounded by nnw sse steeper transfer faults faults controlled sedimentation from a basin scale basin margins and main characteristics and evolution of sediments to a regional and a local scale thickness and facies distribution of the synrift series as well as the location and evolution of lakes and minor alluvial fans the changes between stages 1 and 2 are related to the passing from an independent movement of faults to the movement of all the extensional faults as a whole at a sole detachment level the interval with gypsum was caused by underground water flow changes associated with the interrelation and connection of the faults in the transition period these changes have been correlated with the transition from the rift initial stage to the rift climax stage which took place in the hauterivian barremian transition

basement fabric controls rift nucleation and postrift basin inversion in the continental margin of ne brazil abstract in passive continental margins the brittle reactivation of shear zones and their role in the deformation and deposition of sedimentary basins are still a matter of debate in this research we investigated the role of the brittle reactivation of precambrian shear zones in the nucleation of rift and postrift faults in the onshore portion of the sergipe alagoas and pernambuco basins in northeastern brazil we combine and interpret a dataset of aeromagnetic and topographic data associated with reflection seismic and borehole data to analyze the evolution of a portion of the atlantic continental margin of brazil our results indicate that in the crystalline basement the magnetic lineaments are correlated with ductile structures as shear zones and the continuity of these lineaments in the sergipe alagoas and pernambuco basins is interpreted as the shear zones below the sedimentary cover of these basins we document the following phases of the brittle reactivation of basement shear zones 1 the opening of the south atlantic ocean in the early cretaceous under an extensional stress regime and 2 tectonic inversion induced by the mid atlantic ridge push and the andean cordillera rise in the neogene quaternary under a predominantly strike slip stress regime during the rift phase the brittle reactivation of the shear zones controlled the locations and architectures of the rifts these structures acted as zones of weakness and were reactivated as normal faults the brittle reactivation of shear zones was still active during the postrift phase and was responsible for the development of compressional structures the reverse faulting and related folding pattern indicate tectonic inversion in the late cretaceous cenozoic the structures formed during the postrift phase under a strike slip regime are consistent with the present day stress field indicating that tectonic inversion is an active phase of the brazilian margin

low frequency variability of the north pacific ocean the roles of boundary and wind driven baroclinic rossby waves 1 the effects of the sea level variability along the eastern boundary of the north pacific ocean including those associated with el nino southern oscillation have been considered an important factor in determining the low frequency large scale variability of the ocean interior through rossby waves generated at the eastern boundary this hypothesis is examined in this study using 8 years worth of the sea surface height observations made by the topex poseidon satellite the timescales of interest are longer than 90 days with the annual cycle removed the results indicate that the influence of the eastern boundary of the north pacific ocean has limited offshore extent varying from 3000 4000 km at 10 n to 200 300 km at 50 n the variability in the ocean interior is primarily driven by wind with only a minor influence from the boundary simulations of a linear two layer model of the ocean driven by wind stress curl are correlated with the observations the effects of wind forcing accumulate along the characteristics of long nondispersive rossby waves in the time longitude domain these wind driven rossby waves overwhelm the boundary driven waves in the ocean interior where there are only some small residual effects of the boundary driven waves however these small effects become clearer after the simulated wind driven variability is removed from the observations index terms 4556 oceanography physical sea level variations 4504 oceanography physical air sea interactions 0312 4215 oceanography general climate and interannual variability 3309 keywords rossby waves satellite altimetry el nino north pacific eastern boundary

quaternary fault control on the coastal sedimentation and morphology of the sao francisco coastal plain brazil abstract the role of neotectonic faulting in shaping topography and controlling sediment deposition has been increasingly documented along the stable continental margin of south america but the level of the present day tectonic stability of this margin is still a matter of debate this paper presents an investigation of the effects of quaternary fault reactivation on the sao francisco coastal plain sfcp this feature is a 56 km long progradational coastal plain located in the sergipe alagoas basin along the continental margin of brazil the sfcp is bounded on the west by a system of normal faults striking n s to ne sw the horst that bounds this plain is capped by the miocene barreiras formation and quaternary debris flow and fluvial deposits whereas the graben is filled with braided stream deposits and sandy beach ridge sediments the faulting contributed to the generation of accommodation space for the deposition of coastal sediments on the plain these processes started with the reactivation of cretaceous faults during the miocene during the quaternary fault reactivation and associated soft sediment deformation occurred between 82 and 8 3 ka with minor pulses between 1700 and 60 cal yr bp several faults along this margin are tectonically active and may represent the onshore continuation of gravitational collapses that have been documented offshore along the continental shelf and slope

structural geology and 4d evolution of a half graben new digital outcrop modelling techniques applied to the nukhul half graben suez rift egypt abstract lidar based digital outcrop mapping in conjunction with a new surface modelling approach specifically designed to deal with outcrop datasets is used to examine the evolution of a half graben scale normal fault array in the suez rift syn rift deposition in the nukhul half graben was controlled by the graben bounding nukhul fault the fault can be divided into four segments based on the strike of the fault the morphology of hangingwall strata and the variation in throw along strike the segments of the fault became geometrically linked within the first 2 5 m y of rifting as evidenced by the presence of early syn rift abu zenima formation strata at the segment linkage points fault perpendicular folds in the hangingwall related to along strike variations in throw associated with precursor fault segments persist for a further 1 8 m y after linkage of the segments suggesting that the fault remains kinematically segmented we suggest this occurs because of sudden changes in fault strike at the segment linkage points that inhibit earthquake rupture propagation or because displacement is geometrically inhibited at fault linkage points where the orientation of the intersection line of the segments is significantly different from the orientation of the slip vector on the fault system length throw plots and throw contour patterns for minor faults show that some faults initiated in pre rift strata whereas late east striking faults initiated in the syn rift basin fill the late initiating faults are spatially associated with the east striking baba markha fault which was active throughout the rift history but developed as a transfer fault between major block bounding fault systems around 6 7 ma after rift initiation

stress release process along an intraplate fault analogous to the plate boundary a case study of the 2017 m5 2 akita daisen earthquake ne japan stress accumulation and release in the crust remains poorly understood compared to that at the plate boundaries spatiotemporal variations in foreshock and aftershock activities can provide key con

improved relative locations of clustered earthquakes using constrained multiple event location a new method for improving relative locations of clustered earthquakes is presented and applied to a suite of microearthquakes induced by hydraulic fracturing the method is based on the assumption that clustering of earthquake hypocenters is obscured by the uncorrelated scatter of individual hypocenters the method is implemented as an additional constraint in a joint hypocenter determination jhd scheme the method shifts event hypocenters toward the center of mass of the events within some volume surrounding the event location if the rms misfit between predicted and measured arrival times does not increase significantly the method uses the same basic assumption of jones and stewart 1997 which is that there is greater clustering in actual earthquake locations than there is in locations determined using conventional techniques our method differs in that it is implemented as part of the jhd process so it operates on raw travel time data rather than on derived hypocenters the method produces hypocenters from a demonstration field dataset that are similar to those obtained by phillips et al 1997 from time consuming precise manual repicking of relative arrival times of events the clustering constraint can easily be incorporated as an additional constraint in earthquake location velocity tomography codes and may lead to improved velocity structure determination and earthquake location pattern identification and interpretation

the holocene paleoearthquakes on the 1915 avezzano earthquake faults central italy implications for active tectonics in the central apennines abstract extensive paleoseismological research was conducted in the fucino plain central italy in order to better understand the seismogenic characteristics of the fault responsible for the 1915 avezzano earthquake ms 7 0 and improve the general knowledge regarding active tectonics in the central apennines evidence for late pleistocene holocene surface faulting events was obtained through the study of thirteen sites across four different fault branches the paleoseismological analysis outlined the occurrence of ten surface faulting events in the past 33 000 years seven of which occurred during the holocene radiocarbon thermoluminescence and archaeological dating permitted the definition of an event chronology and the estimation of a recurrence interval for surface faulting events ranging between 1400 and 2600 years on the basis of the observed offsets it was possible to calculate vertical slip rates for the individual fault branches ranging between 0 24 mm yr 1 and 0 5 mm yr 1 and an extension rate across the fucino plain ranging between 0 6 and 1 mm yr 1 the chronology of surface faulting events appears linearly distributed in time and the observed recurrence times are similar to those inferred by other paleoseismological studies along different active apennine faults the general consequence of the large time span between strong earthquakes is that even a 2000 year long historical record such as the italian earthquake catalogue does not cover the entire seismic cycle of all the active apennine faults a comparison of the extension rate across the fucino plain with that across the entire central apennines as inferred from the sum of seismic moments of earthquakes which occurred in the interval 1000 1992 shows a seismicity deficit in the period indicated this confirms that a number of seismogenic faults were not active during the past 1000 years

early tertiary sinistral transpression and fault reactivation in the western voring basin norwegian sea implications for hydrocarbon exploration and pre breakup deformation in ocean margin basins the nyk high is an approximately northeast trending late cretaceous to early tertiary structural high situated in the western voring basin offshore norway it is defined by a thick sequence of upper cretaceous to lower tertiary sediments that dip toward the southeast and are cut by normal faults with throws up to 1500 m 4921 ft across fault sediment thickness variations and stratigraphic onlap relationships show that these faults were active during campanian to early paleocene extension prior to the separation of norway from greenland ca 55 ma sediments preserved in the hanging walls of these rift related normal faults are deformed by two populations of folds one set is oriented clockwise of the fault strike the other is oriented parallel to the fault strike stratigraphic relationships show that both sets of folds formed subsequent to rifting during the latest paleocene to the earliest eocene we interpret these folds as having developed during minor sinistral transpression which was partitioned between the northeast southwest sinistral strike slip reactivation of the normal faults and the northwest southeast coaxial shortening folding within the fault hanging walls the nyk high is oriented counterclockwise to the inferred line of the continental breakup we speculate that transpression was driven by north northwest forces arising from the differential topography along the incipient plate boundary and the presence of hot buoyant material beneath this elevated axial region such deformation will not necessarily impact significantly on source rock maturity or the distribution of reservoir sands but can give rise to unusual structural trap geometries it is also likely to increase the connectivity of trap bounding faults

fault growth mechanisms and scaling properties in foreland basin system the case study of monte alpi southern apennines italy abstract the present work focuses on the comprehension of the growth mechanisms and dimensional properties of the pre pliocene monte alpi fault network by mean of integrated field and laboratory analyses after this multidisciplinary approach detailed throw profiles are computed for each fault belonging to the monte alpi network subsequently the dimensional properties of the individual faults are calculated data obtained from this work are discussed in terms of fault growth mechanisms and timing of deformation and reported in a conceptual tectonic evolution model of the messinian foreland basin system data suggest that originally isolated fault segments developed during the earliest stages of foreland basin formation by re activation of a pre existing early cretaceous fault set and formation of an orthogonal one these two fault sets formed a scale independent network differently the same fault sets were also active during its subsequent development forming a scale dependent fault network characterized by t and y shaped fault intersections this deformation controlled the half graben depocenters evolution filled by up to ca 600 meters of terrigenous deposits during the late messinian time

the passa tres lode gold deposit parana state brazil an example of structurally controlled mineralisation formed during magmatic hydrothermal transition and hosted within granite abstract the passa tres granite is a nne ssw elongated shape intrusion located in the parana state southern brazil this intrusion was emplaced within metapelites of the mesoproterozoic votuverava group which are part of the n040 e trending lancinha shear zone gold mineralisation within the passa tres granite is held by meter scale quartz veins forming orebodies with variable massive banded sheared and or brecciated internal textures structural data indicate the existence of two orthogonal directions of structures n s and e w dipping 60 75 w and 45 70 s respectively mineralised veins contain in addition to the quartz of the gangue and in chronological order fluorite pyrite chalcopyrite gold aikinite molybdenite muscovite carbonate and baryte gold occurs as native grains within fractures that affect pyrite commonly associated with chalcopyrite and aikinite quartz veins are sometimes bordered by aplitic dykes additionally some of the veins exhibit a thin margin of k feldspar minerals that could represent the early stage of vein formation these observations the presence of unidirectional solidification textures ust along with abundant expression of pegmatite rich pockets within granite that crops out close to the surface allow the reconstruction of the granite architecture in terms of late magmatic evolution magmatic hydrothermal transition and position of the cupola n s and e w systems are interpreted to be contemporaneous and conjugate normal displacements are predominant and main mineralised veins are essentially located within extensional pull apart structures the structural model suggests that the normal faults were initiated along former low angle planes associated with aplite and or early quartz veins that subsequently controlled the opening of the pull apart structures that represent the economic orebodies zircon from the granite and muscovite grains from mineralised veins were dated by u pb and ar ar methods respectively zircons from the main facies medium grained gem and microgranite gef provided undistinguishable ages which were pooled to give an age of 611 9 3 6 ma a less abundant leucocratic facies white granite geb yielded a significantly younger age of 592 8 7 1 ma muscovites from quartz veins gave ar ar ages of 612 9 2 to 608 8 2 ma transitional vein with a k feldspar border 611 7 2 to 608 8 2 ma mineralised veins and 608 4 2 ma barren quartz vein thus the passa tres granite and its gold mineralisation appear to represent a unique example of an intrusion related gold system in which the mineralisation concentrates in the core of the magmatic intrusion in the form of meter scale veins strongly controlled by tectonics

fault geometries from the space distribution of the 1990 1997 sannio benevento earthquakes inferences on the active deformation in southern apennines in this study we analyze the recent 1990 1997 seismicity that affected the northern sector sannio benevento area of the southern apennines chain we applied the best estimate method bem which collapses hypocentral clouds to the events of low energy md max 4 1 seismic sequences in order to constrain the location and geometry of the seismogenetic structures the results indicate that earthquakes aligned along three main structures two sub parallel structures striking nw se 1990 1992 benevento sequence and one structure striking ne sw 1997 sannio sequence the southernmost nw se structure which dips towards ne overlies the fault that is likely to be responsible for a larger historical earthquake io max xi mcs 1688 earthquake the northernmost nw se striking structure dips towards sw the ne sw striking structure is sub vertical and it is located at the northern tip of the fault segment supposed to be responsible for the 1688 earthquake the spatio temporal evolution of the 1990 1997 seismicity indicates a progressive migration from se benevento to nw sannio associated to a deepening of hypocenters i e from about 5 to 12 km hypocenters cluster at the interface between the major structural discontinuities e g pre existing thrust surfaces or within higher rigidity layers e g the apulia carbonates available focal mechanisms from earthquakes occurred on the recognized nw se and ne sw faults are consistent with dip slip normal solutions this evidences the occurrence of coexisting nw se and ne sw extensions in southern apennines

the growth of non colinear normal fault systems what can we learn from 3d seismic reflection data abstract many rift zones exhibit a range of fault orientations rather than simple colinear faults that strike orthogonal to the inferred least principal stress the formation of non colinear fault sets has implications for assessing rift zone kinematics as well as determining palaeo stress state in extensional basins using 3d seismic reflection data we deduce the likely mechanisms responsible for the formation of a population of non colinear faults in the maloy slope area of the northern north sea three basement displacing fault populations exist on the maloy slope i large 1 km throw n s striking faults ii smaller

structural controls on jurassic gold mineralization and cretaceous tertiary exhumation in the foreland of the southern patagonian andes new constraints from la paloma area deseado massif argentina abstract fluid rock interaction occurring within high permeability conduits represented by fault fracture meshes is well known to control the development of hydrothermal ore deposits in this study we document the fundamental role of four sets of precursor joints reactivated as dilational faults displaying variable normal dip slip and strike slip components of motion in the formation of epithermal au ag deposits of economic interest paleostress analysis unravels how all the resulting four sets of hybrid extension shear fractures are kinematically compatible with an extensional stress field characterized by multiple permutations between the 3 and the 2 axes such permutations are interpreted to be associated with dominantly normal fault reactivation of suitably oriented early joint sets as a result of continued regional extension and by orthogonal stretching produced by differential downthrow of the hanging wall blocks of laterally terminating jurassic normal faults later fault reactivation appears to be associated with far field propagation of andean stresses marked by superposed strike slip and reverse fault slip components recording roughly e w horizontal compression this late fault reactivation could be related with a late early cretaceous shortening event known to have affected the studied sector of the deseado massif the subsequent tectonic evolution of the study area occurred within the general framework of a slow cretaceous to tertiary exhumation recorded by apatite fission track cooling ages our new thermochronometric results recording steady state cooling at a rate of c 1 c ma during the last 90 ma shed new light onto the post jurassic geodynamic evolution of the foreland of the southern patagonian andes

underlying structural control of small scale faults and fractures in west candor chasma mars 1 orientations of small scale faults and fractures within the interior layered deposits of west candor chasma were measured to investigate what information about the geologic history of valles marineris they can contribute deformational features were separated into six categories based on morphology and their orientations were analyzed the elevations at which the deformational features formed are recorded as a proxy for stratigraphic level deformational features occur over a continuous range of elevations and display regionally consistent preferred orientations indicating their formation was controlled by a regional stress regime the two most abundant preferred orientations of 35 and 110 are approximately parallel to the chasma walls and the inferred underlying normal faults the alignment of three populations of small faults at 140 consistent with the morphology of release faults indicates a large scale fault underlying the southeastern border of ceti mensa the preferred orientations imply these small scale deformational features formed from a continuation of the same imposed stresses responsible for the formation of valles marineris indicating these stresses existed past the formation of the interior layered deposits the origins of a fourth preferred orientation of 70 is less clear but suggests the study area has undergone at least two periods of deformation

growth folds above propagating normal faults abstract growth folds above the upper tips of normal faults are ubiquitous in extensional settings especially during the early phases of extension and in salt rich basins as slip accumulates on the underlying normal fault the geometry and size of the fold changes these changes reflect the dip throw displacement and propagation rate of the underlying normal fault as well as the thickness and rheology of the overlying cover these changes also have a marked impact on the architecture and distribution of synkinematic sediments as well as the styles of secondary deformation accommodating strain within the growing fold here we analyse a large dataset of natural and physically and numerically modelled growth folds to i characterise their diagnostic features ii investigate the controls on their geometry size and differences and iii describe how they grow with increasing extensional strain we demonstrate that larger fault throws and a thicker and weaker cover are associated with larger growth folds in contrast small fault throws as well as thin and strong brittle cover are associated with smaller growth folds we show that the geometry and size of growth folds vary through time the width and thus the wavelength of the fold is established relatively early during fold growth whereas fold amplitude increases gradually with increasing fault throw fold width and amplitude become increasingly similar during fold evolution until the fold is breached by the underlying normal fault we also derive a number of preliminary empirical relationships between readily observable structural and stratigraphic parameters in our dataset that may help estimate the geometry and size of poorly exposed i e in the field or imaged i e in the subsurface growth folds in addition we discuss how fault growth models i e constant length vs propagating may impact the three dimensional evolution of growth folds finally our work shows that growth folds are likely more common than previously thought for example although they are well documented in areas characterised by weak ductile cover strata and low strain rates our dataset illustrates that growth folds may also occur in brittle relatively strong rocks and in regions with high strain rates however the underlying controls on fold occurrence remain elusive

basement involved reactivation in foreland fold and thrust belts the alpine carpathian junction austria the late eocene early miocene alpine carpathian fold and thrust belt ftb lies in the transition between the eastern alps and the western carpathians se of the bohemian crystalline massif our study shows the involvement of crystalline basement from the former european jurassic continental margin in two distinct events a first extensional event coeval with eggerian karpatian c 28 16 ma thin skinned thrusting reactivated the rift basement fault array and resulted from the large degree of lower plate bending promoted by high lateral gradients of lithospheric strength and slab pull forces slab break off during the final stages of collision around karpatian times c 17 16 ma promoted large wavelength uplift and an excessive topographic load this load was reduced by broadening the orogenic wedge through the reactivation of the lower plate deep detachment beneath and ahead of the thin skinned thrust front with the accompanying positive inversion of the basement fault array and ultimately by the collapse of the hinterland summits enhanced by transtensional faulting although this work specifically deals with the involvement of the basement in the alpine carpathian junction the main conclusions are of general interest to the understanding of orogenic systems

complex geometry and kinematics of subsidiary faults within a carbonate hosted relay ramp abstract minor fault geometry and kinematics within relay ramps is strongly related to the stress field perturbations that can be produced when two major fault segments overlap and interact here we integrate classical fieldwork and interpretation of a virtual outcrop to investigate the geometry and kinematics of subsidiary faults within a relay ramp along the tre monti normal fault in the central apennines although the tre monti fault strikes parallel to the regional extension ne sw it shows predominant dip slip kinematics suggesting a nw se oriented extension acting at sub regional scale 1 10 km conversely the slickenlines collected on the front segment of the relay ramp highlight right lateral kinematics the subsidiary faults in the relay ramp show a complex geometry variable attitudes and slickenlines describe multiple kinematics left lateral dip slip right lateral independently of their orientation our fault slip analysis indicates that a local stress field retrieved from the kinematic inversion of the slickenlines collected on the front segment and likely promoted by the interaction between the overlapping fault segments that bound the relay zone can explain most of the geometry and kinematics of the subsidiary faults further complexity is added by the temporal interaction with both the regional and sub regional stress fields

tectonics and sedimentation in a paleo mesoproterozoic rift sag basin espinhaco basin southeastern brazil abstract sedimentologic paleogeographic stratigraphic structural and tectonic studies in a paleo mesoproterozoic metasedimentary succession espinhaco megasequence southeastern brazil indicates deposition in a rift sag basin four basin evolution stages are recognized prerift rift transitional and flexural the four stages can be represented by six unconformity bounded tectonosequences the unconformities are recognized in the field and mappable even on a regional scale the prerift and rift stages of the espinhaco basin were filled by products of continental depositional systems the prerift stage probably represents the first product of the rifting process before the development of the half grabens that characterize the rift stage during the rift stage mechanical subsidence due to lithospheric stretching was predominant and led to episodic rising of the depositional base level as a result the basin fill is characterized by coarsening upward intervals paleocurrent patterns indicate that block tilting and half graben subsidence uplift controlled sediment dispersion the first marine incursion within the espinhaco basin marks the change in the subsidence regime of the basin the evolution of the transitional and flexural stages was probably controlled by thermal subsidence due to thermal contraction of the lithosphere during cooling the transitional stage was characterized by relatively low subsidence rates higher subsidence rates and a consequent sea level rise characterize the flexural stage of the espinhaco basin in which three second order transgressive progradational sequences can be recognized

detailed joint structure in a geothermal reservoir from studies of induced microearthquake clusters microearthquake clusters form distinct planar patterns within five study regions of a geothermal reservoir undergoing hydraulic fracturing at fenton hill new mexico the patterns define individual slipping joint surfaces of dimension 40 120 m containing 80 150 events each sharp straight edges truncate the clusters we interpret these as marking intersections with aseismic joints each edge orientation is consistent with an intersection between the active joint and a plane oriented parallel to one of the other clusters we identify therefore it appears that cluster shapes constrain the geometry of seismic and aseismic joints both could be important components of the fluid flow network the distribution of inferred slip plane orientations is consistent with but fails to provide sufficient constraint to differentiate conclusively between two very different stress field estimates one measured using pressurization and wellbore breakouts the other using focal mechanisms of the largest microearthquakes an impermeable joint model requiring pore pressure in excess of the normal stress on a joint before slip can occur was inconsistent with many of the inferred slip plane orientations the high quality locations were possible because events from the same cluster generated nearly similar waveforms permitting the precise determination of relative arrival times standard deviations of arrival time residuals fall between 0 1 and 1 1 ms for these clusters major axes and aspect ratios of the 90 confidence ellipsoids range from 6 to 28 m and 1 5 to 8 respectively small events dominate the seismic energy release and thoroughly populate the identified active joints allowing the hypocenters to reflect details of the joint structure to further investigate the reservoir structure we applied a source array slant stack technique to waveforms from the well located clusters yielding directions that scattered energy left each cluster by studying paths of scattered waves we expected to pinpoint impedance contrasts that might have indicated concentrations of fluid filled joints however results show that scattered energy in the s wave coda left the source region in the same direction as the direct s wave direct waves may have excited borehole tube waves that became trapped in the vicinity of the geophone tool overwhelming any energy scattered from the reservoir

preserved extensional structures in an inverted cretaceous rift basin northwestern argentina outcrop examples and implications for fault reactivation 1 during the cretaceous eocene interval a system of intracontinental rift basins the salta group rift evolved in northwestern argentina individual segments of the rift later suffered different degrees of inversion during cenozoic shortening the tres cruces subbasin on the west side of the eastern cordillera was strongly deformed being now part of a thick skinned thrust belt with a predominantly n s structural trend on its eastern border tilting due to folding and thrusting and subsequent erosion have produced exceptional outcrops of preserved east trending extensional structures including half grabens rollover anticlines and extensional fault propagation folds farther west the synrift succession is only intermittently exposed although the interference of north and east trending structures as well as peculiar dome shaped anticlines with spur like extensions suggest that north and east trending cretaceous faults were reactivated particularly near their intersections compilation of published data and analysis of our new data focused on the salta rift indicates three main factors favoring the contractional reactivation of normal faults dip angles lower than approximately 60 especially for faults striking roughly normal to contraction strikes no closer to the contraction direction than approximately 30 and low downdip fault curvatures occasional dip slip reactivation of east trending faults does not match the present and long term andean stress regimes and presents an unresolved problem

static stress interactions in extensional earthquake sequences an example from the south lunggar rift tibet 1 an extensional earthquake sequence occurred in 2004 8 across a graben in the south lunggar rift on the tibetan plateau we use insar data to determine the location fault geometry and slip distribution of these earthquakes and to test whether the sequence is compatible with static stress triggering the mw 6 2 and 6 3 earthquakes in 2004 and 2005 both ruptured west dipping faults on the east side of a graben in 2008 a mw 6 7 earthquake ruptured a pair of east dipping fault segments on the other side of the graben offset from the earlier ruptures we compute first order dislocation models of stress change and demonstrate that the order and spatial configuration of this sequence of events is compatible with triggering by static stress transfer a continuation of the sequence would be most likely to occur on the northern extension of the 2008 rupture although variable slip rate along the rift may mean that the sequence has run its course the insar data for the 2008 earthquake also reveal slip on a fault that cuts the graben at a highly oblique angle we suggest that this is a release fault accommodating differential throw in the hanging wall and associate the deformation with a mw 6 0 aftershock activity on such a release fault has not been directly imaged before the zhongba sequence is one of several examples of recent clustered normal fault earthquakes on the plateau and may be an example of phase locking of similar faults

detachment faulting and the evolution of passive continental margins major detachment faults play a key role in the lithospheric extension process in the basin and range province and may also be important in other continental extension terranes such detachment faulting leads to an inherent asymmetry of extensional structure and of uplift subsidence patterns detachment models developed for the formation of metamorphic core complexes can also be applied to the formation of passive continental margins we therefore suggest the existence of upper plate and lower plate passive margins these give rise to a complementary asymmetry of opposing margins after continental breakup transfer faults offset marginal features and allow margins to switch from upper plate to lower plate characteristics along strike

seismicity and shallow slab geometry in the central vanuatu subduction zone the vanuatu arc in the southwest pacific ocean is one of the world s most seismically active regions with almost 39 magnitude 7 earthquakes in the past 43 years convergence rates are around 90 120 mm yr along most of the arc but drop to 25 43 mm yr in the central section probably due to the subduction of the d entrecasteaux ridge we characterize the slab geometry and tectonic state in this central section by analyzing data from a 10 month deployment of 30 seismometers over this section we located more than 30 000 events all less than magnitude 5 5 constructed an improved 1 d velocity model calculated focal mechanisms and cluster geometries and determined the 3 d geometry of the interplate seismogenic zone the seismogenic zone has a shallow bulge in front of the d entrecasteaux ridge which could be explained by the ridge s buoyancy contributing to the uplift of the fore arc islands the seismogenic zone extends to 45 km depth significantly below the 26 27 km depth of the fore arc moho indicating that the upper mantle wedge is not significantly serpentinized which is consistent with the relatively high thermal parameter of the subducting plate the maximum width of the seismogenic zone is 80 km indicating an upper earthquake magnitude limit of mw 7 85 0 4 assuming standard rupture zone aspect ratios the data also reveal a double seismic zone 20 to 30 km below the seismogenic zone which is presumably caused by flexure of the downgoing plate

balanced cross section construction from seismic sections in areas of extensional tectonics abstract the application of the technique of balanced section construction initially developed for areas of compressional folding and faulting is reviewed with reference to extensional tectonics a number of examples are discussed where these techniques have been successfully applied in the north sea the interpretation of geoseismic sections is considered to be greatly assisted by careful application of geometrical balance and a consideration of strain even in areas of low crustal extensions the nature of seismic sections however places limitations on the validity of balancing which must be borne in mind with such interpretations and wherever possible the balancing of a geoseismic section should be confirmed by complete depth conversion the rapid testing of the integrity of the geoseismic section by attempting to balance the section at the interpretational phase can eliminate many problems as well as allowing the fullest use to be made of the geophysical information

the geometry kinematics and rates of deformation within an en echelon normal fault segment boundary central italy abstract the geometry kinematics and rates of deformation have been investigated within an en echelon fault segment boundary between two left stepping major normal faults in the central apennines italy examination of faulted post glacial sediments and geomorphic features attributed to glacial retreat 18 ka reveals that the two major faults dominate the recent slip with rates that are 5 10 times greater than the other faults at the centres of the major faults slip is parallel to the regional extension direction ne sw defined by focal mechanisms and borehole breakouts slip vector azimuths defined by striations on faults in the stepover zone indicate ne sw extension on nw se faults sub parallel to the regional extension direction together with significant and contemporaneous nw se extension along the strike of the apennines on ese wnw and ene wsw faults thus distributed three dimensional strain occurs in the stepover between the two major bounding faults extension rates summed across the stepover are 0 68 mm y parallel to the regional extension compared to 2 mm y at the centre of one of the major faults extension rates along strike of the fault zone are 0 14 mm y within the stepover and zero at the centres of the two major bounding faults the above information is used to discuss how extension is partitioned between different structures during the growth and linkage of normal faults

a review of deformation pattern templates in foreland basin systems and fold and thrust belts implications for the state of stress in the frontal regions of thrust wedges aesthetically appealing thrust systems and related large scale anticlines in both active and fossil foreland fold and thrust belts and the economic potential associated with the m have captured the interest of structural geologists for many decades as a consequence a large amount of data on sub seismic deformation patterns from thrust related an ticlines is available in the literature we provide a review of deformation pattern templates from fi eld data in foreland fold and thrust belts and show that the most frequent tre nds of sub seismic syn orogenic deformation structures hosted in km scale thrust related folds frequently and pa radoxically indicate a syn th rusting strike slip stress fi eld con fi guration with a near vertical 2 and a sub horizontal 3 rather than a contractional one where the latter is expected to be the vertical principal axis of the stress ellipsoid this a pparent inconsistency between sub seismic syn orogenic deformation structures and stress fi eld orientation is here named the 2 paradox field data support a possible expla nation of the paradox provided by the major role played by i nherited early orogenic extensional deformation struc tures on thrust fault nucleation nucleation of major thru sts and their propagation is facilitated and driven by the positive inversion and linkage of the early orogenic sub s eismic extensional inheritance developed in the foreland basin this process eventually leads to the development of l argereversefaultzonesandcanoccurbothincontractional and strike slip stress fi eld con fi gurations

wide and narrow margins of the brazilian south atlantic two contrasting end members of passive continental margins here referred to as wide and narrow margins are present in the south atlantic although some margin segments are intermediate between these two styles narrow margins are characterized by a large bounding fault 4 km throw near the shelf edge a sharp transition zone 10 20 km wide from normal thickness to substantially thinned continental crust or oceanic crust where the total width of extended continental crust is usually less than 100 km wide continental margins are characterized by a broad continental shelf and a wide zone 50 600 km of thinned crust with an even distribution of faults wide margins usually have a more gentle continental shelf and slope narrow narrow wide wide and wide narrow conjugate margin pairs exist in the south atlantic and are suggested to be controlled mainly by the opening kinematics and the thermal structure of the lithosphere during rifting basement structure and strain rate appear to have exerted little control on the style of margin extension although basement architecture appears to control the trend of the initial rifts the positions of fracture zones which separate narrow and wide segments and the rate of lateral rift propagation

a method for determining significant structures in a cloud of earthquakes the interpretation of a cloud of earthquake hypocenters in terms of causative structures is not a simple task locations are subject to uncertainties which will not be the same for every earthquake the data should therefore not be interpreted simply by inspection which is difficult in the case of three dimensional data anyway instead we propose using the location uncertainties as a guide in processing the data earthquake locations are moved inside their uncertainty or confidence ellipsoids until a simplified picture of the earthquake cloud is obtained which can then be interpreted in terms of some simplified structure such as faults the aim of the approach is to give the simplest possible structure that is consistent with all the location and confidence ellipsoid data the method is applied to three synthetic sets of data these illustrate the potential and limitations of the method application to a real earthquake data set from rabaul caldera in papua new guinea gives an image of the caldera ring fault that suggests departures from the simple ring fault structure previously assumed sensitivity analysis on the rabaul data shows that the method is not unduly sensitive to the assumptions that have to be made in applying it

enso and short term variability of the south equatorial current entering the coral sea abstracthistorical section data extending to 1985 are used to estimate the interannual variability of transport entering the coral sea between new caledonia and the solomon islands typical magnitudes of this variability are 5 8 sv sv 106 m3 s 1 in the 0 400 m layer relative to 400 m and 8 12 sv in the 0 2000 m layer relative to 2000 m on a mean of close to 30 sv relative to 2000 m transport increases a few months after an el nino event and decreases following a la nina interannual transport variability is well simulated by a reduced gravity long rossby wave model vigorous westward propagating mesoscale eddies can yield substantial aliasing on individual ship or glider surveys since transport variability is surface intensified and well correlated with satellite derived surface geostrophic currents a simple index of south equatorial current transport based on satellite altimetry is developed

fault growth and linkage implications for tectonosedimentary evolution in the chezhen basin of bohai bay eastern china the chezhen basin has highly representative structural features of the jiyang depression bohai bay area the structural geometry and the boundary fault linkage exert a strong influence on basin development and depositional environment based on structural analysis at least six early fault segments are identified in the northern boundary of the chezhen basin these fault segments are important in controlling stratal architecture and distribution the antecedent structures controlled subbasin initiation and development the cenozoic rift initiated in the early eocene with the development of six isolated fault segments associated with deposition of the es4 member during the deposition of the lower es3 member these six fault segments quickly linked and formed the present architecture frame fault linkage has not resulted in a redistribution of displacement with the expansion of the chezhen basin the depocenters of the upper strata were kept in nearly the same sites until the early miocene then the activity of the chengnan fault ceased fault linkage is a significant event in basin evolution and its process may be very rapid however the fault linkage exerted considerable control on sedimentation and evolution of the basin this study demonstrates that it is necessary to integrate structural and stratigraphic data to reconstruct the temporal and spatial evolution of normal fault zones

comparison of surface slip and focal mechanism slip data along normal faults an example from the eastern gulf of corinth greece abstract focal mechanism and surface slip data are used to investigate whether kinematics are similar at depth and at the surface along an active normal fault in the gulf of corinth greece we present a new database of slip data from the lateral termination of the south alkyonides fault segment safs and the en echelon stepover between it and an adjacent fault and use published data on surface slip and focal mechanism data pertaining to slip at depth during the 1981 alkyonides earthquake sequence the focal mechanisms exhibit similar fault plane orientations and kinematics to those measured at the surface within the stepover both data sets show that contemporaneous c n s and c e w extension is being accommodated by c e w and c n s oriented normal faults and the overall deformation is distributed oblate vertical flattening the deviation of the surface slip direction from 350 increases with distance from the centre of the safs the deviation of the focal mechanism t axes from 350 fit well with the surface data implying that the coseismic slip on the safs at depths of 7 10 km exhibits a similar kinematic pattern as that observed at the surface our results imply that it is critical to know the along strike position of data on a fault if either focal mechanisms or surface slip are to be used to infer regional strain and stress trajectories

linked fault families in basin formation abstract recent models of faulting tectonics in basins and passive margins have emphasized the linked nature of faults in a way that is analogous to that developed for thrust regimes a linked fault system requires three components ramps flats and sidewalls or transfers basins that are the result of other processes are not considered in this contribution and the examples used are drawn from the midland valley and northumberland basins of the u k where existing mapping by the british geological survey as well as field work undertaken by the author indicate that such models are appropriate this paper summarizes the geometric features and constraints of such models and emphasizes the role of each of the three critical components of a linked system for large deformations that result in the formation of major extensional and strike slip basins the principal geometries can be understood by reference to regionally and locally balanced fault models that involve detachment ramp and sidewall or transfer elements tip strains and both lateral and vertical accommodation zones are included in the general model but these probably account for less than 10 of the total upper crustal strain the basic analysis of a linked basin system requires the transfer of displacement on and between the fault and shear zone components the geometry of the stratigraphic units is used to deduce the active linkage on the fault system in oblique slip systems and where the dominant extensional ramp is connected to oblique transfer and detachment systems lateral and sidewall sub basins and intra basin uplifts occur as part of continuing slip on the fault system these control facies distribution and depocentre evolution the existence of a basin forming linked system frequently controls later deformation of basins and margins and an appreciation of basin growth faults and stratigraphic geometry is essential in the interpretation of inverted basins and orogenic belts involving supracrustal formations

longitudinal evolution of the suez rift structure egypt abstract a three dimensional study of the structure of the suez rift has been carried out using field and subsurface data in an attempt to determine the role of transverse faults and the longitudinal evolution of the rift as in most intracontinental rifts the structure of the gulf of suez area is governed by normal faults and tilted blocks whose crests constitute the main target of exploratory wells the fault pattern consists of two major sets of trends 1 1 longitudinal faults parallel to the rift axis and created in an extensional regime where 3 was trending ene wsw and 2 2 transverse faults with a n s to nne ssw dominant trend the transverse faults are inherited passive discontinuities while most of the longitudinal faults were created during neogene times in a purely extensional regime both sets were simultaneously active producing a zigzag pattern and rhombic shaped blocks the transverse faults can show horizontal strike slip components and act as relays between major normal faults although the suez rift appears as a simple narrow elongated trough dominated by two almost symmetrical shoulders its internal structure is asymmetrical cross profiles show that all the major blocks are tilted in the same direction however the tilt direction changes twice along the rift to the north and to the south of the rift the blocks are tilted eastward while in the central part they are tilted westward to the north the change of dip is accompan ed by a graben type twist zone without transverse faulting at least in the neogene series to the south the change of dip is accompanied by a more complex structure involving both a major transverse fault and a horst type twist zone in this latter case the transverse fault does not cut through the entire rift balanced cross sections established from subsurface data show that the tilt angle and the amount of extension increase from north to south while the width of the blocks decreases indicating a pole of opening close to the northern end of the gulf minimum values for the amount of opening range from 5 km in the north to about 20 km in the south

space time clustering of seismic events and hazard assessment in the zabrze bielszowice coal mine poland the results of the statistical analysis of seismic activity recorded in the zabrze bielszowice coal mine in poland are presented in this article the monitoring was conducted by a small network consisting of four triaxial geophones deployed in vertical holes in the roof for over 1000 seismic events recorded during the two month s experiment the location of sources was realized the seismic sources were mostly located ahead of the active face of the longwall since the first day of the monitoring cluster analysis was sequentially performed for increasing number of sources at the end of the experiment 31 clusters were identified they consisted of different numbers of events and were separated in space about 40 of the events were not included in the clusters for each large cluster hazard analysis was separately performed the hazard function evaluated for the largest cluster was compared with hypocenters of high energy tremors e 1000 j recorded by the geophones in that area for some cases recorded tremors occurred after an abrupt decrease of hazard function but only one of them was located in the vicinity of the appropriate cluster we concluded that for the analyzed cluster a correlation between evaluated hazard function and time occurrences of the high energy tremors existed except for one case there is no space correlation between analyzed clusters and high energy tremors

constraining mountain front tectonic activity in extensional setting from geomorphology and quaternary stratigraphy a case study from the matese ridge southern apennines abstract rugged peaks large intermontane basins and frequent seismicity all characterize the active extensional tectonic setting of the southern apennines the matese ridge typifies the active tectonic setting of the southern apennines with steep carbonate mountain fronts and large depositional centres moderate to high magnitude earthquakes have affected the northern western and eastern sectors of the matese ridge in historical times however the seismogenic potential of the extensional fault system bounding the southern matese mountain front has not been fully assessed to date to unravel the active tectonic setting of the southern matese mountain front we have carried out a comprehensive geomorphological and tectonic geomorphology investigation of the mountain front and its piedmont and have constrained results through chronological i e tephrostratigraphical and 40ar 39ar and structural data our study highlights that in the last 600 ka activity along e w trending normal faults has identified a locus of higher slip rate tectonic activity in the central part of the analysed mountain front these active e w striking normal faults are inherited reactivated structures which have interacted with newly formed nw se striking normal faults during ne sw extension active on the regional scale causing fault bending and local extension to be oriented n s consequently lower slip rates have been recorded along the nw se striking normal faults at the north western and south eastern tips of the southern matese front the long term displacement rate of the fault system at the boundary of the central part of the southern matese front is consistent with mean values of displacement of faults that in the southern apennines show evidence of activity during the late quaternary despite strong historical seismicity clustering primarily around the study area our data highlight that it cannot be ruled out that moderate to high magnitude seismicity could affect the southern matese mountain front our case study represents an example of the possible modes of formation and evolution of mountain front basin systems in extensional setting and shows how the combination of different data sets allows unravelling the interaction between tectonic erosional and sedimentary processes which lead to landscape evolution of active mountain belts

calcite twinning strains from syn faulting calcite gouge small offset strike slip normal and thrust faults we have evaluated the stress strain behavior of calcite precipitated and mechanically twinned in small offset strike slip normal and thrust faults of a variety of ages and from a variety of tectonic settings n 3001 twin measurements 63 strain analyses from 18 field sites five strike slip faults with syn faulting horizontally striated calcite rake 0 were studied and we report the orientations of the contemporaneous stress strain field associated with each fault intrusion of the marathon large igneous province mafic dikes 2 1 ga in archean crust minnesota usa post keweenaw rift 1 1 ga faulting island lake fault central ontario canada subduction associated with metamorphic core complex formation cretaceous china subduction cretaceous to miocene italy and continental extension recently active furnace creek fault death valley california usa seven normal faults with synfaulting dip slip striated calcite were studied and are from the following tectonic settings a normal fault slip surface in an ordovician piedmont fold appalachian s paleo subduction associated with cretaceous metamorphic core complex formation china 3 sites the paleo extensional atlantic margin 55 ma ireland 1 site with a u pb calcite age continental extension 1 active site mojave desert a transcurrent margin jamaica 1 active fault site and subduction 2 active faults along the eur african margin in italy with calcite u th disequilibria ages and crete respectively six thrust fault examples are all from convergent orogenic settings the basal thrust of the penokean 1850 ma fold and thrust belt the penokean orogen foreland in mesabi range banded iron formation folds an offset breccia body in the permian gondwanide belt ellsworth mountains antarctica the frontal thrust of the gondwanide cape belt south africa the paleocene frontal prospect thrust sevier belt wyoming and an alpine foreland back thrust lulworth cove u k for each strike slip fault system the twinning shortening strain is horizontal and at an angle of 0 60 to the respective fault plane dextral or sinistral although in the majority of cases the shortening axis is parallel to fault strike 13 of 23 results in each normal fault example dip slip kinematic striations dominate the faulted surface yet the orientation of the maximum principal compressive stress 1 and shortening strain axis e1 are not 45 to the fault plane as predicted but are sub horizontal and either strike parallel 25 of 35 results or strike normal 10 of 35 results thrust faults preserve shortening strain axes parallel to the dip slip kinematic direction within the fault plane plane strain and not at 45 to the principal plane 5 of 5 results none of the fault stress strain field results reported here support the andersonian or mohr coulomb criteria for stress strain relations predicted along faults

fault growth and interactions in a multiphase rift fault network horda platform norwegian north sea abstract physical models predict that multiphase rifts that experience a change in extension direction between stretching phases will typically develop non colinear normal fault sets furthermore multiphase rifts will display a greater frequency and range of styles of fault interactions than single phase rifts although these physical models have yielded useful information on the evolution of fault networks in map view the true 3d geometry of the faults and associated interactions are poorly understood here we use an integrated 3d seismic reflection and borehole dataset to examine a range of fault interactions that occur in a natural multiphase fault network in the northern horda platform northern north sea in particular we aim to i determine the range of styles of fault interaction that occur between non colinear faults ii examine the typical geometries and throw patterns associated with each of these different styles and iii highlight the differences between single phase and multiphase rift fault networks our study focuses on a ca 350 km 2 region around the 60 km long n s striking tusse fault a normal fault system that was active in the permian triassic and again in the late jurassic to early cretaceous the tusse fault is one of a series of large 1500 m throw n s striking faults forming part of the northern horda platform fault network which includes numerous smaller 2 10 km long lower throw nd stage nw se striking faults grew interacted and linked with the n s striking tusse fault documenting a range of interaction styles including mechanical and kinematic isolation abutment retardation and reactivated relays our results demonstrate that i isolated and abutting interactions are the most common fault interaction styles in the northern horda platform ii pre existing faults can act as sites of nucleation for 2 nd stage faults or may form mechanical barriers to propagation iii the throw distribution on reactivated 1 st stage faults will be modified in a predictable manner if they are intersected or influenced by 2 nd stage faults iv sites of fault linkage and relay breaching associated with the first phase of extension can act as preferential nucleation sites for 2 nd stage faults and v the development of fault intersections is a dynamic process involving the gradual transition from one style to another

3d structure and evolution of an extensional fault network of the eastern dampier sub basin north west shelf of australia abstract insights of spatial and temporal development of fault network in 3d is crucial for understanding the process evolution of complex fault network and for evaluating the regional and local stresses control on structure development we demonstrate a fault network on the eastern dampier sub basin north west shelf of australia which consists of 1 a ene trending fault array that has a through going segment at depth and a series of left stepping fault splays at upper levels and 2 a network of ene and nne trending intersecting faults decoupled from the basement structures this research shows that the segmented ene trending fault array developed through three extensional phases in the late paleozoic in the early jurassic and in the late middle jurassic fault analysis shows that the summed displacement of the segmented en echelon faults behaves as a single fault and that the basement fault controlled the fault array in the upper section through vertical linkages a typical coherent fault system the nne and ene trending intersecting faults formed simultaneously in the late middle jurassic as such they might have controlled by 3d strain field released from the rosemary and mermaid fault systems bounding the fault network this implies that fault geometry derived from 3d seismic interpretation need to be treated with caution as the alignment of fault sets may not directly relate to regional far field stress but in some cases significantly modified by local stresses induced by reactivated larger faults this study provides an analogue for the interpretation of other rift systems where structures were controlled by competing forces of regional and local stresses and where reactivated and newly formed structures coexist in polyphase of extensions

locating microearthquakes induced by hydraulic fracturing in crystalline rock microearthquakes induced by hydraulic fracturing in crystalline rock at a depth of 3 5 km were located with a precision of better than 30 m to obtain information about the geometry and dimensions of the fracture system produced the induced microseismicity was monitored by a network of five vorehole seismic stations a total of about 800 induced events were reliably located from arrival times event locations show a tabular distribution that strikes 350 sup 0 and dips 65 sup 0 east subparallel to the injection well the injection was intended to produce a fracture system that would hydraulically connect two subparallel wells a lack of fluid communication between them is consistent with a lack of induced microearthquakes near the target wellbore the 150 m thickness of the zone of seismicity far exceeds the relative locational uncertainties the injected fluid appears to have stimulated a zone of rock rather than simply a single fracture the distribution of microseismic events presumably envelopes the zone of fluid paths created by the fracture experiment

fluid flow evolution in the albanide fold thrust belt insights from hydrogen and oxygen isotope ratios of fluid inclusions tectonic forces generated during thrust emplacement along active margins may drive complex fluid flow patterns in fold thrust belts and foreland basins isotope data 2h and 18o of fluid inclusions hosted in calcite vein cements are used to reconstruct regional fluid migration pathways in the albanide fold thrust system the calcite veins used in this study developed in a sequence of naturally fractured cretaceous eocene carbonate rocks as a result of episodic throughput of fluids from the early stages of burial onward the acquired fluid inclusion isotope data demonstrate that fluids circulating in the carbonates were derived from an underlying reservoir that consisted of a mixture of meteoric water and evolved marine fluids probably derived from deep seated evaporites the meteoric fluids infiltrated in the hinterland before being driven outward into the foreland basin and ascended as soon as fracturing induced a sufficient increase in permeability structural and petrographic observations provide time constraints for the various phases of fracture infilling and reveal an increasing dominance of meteoric water in the system through time as migration pathways shortened and marine formation fluids were progressively flushed out similar fluid flow evolutions have previously been recorded in various fold thrust belt settings elsewhere in the world