localisation of normal faults in multilayer sequences abstract existing conceptual growth models for faults in layered sequences suggest that faults first localise in strong and brittle layers and are later linked in weak and ductile layers we use the discrete element method for modelling the growth of a normal fault in a brittle ductile multilayer sequence the modelling reveals that faults in brittle ductile sequences at low confining pressure and high strength contrast localise first as mode i fractures in the brittle layers low amplitude monoclinal folding prior to failure is accommodated by ductile flow in the weak layers the initially vertically segmented fault arrays are later linked via shallow dipping faults in the weak layers faults localise therefore as geometrically and kinematically coherent arrays of fault segments in which abandoned fault tips or splays are a product of the strain localisation process and do not necessarily indicate linkage of initially isolated faults the modelling suggests that fault tip lines in layered sequences are more advanced in the strong layers compared with weak layers where the difference in propagation distance is most likely related to strength and or ductility contrast layer dependent variations in fault localisation rates generate fringed rather than smooth fault tip lines in multilayers

the summit erosion surfaces of the inner betic cordillera their value as tools for reconstructing the chronology of topographic growth in southern spain erosion surfaces at the top of mountain ranges have suggested to geomorphologists that the earth s crust can undergo rapid pulses of uplift during which rates of denudation fail to balance with rates of crustal uplift thereby preserving much of the initial plateau topography as it rises to greater elevations here we analyze a regionally extensive population of mappable planar surfaces which crown several major tectonically active sierras of the inner south eastern betic cordillera se spain based on a synthesis of long term landscape evolution involving landform reconnaissance dem based morphometric analysis structural geology sediment provenance analysis and field stratigraphy we conclude that the summit surfaces are a mosaic of discrete post orogenic erosion surfaces that each developed in relation to mediterranean marine base levels at a time when the sierras formed a series of low elevation islands they are not therefore fragments of a once regionally continuous paleoplain the summit surfaces were partly the result of shallow angle detachment faulting during the middle miocene in response to lithospheric slab detachment where evidence exists that the resulting low relief topography was reworked by marine abrasion during the tortonian sea level rise the terminal age of the surfaces is latest miocene age bracketing based on stratigraphic correlations among the many depocentres of the region and on published thermochronological data indicates that some erosion surfaces locally formed in less than 3 million years 8 ma 5 7 ma they were subsequently uplifted to their current elevations 1 7 to 2 km by pliocene to quaternary neotectonics in at least two major pulses

late pliocene pleistocene stress field in the teruel and jiloca grabens eastern spain contribution of a new method of stress inversion samples of non striated fracture surfaces within clastic materials of late pliocene pleistocene age from the teruel grabens eastern spain have been analysed using a stress inversion method based on observations of slip sense the results obtained at 21 sites are compared with late miocene early pliocene extensional stress tensors previously inferred from striated faults in the same area the similarity between both sets of stress states suggests that the extensional miocene pliocene stress field essentially continues with minor changes into pliocene pleistocene times the main changes involve a the dominant trend of 3 trajectories which evolve from ese to ene b the waning of the compressional component caused by europe iberia africa convergence and c the progressive trend towards a multidirectional extension regime stress deflection caused by large scale extensional faults as well as switching of 2 and 3 axes induced by fracture development are common within this stress field they produce groups of local stress ellipsoids with 3 axes orthogonal to each other and either orthogonal or parallel to the faults bounding the grabens the regional consistency of the new results gives support to the new inversion method and demonstrates its utility in research on young sedimentary rocks where gaps in palaeostress records may exist due to absence of striated faults

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

the western mediterranean extensional basins and the alpine orogen the western mediterranean late oligocene miocene basins alboran valencia and provencal basins are a coherent system of interrelated troughs in all basins normal faults and thermal subsidence migrated toward the east progressively moving to the miocene to pleistocene algerian and tyrrhenian basins all those troughs appear elements of the back arc opening related to the eastward roll back of the w directed apennines maghrebides subduction zone similarly to western pacific back arc settings these late oligocene early miocene basins nucleated both within the betic cordillera e g alboran sea and in its foreland valencia and provencal troughs the n40 70 direction of grabens is oblique to the coexisting n60 80 trending orogen and shows its structural independence from the orogenic roots thus as the extension cross cuts the orogen and developed also well outside the thrust belt front the westernmost basins of the mediterranean had to develop independently from the alps betics orogen therefore the alboran extension considered a classic example of a basin generated by the collapse of an orogen cannot be ascribed to the detachment or annihilation of the lithospheric root in contrast with the eastward migrating extensional basins the betic balearic thrust front was migrating westward producing interference or inversion structures

a new chronology for the middle to late miocene continental record in spain abstract the first detailed chronology for the middle to late miocene continental record in spain is presented based on high resolution magnetostratigraphic data of mammal bearing sections which were studied in several basins calatayud daroca teruel valles penedes duero and jucar cabriel our results indicate that these sections compose an almost complete magnetostratigraphic succession from the lower aragonian mn4 to the middle turolian mn12 seven successive mammal neogene mn zone boundaries are directly dated in these sections which often contain faunas of two successive zones in superposition the three oldest boundaries are dated in the aragonian type area calatayud daroca basin the mn4 mn5 boundary vargas section occurs in chron c5cr o with a corresponding age of 17 26 0 01 ma the mn5 mn6 boundary aragon section in chron c5acn 0 8 with an age of 13 75 0 03 ma and the mn6 mn7 8 boundary aragon section in the interval c5ar 1n c5ar 3r with an age of 12 75 0 25 ma the mn7 8 mn9 aragonian vallesian boundary occurring in chron c5r 1n at 11 1 ma and the mn9 mn10 boundary in chron c4ar 3r at 9 7 0 1 ma are recorded in the valles penedes basin vallesian type area and are supported by the results from the duero basin torremormojon section in the turolian type area teruel basin the mn10 mn11 vallesian turolian boundary la gloria section occurs in chron c4an y at 8 7 0 1 ma taking into account the pre existing data from the jucar cabriel basin the mn11 mn12 boundary cabriel valley section is recalibrated to c4n 1n at an age of 7 5 0 1 ma

seismites from a well core of palustrine deposits as a tool for reconstructing the palaeoseismic history of a fault abstract the concud fault is located at the junction between the jiloca and teruel grabens central eastern iberian chain spain the late pleistocene activity of this fault has been well logged from structural and palaeoseismological trench studies but only scattered data of the late pliocene seismic activity exist the late pliocene early pleistocene syn tectonic infill consists of an endorheic continental succession in which a 75 m long continuous well was drilled near the concud fault along the entire well core several types of soft sediment deformation structures with variable morphology size and frequency have occurred including clastic dykes load structures and slumps the rigorous analysis of the deformation structures their relationships with the involved sedimentary facies and the discrimination of possible deformation mechanisms and trigger processes allow us to interpret part of them as seismically induced structures the recognition of 21 deformed beds seismites allow the late pliocene early pleistocene seismic history of the concud fault to be reconstructed therefore 21 seismic events with m 5 and an apparent recurrence period of about 45 ka have been inferred

the neogene structure of the eastern iberian margin structural constraints on the crustal evolution of the valencia trough western mediterranean abstract the presence of a thinned crust beneath the valencia trough has been recognized for a long time however to date no attempt to link this thinning inferred from geophysical data with the superficial structures has been made a quantification of the neogene extensional processes in the crustal evolution of the valencia trough is presented as a consequence of the complexity of the betic balearic domain the analysis has been done for the catalan valencian domain northwestern areas of the trough crustal and superficial data in this area show that neogene extension was accommodated by a listric normal fault system detached in a deep upper crustal level 13 15 km in the marginal zone of the domain quantitative analysis of the neogene structure shows the incoherence between the upper crustal thinning inferred from the geometric analysis of the superficial structures factor 1 4 1 5 and from geophysical data 1 8 although the latter value agrees with that deduced from the analysis of neogene subsidence this incoherence suggests that the present thinned crust would be partially inherited from the mesozoic extension in this way mesozoic subsidence analysts and the recognized mesozoic structure show that the mesozoic extension was almost as important as the neogene one

the florence rise the western bend of the cyprus arc the florence rise is a submarine feature extending from the island of cyprus in the southeast to the anaximander mountains which form the northwestern end of the cyprus arc south of western turkey the eastern florence rise includes a topographic high near cyprus while its central domain displays relatively low relief most of the major elements of relief appear to be bounded by faults in the light of new geophysical data an underlying core ridge likely made of pre pliocene nappes emplaced from the north separates relatively undeformed sediments to the northeast from actively shearing sediments and seismic basement to the southwest a dextral arc parallel wrench zone at least 15 km wide has created a lineated seafloor texture and accompanying flower structures within the central florence rise apparent riedel type conjugate shears within this system cut across the florence rise and mark changes in the relief along the arc several mud volcanoes are observed within the wrench zone and along associated faults indicating that overpressuring at depth is relieved by these faults there is no evidence for any typical subduction along this arcuate trend which is considered to act as the present boundary between the african and anatolian aegean plates in contrast both the nature of faulting and the morphology of the florence rise seem to indicate some degree of transpressional coupling between the two plates even though they appear disconnected by a tectonic boundary in the form of a major shear zone

three dimensional distinct element modelling of relay growth and breaching along normal faults three dimensional numerical models of neutral i e slip parallel relay zones on normal faults that cut massive sandstone host rocks have been constructed using the distinct element method code particle flow code in 3 d pfc3d the models successfully reproduce the geometries displacement profiles and strains observed in natural relay zones in contrast to boundary element method simulations the modelled relay ramps dip towards the hanging wall consistent with observations of most natural relay zones the modelling shows that relay zones are stable structures that grow by progressive rotation of an approximately planar relay ramp without significant propagation of the relay bounding faults prior to breaching stable growth is terminated when a breaching fault propagates across the top or bottom of the relay ramp breaching fault propagation is not instantaneous and the ramp continues to rotate and therefore transfer displacement between the relay bounding faults until they become fully hard linked following hard linkage displacement is accommodated by slip on the through going fault surface the modelling results confirm previous conceptual models of relay growth and breaching based on geometric and kinematic analysis of natural relay zones

p wave tomography of the mantle under the alpine mediterranean area 1 we study the upper mantle p wave velocity structure below the euro mediterranean area down to 1000 km depth by seismic travel time tomography we invert summary residuals constructed with both regional and teleseismic first arrival data reported by the international seismological centre isc 1964 1995 introducing some alternative strategies in the travel time tomographic approach and a new scheme to correct teleseismic data for global mantle structure our high resolution model pm0 5 is parameterized with three dimensional 3 d linear splines on a grid of nodes with 0 5 spacing in both horizontal directions and 50 km vertical spacing we obtain about 26 root mean square rms reduction of residuals by inversion in addition to roughly 31 reduction after summary rays formation and selection sensitivity analyses are performed through several test inversions to explore the resolution characteristics of the model at different spatial scales the distribution of large scale fast anomalies suggests that two different stages of a convection process presently coexist in very close regions the mantle dynamics of western central europe is dominated by blockage of subducted slabs at the 660 km discontinuity and ponding of seismically fast material in the transition zone contrarily in the eastern mediterranean fast velocity material sinks into the lower mantle suggesting that the flow of the cold downwelling here is not blocked by the 660 km discontinuity on a smaller scale the existence of tears in the subducted slab lithospheric detachment all along both margins of the adriatic plate as proposed by some authors is not supported by our tomographic images

segmentation and increasing activity in the neogene quaternary teruel basin rift spain revealed by morphotectonic approach abstract the nnw sse trending teruel basin rift is the largest late miocene quaternary extensional intracontinental structure located within the central eastern iberian chain spain the structural and morphotectonic study carried out in the central northern part of this half graben basin north of teruel city has allowed us to analyse rift segmentation deformation partitioning and rift evolution results are based on vertical displacement calculations fault throw and bending of the main border and intrabasin fault zones we use two geomorfological stratigraphical markers the intramiocene erosion surface ies 11 2 ma and the fundamental erosion surface fes 3 5 ma while the first marker reveals rift initiation under an e w extension the late marker records vertical displacements associated to a second late pliocene quaternary rifting stage characterized by a nearly multidirectional extension regime with prevailing ene wsw trending o3 despite the along axis rift segmentation into three structural domains northern central and southern and the distribution of deformation among border and intrabasin faults in the central and southern domains a consistent average slip rate post ies of 0 09 mm a has been calculated on distinct transects across the basin suggesting a homogeneous crustal scale extension process in the region the results also reveal that slip rates during the late pliocene quaternary 0 12 0 16 mm a are higher than the late miocene early pliocene 0 05 0 07 mm a slip rate increase is caused by i a westward propagation of deformation from the valencia through and ii a change in the regional stress field both enhanced by crustal doming affecting central eastern iberia as well as progressive fault linkage throw vs distance graphs suggest that the main faults are in a transient stage towards coalescence less advanced within the southern domain regional late pliocene quaternary uplift concomitant with increasing slip rates in the teruel basin rift has caused the basin to rise so that synrift sedimentation only took place in rapidly subsiding residual basins until the region became exorheic and the basin was incised by the present day fluvial network

successive orthogonal and oblique extension episodes in a rift zone laboratory experiments with application to the ethiopian rift small scale modeling was performed to examine the effects of the superposition of two successive extensional phases from orthogonal to oblique type 1 and from oblique to orthogonal type 2 in both the type 1 and type 2 models faults produced during the first stage strongly control fault development during the second stage in type 1 models the oblique faults developed during the second oblique phase are confined within a first phase graben whereas in type 2 models the oblique faults produced during the first phase continue to develop during orthogonal extension and connect with each other to give sigmoidal fault blocks type 1 models are compared with the structural setting of the ethiopian rift the evolution of the rift is related to a recent extensional event whose principal direction of stretching trends at around 50 to preexisting major normal faults type 1 laboratory models are fairly comparable to the northern sector of the ethiopian rift referred to here as mer they account for both the development of the en echelon oblique faults of the wonji fault belt and the sinistral shear gradient running parallel to the eastern border of the mer which formed during an oblique rifting extension the statistical analysis of the whole ethiopian rift fault pattern by reference to the experimental data allows the determination of a n100 n110 mean direction of stretching

plio quaternary extensional seismotectonics and drainage network development in the central sector of the iberian chain ne spain abstract westward propagation of postorogenic rifting in the central sector of the iberian chain generated the teruel and calatayud mio pliocene grabens and the jiloca daroca and munebrega plio quaternary half grabens partially superimposed on the western margins of the pre existing basins the progressive capture and transformation from endorheic aggradational to exorheic incisional drainage of the active grabens resulted in the development of a drainage network dominated by axial streams controlled by neotectonic activity and the distribution of basin fill lithofacies this paper reviews the geomorphic and stratigraphic evidence of plio quaternary extensional tectonics and provides new chronological data radiocarbon and osl dating on offset deposits and the associated paleoseismic record the daroca fault offsets mantled pediment deposits dated at 113 119 ka based on a radiocarbon age of the colluvial sequence 43 ka affected by the rubielos de la cerida fault a vertical slip rate of 0 05 0 07 mm yr has been estimated for this fault four paleoearthquakes subsequent to 72 ka have been inferred from the classic exposure of the concud fault indicating a recurrence interval of less than 18 ka a gravitational origin related to the dissolution of subjacent evaporites is attributed to two faults affecting an upper pleistocene terrace 15 ka in the alfambra valley close to the concud fault these structures have recently been interpreted as evidence of coseismic deformation on the concud fault although the faults have a low slip rate and a long seismic cycle their length

european cenozoic rift system abstract the european cenozoic rift system extends from the coast of the north sea to the mediterranean over a distance of some 1100 km it finds its southern prolongation in the valencia trough and a plio pleistocene volcanic chain crossing the atlas ranges development of this mega rift was paralleled by orogenic activity in the alps and pyrenees major rift domes accompanied by subsidence reversal of their axial grabens developed 20 40 ma after beginning of rifting uplift of the rhenish shield is related to progressive thermal lithospheric thinning the vosges black forest and the massif central domes are probably underlain by asthenoliths emplaced at the crust mantle boundary evolution of this rift system is thought to be governed by the interaction of the eurasian and african plates and by early phases of a plate boundary reorganization that may lead to the break up of the present continent assembly

a model of rift basin evolution constrained by first order stratigraphic observations the stratigraphy of many nonmarine rift basins records a common sedimentological history consisting of a relatively abrupt increase of water depth followed by a slower shoaling upward trend we explore in this paper the origin of these sequences through a three dimensional physical model that incorporates the affects of fault growth flexure erosion sedimentation and isostasy fault growth is assumed to occur in a self similar manner and is treated as dislocations inducing flexure in a thin elastic plate topography generated by faulting and flexure is allowed to undergo diffusion to simulate erosive and sedimentary processes isostatic response to the redistribution of mass results in additional flexure of the thin plate the model is tested using two models of fault growth and we compare the numerical results with the stratigraphy observed in nonmarine rifts basins generated using a constant lengthening rate mode of fault growth fail to reproduce the stratigraphy of continental rift basins we find that the commonly observed stratigraphic succession of lacustrine to fluvial conditions requires the displacement rate of the bounding fault to decrease with time consistent with opening at a relatively constant areal extension rate

the valencia trough western mediterranean an overview abstract the valencia trough located between the spanish mainland and the balearic islands corresponds to a late oligocene to recent sedimentary basin that is characterized by a highly attenuated continental crust its northwestern part evolved in response to a late oligocene to early miocene rifting phase that was followed by a period of post rift subsidence and a late miocene pleistocene phase of renewed crustal extension and magmatism its southeastern part is characterized by late oligocene to mid miocene compressional deformation and subsequent extension in the axial parts of the basin the crust has been thinned by a factor of 3 whereby the lower crust is either absent or very thin upper crustal extension appears to be considerably smaller than indicated by the crustal configuration of the basin a major problem in understanding the evolution of the valencia trough is the lack of knowledge about the physical state and structure of the lithosphere before late oligocene extension evolution of the northwestern part of the basin appears to be linked with the development of the oceanic provencal basin middle miocene compressional deformation of the balearic fold belt forming the southeastern margin of the valencia trough appears to have interfered with the tensional evolution of the latter which only resumed after crustal shortening in the balearic domain had given way to extensional tectonics during the late miocene

plio quaternary uplift of the iberian chain central eastern spain from landscape evolution experiments and river profile modeling abstract the iberian chain central eastern spain is characterized by a dome shaped topography with poorly incised and relatively flat landscape in its interior at an elevation of 1300 m a recent regional tectonic event started during or after the late pliocene inducing deep valley incision on the flanks of the iberian chain the rate and timing of this deformation as well as the magnitude of the uplift induced erosion processes still lack a quantitative validation we used 3d signum and 1 d river profile numerical models to investigate the landscape evolution of the iberian chain from the late pliocene to the present and to study the response of topography and rivers to tectonically induced base level lowering our model results are supported by geological geomorphological and geochronological data the results of the signum experiments show that the iberian chain topography has experienced regional uplift since ca 3 ma with rates between 0 25 and 0 55 mm y 1 in response to this uplift rivers have incised at an average long term incision rate of about 0 22 mm y 1 and have progressively captured drainage areas from the chain interior to further validate the results of landscape evolution modeling we use a 1 d river incision model to explore the incision history of several rivers draining the iberian chain the results constrain the range of values of bedrock erodibility from 5 8 10 5 to 5 0 10 4 m 0 4 y 1 and predict long term incision rates similar to those from the signum experiments

the optimal state for gravity currents in shear this study examines the lifting of sheared environmental air by gravity currents focusing primarily on the theoretical optimal state in which near surface flow is turned into a vertically oriented jet theoretical models are presented from multiple perspectives including the vorticity perspective that was first presented by rotunno klemp and weisman and a flow force balance perspective based on conservation of mass and momentum the latter approach reveals a constrainton the depth of the environmental shearlayer relative to the depth of the cold pool based on these control volume constraints a numerical solution for steady inviscid isentropic flow is obtained that shows how the cold pool interface has a slightly concave shape and is nearly although not strictly vertical then by initializing a time dependent numerical model with a stagnant cold pool in an environment with low level shear it is shown that a statistically steady flow can be maintained with all the important elements of the analytic solution most notably the front relative flow is negligible behind the surface gust front at all levels the interface of the cold pool maintains a predominantly vertical structure and the net generation of vorticity by buoyancy within a control volume closely matches the horizontal flux of environmental vorticity on the side of the control volume sensitivity simulations confirm that the constraints identified by the analytic study must be met for the optimal state to be realized and that lifting of near surface environmental air is optimized when a vertically oriented jet is created and maintained

cenozoic tectonic activity in a variscan basement evidence from geomorphological markers and structural mapping nw iberian massif abstract the nw iberian massif is part of an ancient basement that has been considered a seismically stable area with no outstanding cenozoic tectonics however recent seismic activity revealed the need for better knowledge of the cenozoic structures in the area because of the lack of mesozoic deposits and the scarcity of cenozoic sediments as well as the intense deformation of the pre mesozoic variscan basement it is difficult to study the cenozoic tectonic structures in this work the combination of detailed structural mapping and study of geomorphological markers in the variscan basement has allowed recognition of cenozoic tectonic structures kinematics and processes that otherwise would not have been identified the identified structures have been gathered into three groups a ne sw trending strike slip faults mainly sinistral b nnw vergent thrusts that uplift the caurel mountains and galaico leoneses mountains and c e w and ene wsw thrusts that uplift the ancares mountains in a pop up structure the structures cut the pre cenozoic erosion surface and affect the drainage network that shows patterns characteristic of tectonic activity the three groups of structures define sectors with different relief showing a strong link between geomorphological elements and tectonic structures the intense drainage reorganisations observed in the area and the deformation of miocene pliocene deposits point out to a significant late miocene tectonic activity in the region thus the cenozoic tectonic activity in the northwest of the iberian peninsula takes place during an extensive period of time which started with the episodes of compression in the cantabrian margin and it is identified nowadays by the recent seismic activity recorded in the north western iberian peninsula 1995 and 1997 lugo events the seismicity is related to the cenozoic structures identified in the area which move under the present se nw horizontal maximum compression and coincide with the proposed seismogenic faults