faulting of rocks in three dimensional strain fields i failure of rocks in polyaxial servo control experiments abstract the dependence of the number of sets of faults and their orientation on the intermediate strain axis is investigated through polyaxial tests reported here and theoretical analysis reported in an accompanying paper in the experiments cubic samples of berea sandstone sierra white and westerly granites and candoro and solnhofen limestones were loaded on their three pairs of faces by three independent mutually perpendicular presses at room temperature two of the presses were servo controlled and applied constant displacement rates throughout the experiment most samples display three or four sets of faults in orthorhombic symmetry these faults form in several yielding events that follow a stage of elastic deformation in many experiments the maximum and the intermediate compressive stresses interchange orientations during the yielding events where the corresponding strains are constant the final stage of most experiments is characterized by slip along the faults

the influence of surface and tectonic processes on landscape evolution of the iberian chain spain quantitative geomorphological analysis and geochronology abstract in tectonically active areas the landscape response to tectonic forcing is described and possibly quantified by regional topographic and hydrographic features as well as by spatial variation in rates of surface processes we investigated the recent landscape evolution of the iberian chain ne spain an intraplate thrust belt formed in cenozoic times and characterized by a dome shaped topography in its central sector the landscape is dominated by low relief surfaces late neogene in age presently standing at an average altitude of 1300 m a recent regional uplift controlled the organization of the present fluvial network and dissection of the landscape in this framework we investigated the geomorphic responses to tectonic forcing by the calculation of morphometric parameters focusing on topography map of local relief swath profiles and hydrography basin hypsometric curve and integral basin asymmetry factor river longitudinal profiles and relative indices and using srtm dem the results of morphometric analysis have been coupled with radiometric uranium series dating of calcareous tufas lying on fluvial strath terraces the obtained ages allow the estimation of incision rate along the high tajo and martin rivers our results indicate that uplift and rock type erodibility are the main factors influencing landscape evolution of the study area the incision rates are very similar throughout the central sector of the range indicating that despite subtle local variation the rivers are responding to a main tectonic input the regional uplift in conclusion the iberian chain landscape is in a transient state in response to a recent dome like uplift indeed the fluvial processes that weakly incised this landscape at a rate of 0 6 mm yr are approaching a radial pattern on the basis of geological and geomorphic constraints we hypothesize that the uplift started around or after 3 ma

superposed deformation in the peninsula mitre recess fuegian thrust fold belt southern argentina and implications for orogenic curve kinematics abstract a detailed study of the structure of the peninsula mitre recess in the fuegian thrust fold belt of southern argentina reveals superposed deformation related to contrasting shortening directions one group of structures trend parallel to the recess and verge either towards the foreland or towards the hinterland a second group of structures accommodate contraction superposed on the previous group analysis of fault slip data reveals that the first group is related to 1 perpendicular to the surface traces of thrusts and or fold axes and are therefore compressive structures in contrast the paleostress tensors of the second group of structures show 1 orientations parallel or at a low angle with respect to local structural trends the style of the superposed structures of the second group which mostly indicate contraction subparallel to the trend of the recess is consistent with structures resulting from tangential longitudinal shortening associated with oroclinal bending this scenario implies that the peninsula mitre recess formed as a progressive curve involving rotation due to slip trajectories convergent toward the recess causing the observed tangential contraction this kinematic model supports previous interpretations of buttressing of the thrust fold belt against a basement promontory

the importance of small scale faulting in regional extension a recurring observation in many studies of extensional basins has been that the amount of extension visible on normal faults for example on seismic reflection profiles is significantly less than the amount of extension indicated by crustal thickness and thermal subsidence1 5 one mechanism suggested to account for this discrepancy is small scale faulting with offsets too small to be resolved seismically6 7 but earthquake studies8 10 indicate that small faults are responsible for only a small fraction of the total seismic moment in an active area scholz and cowie11 have recently attempted to extend this approach to the total strain at the end of a finite deformation interval by combining scaling laws describing the distributions of fault lengths and displacements here we present fault displacement data that directly conflict with scholz and cowie s conclusions and imply that up to 40 of the extension may be missed by summing fault offsets on basin profiles the fault population at the end of a long deformation interval may differ substantially from that responsible for the earthquake population at any one time

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

stress evolution and structural inheritance controlling an intracontinental extensional basin the central northern sector of the neogene teruel basin abstract the teruel basin is a nne ssw trending intracontinental extensional basin located in central eastern iberia it is asymmetrically bounded to the east by a major fault zone but intrabasinal faults with diverse orientation nne ssw to ne sw e w or nw se also appear offsets of the successive sedimentary units and of two planation surfaces reveal that tectonic activity initiated at the border faults while intrabasinal ones mainly developed in a later stage fractures on a map scale show a prevailing n s strike in neogene synrift rocks while a dense network made of four main fracture sets ne sw e w to ese wnw n s and nnw sse likely inherited from mesozoic rifting stages is observed in pre rift units the results of palaeostress analyses indicate an overall predominance of 3 directions around e w although two stress episodes have been distinguished during the late miocene pleistocene i triaxial extension with 3 e w ii almost radial extension 1 vertical 2 3 with a somehow prevailing 3 ene wsw a scenario in which the evolving extensional stress field was able to gradually activate major basement structures with different orientation inherited from previous tectonic events is proposed as responsible for the evolution and overall pattern of both the eastern active margin and central parts of the central northern sector of the teruel basin

evolution of the stress field pattern in the south of the rhine graben from the eocene to the present a stress field evolution from the eocene to the present is proposed for the southern part of the rhine graben stress tensor determinations are supported by striated microfaults and calcite twin lamellae analyses both methods lead to the determination of 1 a an e w extension contemporaneous with the opening of the graben and 2 b a n s compressive event which may be related with alpine tectonics it is shown that a n s compressive event occurred prior to the oligocene extension a permutation between the 1 and 2 axes is proposed to explain the transition between compression and extension a 1 2 inversion during the oligocene is compatible with compression in the southern part of the rhine graben infilling horizontal 1 and extension vertical 1 more to the north during the miocene the jura emplacement corresponds to a n s compression in this area there is no significant variation of the 1 direction south of the rhine graben from the eocene to the late miocene the 1 direction only turns to a n140 direction during the pliocene or the quaternary

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

analysis of a gradual change in stress regime example from the eastern iberian chain spain abstract the compression extension passage in the eastern iberian chain during the miocene is analyzed structural data suggest that it is a gradual change in stress regime which does not involve rotation but interchange of 1 and 2 axes one of them remaining always vertical the gradual stress evolution is interpreted by a numerical graphic method y r diagram which optimizes combinations of y azimuth of the maximum horizontal axis and r stress ratio explaining groups of fault movements the y r diagrams of some fault populations measured in the castellon region provide optimum tensors appearing within a continuous cloud of solutions from the compressional field to the extensional one movement sequences obtained from superimposed striations indicate a systematic stress change between these two regimes

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

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

analysis of non striated faults in a recent extensional setting the plio pleistocene concud fault jiloca graben eastern spain the integration of palaeostress results obtained from the analysis of non striated faults and joints affecting plio pleistocene deposits near the concud fault southern jiloca graben eastern spain yields a multidirectional tension stress field vertical s1 s2zs3 where the primary s3 trajectories trend ene the results also show strong deflections of stress trajectories with many local s3 axes being either orthogonal or parallel to the trace of the concud fault the stress field persisted throughout the period of activity of the fault i e late pliocene and pleistocene the agreement between the present results and the regional picture gives support to the stress inversion method and shows its usefulness in palaeostress analysis of young poorly lithified rocks

tectonic subsidence v erosional lowering in a controversial intramontane depression the jiloca basin iberian chain spain the jiloca basin is a large intramontane nnw sse trending topographical depression in which the relative role of tectonic subsidence and erosional lowering is currently a matter of discussion geometry and facies of the sedimentary infill at its central sector have now been characterized from compiled borehole data which allows discussions of how the evolutionary model is constrained the central jiloca depression contains a late pliocene to pleistocene sedimentary sequence made up of alluvial fan pediment mantle and episodic palustrine deposits overlying a carbonate unit that could represent an early lacustrine stage of late miocene early pliocene age the geometry of these units is partially controlled by nw se striking normal faults both the morphological depression and the sedimentary basin truncate previous folds whose traces beneath the neogene quaternary infill have been interpreted from the geology of the basin margins borehole data and hydrogeological criteria the northern and southern sectors of the jiloca depression are bounded by faults showing measurable hectometric scale throws calamocha and concud faults moreover in the central sector the 350 400 m tectonic uplift of sierra palomera has been interpreted from a morphostructural reconstruction of the tilted block which separates the teruel and jiloca graben being similar to the height of the sierra palomera mountain front all these features are consistent with a tectonic basin developed within the framework of the neogene quaternary extensional evolution of eastern spain in contrast they are hardly compatible with genetic models based on erosional deepening either topographic lowering by numerous nested tertiary erosion pediplains or sub alluvial pliocene quaternary karstic corrosion

an inverse problem in microtectonics for the determination of stress tensors from fault striation analysis abstract a method is proposed to compute some characteristics of a possible stress tensor related to striations measured in a given faulted area if several tectonic phases are responsible for the striations the method separates and determines the successive stress tensors the iterative algorithm consists of alternatively a sorting the data attributed to a tectonic phase and b computing the characteristics of the stress tensor of this phase the method is tested using an application to synthetic and actual data

stress fields about strike slip faults inferred from stylolites and tension gashes abstract in general the long axis of the tension gashes and stylolitic columns developed in limestones during a single phase of compressional deformation occur parallel to the direction of the maximum compressive stress 1 this is the case in the languedoc for structures developed in the jurassic limestones during the n s pyrenean compression exceptionnally however these microstructures turn in direction and become oblique even orthogonal one to the other probably as a consequence of a variation in intensity and direction of the stress field at the end of a microfault this mechanism also occurs in a larger scale structure involving segments of pre tectonic joints that act as en echelon microfaults in a brittle kink band equivalent to a peculiar type of potential wrench fault

space time coupling in brittle deformation at geophysical scales strong intermittency as well as spatial heterogeneity characterize the brittle deformation of geophysical objects such as the earth s crust or the arctic sea ice cover they can be expressed through specific scaling laws that relate for a space time domain a the number of earthquakes or b the strain rate vs the size of the domain for the earth s crust or the arctic sea ice respectively however in both cases spatial respectively temporal scaling depends on the time respectively spatial scale considered i e the space and time scaling dependences are coupled here we show that this space time coupling of brittle deformation at geophysical scales can be summarized through a unique scaling law characterizing the discrete fracturing events earthquakes or displacement events along sea ice leads as suggested by an analysis of southern californian seismicity we argue that this space time coupling is likely to emerge from the complex correlation patterns related to chain triggering of earth or ice quakes

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

coral reefs at 34 n japan exploring the end of environmental gradients we describe the architecture and development of the highest latitude coral reefs currently known on earth located in japan at 34 n the reefs are distributed within turbid inner bays and undergo winter sea surface temperatures ssts that fall to 13 c well below the generally accepted lower limit 18 c in winter of tropical coral reef formation despite low ssts and high turbidity coring indicates reefs ranging to 555 cm in thickness since ca 4 3 k y ago the reefs exhibit high adaptability to this extremely marginal environment variability of the tsushima warm current and the asian monsoon could have affected the evolution of these reefs the corals are dominantly faviids in contrast to acropora and porites that tend to dominate low latitude tropical subtropical reefs defining the end of the distributional range the reefs serve as baselines for understanding coral reef distribution along sst and turbidity gradients

orthogonal cross joints do they imply a regional stress rotation abstract orthogonal cross joints extend across intervals between systematic joints in brittle sedimentary strata and abut the systematic joints at about 90 angles these joints typically form a ladder like pattern if viewed on a bedding surface a common interpretation is that orthogonal cross joints define the orientation of the regional stress field during their formation least compressive stress perpendicular to the joints it follows that they indicate a rotation of regional principal stresses by 90 after the formation of the systematic joints using a three dimensional boundary element code poly3d we considered a simple geologic case of vertical systematic fractures developing in horizontal strata under a triaxial remote load with the maximum principal tensile stress being horizontal and perpendicular to the strike of the fractures the intermediate principal stress being horizontal and parallel to the strike of the fractures and the least principal tensile stress i e maximum compressive stress being vertical the results show that the local maximum principal stress is first perpendicular and then parallel to the strike of the systematic fractures as the ratio of fracture spacing to height changes from greater than to less than a critical value when the horizontal remote principal stress ratio the ratio of the intermediate remote principal stress to the maximum remote principal stress under the sign convention of positive for tensile stresses is greater than a threshold value 0 2 thus the fracturing process changes from infilling of systematic fractures to the formation of orthogonal cross fractures this provides an alternative mechanism for the formation of orthogonal cross joints that does not require a systematic rotation of the regional stress field by 90 the critical spacing to height ratio for the local principal stress switch is independent of the least remote principal stress i e overburden it increases nonlinearly with increasing ratio of the horizontal remote principal stresses and decreases nonlinearly with increasing poisson s ratio of the material

stress perturbations registered by jointing near strike slip normal and reverse faults examples from the ebro basin spain stress perturbation patterns created by coeval and preexisting fault planes are characterized by means of detailed mapping and analysis of joint sets in miocene carbonates of the tudela area strike and spacing of the pervasive n s joint set have been specially surveyed for this purpose their spatial variations have been analyzed and interpreted in the light of different theoretical models proposed by other authors perturbations inferred near strike slip faults correspond to the classical examples related to compressional and extensional fault tips a normal fault striking oblique to the horizontal stress axes deflects the latter toward making 2 and 3 trajectories parallel and perpendicular respectively to the fault strike while causing an abrupt stress release within the footwall near a reverse fault with a small dextral component the deflection of 1 trajectories is gentle but a significant increase of differential stress occurs in the hanging wall

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

assessing interaction of active extensional faults from structural and paleoseismological analysis the teruel and concud faults eastern spain abstract the relationship of independence interaction or linkage between two neighbouring intraplate active extensional faults the teruel and concud faults are investigated from structural and paleoseismological data and the results are discussed to improve seismic hazard assessment for the region this paper provides the structural and paleoseismological characterization of the almost unknown teruel fault from detailed mapping and trench analysis and discusses its kinematic and dynamic relationships with the concud fault four individual events occurred between 76 0 ka and 9 2 ka bp have been recorded at two branches of the teruel fault unfortunately these only represent a small fraction of its overall activity during such time lapse and their time constraints do not allow correlating them with those at the concud fault the teruel and concud faults are independent structures from the geometric and kinematic point of view as evinced by their distinct i transport directions n275 e and n220 e respectively and ii average coseismic displacements 0 5 m and 1 9 m respectively these displacements are consistent with their respective lengths 9 0 km and 14 2 km and significantly smaller than those expected for a hypothetically joint concud teruel 23 km long fault however their displacement gradients close to the relay zone indicate that both faults undergo dynamic interaction thus suggesting a transient stage from independence to linkage we hypothesize that slip on both structures occurred at the scale of the seismic cycle in a broadly alternating manner which induced strain partitioning between them and allowed accommodating bulk biaxial extension in the region such deformation pattern would have increased the earthquake frequency with respect to the scenario of a hypothetically linked concud teruel fault but diminished the potential seismic magnitude

neogene paleostress changes in the basin and range a case study at hoover dam nevada arizona at hoover dam 40 km southeast of las vegas nevada well exposed highly faulted miocene rocks provide an excellent opportunity to study the paleostress history of a very small area within a region where previous geologic studies indicate clockwise rotation of paleostress and a nearness to a major strike slip fault zone boundary within 0 5 km3 of rock the sense of slip was determined on almost 500 separate faults the fault slip data show internal consistency with respect to lithology size of faults and location within the small area with respect to fault slip however the data represent an in homogeneous mixture of primarily strike slip and dip slip motions from this mixture it is possible to resolve two distinct stress fields with directions of extension that differ by 60 each stress field corresponds to a mixture of strike slip and dip slip faults and thus the orientations of 1 and 2 are not tightly constrained if however the data are first separated into strike slip and dip slip faulting modes and subsequently searched for sub populations that correspond to contrasting paleostress orientations the computations yield tightly constrained tensors that illustrate two distinct stress fields with subhorizontal 3 axes that trend n50 e and n75 w the 1 and 2 axes permutate in two vertical planes that strike n40 w and n15 e because 1 and 2 are close in value relative to 3 these relationships suggest that strike slip and dip slip faulting belong to the same tectonic regime qualitative observations of polyphase slip fault fault offsets and fault bedding geometric relationships when evaluated in the context of changes in 3 orientation and permutations of 1 and 2 provide a basis for a two stage late cenozoic structural evolution at hoover dam these stages are 1 strike slip faulting partly pre tilt and dip slip faulting and associated stratal tilting and 2 mostly post tilt complexly interrelated strike slip oblique slip and dip slip faulting the qualitative evaluations indicate that strike slip and dip slip faulting alternated in time during the second stage of deformation and may have done so during the first these mixed mode movements probably represent stress oscillations in time and space rather than discrete stress reorganizations in contrast the two different orientations of 3 either represent a major clockwise rotation of the stress field or a major counterclockwise rotation of the rocks during the faulting history each alternative is consistent with regional geologic relationships and the choice of which is correct cannot be made within the small area that was studied

fault relay zones evolving through distributed longitudinal fractures the case of the teruel graben system iberian chain spain abstract a new type of fault relay zone in extensional contexts dominated by distributed along strike or longitudinal fractures is defined it contrasts with the classical models reported in the literature in which transverse connecting faults controlled by the own relay kinematics prevail the new model is based on structural features of the teruel graben system as well as on analogue modelling relay zones between the nw se to nnw sse striking faults that delimit the eastern boundary of the jiloca graben calamocha sierra palomera and concud faults together with the teruel fault have been studied all of these relay faults show recent neogene quaternary ruptures at different scales mostly parallel to the macrostructural trend and to the maximum horizontal stress shmax trajectories i e orthogonal to the ene wsw regional extension direction that characterises the nearly biaxial or radial stress regime active during upper pliocene quaternary times transverse ruptures are almost absent with the exception of the northern relay zone calamocha sierra palomera where an incipient ne sw striking connecting fault does exist analogue models have been run under a biaxial extension regime similar to the regional one they allowed analysing the main factors controlling fracture propagation depending on the ratio of extension velocities and the orientation of the master faults relative to extension directions laboratory fracture patterns as in the natural studied examples are mostly controlled by the inherited anisotropies and in a greater extent by the imposed extension trajectories which results in a clear prevalence of longitudinal fractures such external controls usually disregarded in numerical and analogue modelling tend to induce fault coalescence through along strike parallel or at very low angle propagation resulting in a final braided fault pattern

a new estimation of the decay of aftershock density with distance to the mainshock we investigate how aftershocks are spatially distributed relative to the mainshock compared to previous studies ours focuses on earthquakes causally related to the mainshock rather than on aftershocks of previous aftershocks we show that this distinction can be made objectively but becomes uncertain at long time scales and large distances analyzing a regional earthquake data set it is found that at time t following a mainshock of magnitude m the probability of finding an aftershock at distance r relative to the mainshock fault decays as r where is typically between 1 7 and 2 1 for 3 m 6 and is independent of m for r less than 10 to 20 km and t less than 1 day uncertainties on this probability at larger r and t do not allow for a correct estimation of this spatial decay we further show that a static stress model coupled with a rate and state friction model predicts a similar decay with an exponent 2 2 in the same space and time intervals this suggests that static stress changes could explain the repartition of aftershocks around the mainshock even at distances larger than 10 times the rupture length

monitoring ice thickness and elastic properties from the measurement of leaky guided waves a laboratory experiment the decline of arctic sea ice extent is one of the most spectacular signatures of global warming and studies converge to show that this decline has been accelerating over the last four decades with a rate that is not reproduced by climate models to improve these models relying on comprehensive and accurate field data is essential while sea ice extent and concentration are accurately monitored from microwave imagery an accurate measure of its thickness is still lacking moreover measuring observables related to the mechanical behavior of the ice such as young s modulus poisson s ratio etc could provide better insights in the understanding of sea ice decline by completing current knowledge so far acquired mostly from radar and sonar data this paper aims at demonstrating on the laboratory scale that these can all be estimated simultaneously by measuring seismic waves guided in the ice layer the experiment consisted of leaving a water tank in a cold room in order to grow an ice layer at its sur

are aftershocks of large californian earthquakes diffusing we analyze 21 aftershock sequences of california to test for evidence of space time diffusion aftershock diffusion may result from stress diffusion and is also predicted by any mechanism of stress weakening here we test an alternative mechanism to explain aftershock diffusion based on multiple cascades of triggering in order to characterize aftershock diffusion we develop two methods one based on a suitable time and space windowing the other using a wavelet transform adapted to the removal of background seismicity both methods confirm that diffusion of seismic activity is very weak much weaker than reported in previous studies a possible mechanism explaining the weakness of observed diffusion is the effect of geometry including the localization of aftershocks on a fractal fault network and the impact of extended rupture lengths which control the typical distances of interaction between earthquakes

southern california hypocenter relocation with waveform cross correlation part 2 results using source specific station terms and cluster analysis we obtain precise relative relocations for more than 340 000 southern california earthquakes between 1984 and 2002 by applying the source specific station term ssst method to existing p and s phase picks and a differential lo cation method to about 208 000 events within similar event clusters identified with waveform cross correlation the entire catalog is first relocated by using existing phase picks a reference 1d velocity model and the ssst method of richards dinger and shearer 2000 we also perform separate relocations of imperial valley events by using a velocity model more suited to this region next we apply cluster analysis to the waveform cross correlation output to identify similar event clusters we re locate earthquakes within each similar event cluster by using the differential times alone keeping the cluster centroid fixed to its initial ssst location we estimate standard errors for the relative locations from the internal consistency of differential locations between individual event pairs these errors are often as small as tens of meters in many cases the relocated events within each similar event cluster align in planar features suggestive of faults we observe a surprising number of such faults at small scales that strike nearly perpendicular to the main seismicity trends in general the fine scale details of the seismicity reveal a great deal of structural com plexity in southern california fault systems

arctic ice dynamics joint experiment aidjex assumptions revisited and found inadequate 1 this paper revisits the arctic ice dynamics joint experiment aidjex assumptions about pack ice behavior with an eye to modeling sea ice dynamics the aidjex assumptions were that 1 enough leads were present in a 100 km by 100 km region to make the ice isotropic on that scale 2 the ice had no tensile strength and 3 the ice behavior could be approximated by an isotropic yield surface these assumptions were made during the development of the aidjex model in the 1970s and are now found inadequate the assumptions were made in part because of insufficient large scale 10 km deformation and stress data and in part because of computer capability limitations upon reviewing deformation and stress data it is clear that a model including deformation on discontinuities and an anisotropic failure surface with tension would better describe the behavior of pack ice a model based on these assumptions is needed to represent the deformation and stress in pack ice on scales from 10 to 100 km and would need to explicitly resolve discontinuities such a model would require a different class of metrics to validate discontinuities against observations

long term earthquake clustering summary we analyse statistically the long term properties of several instrumental earthquake catalogues complete catalogues exhibit both short and long term clustering for earthquakes of all depth ranges after accounting for the effect of short term clustering we find that in residual declustered catalogues long term clustering not periodicity characterizes the occurrence of all earthquakes shallow intermediate and deep the degree of clustering in residual catalogues is the same for earthquakes in different depth ranges circumstantial evidence indicates that the long term v ariation of seismicity is governed by a power law temporal distribution as in short term clustering it is scale invariant the fractal dimension of an earthquake set on the time axis is of the order of 0 8 0 9 therefore mainshock occurrence is closer to a stationary poisson process than standard aftershock sequences of shallow earthquakes

stress variability and brittle tectonic structures the problem of stress variability both in space and time during brittle deformation of rocks is faced in this note several possible causes of the temporal and spatial variations of the stress tensor are reviewed and discussed a genetic partitioning of the stress tensor is proposed showing that any stress field within a crustal volume can be seen as the sum of relatively simple stress tensors associated to specific genetic components the genetic components discussed in this note are the gravitational the tectonic the fluid the thermal and the diagenetic one each genetic component is a function of several parameters but for all of them the possible important role played by the variable time is emphasised according to numerous researches based on theoretical and experimental grounds brittle deformation in a rock mass occurs when some critical conditions are reached starting from initial equilibrium conditions and leading to even different stress conditions as a consequence of failure field examples are presented and data from literature are discussed to exhibit evidences from complex tectonic structures and to argue about small and large scale spatial variations as well as about short and long term temporal variations of the stress trajectories and of the stress magnitudes that continuously occur during a brittle deformational event the relationships between local and temporal stress variations and what is commonly defined the regional stress field are discussed adding recommendations for future researches

characterization of stress perturbations near major fault zones insights from 2 d distinct element numerical modelling and field studies jura mountains abstract we consider and discuss the presence of discontinuities in the crust as a major source of stress perturbations based on 2 d distinct element modelling we reconstruct the local stress field around a vertical discontinuity in various geological contexts the resulting stress distribution reveals that major directional stress changes occur near the tips of the discontinuity so that stress deviations can reach values as large as 50 we establish simple relationships controlling stress changes around a pre existing fault zone as a function of 1 the remote differential stress magnitude 1 3 2 the friction coefficient on the discontinuity and 3 the strike of the discontinuity relative to the far field stress as a geological example we present the morez fault zone in the internal jura paleostress reconstruction in forty two sites indicates that the trends of the mio pliocene compression are n110 on average near the fault whereas they are n130 in the surrounding areas a comparison between the results of the tectonic study and those of theoretical modelling suggests that the 20 counterclockwise deviation is directly related to the reactivation of this large weak zone we thus evaluate the role of mechanical decoupling along pre existing zones of weakness especially with consideration to the accommodation of the alpine deformation in the jura belt

edge wave observation using remote seismoacoustic sensing of ice events in the arctic as part of the office of naval research sea ice mechanics initiative a real time monitoring and processing program for acoustic emission from ice fracture and ridge building events was established a wide aperture horizontal hydrophone array was used in combination with a vertical line array to record the acoustic signals which were then passed through a focused beam former for real time generation of ice seismicity maps a number of rapidly deployable geophone arrays were used in active zones to measure the acoustic emissions in the near field for detailed seismic event analysis during one such deployment a highly regular transient arrival structure was recorded on all sensors located near a major lead with a transient appearing every 5 s these data have been processed using frequency wavenumber analysis to show that the transients correspond to edge waves propagating forth and back along the edges of the lead with the probable source being a stick slip mechanical phenomenon toward the ends of the lead

compressive shear faults within arctic sea ice fracture on scales large and small 1 we examined fracture features within arctic sea ice as revealed by landsat 7 and radarsat imagery by an aerial survey and through observations in the laboratory of specimens loaded to brittle failure under biaxial compression regardless of scale which spans the range from kilometers to millimeters the features look alike they consist mainly of narrow lineaments that traverse the field of view plus wing like and comb like secondary cracks the lineaments occasionally intersect and generally exhibit either right lateral or left lateral relative movement like strike slip faults within earth s crust we term them brittle compressive shear faults they form through the linking of en echelon arrays of deformation induced secondary cracks from an application of wing crack and comb crack mechanics we estimated the maximum compressive stress near the onset of faulting and found that our estimates compare favorably with in situ measurements by earlier investigators of ice sheet failure stresses to account for the brittle behavior of the sea ice cover we applied a recent model of the ductile to brittle transition in which the key idea is the competition between stress buildup and stress relaxation at stress concentrators in identifying the nature of sea ice fracture features we advance the view that failure occurs on many scales through highly localized as opposed to uniformly distributed deformation via the operation of scale independent mechanisms

spatial and temporal variation of palaeoseismic activity at an intraplate historically quiescent structure the concud fault iberian chain spain abstract several faults in the teruel and jiloca grabens iberian chain ne spain particularly the targeted concud fault show evidences of recent continuous activity despite their scarce instrumental and historic seismic record three trenches are studied in two locations central and southeastern sectors of the concud fault respectively after comparing with previous works we reconstruct a palaeoseismic succession with nine events distributed along a maximum time lapse bracketed between 81 6 and 14 0 ka this succession involves an average recurrence interval of 7 4 2 8 ka with individual interseismic periods between 4 and 11 ka the calculated coseismic displacements range from 0 6 to 2 7 m with an average value of 1 9 m that results in a slip rate of 0 26 mm a due to the incomplete sedimentary record for holocene times we cannot affirm that the youngest event detected was actually the last one we conjecture that some other events may have occurred during the period between 15 0 and 3 4 ka temporal and spatial variations have been detected in palaeoseismic activity specifically in the distribution of coseismic displacements first a non steady slip rate is evidenced during plio pleistocene times a long term tendency towards increasing slip rate is modulated in detail by the occurrence of minor cycles as the sequence of increasing decreasing activity recorded within the studied time window suggests secondly an asymmetric distribution of coseismic slip along the fault trace is observed paralleling the distribution of total fault throw which shows an absolute maximum close to the southeastern tip a combination of factors is proposed to explain this branching of the main fault dominant remote stress driven slip towards n 220 e on the nw se fault segment guided movement on the passive nnw sse segment giving rise to an oblique roll over monocline and decoupling of the hanging wall block owing to the transverse los mansuetos valdecebro fault zone

paleoseismological analysis of an intraplate extensional structure the concud fault iberian chain eastern spain the concud fault is a 13 5 km long nw se striking normal fault at the eastern iberian chain its recent late pleistocene slip history is characterized from mapping and trench analysis and discussed in the context of the accretion incision history of the alfambra river the fault has been active since late pliocene times with slip rates ranging from 0 07 to 0 33 mm year that are consistent with its present day geomorphologic expression the most likely empirical correlation suggests that the associated paleoseisms have potential magnitudes close to 6 8 coseismic displacements of 2 0 m and recurrence intervals from 6 1 to 28 9 ka at least six paleoseismic events have been identified between 113 and 32 ka the first three events u to w involved displacement along the major fault plane the last three events x to z encompassed downthrow and hanging wall synthetic bending prompting fissure opening this change is accompanied by a decrease in slip rate from 0 63 to 0 08 0 17 mm year and has been attributed to activation of a synthetic blind fault at the hanging wall the average coseismic displacement 1 9 2 0 m and recurrence period 6 7 7 9 ka inferred from this paleoseismic succession are within the ranges predicted from empirical correlation such paleoseismic activity contrasts with the moderate present day seismicity of the area maximum instrumental mb 4 4 which can be explained by the long recurrence interval that characterizes intraplate regions

scaling properties of sea ice deformation from buoy dispersion analysis 1 a temporal and spatial scaling analysis of arctic sea ice deformation is performed over timescales from 3 h to 3 months and over spatial scales from 300 m to 300 km the deformation is derived from the dispersion of pairs of drifting buoys using the iabp international arctic buoy program buoy data sets this study characterizes the deformation of a very large solid plate the arctic sea ice cover stressed by heterogeneous forcing terms like winds and ocean currents it shows that the sea ice deformation rate depends on the scales of observation following specific space and time scaling laws these scaling properties share similarities with those observed for turbulent fluids especially for the ocean and the atmosphere however in our case the time scaling exponent depends on the spatial scale and the spatial exponent on the temporal scale which implies a time space coupling an analysis of the exponent values shows that arctic sea ice deformation is very heterogeneous and intermittent whatever the scales i e it cannot be considered as viscous like even at very large time and or spatial scales instead it suggests a deformation accommodated by a multiscale fracturing faulting processes

a stress inversion method requiring only fault slip sense in numerous cases the use of standard methods of palaeostress inversion from fault slip data is prevented by the absence of structures that indicate the direction of slip on the fault in such instances however the offset of planar markers such as beds matched in the footwall and hanging wall often allows the sense of dip separation normal or reverse to be observed where such displaced markers are horizontal or at least where their cut off lines are horizontal it can be readily demonstrated that the sense of the dip slip component of net slip is the same as the sense of dip separation ways are explored for characterizing the stress tensor from data consisting of the orientations of a collection of faults each with known dip slip sense normal or reverse on the basis of properties of the stress quadric the relationship between dip slip sense fault plane orientation and the stress tensor is discovered this relationship is used as the basis of a grid search method of stress inversion in which a large number of stress tensors differing in orientation and shape are systematically considered those tensors that successfully explain the senses of offset on the observed faults are considered potential solutions to the palaeostress problem examples of different applications of the new stress inversion method are described including the analysis of fault data from boreholes these examples illustrate the way the new method potentially broadens the scope of palaeostress analysis

arctic sea ice leads from advanced very high resolution radiometer images a large number of advanced very high resolution radiometer avhrr images from throughout 1989 are analyzed to determine lead characteristics the units of analysis are square 200 km cells and there are 270 such cells in the data set clouds are masked manually leads are determined from images of the potential open water a scaled version of the surface temperature or albedo that weights thin ice by its thermal or brightness impact the lead fraction is determined as the mean the monthly mean lead fraction ranges from 0 02 in winter to 0 06 in summer in the central arctic and is near 0 08 in the winter in the peripheral seas a method of accounting for lead width sampling errors due to the finite sample areas is introduced in the central arctic the observed mean lead width for a threshold of 0 1 ranges from 2 or 3 km near the resolution of the instrument in the winter to 6 km in the summer in the peripheral seas it is about 5 km in the winter width distributions are often more heavily weighted in the tail than exponential distributions and are well approximated by a power law the along track number density power law n aw b has a mean exponent of b 1 60 standard deviation 0 18 and shows some seasonal variability mean floe widths in the central arctic are 40 to 50 km in the winter dropping to about 10 km in the summer for floes the power law has a mean exponent of 0 93 and exhibits a clearer annual cycle lead orientation is determined with a method based on the direction of maximum extent

aeolian construction and alluvial dismantling of a fault bounded intracontinental aeolian dune field teruel basin spain a continental perspective on late pliocene climate change and variability an aeolian dune field migrating to the east encroached on the toes of alluvial fans in the teruel basin eastern spain during a short interval in the late pliocene ca 2 9 to 2 6 ma when northern hemisphere glaciation and strong glacial interglacial cycles began preservation of the dune field was controlled by syn sedimentary activity of a normal fault ephemeral water discharge eroded aeolian sands and formed v shaped channels in which aeolian sandstone blocks accumulated the incorporation of loose aeolian sand in wadi waters modified the sediment water ratio changing the physical properties of the flows as they penetrated the aeolian dune field the erosion and cover of aeolian dune foresets by sheetflood deposits suggest that dune damming caused the intermittent ponding of water behind the dunes and its flashy release the arid climate in the late pliocene western mediterranean realm favoured the transport of windblown sediments from northern africa and western mediterranean land masses into the mediterranean the formation of the studied aeolian dune field 2 9 to 2 6 ma and possibly others for example the atacama namib and sahara deserts correlates with a strong increase of the influence of obliquity which can be attributed to the combination of a regional expression related to the reduced effect of precession due to a minimum in the long period 2 3 ma eccentricity cycle and a remote expression of the onset of the northern hemisphere glaciation

small scale sea ice deformation during n ice2015 from compact pack ice to marginal ice zone we studied small scale 50 m to 5 km sea ice deformation from ship radar images recorded during the n ice2015 campaign the campaign consisted of 4 consecutive drifting ice stations floes 1 to 4 north of svalbard with a total duration of nearly 5 months deformation was calculated using 5 different time intervals from 10 min to 24 h and the deformation rate was found to depend strongly on the time scale floes 1 to 3 had a mean deformation rate within the range of 0 06 to 0 07 h 1 with the interval of 10 min and 0 03 to 0 04 h 1 with the interval of 1 h floe 4 represented marginal ice zone miz with very high deformation rate 0 14 0 08 h 1 with the interval of 10 min 1 h deep in the ice pack high deformation rates occurred only with high wind and drift speed while in miz they were found also during calm conditions the deformation rates were found to follow power law scaling with respect to length and time scale even on this small scales and in small domain 15 km 15 km the length scale dependence of deformation rate depends on the time scale the power law scaling exponent of the whole study period decreases from 0 82 to 0 52 with the time interval increasing from 10 min to 24 h ship radar images reveal the importance of the deformation history of the ice pack since the deformation events were initialized along the lines of previous damages

neogene quaternary tectonic stratigraphy of the eastern southern alps ne italy abstract in order to reconstruct the neogene quaternary tectonic stratigraphy of the eastern southern alps the late tortonian lower pleistocene foredeep clastic sequences cropping out in the veneto and friuli piedmont areas have been extensively investigated focusing on the contractional features observed in the frequent conglomerate layers pitted pebbles the eastern southern alps is the result of a typical polyphase tectonic activity initiated in late oligocene characterised by the occurrence of several non coaxial stress regimes based on careful analyses of the pebbles surfaces shape and orientation of the indented features and following a systematic and statistical approach the mean orientation of the maximum compressive stress axis 1 has been obtained for more than 30 sites of measurements along the ca 120 km long investigated piedmont area the affected lithostratigraphic units and the orientation pre versus post tilting of the stereonets density peaks make it possible to recognize four distinct deformational events and characterize them in terms of mean 1 direction and timing late tortonian 1 313 00 late messinian early pliocene 338 04 late pliocene 314 03 and early middle pleistocene 160 03 the tectonic stratigraphy of the eastern southern alps during the last ca 10 ma shows the occurrence of several variations of the stress field characterized by a repeated oscillation of the 1 axis between an nnw sse and nw se directions twist tectonics taking also into account literature data about older deformational events chattian burdigalian and serravallian tortonian we analyse the neogene quaternary tectonic evolution in the frame of the central mediterranean realm and compare it with the convergence direction between the adria africa and europe lithospheric plates we show that compressional directions within the eastern southern alps are basically governed by the remote plate convergence though since late messinian the approaching northern apennines started to play a crucial role within the investigated area alternating short lived phases 1 2 ma of coupling and decoupling along the basal detachment of the apennines accretionary wedge probably caused temporary perturbations of the local stress field and complex accommodation structures in this region of ongoing crustal collision

one slope or two detecting statistically significant breaks of slope in geophysical data with application to fracture scaling relationships the scaling of displacement as a function of length is important for a variety of applications which depend on the mechanical and hydraulic properties of faults and fractures recently it has been suggested that the power law exponent which has been found to characterise this relationship may change significantly at a characteristic length for a variety of reasons for example when cracks begin to interact or when faults grow to a length comparable to a characteristic size in the brittle layer such a break of slope requires a second straight line requiring two extra model parameters here we present a new method for analysing such data which penalises the extra parameters using a modified form of schwarz s information criterion and a bayesian approach which represents uncertainty in the unknown parameters we apply the method to data from the krafla fissure zone in the north of iceland and find a significant break of slope from 3 2 to 2 3 at a characteristic length of 12m

the recent upper miocene to quaternary and present tectonic stress distributions in the iberian peninsula a general synthesis of the recent and present stress situation and evolution in the iberian peninsula was obtained from microstructural and seismological analysis the stress evolution was deduced from 1 fault population analysis fpa from 409 sites distributed throughout the iberian peninsula 2 paleostress indicators given by 324 stations taken from the bibliography and 3 seismic data corresponding to 161 focal mechanisms evenly spread in the studied region the application of fpa together with the determination of stress tensors and focal mechanisms for the whole iberian microplate has provided two main results 1 the iberian peninsula is undergoing a nw se oriented compression except for the northeastern part pyrenees ebro basin and iberian chain where it is n s to ne sw and the gulf of cadiz where it seems to be e w and 2 the main trends of the stress field have remained almost constant since the upper miocene the analysis performed by zones suggests the presence of local heterogeneities in the stress field

palustrine sedimentation in an episodically subsiding basin the miocene of the northern teruel graben spain lacustrine deposits form most of the sedimentary record accumulated throughout the miocene in the northern part of the teruel graben a landlocked basin situated in ne spain three main stratigraphic units units i iii spanning late vallesian to late turolian in age are distinguished in the area the two former units comprise mainly carbonate lacustrine deposits that were deposited in a palustrine or a more permanent but shallow lacustrine setting the latter being related mainly to periods of lake expansion under more humid and cooler climatic conditions in contrast deposition of unit iii characterised by gypsiferous lacustrine sediments in central parts of the basin reflects the influence of source rocks of evaporitic nature upper triassic formations that were emplaced by diapiric uplift in the eastern margin during the middle turolian carbonate lake sediments belonging to units i and ii consist of four main lithofacies associations a distal alluvial lake margin deposits b lacustrine carbonates and pedogenically modified lacustrine carbonates c carbonate fill channels and d organic rich marlstone and carbonate marshes lithofacies association a shows typically a sequential arrangement formed from bottom to top of red mudstone carbonate palaeosols and biomicrite beds sequence type 1a these sequences are interpreted as a result of slow but continuous aggradation of the floodplain areas and subsequent rise of the water table probably reflecting equilibrium between subsidence and sedimentation lithofacies association b consisting of biomicrite beds passing upward into palaeosols sequence type 1b is thought to be caused by marked pulses of tectonic subsidence that created the accommodation space required for fast development of a carbonate lake carbonate fill channels showing erosive lower surfaces dig out on previous channels marsh deposits and or lacustrine carbonates exhibit well developed prismatic structure at their bed tops the sequential arrangement suggests similar tectonic constrains than the envisaged for lithofacies 1b the comparison of depositional styles of the lake systems with the palaeoclimatic evolutionary pattern of the basin throughout the miocene indicates that the combined effect of tectonism climate and source rock played a major role in the stratigraphic framework of the basin during this period

mantle structure and dynamic topography in the mediterranean basin 1 we study the contribution of mantle flow to surface deformation within the mediterranean basin flow is modeled numerically based on lateral changes in mantle temperature estimated from tomography models we find that modeling results are significantly affected by the properties of the selected tomography models shear velocity models based on surface wave observations achieve the highest resolution of upper mantle structure and as a result are most successful in predicting microplate motion and dynamic topography

sea ice rheology from in situ satellite and laboratory observations fracture and friction on the basis of an analysis of in situ ice stresses and of satellite derived ice strain rates as well as of a comparison between field and laboratory behaviour we describe an alternative viewpoint for modelling sea ice deformation during winter we propose that fracture and frictional sliding govern inelastic deformation over all spatial and temporal scales even under small stresses consequently winter and or perennial sea ice does not behave as a viscous material even at large scales the normal flow rule is not obeyed as observed during laboratory tests on sea ice samples harvested from the field and stresses are highly intermittent and poorly correlated spatially

extending earthquakes reach through cascading earthquakes whatever their size can trigger other earthquakes mainshocks cause aftershocks to occur which in turn activate their own local aftershock sequences resulting in a cascade of triggering that extends the reach of the initial mainshock a long lasting difficulty is to determine which earthquakes are connected either directly or indirectly here we show that this causal structure can be found probabilistically with no a priori model nor parameterization large regional earthquakes are found to have a short direct influence in comparison to the overall aftershock sequence duration relative to these large mainshocks small earthquakes collectively have a greater effect on triggering hence cascade triggering is a key component in earthquake interactions

late cenozoic stress field and fracturing in the iberian chain and ebro basin spain detailed study of mesoscopic faults and joints affecting neogene and pleistocene deposits in the iberian chain and the ebro basin involving statistical study of fracture directions and palaeostress analysis from striated fault planes together with analysis of macrostructures suggest a complex late cenozoic stress field in which both primary and secondary stress systems are superposed 1 regional n s compression was caused by convergence between the iberian and african plates 2 multidirectional extension was caused by crustal doming in the iberian chain 3 stress trajectories were deflected near major faults 4 small scale swapping of the horizontal tension axes 2 and 3 was caused by development of fractures at right angles to either the primary or the deflected 3 axis

ice the paradigm of wild plasticity ice plasticity has been thoroughly studied owing to its importance in glaciers and ice sheets dynamics in particular its anisotropy easy basal slip has been suspected for a long time then fully characterized 40 years ago more recently emerged the interest of ice as a model material to study some fundamental aspects of crystalline plasticity an example is the nature of plastic fluctuations and collective dislocation dynamics twenty years ago acoustic emission measurements performed during the deformation of ice single crystals revealed that plastic flow proceeds through intermittent dislocation avalanches power law distributed in size and energy this means that most of ice plasticity takes place through few very large avalanches thus qualifying associated plastic fluctuations as wild this launched an intense research activity on plastic intermittency in the material science community the interest of ice in this debate is reviewed from a comparison with other crystalline materials in this context ice appears as an extreme case of plastic intermittency characterized by scale free fluctuations complex space and time correlations as well as avalanche triggering in other words ice can be considered as the paradigm of wild plasticity

sea ice tracking by nested correlations spatial differences in sea ice displacement affect ice stress ice production and the mass balance of the ice cover our concepts about the spatial structure of this field have been undernourished because of a paucity of data with high spatial detail and because of the tedium of extracting such measurements from images manually a method is described that measures displacements from synthetic aperture radar digital imagery with fine spatial resolution and does so fully automatically many small areas of ice common to two images are identified by correlating the two images the strategy is to acquire a crude displacement field first from highly averaged images and to refine this field with images of successively higher resolution the median discrepancy between automatically and manually measured displacements is three pixels 0 075 km the algorithm operates successfully on compact ice with large floes and modest rotation rates we believe it will prove applicable to most of the arctic ice cover throughout the year