evidence for postseismic viscoelastic relaxation following the 1959 m 7 5 hebgen lake montana earthquake a 1983 releveling survey conducted by the national geodetic survey combined with previous surveys in 1923 1960 1967 and 1975 provides evidence for ongoing vertical deformation of a broad region diameter of 150 km surrounding the site of the 1959 hebgen lake earthquake deformation consists of relative uplift centered roughly on the coseismic fault and a smaller amplitude zone of relative subsidence south of the fault maximum observed elevation change during the postseismic period 1960 1983 exceeds 30 cm assuming that the entire uplift i e 1923 1983 occurred following the 1959 earthquake i e uplift measured between 1923 and 1960 was entirely postseismic the rate of vertical deformation appears to have decreased exponentially with a characteristic decay time of about 10 years the spatial pattern and time behavior of the observed movements are consistent with simple models of postseismic deformation following normal faulting in an elastic layer thickness of 30 40 km overlying a viscoelastic half space viscosity of 1019 pa s this model may also account for the anomalously large horizontal strain around the hebgen lake region measured by repeated trilateration surveys during the period 1973 1984 the releveling measurements in the hebgen lake region appear to provide the first observations of viscoelastic relaxation in the asthenosphere following an intraplate earthquake in the united states

fault related folding near the wind river thrust wyoming usa reflection profiles across the wind river uplift in wyoming usa show that folding of basement rocks occurs in the footwall of the main fault at depths between 6 and 10km it is shown using elastic modelling that these features are a consequence of uneven fault slippage slip on the fault must be greater at depths between 3 and 18 km but reduced outside this range this is the depth range of catastrophic rupture associated with earthquakes in the continental crust

late eocene southern ocean cooling and invigoration of circulation preconditioned antarctica for full scale glaciation during the eocene oligocene transition eot 34 33 5 ma antarctic ice sheets relatively rapidly expanded leading to the first continent scale glaciation of the cenozoic declining atmospheric co2 concentrations and associated feedbacks have been invoked as underlying mechanisms but the role of the quasi coeval opening of southern ocean gateways tasman gateway and drake passage and resulting changes in ocean circulation is as yet poorly understood definitive field evidence from eot sedimentary successions from the antarctic margin and the southern ocean is lacking also because the few available sequences are often incomplete and poorly dated hampering detailed paleoceanographic and paleoclimatic analysis here we use organic dinoflagellate cysts dinocysts to date and correlate critical southern ocean eot successions we demonstrate that widespread winnowed glauconite rich lithological units were deposited ubiquitously and simultaneously in relatively shallow marine environments at various southern ocean localities starting in the late eocene 35 7 ma based on organic biomarker paleothermometry and quantitative dinocyst distribution patterns we analyze southern ocean paleoceanographic change across the eot we obtain strong indications for invigorated surface and bottom water circulation at sites affected by polar westward flowing wind driven currents including a westward flowing antarctic countercurrent starting at about 35 7 ma the mechanism for this oceanographic invigoration remains poorly understood the circum antarctic expression of the phenomenon suggests that rather than triggered by tectonic deepening of the tasman gateway progressive pre eot atmospheric cooling played an important role at localities affected by the antarctic countercurrent sea surface productivity increased and simultaneously circum antarctic surface waters cooled we surmise that combined these processes contributed to preconditioning the antarctic continent for glaciation

de glauconiarum origine the glauconitic facies is widespread on present day continental shelves from 50 s to 65 n and at water depths between 50 and 500 m and is in particularly great abundance on the upper slope and outer shelf between 200 and 300 m it is also common in many ancient rocks of post late precambrian age it occurs as sand to pebble sized essentially green particles granular facies but also as a surface coating on particles and hardgrounds and as a diffuse impregnation film and diffuse facies we suggest the replacement of the term glauconite which has been interchangeably used to designate a morphological form and a specific mineral by glaucony facies and glauconitic smectite and glauconitic mica as end members of the glauconitic mineral family the widely accepted model of burst and hower for glauconitization requires a degraded micaceous 2 1 layer lattice structure parent clay mineral however detailed analysis of numerous samples of recent glaucony reveals that such a parent substrate is exceptional the model therefore requires modification generally the parent material is carbonate particles argillaceous kaolinitic faecal pellets infillings of foraminiferal tests various mineral grains and rock fragments that pass gradually into the commonly occurring green grains we show that the process of glauconitization is achieved by de novo authigenic growth of automorphous crystallites in the pores of the substrate accompanied by progressive alteration and replacement of the substrate it is this two fold evolution that causes the verdissement of granular substrates macrofossils and hardgrounds the authigenic mineral is an iron rich and potassium poor glauconitic smectite while new smectites are growing into the remaining pore space the earlier smectites are modified by incorporation of potassium producing decreasingly expandable minerals with a non expandable glauconitic mica as the end member this mineralogical diversity of the glauconitic mineral family explains the highly variable physical and chemical properties of glaucony four categories nascent little evolved evolved and highly evolved glaucony are distinguished glauconitization appears to be controlled by a delicate balance between degree of physical confinement of a particle and the amount of ionic exchange between the micro environment and ambient open marine sea water the optimum conditions for glauconitization are those of semi confinement as a result the interior of a grain is more glauconitized than its less confined periphery similarly for identical substrate types large grains 500 m provide more favourable substrates for glauconitization than lesser confined small grains on a larger scale the formation of glaucony is governed by the availability of iron and potassium and the balance between detrital influx and winnowing low accumulation rates expose grains to the open marine environment for sufficiently long times 105 106 years for highly evolved glaucony

glaucony and sequence stratigraphy a conceptual framework of distribution in siliciclastic sequences abstract detailed analysis of recent literature on glaucony and selected case studies eocene isle of wight miocene northern apennines shows that the presence of glaucony alone is not diagnostic of a specific systems tract of a depositional sequence a reliable sequence stratigraphic interpretation of glaucony bearing units requires additional information on glaucony including 1 spatial distribution 2 maturity distinction between nascent slightly evolved evolved and highly evolved glaucony and 3 genetic attributes differentiation of autochtonous from allochthonous and intrasequential from extrasequential glaucony autochthonous glaucony is common at various stratigraphic levels in the transgressive systems tract tst and the lower highstand systems tract hst showing an upward increase tst and then decrease hst in abundance and maturity the condensed section can be distinguished from the overlying and underlying deposits by the higher concentration and maturity of glaucony allochthonous intrasequential parautochthonous glaucony can be present in the entire tst hst and lowstand systems tract lst generally showing lower concentration and maturity than its autochthonous counterpart allochthonous extrasequential detrital glaucony is present mainly in the lst its concentration and composition depending on the characteristics of the source horizon the associa ion between autochthonous and allochthonous intrasequential and extrasequential glaucony commonly exists in the lst and in the lower tst

seismic potential revealed by surface folding 1983 coalinga california earthquake the 2 may 1983 coalinga california earthquake magnitude 6 5 failed to rupture through surface deposits and instead elastically folded the top few kilometers of the crust the subsurface rate of fault slip and the earthquake repeat time are estimated from seismic geodetic and geologic data three larger earthquakes up to magnitude 7 5 during the past 20 years are also shown to have struck on reverse faults concealed beneath active folds

imaging topographic growth by long lived postseismic afterslip at sefidabeh east iran this paper describes observations and models of the postseismic deformation following the 1994 sefidabeh earthquake sequence in east iran which shed light on the nature of the earthquake cycle and the mechanisms of topographic growth in the region interferometric synthetic aperture radar observations show creeping fault motion postseismic afterslip on an array of faults some of these faults probably represent the extensions of those that ruptured in the blind thrust faulting earthquakes in 1994 and cut through the entire seismogenic layer while others are shallow and break up the hanging walls of the coseismic faults the postseismic slip accommodates at least part of the vertical displacement gradient resulting from the buried coseismic slip which was concentrated at depths of greater than 5 km the postseismic afterslip is visible for over 16 years following the earthquakes agreement between the areas of postseismic uplift and indications of long term motion preserved in the geomorphology suggest that shallow fault slip during seismic cycles similar to the one we have observed governs the development of the landscape in the region slip on an array of shallow faults provides a mechanism for the development of short wavelength topography and geological structures above active thrust faults and has important implications for the interpretation of shallow geological features produced in regions experiencing similar seismic cycles to that at sefidabeh

the glauconite fe illite fe smectite problem a critical review iron silicate minerals are a significant component of sedimentary systems but their modes of formation remain controversial our analysis of published data identifies end member compositions and mixtures and allows us to recognize controls of formation of different mineral species the compositional fields of glaucony fe illite fe al smectites are determined in the m 4si vs fe sum of octahedral cations m interlayer charge solid solutions could exist between these phases the fe al and fe rich clay minerals form two distinct solid solutions the earliest phases to be formed are fe al smectites or berthierine depending on the sedimentation rate reductive microsystems appear in the vicinity of organic debris in unconsolidated sediments the fe is incorporated first in pyrite and then in silicates after oxidation potassium ions diffuse from the sea water sediment interface if not interrupted the diffusion process is active until reaction completion is reached i e formation of fe illite or glauconite or a mineral assemblage berthierine nontronite according to the available al ion amounts in the microsystem mixed layer minerals are formed when the diffusion process is interrupted because of sedimentation compaction or cementation despite the common belief of their value as palaeoenvironment indicators these minerals can form in a variety of environments and over a period of millions of years during sediment burial

three dimensional normal faulting models of the valles marineris mars and geodynamic implications inversion of martian topography using a three dimensional boundary element model permits revised estimates of fault dip angle depth of faulting paleogeothermal gradient and extensional strain in the valles marineris region the major normal faults dip at 40 55 to depths of 60 75 km with comparatively small footwall uplifts 500 m for throws to 10 km implying that paleogeothermal gradients during faulting were 10 k km 1 or less assuming relatively rapid strain rates appropriate to the extending martian crust accumulation of dip slip offsets along the main normal faults likely was associated with anticlinal flexure and deformation of preexisting strata within the troughs the magnitudes of the predicted vertical and horizontal displacements outside the troughs as well as extensional strains are spatially variable depending on both cross and along strike position relative to the troughs the predicted displacements and strains attain maximum values at the troughs and decay to background values at cross strike distances of 250 km corresponding to 3 4 times the depth of faulting with an average province wide strain of 4 15 by implication the aggregate strain field surrounding tharsis is a highly variable spatial and temporal composite of the inhomogeneous strain fields each associated and scaling in size with an individual graben from the smallest structures through the largest valles marineris troughs

effects of rigidity layering gravity and stress relaxation on 3 d subsurface fault displacement fields summary elastic dislocation theory has been modified to determine 3 d subsurface displacements for faults in a three layer elastic gravitational medium a new set of kernel functions for fourier bessel integrals describing subsurface displacements have been derived using the thomson haskell propagator matrix technique and has been used to investigate the effect of layering and gravity on subsurface displacement fields within our three layer model layer 1 may be used to represent the seismogenic upper crust layer 2 the ductile lower crust and layer 3 the ductile mantle for a point source within the upper layer lower layer rigidity moduli control the amplitude and wavelength of displacements within the upper layer and the relative distribution of uplift and subsidence within foot and hanging wall displacement variations due to lower layer rigidity moduli changes increase with depth and are profound at the base of the upper layer and within the lower layers high rigidity moduli lower layers attenuate the upper layer displacement field while a decrease gives amplification the effect of gravity on the subsurface displacement field is more pronounced when the rigidity of the lower layers is small the elastic gravitational dislocation model has been used to examine co seismic and post seismic components of surface and subsurface displacement during extension of continental lithosphere the model predicts surface co seismic footwall uplift and hanging wall subsidence the co seismic subsidence being greater than the uplift post seismic relaxation of stress within the lower crust and mantle by post seismic ductile deformation gives an increase in footwall uplift and a decrease in maximum hanging wall subsidence within the upper layer a decrease in upper layer rigidity due to post seismic brittle or plastic deformation within the upper crust leads to a decrease in the wavelength of surface footwall uplift and hanging wall subsidence the elastic gravitational dislocation model has also been used to investigate the development of moho topography during continental extension co seismically moho under footwall is predicted to uplift while that under hanging wall subsides but by a smaller magnitude during post seismic relaxation moho topography is predicted at first to increase in magnitude and then to decay the existence of preserved moho topography uplift associated with old continental rifts implies a finite long term ductile strength within the lower crust and mantle

crustal structure off norway 62 to 70 north abstract extensive geophysical surveys have been undertaken on the volcanic passive continental margin offshore norway between 62 and 70 n during the last 25 years three main margin segments have been identified the lofoten vesteralen margin the voring margin and the more margin the main features of the margins are prominent marginal highs including seaward dipping reflector sequences and an up to 22 km thick volcanic and transitional crust prominent escarpments the voring plateau escarpment and the faeroe shetland escarpment and up to 12 km deep post jurassic sedimentary basins east of the escarpments velocity depth solutions from about 250 sonobuoys expanding spread profiles and refraction profiles have been compiled and contoured isovelocity horizon contour maps and velocity transects outline a crust which broadly thickens from an oceanic crust with a normal oceanic type velocity structure to a ca 35 km thick continental crust with a continental velocity structure beneath the norwegian coast anomalous features include local crustal thickening below the more and vering marginal highs and high velocity bodies in the lower crust in the extension of the precambrian lofoten vesteralen archipelago the free air seasat derived gravity anomalies show a good correlation with the high velocity bodies and show prominent ne trending highs from the rockall plateau porcupine plateau region over the more voring and lofoten vesteralen margins to the southwestern barents sea

a crustal study off lofoten n norway by use of 3 component ocean bottom seismographs abstract twenty four 3 component ocean bottom seismographs obs were used in august 1988 in a combined seismic refraction and reflection study off lofoten n norway the purpose of the experiment was to map the crustal structure from the continental shelf to the oceanic crust off lofoten the very high data quality is demonstrated by the strong p wave and shear wave reflections as well as converted waves from the moho observed on the continental shelf these arrivals are observed continuously from near vertical to wide angle incidence very high seismic sea floor velocities in this area 3 1 km s to 5 1 km s indicates absence or very thin sequences of mesozoic sediments the 5 1 km s refractor coincides with the base cretaceous reflection interpreted from the multichannel reflection data the crystalline continental crust is here divided in layers with velocities of 6 0 km s 6 4 km s and 6 8 km s respectively on the seaward side of the escarpment tertiary sediments varying in thickness from 1 0 1 5 km are situated on top of a 1 5 2 0 km thick layer of flood basalt containing seaward dipping reflectors a layer with velocity of 6 7 km s is observed above the lower crust which in this area is found to have a velocity as high as 7 3 km s these high velocities indicate that the crust in this area is of oceanic origin or alternatively the high velocity layer in the lower crust might represent a magmatic body underplating highly thinned and intruded continental crust seven obss were deployed in the area that was covered by landward flowing basalt deposited during the early eocene breakup between norway and greenland the survey was partly performed to investigate whether this method can be used to map structures below the basalt which is impenetrable with conventional seismic reflection techniques the obs data contain considerable information about structures below the flood basalt pre opening sediments up to 4 0 km thick are indicated below the 1 0 2 5 km thick landward flowing basalt the velocities of the crystalline portion of the crust are found to be similar to those observed under the continental shelf 6 0 6 8 km s which implies that the crust east of the escarpment is of continental origin the crystalline crust is strongly thinned in this area showing a minimum thickness of about 6 km the depth to the moho increases from about 15 km in the western part of the area to about 26 km on the continental shelf the success of the obs survey indicates that such measurements can become an important tool in investigations on passive volcanic margins and potentially in other areas where highly reflective surfaces make the reflection technique inefficient

causes and consequences of variations in faulting style at the mid atlantic ridge both volcanism and faulting contribute to the rugged topography that is created at the mid atlantic ridge mar and preserved off axis in atlantic abyssal hill terrain distinguishing volcanic from fault generated topography is essential to understanding the variations in these processes and how these variations are affected by the three dimensional pattern of mantle upwelling ridge segmentation and offsets here we describe a new quantitative method for identifying fault generated topography in swath bathymetry data by measuring topographic curvature the curvature method can distinguish large normal faults from volcanic features whereas slope methods cannot because both faults and volcanic constructs can produce steep slopes the combination of curvature and slope information allows inward and outward facing fault faces to be mapped we apply the method to sea beam data collected along the mar between 28 and 29 30 n the fault styles mapped in this way are strongly correlated with their location within the ridge segmentation framework long linear small throw faults occur toward segment centers while shorter larger throw curved faults occur toward ends these variations reflect those of active faults within the axial valley we investigate two different physical mechanisms that could affect fault interactions and thus underlie variations in abyssal hill topography at the mar in the first model only one fault is active at a time on each side of the rift valley each fault grows while migrating away from the volcanic center due to dike injection extension across the fault causes a flexural rotation of nearby inactive faults the amount of stress necessary to displace the fault increases as the fault grows when reaching a critical size the fault stops growing as fault activity jumps inward as a new fault starts its growth near the rift valley this model yields a realistic terracelike morphology from the rift valley floor into the rift mountains the relief is caused by the net rotation accumulated in the lithosphere from the active faults e g 10 reached 20 km from the active fault fault spacing is controlled by lithospheric thickness fault angle and the ratio of amagmatic to magmatic extension we hypothesize that this mechanism may be dominant toward ridge segment offsets an alternative model considers multiple active faults each fault relieves stresses as it grows and inhibits the growth of nearby faults causing a characteristic fault spacing such fault interactions would occur in a region of necking instability involving deformation over an extended area this mode of extension would drive a feedback mechanism that would act to regulate the size of nearby faults we hypothesize that this mechanism may be active in the relatively weak regions of strong mantle upwelling near segment midpoints causing the homogeneous abyssal hill fabric in these regions

geodetic constraints to the kinematics of the kapareli fault reactivated during the 1981 gulf of corinth earthquakes abstract comparison of historical and of post seismic triangulation data is used to model vertical crustal movements in the vicinity of the kapareli fault or the alkynonides earthquakes north fault one of the two antithetic normal faults which reactivated during the 1981 gulf of corinth ms 6 7 earthquakes this fault is characterized by a much smaller geomorphological signature than the south or perachora fault of the same seismic sequence analysis of geodetic data on the basis of polynomial filtering and elastic dislocation modelling as well as analysis of structural and coastal change data permits us to conclude that the upper bound in the uncertainty level of most of the available elevation changes is 20 30 cm usually lower than the corresponding dislocation signal in addition the available geodetic data have a systematic pattern and are consistent with structural data for this reason they permit more precise constraints on the geometry and the role of the kapareli fault or the alkyonides earthquakes north fault its total length is estimated about 17 km about 50 longer than its surface trace about 30 40 cm subsidence of its hanging wall as well as at least 15 cm maximum uplift of its footwall is also inferred this new evidence suggests that although in the long term the kapareli fault may represent a rather secondary antithetic fault to the alkyonides earthquakes south perachora fault during the 1981 earthquakes it probably had a more important structural role

active faulting and seismicity along the siculo calabrian rift zone southern italy abstract southern italy is dominated by extensional tectonics that in the calabrian arc and eastern sicily produced the development of the siculo calabrian rift zone scrz this zone is represented by a 370 km long fault belt consisting of 10 to 50 km long distinct fault segments which extend both offshore and on land being also responsible of the crustal seismicity of this region the geological and morphological observations indicate that the active normal faults of the scrz are characterized by throw rates ranging from 0 7 to 3 1 mm a they accommodate an almost uniform horizontal extension rate of about 3 0 mm a along a wnw ese regional extension direction based on our field observations and following empirical relationships between magnitude and surface rupture length connections between large crustal earthquakes and distinct fault segments of the scrz have been also tentatively tested our data indicate moreover that the magnitudes m of the historical and instrumental earthquakes are consistent with the estimated values and that the geometry and kinematics of the fault segments and the related different crustal features of the scrz control the different seismic behaviours of adjacent portions of the active rift zone

viscoelastic gravitational deformation by a rectangular thrust fault in a layered earth previous papers in this series have been concerned with developing the numerical techniques required for the evaluation of vertical displacements which are the result of thrust faulting in a layered elastic gravitational earth model this paper extends these methods to the calculation of fully time dependent vertical surface deformation from a rectangular dipping thrust fault in an elastic gravitational layer over a viscoelastic gravitational half space the elastic gravitational solutions are used together with the correspondence principle of linear viscoelasticity to give the solution in the laplace transform domain the technique used here to invert the displacements into the time domain is the prony series technique wherein the transformed solution is fit to the transformed representation of a truncated series of decaying exponentials purely viscoelastic results obtained are checked against results found previously using a different inverse transform method and agreement is excellent the major advantage in using the prony series technique is that deformations can be computed for arbitrary time intervals a series of results are obtained for a rectangular 30 dipping thrust fault in an elastic gravitational layer over viscoelastic gravitational half space time dependent displacements are calculated out to 50 half space relaxation times a or 100 maxwell times 2 m a significant effects due to gravity are shown to exist in the solutions as early as several a the difference between the purely viscoelastic solution and the viscoelastic gravitational solutions grows as time progresses typically the solutions with gravity reach an equilibrium value after 10 20 relaxation times when the purely viscoelastic solutions are still changing significantly additionally the length scaling which was apparent in the purely viscoelastic problem breaks down in the viscoelastic gravitational problem two independent length scales one of which changes with time are now seen to characterize the problem

patterns and timing of late quaternary faulting in the great basin province and relation to some regional tectonic features large scale surface faulting events each tens of kilometers long and involving more than a meter of displacement of late quaternary age have not been uniformly distributed but have been concentrated in subprovincial and smaller belts and areas within the great basin province furthermore faulting apparently has not been uniformly distributed over time the average recurrence interval of large scale faulting events on individual faults in the province is measured in thousands or tens of thousands of years in contrast to such long recurrence intervals in the central nevada and eastern california seismic belts large scale faulting events have occurred during the last 111 years in an apparently coherent sequential belt filling pulse of activity in which events were separated by only a few years or a few decades the questions are where are other pulses of large scale faulting likely to occur and what controls the localization of such belts and areas characterized by higher rates of faulting two examples of tectonic subprovinces that may play a role in delimiting smaller zones of faulting are the black rock carson sink zone of extension and the central nevada downwarp the central nevada seismic belt lies along the dividing line between these two subprovinces and the northwest margin of the black rock carson sink zone of extension coincides with the margin of a fingerlike belt of dense faulting in northwestern nevada

lithospheric flexure and the evolution of sedimentary basins the sediments that have accumulated in sedimentary basins during geological time represent a load on the lithosphere that should respond by flexure simple elastic and viscoelastic maxwell plate models have been used to examine quantitatively the contribution of flexure to basin formation the models have been used to predict the stratigraphy and gravity anomalies associated with basins for different thermal and loading histories the predictions of the models have been compared with observed stratigraphy and free air gravity anomalies from interior and cratonic basins the best overall fit to the observations is for an elastic plate model in which the flexural strength of the lithosphere increases with age a similar model has recently been used successfully to explain observations from continental margin basins oceanic islands and seamounts and deep sea trench outer rise systems this model explains the increase in the overall width of basins during their evolution as well as the stratigraphy of the basin edges the apparent decrease in the widths of some basins through time can be explained by the model if sediment deposition is followed by erosion of the basin and its edges the models results suggest that the flexural properties of continental and oceanic lithosphere are generally similar and that flexure is an important factor to consider in backstripping studies in which the tectonic subsidence of a basin is isolated and stratigraphic studies in which relative changes of sea level are estimated

seismicity and tectonic deformation rate in soviet armenia implications for local earthquake hazard and evolution of adjacent regions the spitak armenia earthquake of december 7 1988 ms 6 7 mo 10 1018 nm was the largest this century in soviet transcaucasia in the northern part of the zone where the arabian and eurasian plates converge at 30 mm yr 1 field observations in its epicentral area and information from historical and recent earthquakes in and around armenia are used to determine shortening rates and hence to investigate how shortening is partitioned between the great caucasus armenia and other parts of soviet transcaucasia and eastern turkey and nw iran farther south this earthquake produced more than 20 km of surface faulting with up to 1 5 m reverse slip and 0 4 m right lateral slip on a fault with wnw strike and southward slip vector azimuth much of the local topography has formed by slip on faults with similar orientation there is no evidence of substantial recent folding elsewhere in armenia suggesting that shortening in armenia occurs mainly by slip on these faults shortening rate across armenia is 1 mm yr 1 at strain rate 2 10 16 s 1 with likely slip rate on each fault 0 2 mm yr 1 the local topography has formed in 1 myr shortening rate in the eastern great caucasus farther north can be estimated using quaternary uplift rate assuming uplift is caused by crustal thickening and occurs in isostatic equilibrium although quaternary uplift rates from 0 05 to 10 mm yr 1 have been previously suggested any rate above 1 mm yr 1 is too rapid to be explained by this process the remaining rates range from 0 05 to 0 2 mm yr 1 and imply 1 to 5 mm yr 1 local shortening rate suggesting overall shortening rate across the soviet part of the convergent zone is only 2 to 6 mm yr 1 historical seismicity suggests that at least 1 mm yr 1 of this shortening is coseismic most of the convergence between arabia and eurasia is thus taken up at present farther south in eastern turkey and nw iran along with probable substantial westward expulsion of crustal material and most of the topography and crustal thickness in the great caucasus probably already existed at least 10 myr ago

crustal deformation the earthquake cycle and models of viscoelastic flow in the asthenosphere summary the crustal deformation patterns associated with the earthquake cycle can depend strongly on the rheological properties of subcrustal material substantial deviations from the simple patterns for a uniformly elastic earth are expected when viscoelastic flow of subcrustal material is considered the detailed description of the deformation pattern and in particular the surface displacements displacement rates strains and strain rates depend on the structure and geometry of the material near the seismogenic zone in the past few years various viscoelastic models of crustal deformation have been published these models differ in their predictions concerning the temporal and spatial patterns of crustal deformation in some cases these differences are due to varying choices for the physical mechanism under study in other cases however the differences are the result of the details of the mathematical treatment or the choice of model parameters we seek to resolve the origin of some of these differences by analysing several different linear viscoelastic models with a common finite element computational technique the models involve strike slip faulting and include a thin channel asthenosphere model a model with a varying thickness lithosphere and a model with a viscoelastic inclusion below the brittle slip plane the calculations reveal that the surface deformation pattern is most sensitive to the rheology of the material that lies below the slip plane in a volume whose extent is a few times the fault depth if this material is viscoelastic the surface deformation pattern resembles that of an elastic layer lying over a viscoelastic half space when the thickness or breadth of the viscoelastic material is less than a few times the fault depth then the surface deformation pattern is altered and geodetic measurements are potentially useful for studying the details of subsurface geometry and structure distinguishing among the various models in best accomplished by making geodetic measurements not only near the fault but out to distances equal to several times the fault depth this is where the model differences are greatest these differences will be most readily detected shortly after an earthquake when viscoelastic effects are most pronounced for a thin channel asthenosphere model we have found that the predicted displacements are less than those for a half space asthenosphere this result is contrary to recently published results based on analytical approximations the deficiencies of the latter work result from ignoring material below the asthenosphere and in using thickness averaged deformation parameters although the displacements predicted for a thin channel asthenosphere are less than those for a half space asthenosphere the post seismic strain rates at intermediate distances from the fault are greater in an absolute value sense in the former model

bacterially mediated authigenesis of clays in phosphate stromatolites authigenic clays in close textural relation to carbonate fluorapatite within finely laminated phosphate stromatolites of upper jurassic age have been studied using scanning electron microscopy sem transmission electron microscopy tem and analytical electron microscopy aem stromatolite laminae consist of hexagonal prisms of francolite sizes ranging between 0 1 and 1 m that are surrounded by poorly crystalline smectite and amorphous fe si al oxyhydroxides microanalyses show that smectite is fe rich with highly variable composition particularly regarding fe and si contents smectite has significant beidellitic montmorillonitic and non tronitic substitutions although the lack of fringe contrast in some areas adjacent to the smectite packets with 1 0 1 3 nm spacing is due to differences in orientation of layers textural and analytical data clearly indicate the presence of fe si al amorphous phases intimately intergrown with smectite the occurrence of poorly crystalline smectite and associated amorphous phases within microbially precipitated stromatolite laminae both as envelopes around and as pore fillings between extremely small calcium phosphate crystals demonstrates authigenic smectite growth from a precursor fe si al amorphous material this material is formed in close association with a phosphate rich precursor the textural and structural relations the preservation of chemical precursors of glauconite such as nontronitic montmorillonite and the presence of fe si al amorphous mineral phases imply crystallization of the observed crystalline phases from synsedimentary bacterially precipitated amorphous precursors during early diagenesis in postoxic environments carbonate fluorapatite was the first phase to crystallize from the primary gel smectite and associated amorphous fe si al oxyhydroxides were the residual material of the crystallization process the slow rate of transformation at low temperatures from fe si al rich gels to smectite explains the textural relations between the poorly crystalline phases and the phosphate crystals as well as the preservation of amorphous substances in relation to clays authigenic smectite represents the first step in glauconitization

lateral variations in tectono magmatic style along the lofoten vesteralen volcanic margin off norway abstract the 400 km long passive continental margin west of the lofoten vesteralen archipelago off northern norway links the volcanic rifted voring margin and the sheared w barents sea margin multi channel seismic reflection profiles supplemented with crustal velocity gravity and magnetic anomaly data are used to outline the regional setting and main tectono magmatic features a well defined along strike margin segmentation comprising three segments characterized by distinct crustal properties structural and magmatic styles sediment thickness and post opening history of vertical motion is revealed the margin segments are governed by changes in fault polarity on late jurassic early cretaceous border faults and are separated by coeval cross margin transfer zones which acted as persistent barriers to rupture propagation and reflect the trend and character of older structural heterogeneities the transfer zones spatially correlate to small offset early opening oceanic fracture zones implying a structural inheritance from one rift episode to another culminating with lithospheric breakup at the paleocene eocene transition the pre seafloor spreading margin structural evolution is governed by the older predominantly late jurassic early cretaceous structural framework however the margin also provides evidence for mid and late cretaceous extension events that are poorly understood elsewhere off norway furthermore the lofoten vesteralen post breakup subsidence history contrasts with the adjacent margins reflecting breakup in thicker crust and a diminishing volume of high velocity lower crust emplaced during breakup

surface deformation related to the 2008 wenchuan earthquake and mountain building of the longmen shan eastern tibetan plateau abstract the 12 may 2008 ms 8 0 wenchuan earthquake china was one of largest continental thrusting events worldwide based on interpretations of post earthquake high resolution remote sensing images and field surveys we investigated the geometry geomorphology and kinematics of co seismic surface ruptures as well as seismic and geologic hazards along the longmen shan fold and thrust belt our results indicate that the wenchuan earthquake occurred along the ne sw trending yingxiu beichuan and guanxian anxian faults in the longmen shan fold and thrust belt the main surface rupture zones along the yingxiu beichuan and guanxian anxian fault zones are approximately 235 and 72 km in length respectively these sub parallel ruptures may merge at depth the yingxiu donghekou surface rupture zone can be divided into four segments separated by discontinuities that appear as step overs or bends in map view surface deformation is characterized by oblique reverse faulting with a maximum vertical displacement of approximately 10 m in areas around beichuan county earthquake related disasters e g landslides are linearly distributed along the surface rupture zones and associated river valleys the wenchuan earthquake provides new insights into the nature of mountain building within the longmen shan eastern tibetan plateau the total crustal shortening accommodated by this great earthquake was as much as 8 5 m with a maximum vertical uplift of approximately 10 m the present results suggest that ongoing mountain building of the longmen shan is driven mainly by crustal shortening and uplift related to repeated large seismic events such as the 2008 wenchuan earthquake furthermore rapid erosion within the longmen shan fold and thrust belt occurs along deep valleys and rupture zones following the occurrence of large scale landslides triggered by earthquakes consequently we suggest that crustal shortening related to repeated great seismic events together with isostatic rebound induced by rapid erosion related unloading is a key component of the geodynamics that drive ongoing mountain building on the eastern tibetan plateau

the earthquake deformation cycle at the nankai trough southwest japan geodetic measurements made landward of the nankai trough site of great subduction zone thrust earthquakes in 1854 and 1946 provide a uniquely detailed picture of the strain buildup process supply constraints on the mechanism of strain accumulation and allow for improved estimates of earthquake recurrence provided the two most recent movement cycles are similar the observations dating from about 1890 may be used to reconstruct a single complete deformation cycle coseismic strain release postseismic transients interseismic strain accumulation very complete leveling and tidal gage data indicate that postseismic deformation extends more than 300 km inland from the plate boundary persists for at least 30 years and shows a clear tendency to become longer wavelength with increasing time the transient movements have two timescales the first of about a year or less corresponds to deformation largely uplift concentrated close to the coseismic fault and is most easily explained by aseismic slip or very localized deformation downdip of the earthquake rupture plane the second longer timescale is associated with a diffusion like spread of the deformation further landward an effect qualitatively similar to that first predicted by elsasser to be an expected consequence of faulting in an elastic plate overlying a viscoelastic asthenosphere cumulative uplift since 1890 correlates well with the distribution of uplifted marine terraces although average post 1890 tilt rates exceed late quaternary and holocene averages by at least a factor of three because of the nonlinearity of strain buildup and the significant permanent deformation simple recurrence calculations typically overestimate the true interval between great earthquakes by a factor of 2 to a factor of 3 strict application of the time predictable model assumed correct overcomes these difficulties provided the cumulative transient deformation and the proportion of permanent deformation per cycle can be estimated

compositional variation within some glauconites and illites and implications for their stability and origins textural mineralogical and chemical data are presented for glauconites and illites from the lower cretaceous glauconitic sand formation alberta canada single crystal analyses by scanning transmission electron microscopy stem indicate that both glauconite 29 analyses and illite 44 analyses correspond very closely to ideal dioctahedral structures al dominates the octahedral sheet in illite very extensive a1 for feiii substitution was also found in some of the glauconites much more than previously recorded the dioctahedral mica structure is clearly very stable and flexible with respect to a1 for feiii substitution iron poor glauconites were found associated with pyrite we believe that glauconites tend to lose iron progressively during burial diagenesis especially where pore water iron activities are low high hs activity and low eh it seems probable that a1 for si tetrahedral substitution also takes place during diagenesis with consequent loss of swelling properties this is the same trend which is responsible for conversion of smectite to illite glauconite forms only where sediments reside for lengthy periods at the interface between oxidizing and reducing environments where fe3 is transiently available in solution related marine and terrestrial nontronites also form only in similar interface environments

stratigraphic condensed deposition and diagenetic evolution of green clay minerals in deep water sediments on the ivory coast ghana ridge abstract green grains concentrations were studied through the 22 m pleistocene sedimentary column recovered from ocean drilling project site 959 in 2100 m water depth located on a small plateau on the northern flank of the cote d ivoire ghana marginal ridge the green clay material usually fills the chambers of pelagic foraminifers taking into account the variance in color and mineralogic composition of the bulk green grains fraction observed in each level a methodological approach was especially performed mineralogical and chemical analyses were done successively on the bulk green material then on hand picked white pale green medium green and dark green grains and lastly surface and spot analysis of nanno structures were obtained using an energy dispersive microprobe coupled with a scanning electron microscope green grains concentrations are evidenced showing both rising up of green white ratio and increasing abundance of cracked dark green grains these irregular concentrations are not consistent directly with a general climatic forcing as evidenced by 18 o isotopic curve but are the result of recurrent bottom current activity thus winnowing process is the cause of the long lasting ionic exchange and mineralogical evolution at the water sediment interface clay infilling composed of smectite 35 40 kaolinite 45 50 traces of mica calcite and quartz was a precursor material along with dissolution of kaolinite crystallochemical modifications of smectites were observed both to the sequential concentration scale bulk samples and to the individual grain scale from white to dark green increment of fe content associated decrease of al and increase of layer charge and k content in the layers with the highest green grain concentrations and in agreement with crystallochemical formulae fe 3 rich montmorillonite displays octahedral charge tetrahedral charge appears only when fe content increased 1 2 fe per formulae with the maturation process the growing of the closed layers is observed mixed layer smectite glauconite 80 20 nearly similar evolution patterns were recorded at various levels 0 01 0 85 2 2 ma of the pliocene pleistocene accumulation however the nontronite way is evidenced in the lowest green grains concentrations and remind the previously described shelf processes independently of the morphologically induced winnowing in these marine tropical deposits the glauconitization process was especially favored by abundant iron supply and was not affected by low temperature 3 c it is suggested that in deep water environment bottom current controlled iron deposition and disponibility strongly influencing the mineralogic evolution a too lengthy dispersal of iron microparticles played an ultimate role in the development of the montmorillonite way rather than the nontronite way this would be the most commonly found in shallow water environment

vertical deformation associated with normal fault systems evolved over coseismic postseismic and multiseismic periods vertical deformation of extensional provinces varies significantly and in seemingly contradictory ways sparse but robust geodetic seismic and geologic observations in the basin and range province of the western united states indicate that immediately after an earthquake vertical change primarily occurs as subsidence of the normal fault hanging wall a few decades later a 100 km wide zone is symmetrically uplifted the preserved topography of long term rifting shows bent and tilted footwall flanks rising high above deep basins we develop finite element models subjected to extensional and gravitational forces to study time varying deformation associated with normal faulting we replicate observations with a model that has a weak upper mantle overlain by a stronger lower crust and a breakable elastic upper crust a 60 dipping normal fault cuts through the upper crust and extends through the lower crust to simulate an underlying shear zone stretching the model under gravity demonstrates that asymmetric slip via collapse of the hanging wall is a natural consequence of coseismic deformation focused flow in the upper mantle imposed by deformation of the lower crust localizes uplift under the footwall the breakable upper crust is a necessary model feature to replicate footwall bending over the observed width 10 km which is predicted to take place within 1 2 decades after each large earthquake thus the best preserved topographic signature of rifting is expected to occur early in the postseismic period the relatively stronger lower crust in our models is necessary to replicate broader postseismic uplift that is observed geodetically in subsequent decades

deformation gravity and potential changes due to volcanic loading of the crust a method for calculating deformation gravity and potential changes induced by volcanic loads imposed within and on the earth s crust is presented the method involves application of techniques developed for earthquake loading problems in elastic gravitational earth models by considering the elastic gravitational equilibrium of the layered system the gravitational and displacement response due to intruding masses and to pressurized magma chambers can be computed for applications involving seamount loading variations in the height of sea level can be calculated by requiring that seawater lie along an equipotential in continental loading problems the change in potential can be used to calculate the orthometric height cahnge as distinct from the geometric height change for some plausible loading geometries the difference between these two qunatities can be significant results for various loads and earth structures are shown and discussed in particular a magmatic mass intruding into an elastic gravitational lithosphere overlying a compressible gravitating asthenosphere produces distinct gravity anomalies which depend on the depth of intrusion applications of this result can be made to problems of isostatic compensation the intrusion of a magmatic mass together with the associated pressurization of the magma chamber produces distinctive surface gravity and deformation in the near field gravity gradients more defined as surface gravity divided by uplift vary with distance from the source moreover orthometric elevations can be significantly 25 less than geometric elevations these results have clear application to data from events such as the posteruption deflation of kilauea volcano less

substantial iron sequestration during green clay authigenesis in modern deep sea sediments pyrite formation has been considered a key iron sink in organic rich marine sediments analyses of sediments from the ivory coast ghana marginal ridge demonstrate that iron can be buried at greater rates during green clay formation

orientation of absolute african plate motion revealed by tomomorphometric analysis of the ethiopian dome the ethiopian dome comprising the ethiopian and yemeni plateaus formed as a result of the uplift of red sea gulf of aden and ethiopian rift shoulders the uplift was essentially due to a mantle plume activity a digital elevation model of this region before rifting constructed by using the rotation of its constituent plates and pulling down the rift shoulders reveals that important high areas existed before rifting these highs are interpreted to be the result of mantle plume activity a fast fourier transform was used to smooth the digital elevation model prerift dome before a tomomorphometric analysis was applied to quantify the orientation of each digital elevation model horizontal slice this procedure allowed us to determine a bearing of n30 e for absolute african plate motion since the paleogene

depositional controls on glaucony texture and composition upper jurassic west siberian basin this study examines textural inhomogeneity and variable chemical composition of upper jurassic glaucony in relation to small scale synsedimentary and postsedimentary authigenic processes controlled by the palaeonvironmental and palaeogeographical context four glaucony types with complex textural and compositional features have been recognized in cores of the georgiev formation of the west siberian basin samples exclusively made of light green type 1 glaucony k2o 6 5 the less mature type richer in glauconite smectite mixed layer formed under dysoxic conditions in the deepest distal marine environments of the northern sectors of the west siberian basin dark green type 2 glaucony is the most mature richest in glauconitic mica k2o up to 8 5 is sometimes associated with type 1 glaucony and is typical of high bottom areas with a low sedimentation rate within the central sectors of the basin type 3 glaucony is formed by brown grains poorer in k and fe but richer in al and si than type 2 glaucony and is only present in strongly condensed successions of the central eastern sectors of the west siberian basin type 4 glaucony is much richer in fe than any other type shows fresh yellowish green cores slightly less mature than type 2 glaucony and brown rims and cracks with composition similar to that of type 3 grains it was formed in western sectors of the west siberian basin close to urals weathering under a subtropical to temperate climate and erosion of badly drained peneplaned lowland areas around the basin provided al rich terrigenous clays as substratum for glauconitization which explains al and si enrichment in siberian glaucony maturation from glauconite smectite to glauconitic mica is monitored by a change from light to dark green colour related to decrease in al si mg ca and na and to increase in k and fe brown rims of type 4 glaucony and brown type 3 grains formed after leaching of fe and k from mature glauconite with formation of clays and fe oxyhydroxides as reaction products as a result of free oxygen exposure related to a hydrodynamic regime and temporary sea level fall glauconitization stopped and diagenetic pyrite formed due to basin deepening and burial under black shales during the latest jurassic earliest cretaceous transgression this study demonstrates that due to the complex nature of glaucony the authigenesis of glauconitic minerals in the rock record cannot be correctly understood if the palaeoenvironmental context and the palaeogeographical context of glaucony bearing sediments are not considered

spatial and temporal distribution of deformation at the front of the andean orogenic wedge in southern bolivia new observations from an active orogenic wedge help link the seismotectonic behavior of individual faults to wedge deformation rates and patterns over multiple timescales we provide the first detailed constraints on the distribution and timing of deformation at the front of the andean orogenic wedge in southern bolivia where a recent study suggests that great mw 8 earthquakes could rupture the master fault underlying the wedge we use stratigraphic relationships across fault related folds and elastic dislocation modeling of seismic reflection horizons to obtain probabilistic estimates of wedge front fault ages and slip rates our analyses reveal that at least half of the previously determined gps based wedge loading and quaternary whole wedge shortening rates are absorbed across a 20 40 km wide wedge front zone consisting of 1 4 en echelon and partially to fully overlapping faults and folds associated with blind thrust faults the difference between our slip rates and the geodetic geologic observations combined with evidence for activity across internal wedge structures supports the notion that nonsteady state mass balance conditions coupled with elevated erosional efficiency result in distributed wedge deformation the orogenic wedge in southern bolivia behaves in a similar fashion to the taiwanese and himalayan ranges slip accumulates at downdip locations along the master fault and is released incrementally by earthquakes that rupture the wedge front fault zone the faults and folds comprising this zone pose a major source of seismic hazard accumulating slip is also released in the wedge interior and older internal wedge faults must be considered in any future assessment of regional earthquake risk

coastal uplift earthquakes and active faulting of rhodes island aegean arc modeling based on geodetic inversion the geodetic inversion technique was used to model the fault pattern responsible for the uplifted holocene notches along the ne rhodes island coast se edge of the hellenic aegean arc input in the modeling was the elevation of uplifted notches up to 6000 yr old which are interpreted to reflect remains of fossil shorelines to testify to a series of earthquakes producing both uplift and subsidence i e to elastic dislocations and to correspond to geodetic data senso lato these shorelines up to 3 8 m high were probably originally continuous along the whole of the 75 km long se rhodes coast possibly locally disturbed by minor normal faults and reflect the last phases of the uplift and tilting of the island as a rather rigid block since late pliocene their radiocarbon dating was further refined from archeological data testifying to an about 1 m subsidence associated with the 227 bc earthquake followed by 3 m seismic uplift inversion constrained by the hypothesis of a compressional fault offshore rhodes was based on standard uniform slip elastic dislocation analysis it proved to depend only weakly even on extreme glacio isostatic corrections and indicated that coastal uplift is dominated by a main compressional fault zone offshore sub parallel to the island coast with normal faults inland reflecting thin skin tectonics this fault pattern similar to that of western crete is confirmed by seismic reflection profiles indicating a major reverse close to the modeled fault and can explain 1 the occurrence of strong m 7 5 historical earthquakes producing tsunamis and destruction on an east mediterranean scale 2 the alternation of uplift and subsidence as a result of fault shift inside the same fault zone and 3 the long term uplift of the island as a rather conjugate effect of the formation of an about 4 5 km deep 5 myr old marine basin se of rhodes bounded to the nw by the modeled fault zone the seismic risk of rhodes higher in its ne part of the island and than what was previously believed is associated with strong m 7 5 earthquakes producing widespread destruction tsunamis coastal uplift and coastal subsidence

paleoseismology in venezuela objectives methods applications limitations and perspectives abstract the privileged location of venezuela along an active interplate deformation belt despite of being a so called developing country has led to a long paleoseismic tradition as attested by 45 trench assessments since 1968 since then a first 2 trench study was carried out by the american woodward clyde company across the oca fault at sinamaica since 1980 all further paleoseismic studies have been performed by funvisis and the uribante caparo hydroelectric project southern merida andes became their first assessment where 22 huge trenches were bulldozer dug except for these compania anonima de administracion y fomento electrico cadafe financed trenches and two others all other assessments were for petroleos de venezuela s a pdvsa in this paper geographic and geologic factors as well as logistic limitations conditioning success in paleoseismic studies by trenching shall be discussed based on the venezuelan experience developed over the years the scientific contribution of this approach refer to confirmation of holocene fault activity slip per event and average slip rate of a given fault or segment seismic potential repeat of maximum credible earthquakes of known faults fault segmentation fault interaction as consequence of stress loading by stick slip on contiguous faults time space distribution of seismic activity along a given tectonic feature seismotectonic association of historical earthquakes and landscape evolution on the short term and its implications on the long term evolution poorly discussed since this is really part of the field of neotectonics in recent years since 1999 a new approach has been introduced in venezuela consisting in complementing the seismic history derived from trenching studies with the evaluation of seismically induced perturbations in the continuous quaternary sedimentary record of either active or fossil lakes the future of this discipline in venezuela heads to more trenching and lake coring in order to gather more data on the previously mentioned aspects other paleoseismic approaches have been developed very little in venezuela since either climate or the geodynamic setting do not favor their application

fe illites in a proterozoic deep marine slope deposit in the penganga group of the pranhita godavari valley their origin and environmental significance ferric illite fe illite developed extensively in a siliciclastic submarine fan sequence within a lime mud succession in the proterozoic penganga group at adilabad south india the minerals formed as de novo by preferentially replacing high k minerals like alkali feldspar and mica it is compositionally intermediate between glauconite and illite in a continuously varying chemical spectrum the mineral exhibits an r1 or r3 type stacking sequence with low 10 interlayering of illite and smectite i s all the analyzed grains are characterized by high potash content and it has been inferred that the maturity is dictated by high ak in the microenvironment this occurrence strongly calls into question the environmental significance that has so far been attributed to glauconitic minerals

a model of damage mechanics for the deformation of the continental crust 1 we derive a continuum rheology for the deformation of the continental crust using continuum damage mechanics it is hypothesized that when a constant strain rate is applied to a solid material the stress and damage increase until failure occurs which is analogous to an earthquake we further assume that this process is repeated in analogy to the reoccurrence of earthquakes on a fault our model assumes that the continental crust behaves elastically below a yield stress y above this stress the continuum deformations can be modeled as a non newtonian viscous flow with y n where n is constant we derive the modified omori s law for aftershock decay using a viscoelastic version of our model and get good agreement with observations taking n 6 using parameter values appropriate for aftershocks we obtain a continuum crustal rheology that can explain major orogenies such as the indian asian collision

the role of fe on the formation and diagenesis of interstratified glauconite smectite and illite smectite a case study of upper cretaceous shallow water carbonates abstract the widespread formation of interstratified glauconite smectite gl s and illite smectite i s in modern and ancient diagenetic settings records the physicochemical conditions prevailing during clay mineral authigenesis to date however significant gaps in our knowledge persist in respect to the influence of interstitial solution chemistry temperature and reaction kinetics on the evolution of composition mineralogy and microstructure of gl s and i s herein we present a study on the reaction mechanisms and the physicochemical conditions that led to the precipitation of early diagenetic gl s and late diagenetic i s on a stable carbonate platform during the cenomanian at langenstein in the northern german basin the texture and the k ar age 95 0 1 8 ma of the green glauconitized grains revealed that green clay authigenesis progressed in initially organic rich semi confined micromilieus i e in fecal pellets and in foraminifera close to the sediment seawater interface the composition of gl s varied in the range k 0 20 0 74 na 0 0 10 ca 2 0 0 05 0 28 0 75 fe 3 0 63 1 20 fe 2 0 08 0 24 al 3 0 19 0 97 mg 2 0 29 0 52 2 01 2 12 al 3 0 09 0 35 si 4 3 65 3 91 o 10 oh 2 and depended on the rate of aqueous fe 2 and k ion diffusion the micromilieu of glauconitization and on the bulk sedimentation rate the mineralogical microstructural and chemical changes of the ongoing gl s products revealed the following reaction for green clay authigenesis at langenstein fe iii smectite reacted with monosilicic acid goethite and aqueous k mg 2 and fe 2 to form glauconite and aqueous na ca 2 and h ions this process considers complex mineral transformations commonly associated with glauconitization such as early diagenetic oxidation of organic matter and microbial catalyzed dissolution of fe oxy hydroxides carbonates and detrital silicates in contrast the k ar age of i s 68 0 1 6 ma and its compositional variability k 0 29 0 45 na 0 0 10 ca 2 0 0 06 0 30 0 55 fe 3 0 16 0 29 fe 2 0 0 10 al 3 1 37 1 68 mg 2 0 18 0 43 2 00 2 12 al 3 0 17 0 39 si 4 3 61 3 83 o 10 oh 2 indicate a burial diagenetic origin for this mineral phase rather than transformation of illitic clays into i s during weathering under warm and humid climatic conditions the results from kinetic modelling support a diagenetic origin of i s 50 60 i layers and 50 40 s layers and imply its formation by the replacement of pre existing k feldspar at high pore fluid activity k na ratios and at low fe 2 concentrations we propose that the substitution of al 3 for fe 3 fe 2 and mg 2 in the octahedral sheet shifts the stability field of the kaolinite fe al mg smectite fe al mg illite or glauconite triple point to much lower monosilicic acid activities and stabilizes the i s or gl s structure this reaction supports the idea that the bio availability of fe is the rate limiting factor for glauconitization which is not the case for the diagenetic growth of i s whereby the pore water fe 2 concentration may be limited by the competing formation of fe oxy hydroxides and or fe sulfides

structural and geomorphological constraints on active normal faulting and landscape evolution in calabria italy calabria is one of the fastest uplifting and most seismically active regions in the mediterranean yet the time averaged c 10 6 years rates of normal faulting remain poorly constrained here we use digital elevation model analysis geological cross sections and a compilation of published data to quantify systematically along strike the fault throws and time averaged throw rates of the serre cittanova armo east crati and west crati faults we show that regional uplift has uplifted both their hanging wall and footwall blocks by c 200 400 m and the aspromonte massif by up to c 1150 1300 m we find that these faults have throws between c 640 and 1430 m and throw rates between c 0 6 and 1 4 mm a 1 their footwall ranges have variable proportions of inherited relief up to c 300 800 m the channels draining these ranges reflect the active normal faulting and relief in their steepness indices becoming c 5 8 m 0 9 steeper for each 0 1 mm a 1 throw rate increment and each 100 m relief increase finally the presence of knickpoints suggests that these channels are transiently responding to changes in relative base level which could be due to fault linkage or regional strain rate increases for the southern calabrian faults and to regional uplift acceleration in the case of the crati faults supplementary material topographic profiles of the marine terraces and long profiles of rivers are available at https doi org 10 6084 m9 figshare c 3689464

lithospheric elasticity promotes episodic fault activity based on the agreement between geodetic and geological plate velocities interplate fault slip rates are usually considered constant over long periods of time however measurements made at different time scales on intracontinental faults suggest that slip rate evolves with time we examine the slip evolution of a fault embedded in an elastic lithosphere loaded by plate motion we first assume that the fault friction varies due to a climatic cause then we show that high fault stress and low lithospheric stiffness favour large variations of slip rate in the case where fault weakening is controlled by slip rate we find that high loading velocity leads to a low stress constant slip rate while low loading velocity drives the fault slip rate to cycle between high and low values this suggests that paleoseismic slip rate could overpass the loading velocity but also fall to zero for some period of time

interaction between normal fault slip and erosion on relief evolution insights from experimental modelling the growth of relief in active tectonic areas is mainly controlled by the interactions between tectonics and surface processes erosion and sedimentation the study of long lived morphologic markers formed by these interactions can help in quantifying the competing effects of tectonics erosion and sedimentation in regions experiencing active extension river long profiles and faceted spurs triangular facets can help in understanding the development of mountainous topography along normal fault scarps in this study we developed analogue experiments that simulate the morphologic evolution of a mountain range bounded by a normal fault this paper focuses on the effect of the fault slip rate on the morphologic evolution of the footwall by performing three analogue experiments with different fault slip rates under a constant rainfall rate a morphometric analysis of the modelled catchments allows comparing with a natural case tunka half graben siberia after a certain amount of fault slip the modelled footwall topographies of our models reaches a dynamic equilibrium i e erosion balances tectonic uplift relative to the base level close to the fault whereas the topography farther from the fault is still being dissected due to regressive erosion we show that the rates of vertical erosion in the area where dynamic equilibrium is reached and the rate of regressive erosion are linearly correlated with the fault throw rate facet morphology seems to depend on the fault slip rate except for the fastest experiment where faceted spurs are degraded due to mass wasting a stream power law is computed for the area wherein rivers reach a topographic equilibrium we show that the erosional capacity of the system depends on the fault slip rate finally our results demonstrate the possibility of preserving convex river long profiles on the long term under steady external tectonic uplift and rainfall conditions

north atlantic volcanic margins dimensions and production rates early tertiary lithospheric breakup between eurasia and greenland was accompanied by a transient 3 m y igneous event emplacing both the onshore flood basalts of the north atlantic volcanic province navp and huge extrusive complexes along the continent ocean transition on the rifted continental margins seismic data show that volcanic margins extend 2600 km along the early eocene plate boundary in places underlain by high velocity 7 2 7 7 km s lower crustal bodies quantitative calculations of navp dimensions considered minimum estimates reveal an areal extent of 1 3 106 km2 and a volume of flood basalts of 1 8 106 km3 yielding a mean eruption rate of 0 6 km3 yr or 2 4 km3 yr if two thirds of the basalts were emplaced within 0 5 m y the total crustal volume is 6 6 106 km3 resulting in a mean crustal accretion rate of 2 2 km3 yr thus navp ranks among the world s larger igneous provinces if the volcanic margins are considered the velocity structure of the expanded crust seaward of the continent ocean boundary differs from standard oceanic and continental crustal models based on seismic velocities this volcanic margin crust can be divided into three units of which the upper unit corresponds to basaltic extrusives the regionally consistent velocity structure and geometry of the crustal units suggest that the expanded crust including the high velocity lower crust which extends some distance landward of the continent ocean boundary was emplaced during and subsequent to breakup the volcanic margin crust was formed by excess melting within a wide zone of asthenospheric upwelling probably reflecting the interaction of a mantle plume and a lithosphere already extending

the growth of geological structures by repeated earthquakes 2 field examples of continental dip slip faults a strong test of our understanding of the earthquake cycle is the ability to reproduce extant fault bounded geological structures such as basins and ranges which are built by repeated cycles of deformation along strike slip faults the coseismic and interseismic deformation can be nearly equal in magnitude and opposite in sign resulting in little permanent deformation except for the fault offset for dip slip faults portions of the crust are lifted and dropped and so buoyancy forces are exerted the seismic and interseismic deformations do not balance and structures grow and become subject to erosion and deposition we consider three examples for which the structure and fault geometry are well known the white wolf reverse fault in california site of the 1952 kern county m 7 3 earthquake the lost river normal fault in idaho site of the 1983 borah peak m 7 0 earthquake and the cricket mountain normal fault in utah site of quaternary slip events basin stratigraphy and seismic reflection records are used to profile the structure and coseismic deformation measured by leveling surveys is used to estimate the fault geometry to reproduce these structures we add the deformation associated with the earthquake cycle the coseismic slip and postseismic relaxation to the flexure caused by the observed sediment load treating the crust as a thin elastic plate overlying a fluid substrate the cumulative deformation is principally dependent on the elastic plate thickness modestly sensitive to the sediment substrate density difference and insensitive to the fluid viscosity for the 4 to 8 ma structures we deduce a longterm flexural rigidity of 2 15 1019 nm this is equivalent to an elastic plate thickness of 2 4 km for a young s modulus of 2 5 1010 nm 2 this value is found where independent estimates of the elastic thickness from the coherence between surface topography and gravity yield values of about 4 km but where coseismic fault slip extends to a depth of 10 15 km thus much of the seismogenic crust must weaken substantially during the life of active faults causing the fault bounded basins to narrow over time

fault kinematic and geomorphic observations along the north tehran thrust and mosha fasham fault alborz mountains iran implications for fault system evolution and interaction in a changing tectonic regime summary neighbouring faults can interact potentially link up and grow and consequently increase the seismic and related natural hazards in their vicinity despite evidence of quaternary faulting the kinematic relationships between the neighbouring mosha fasham fault mff and the north tehran thrust ntt and their temporal evolution in the alborz mountains are not well understood the ene striking ntt is a frontal thrust that delimits the alborz mountains to the south with a 2000 m topographic front with respect to the proximal tehran plain however no large instrumentally recorded earthquakes have been attributed to that fault in contrast the sigmoidally shaped mff is a major strike slip fault located within the alborz mountains sinistral motion along the eastern part of the mff is corroborated by microseismicity and fault kinematic analysis which documents recent transtensional deformation associated with nne ssw oriented shortening to better understand the activity of these faults on different timescales we combined fault kinematic analysis and geomorphic observations to infer the kinematic history of these structures our fault kinematic study reveals an early dextral shear for the ntt and the central mff responsible for dextral strike slip and oblique reverse faulting during nw oriented shortening this deformation regime was superseded by ne oriented shortening associated with sinistral oblique thrusting along the ntt and the central western mff sinistral strike slip motion along subsidiary faults in the central mff segment and folding and tilting of eocene to miocene units in the mff footwall continued thrusting along the ntt took place during the quaternary however folding in the hanging wall and sinistral stream offsets indicate a left oblique component and quaternary strike slip reactivation of the eastern ntt segment close to its termination this complex history of faulting under different stress directions has resulted in a composite landscape with inherited topographic signatures our study shows that the topography of the hanging wall of the ntt reflects a segmentation into sectors with semi independent uplift histories areas of high topographic residuals and apparent high uplift underscore the fault kinematics combined our data suggest an early mechanical linkage of the ntt and mff fault systems during a former dextral transpressional stage caused by nw compression during ne oriented shortening the ntt and mff were reactivated and incorporated into a nascent transpressional duplex the youngest manifestation of motion in this system is sinistral transtension however this deformation is not observed everywhere and has not yet resulted in topographic inversion

an intra oceanic crustal seismic reflecting zone below the dipping reflectors on lofoten margin multichannel seismic reflection measurements off lofoten northern norway show an uneven discontinuous reflector within the crystalline oceanic crust at a depth of 7 8 s two way traveltime this intra oceanic crustal reflector is observed seaward as well as beneath sub basement dipping reflectors which are of disputed oceanic or continental origin our observations indicate that the dipping reflectors are an integrated part of the oceanic crust

the seismicity geomorphology and structural evolution of the corinth area of greece in the eastern gulf of corinth geological structure is closely reflected in the topography in the 1981 corinth earthquakes ground deformation accentuated existing geomorphological patterns we explore the relationship between seismicity and landforms in space and time the area examined extends beyond the epicentral region of the 1981 events and its evolution is traced over the last 40000 years to understand the relation between deep and superficial structures we discuss processes that occurred in the 1981 earthquakes and go on to propose that surface faulting appears only above linear faults at depth that move in earthquakes with magnitudes m s greater than six where faults at depth intersect or bend the faulting becomes distributed and prim ary faulting does not reach the surface here the surface manifestation of faulting at depth is surface folding and secondary faulting such regions are identified in maps of the eastern gulf of corinth evidence for the evolution of the fault systems is provided by eyewitness accounts of shoreline changes following the recent earthquakes historical and archaeological data pertaining to old sea levels and 14 c dates for molluscs collected from fossil shorelines the results of these studies broadly confirm an earlier view of j a jackson et al earth planet sci lett 57 377 397 1982 that motion has shifted from faulting south of the city of corinth to faulting in the perachora peninsula but the transfer is not complete areas lying between the two fault systems have moved up and down in historical and archaeological times indicating that both systems are still active the evidence for activity of the northern system points to a repeat time of 300 years for earthquakes com parable with those of 1981 the work discussed in this paper suggests that some of the features previously described as m arine terraces are fault controlled continental surfaces furtherm ore beach deposits at a num ber of different levels long regarded as successive shorelines are in fact contemporaneous the critical ages were obtained by radiocarbon dating of shell carbonate a technique which yields dependable results if applied to samples which have been carefully selected and pretreated palaeontological dating of the terraces in contrast is found to be misleading because the faunas are environm entally controlled and consequently diachronous

relationship between deeper lithospheric processes and near surface tectonics of sedimentary basins interactions between upper lithosphere deformation as manifested in the structure and evolution of sedimentary basins and lower lithospheric deformation presumably reflect large scale regional or global tectonic events we review the current state of knowledge regarding these interactions and suggest areas of research which may lead to an improvement in this knowledge understanding the development of sedimentary basins requires insight into the processes responsible both for basin subsidence and also for distribution and preservation of sediments within the basins while some classes of basins are better understood than others there remain significant gaps both in our ability to account for available data and also in the data available to test current models and develop new ones subsidence in some classes of basins can be related to lithospheric scale processes occurring as part of the overall plate tectonic paradigm for example it is widely accepted that passive margin basins subside as a result of lithospheric extension mckenzie 1978 and that foreland basins are flexural consequences of collision between a continent and outboard terranes beaumont 1981 on the other hand models for the origin of intracratonic forearc and trans tensional basins are essentially still at cartoon level involving processes that are difficult to quantify and evaluate in the following we review a number of fundamental questions of vital interest for understanding of the relationship between deeper lithospheric processes and near surface tectonics

a new multilayered model for intraplate stress induced differential subsidence of faulted lithosphere applied to rifted basins in plane horizontal stresses acting on predeformed lithosphere induce differential flexural vertical motions a high precision record of these motions can be found in the sedimentary record of rifted basins originally it was proposed that rifted basins experience flank uplift and basin center subsidence in response to a compressive change of in plane stress which agrees well with observed differential motions subsequently published models predicted that the vertical motions may be opposite because of the flexural state of the lithosphere induced by necking during extension however the total flexural and permanent geometry of the lithosphere underlying the rifted basin is the controlling parameter for the in plane stress caused vertical motions the largest part of this preexisting geometry is caused by faulting in the uppermost brittle part of the crust and ductile deformation in the underlying parts of the lithosphere we present a new multilayered model for stress induced differential subsidence taking into account the technically induced preexisting geometry of the lithosphere including faults in the upper crust as continental lithosphere may exhibit flexural decoupling due to a weak lower crustal layer the new multilayer in plane stress model discriminates the geometries of the separate competent layers at a basin wide scale the new model predicts that a compressive change of in plane force results in basin center subsidence and flank uplift confirming the original hypothesis compared to all previous models the new model requires a lower horizontal stress level change to explain observed differential vertical motions

re evaluation of extension across the pearl river mouth basin south china sea implications for continental lithosphere deformation mechanisms abstract the tertiary pearl river mouth basin in the south china sea is one of relatively few localities where independent estimates of extension from upper crustal normal faulting crustal thinning and subsidence have been compared previous work indicates that these methods all support extension factor 1 8 for this basin however the estimate from faulting used the controversial rigid domino method whereas summing normal fault heaves gives only 1 3 instead this study pursues the possibility that the true value for this basin is 1 3 and the published estimates of extension from subsidence and crustal thinning are exaggerated because they do not take account of outflow of lower crustal material from beneath this basin such outward channel flow will occur when the lithostatic pressure at the base of the brittle upper crust is greater beneath a basin than beneath its surroundings in response to such a pressure gradient material lost from beneath this basin has probably flowed to beneath the adjacent chinese landmass where it isostatically compensates the erosion that has supplied much of the basin s sediment

reverse drag revisited why footwall deformation may be the key to inferring listric fault geometry abstract although reverse drag the down warping of hanging wall strata toward a normal fault is widely accepted as an indicator of listric fault geometry previous studies have shown that similar folding may form in response to slip on faults of finite vertical extent with listric or planar geometry in this study we therefore seek more general criteria for inferring subsurface fault geometry from observations of near surface deformation by directly comparing patterns of displacement stress and strain around planar and listric faults as predicted by elastic boundary element models in agreement with previous work we find that models with finite planar planar detached and listric detached faults all develop hanging wall reverse drag folds all of these model geometries also predict a region of tension and elevated maximum coulomb stress in the hanging wall suggesting that the distribution and orientation of near surface joints and secondary faults may also be of limited utility in predicting subsurface fault geometry the most notable difference between the three models however is the magnitude of footwall uplift footwall uplift decreases slightly with introduction of a detachment and more significantly with the addition of a listric fault shape a parametric investigation of faults with constant slip ranging from nearly planar to strongly listric over depths from 1 to 15 km reveals that footwall fold width is sensitive to fault geometry while hanging wall fold width largely reflects fault depth application of a graphical approach based on these results as well as more complete inverse modeling illustrates how patterns of combined hanging wall and footwall deformation may be used to constrain subsurface fault geometry

quaternary evolution of the corinth rift and its implications for the late cenozoic evolution of the aegean summary we present geological and morphological observations at different scales to constrain rates of faulting and the distribution of deformation in the seismically active aegean region we focus first on the 130 km long corinth rift an asymmetric graben where a flight of terraces of marine origin are uplifted we show that the edges of the terraces lie in the footwall of the normal fault bounding the corinth rift and correspond to sea level highstands of laic pleistocene age using a detailed analysis of aerial and spot imagery supported by field observations we have mapped 10 terrace platforms and strandlines ranging in elevation from 10 to 400 m over distances of 2 to 20 km from the fault the elevation of the terraces inner edges was estimated at 172 sites with an error of 5m this data set contains a precise description of the uplift and flexure of 10 different palaeohorizontal lines with respect to the present sea level to date the deformation we correlate the corinth terraces with late pleistocene oxygen isotope stages of high sea level stands and with global sea level fluctuations using a thick elastic plate model consistent with our current understanding of the earthquake cycle and a boundary element technique we reproduce the geometry of the shorelines to constrain both mechanical parameters and the slip on the fault we show that the seismogenic layer behaves over the long term as if its elastic modulus were reduced by a factor of about 1000 all the terraces are fitted for fault slip increasing in proportion to terrace age and the component of regional uplift is found to be less than 0 3 mm yr 1 the best fits give a slip rate of 11 3 mm yr 1 on the main rift bounding fault over the last 350 kyr other geological and morphologic information allows us to estimate the total age of the main fault 1 ma and to examine the mechanical evolution of the corinth rift the minimum observed sediment thickness in the gulf places an extreme check on the results of the modelling and a lower bound on slip rate of 6 7 mm yr 1 40 per cent less than estimated with modelling even this slip rate is nearly 10 times higher than for comparable features in most of the aegean and elsewhere in the world at a larger scale the spacing and asymmetry of the rift systems in the aegean suggest strain localization in the upper mantle with slow extension starting 15 myr ago or earlier the more recent 1 myr rapid phase of rifting in corinth partly reactivated this earlier phase of extension the younger faulting in corinth appears to result from its present location in the inhomogeneous stress field process zone of the south westward propagating tip of the southern branch of the north anatolian fault we extend these relations to propose a mechanical model for the late cenozoic evolution of the aegean as the arabia europe collision progressed in eastern turkey it caused anatolia to move to the west and the north anatolian fault to propagate into the aegean where the early slow extension started to be modified about 5 ma ago the process of propagation dramatically increased the activity of some but not all of the earlier rifts the model we present is compatible with tectonic observations as well as with the seismicity the palaeomagnetic rotations and the displacement field now observed with gps and slr

the growth of geological structures by repeated earthquakes 1 conceptual framework in many places earthquakes with similar characteristics have been shown to recur if this is common then relatively small deformations associated with individual earthquake cycles should accumulate over time to create geological structures following this paradigm we show that existing models developed to describe leveling line changes associated with the seismic cycle can be adapted to explain geological features associated with a fault in these models an elastic layer containing the fault overlies a viscous half space with a different density fault motion associated with an earthquake results in immediate deformation followed by a long period of readjustment as stresses relax in the viscous layer and isostatic equilibrium is restored deformation is also caused as a result of the loading and unloading due to sediment deposition and erosion in this paper the parameters that control the growth of dip slip structures are identified we find that the flexural rigidity of the crust or the apparent elastic thickness provides the main control of the width of a structure the loading due to erosion and deposition of sediment determines the ratio of uplift to subsidence between the two sides of the fault the flexure due to sediment load is much more important in this respect than whether the fault is normal or reverse in character we find that in general real structures are associated with apparent elastic thicknesses of 4 km or less and thus with very low flexural rigidities

thick plate flexure summary we derive analytical expressions for the displacements and stresses due to loading of a floating uniform elastic plate of arbitrary thickness by a plane or axisymmetric harmonic load the solution is exact except for assumptions of small strains and linear boundary conditions and gravitation within the plate is neglected for typical earth parameters its predictions are comparable to those of the usual thin plate theory frequently assumed in studies of lithospheric flexure gravity and regional isostasy even for a very thick lithosphere which may exist in some regions of mars the thin plate theory is a better approximation to the thick plate solution than the elastic half space limit except for short wavelength loads

quaternary normal faulting in southeastern sicily italy a seismic source for the 1693 large earthquake summary we present geological and morphological data combined with an analysis of seismic reflection lines across the ionian ovshore zone and information on historical earthquakes in order to yield new constraints on active faulting in southeastern sicily this region one of the most seismically active of the mediterranean is avected by wnw ese regional extension producing normal faulting of the southern edge of the siculo calabrian rift zone our data describe two systems of quaternary normal faults characterized by diverent ages and related to distinct tectonic processes the older nw se trending normal fault segments developed up to 400 kyr ago and striking perpendicular to the main front of the maghrebian thrust belt bound the small basins occurring along the eastern coast of the hyblean plateau the younger fault system is represented by prominent nnw sse trending normal fault segments and extends along the ionian ovshore zone following the ne sw trending avola and rosolini ispica normal faults these faults are characterized by vertical slip rates of 0 7 3 3 mm yr 1 and might be associated with the large seismic events of january 1693 we suggest that the main shock of the january 1693 earthquakes m 7 could be related to a 45 km long normal fault with a right lateral component of motion a long term net slip rate of about 3 7 mm yr 1 is calculated and a recurrence interval of about 550 50 yr is proposed for large events similar to that of january 1693

morphology seismic structure and tectonic development of the powell basin antarctica the powell basin located near the scotia antarctica strike slip plate boundary is bounded on three sides by continental crustal blocks and it separates the south orkney microcontinent from the northeastern antarctic peninsula on the basis of the entire geophysical data set available the main structural and geological elements of the basin are identified the northern domain is characterized by an oceanic like environment with a ridge axis in the centre of the basin two conjugate deep restricted sedimentary basins are located at the base of the northeastern and northwestern margins and filled by thick sedimentary sequences the southern domain is mainly floored by transitional crust and presents rift related basement graben the margins surrounding the basin are different with the northern and southern margins mainly transcurrent whereas most of the eastern and western margins show passive margin characteristics the sedimentary sequences filling the basin have been correlated to the main tectonic processes responsible for powell basin opening and partially dated using marine magnetic anomaly identifications three main evolutionary phases are recognized that explain the geological setting of the powell basin an early phase of separation between the antarctic peninsula and the south orkney microcontinent produced stretching and progressive continental lithospheric thinning with the creation of restricted pull apart basins proto powell phase this phase was followed by a northward movement possibly accomplished with a clockwise rotation of the south orkney microcontinent drift phase with consequent oceanic crustal accretion in the northern sector of the basin and development of rift related structures in the southern sector phase spanning 27 18 ma as determined from the marine magnetic anomalies a successive clockwise rotation of the south orkney microcontinent determined the complete development of the northern sector of the basin with spreading and final structuration of the margins encircling the basin plain

coseismic and postseismic subsurface displacements and strains for a dip slip normal fault in a three layer elastic gravitational medium a three layer elastic gravitational fault displacement model has been developed using elastic dislocation and employed to examine the effects of rigidity layering gravity and stress relaxation on surface and subsurface displacements fields for a dip slip normal fault within our three layer model layer 1 represents the upper crust layer 2 the lower crust and layer 3 the upper mantle the fault is embedded in the upper crust horizontal as well as vertical displacement components have been determined displacement field changes due to postseismic stress relaxation have been calculated using both the correspondence principle and relaxed rigidity moduli and results are in close agreement the relaxed rigidity method provides an accurate and computationally efficient method of examining postseismic relaxation postseismic relaxation within the lower two layers only gives surface uplift increasing footwall uplift and decreasing hangingwall subsidence and also increases the wavelength of surface vertical displacement postseismic stress relaxation within all three layers i e uniform half space produces a shorter wavelength of surface vertical deformation with respect to the coseismic response moho topography created during coseismic deformation is initially amplified during postseismic relaxation the relaxed moho topography is dependent on the strength of the upper crust as well as the strength of the lower crust and mantle gravity has a significant influence on displacements only at the postseismic stage when the effective rigidity of the lower layers is small coseismic and postseismic normal strains associated with dip slip normal faulting have been examined for a large normal basement fault intersecting the free surface the coseismic horizontal surface strain perpendicular to fault strike is compressive adjacent to the fault and in the footwall and tensile in the hangingwall away from the fault coseismic stress redistribution may generate significant tensile brittle failure of the upper crust adjacent to large basement faults

lake bonneville constraints on lithospheric thickness and upper mantle viscosity from isostatic warping of bonneville provo and gilbert stage shorelines the deformed shorelines of the late pleistocene lake bonneville provide an excellent opportunity to analyze the response of the earth to surface loads of relatively short wavelengths 400 km and short duration 30 kyr recently revised estimates of the lake loading history and an expanded compilation of shoreline elevations for the bonneville 1550 m provo 1440 m and gilbert 1300 m shorelines have prompted us to reexamine the deflection the earth model we use is identical with that employed by nakiboglu and lambeck and consists of an elastic plate overlying a maxwell viscoelastic channel and a rigid base our calculation differs from that of nakiboglu and lambeck in two respects we used a significantly more detailed load model and we compared our results with observations from three distinct shorelines the lake elevation history spans 32 kyr in 18 piecewise linear segments the water load is computed at each time step from a digital terrain model 4 4 km cell size and a specified lake elevation we find that the use of three separate shorelines significantly reduces the acceptable region of parameter space the effective elastic lithospheric thickness is 23 2 km the mantle viscosity is 1 2 0 2 1020 pa s and the depth to a significant viscosity increase is no less than 300 km though it might be much more examination of the residual deflections differences between observed and computed shoreline elevations reveals a regional tilt down to the ne of 6 10 5 which we attribute to collapse of the peripheral bulge produced by the laurentide ice sheet

spatio temporal evolution of strain accumulation derived from multi scale observations of late jurassic rifting in the northern north sea a critical test of models for lithospheric extension abstract we integrate observations of lithospheric extension over a wide range of spatial and temporal scales within the northern north sea basin and critically review the extent to which existing theories of lithospheric deformation can account for these observations data obtained through a prolonged period of hydrocarbon exploration and production has yielded a dense and diverse data set over the entire viking graben and its flanking platform areas these data show how syn rift accommodation within the basin varied in space and time with sub kilometer scale spatial resolution and a temporal resolution of 2 3 myr regional interpretations of 2d seismic reflection refraction and gravity data for this area have also been published and provide an image of total basin wide stretching for the entire crust these image data are combined with published strain rate inversion results obtained from tectonic subsidence patterns to constrain the spatio temporal evolution of strain accumulation throughout the lithosphere during the 40 myr 170 130 ma period of late jurassic extension across this basin for the first 25 30 myr strain localisation dominated basin development with strain rates at the eventual rift axis increasing while strain rates over the flanking areas declined as strain rates across the whole basin were consistently very low 16 s l thermally induced strength loss cannot explain this phenomenon the strain localisation is manifest in the near surface by a systematic migration of fault activity the pattern and timing of this migration are inconsistent with flexural bending stresses exerting an underlying control especially when estimates of flexural rigidity for this area are considered the best explanation for what is observed in this time period is a coupling between near surface strain localisation driven by brittle or plastic failure and the evolving thermal structure of the lithosphere we demonstrate this process using a continuum mechanics model for normal fault growth that incorporates the strain rate dependence of frictional strength observed in laboratory studies during the final 10 myr of basin formation strain accumulation was focused within the axis and strain rates declined rapidly replacement of weak crust by stronger mantle material plus crustal buoyancy forces can adequately explain this decline

conditions and mechanism for the formation of iron rich montmorillonite in deep sea sediments costa rica margin coupling high resolution mineralogical characterization and geochemical modeling abstract iron rich smectite is commonly described in the diagenetic fraction of deep sea sediment as millimeter to centimeter aggregates dispersed in the sediment or as a coating on sedimentary particles or nodules this study examines several factors to elucidate formation mechanisms of a particular iron rich smectite and its potential transformation to glauconite the study combines a detailed mineralogical investigation on natural samples and a chemical modeling approach to assess mineralogical reactions and pathways transmission electron microscopy tem observations and analytical electron microscopy tem aem analyses were conducted on microtomed samples of millimeter to centimeter long green grains these grains are widespread in pelagic calcareous sediment from the costa rica margin they are composed of pyrites that are partially dissolved and are surrounded by amorphous or very poorly crystallized iron rich particles iron rich montmorillonite grows from an amorphous precursor and its formation requires the input of si o mg k na and ca our results suggest that these inputs are supported by the dissolution of sedimentary phases such as volcanic glasses siliceous fossils and silicates thermodynamic modeling of fluid sediment interactions was conducted with the geochemical computer code phreeqc using mineralogical and pore fluid compositions from sediment samples and calculated estimates for thermodynamic constants of smectites that are not maintained by the computer code simulations confirm the possibility that the green grains are the product of pyrite alteration by seawater under oxidizing conditions the extent of smectite production is controlled by the kinetics of pyrite dissolution and fluid migration the absence of aluminum in the costa rica margin system explains the formation of an iron rich montmorillonite instead of glauconite whereas the presence of calcite that buffers the system explains the formation of an iron rich montmorillonite instead of iron oxides

the process of glauconitization chemical and isotopic evidence sequential leaching experiments were made on recent glauconies and clay fractions of the associated mud from off shore africa near the estuary of the congo river analyses of major rare earth elements ree and nd isotopic compositions on the resulting leachate and residue pairs allow identification of at least three important and isotopically distinct components which contributed to the glauconitization process 1 a detrital component with relatively high 87sr 86sr and relatively low 143nd 144nd isotopic ratios 2 a phosphate phase rich in ree and sr with sea water sr and nd isotopic characteristics 3 a component rich in organic matter and ca with a sea water sr isotopic signature a relatively low nd isotopic composition and elevated sm nd ratios this latter component probably represents the suspended organic and carbonate rich river load the detrital and the river components were mixed up in the muddy off shore sediment ingested by worms and integrated into faecal pellets the resulting material has sr and nd isotopic signatures intermediate between those of the detrital and river components and represents the precursor of the glaucony minerals during the subsequent dissolution crystallization process the glauconitic pellets remain isotopically closed to any external supply but expulsion of sr and nd with increasing degree of maturation is observed without any effect on the sr and nd isotopic compositions at a higher maturation stage k2o 4 5 the sr and nd isotopic compositions tend to decrease and increase respectively approximating the isotopic composition values of the phosphate rich phase because the sr and nd concentrations decrease the evolution of the glauconies toward lower sr and higher nd isotopic compositions can only be explained by expulsion of sr and nd of the detrital component with high sr and low nd isotopic signatures dissolution of the chemically unstable wormdigested clay material from mud may be responsible for the liberation of these elements consequently the phosphate rich phase with sea water sr and nd isotopic signatures becomes increasingly important for the isotopic characteristics of the maturing glauconite grains and sea water isotopic signatures can be reached during the stage of mature glauconite k2o 6 5 without chemical exchange with the depositional environment

southward younging apatite u th he ages in the northern california coast ranges due to a northward migrating crustal welt abstract u th he in apatite dating of franciscan formation samples from between 39 47 n and 39 08 n in the northern california coast ranges nccr reveals a southward and downward younging pattern of ages 21 8 0 6 ma to 7 9 0 9 ma these ages are interpreted to represent a northward or northeastward dipping fossil he partial retention zone that was tilted and exhumed by a northward migrating pulse of crustal thickening that begins 150 200 km ahead of the migrating mendocino triple junction mtj k p furlong r govers ephemeral crustal thickening at a triple junction the mendocino crustal conveyor geology 27 1999 127 130 the 8 ma ages from the southern end of the sample transect are interpreted to come from rocks that were immediately below the he partial retention zone when crustal thickening began 5 my before the mtj passed by these rocks have now reached the surface 3 my after passage of the mtj the older ages from the central and northern portions of the sample transect are interpreted to represent rocks that were within the he partial retention zone prior to crustal thickening ahead of the mtj and which therefore record ages transitional from older subduction related cooling and exhumation to more recent transform related cooling and exhumation in addition to providing support for the model of a migrating crustal welt associated with the mtj the existence of an essentially intact gently tilted fossil partial retention zone in the northern california coast range raises the possibility of using isochronous surfaces as neotectonic structural markers in this geologically complex and heavily vegetated region

the margins of the south orkney microcontinent marine geophysical studies of the south orkney microcontinent show two intersecting tectonic fabrics of different age the older fabric is oriented e w and represents the magmatic arc and fore arc created by subduction related processes at the pacific margin during the mesozoic the younger oriented nnw to sse comprises half graben related to e w rifting at both the eastern and western margins of the microcontinent both fabrics provide constraints on a 40 ma reconstruction which shows a highly systematic distribution of arc and fore arc provinces and points to the importance of e w strike slip in regional tectonic evolution the rifting apparently of oligocene age is associated with back arc extension which created the oceanic basins to either side of the microcontinent this strongly supports the existence of subduction with the same orientation as the present south sandwich arc as far back as 35 or 40 ma

active faulting on the island of crete greece in order to characterize and quantify the middle late quaternary and ongoing deformation within the southern aegean forearc we analyse the major tectonic structures affecting the island of crete and its offshore the normal faults typically consist of 4 30 km long dipslip segments locally organised in more complex fault zones they separate carbonate and or metamorphic massifs in the footwall block from loose to poorly consolidated alluvial and colluvial materials within the hangingwall all these faults show clear evidences of recent re activations and trend parallel to two principal directions wnw ese and nne ssw based on all available data for both onland and offshore structures morphological and structural mapping satellite imagery and airphotographs remote sensing as well as the analysis of seismic profiles and the investigation of marine terraces and holocene raised notches along the island coasts for each fault we estimate and constrain some of the principal seismotectonic parameters and particularly the fault kinematics the cumulative amount of slip and the slip rate following simple assumptions and empirical relationships maximum expected magnitudes and mean recurrence periods are also suggested summing up the contribution to crustal extension provided by the two major fault sets we calculate both arc normal and arcparallel long term strain rates the occurrence of slightly deeper and more external low angle thrust planes associated with the incipient continental collision occurring in western crete is also analysed although these contractional structures can generate stronger seismic events m 7 5 they are probably much rarer and thus providing a minor contribution to the overall morphotectonic evolution of the island and the forearc a comparison of our geologicallybased results with those obtained from gps measurements show a good agreement therefore suggesting that the present day crustal deformation is probably active since middle quaternary and mainly related to the seismic activity of upper crustal normal faults characterized by frequent shallow 20 km moderate to strong seismic events seldom alternating with stronger earthquakes occurring along blind low angle thrust planes probably ramping from a deeper aseismic detachment ca 25 km this apparently contradicting co existence of juxtaposed upper tensional and lower compressional tectonic regimes is in agreement with the geodynamics of the region characterised by continental collision with nubia and the aegean mantle wedging

inferring fault characteristics using fold geometry constrained by airborne laser swath mapping at raplee ridge utah 1 we used airborne laser swath mapping alsm data to define the geometry of strata in raplee ridge in southeastern utah that were likely deformed by slip on an underlying fault the fold geometry was used to infer the fault geometry and loading responsible for the folding using the boundary element model poly3d monte carlo markov chain mcmc methods created probability density functions pdfs that reveal the most likely fault geometry and loading conditions and their uncertainties despite the restrictive assumptions of poly3d in which body deformations occur from slip on displacement discontinuities in a homogeneous linear elastic half space the strata deflections are matched remarkably well and the resulting inferences of fault geometry and stress field appear reasonable we propose that similar methods may be used with models that include more complicated rheologies and heterogeneous and anisotropic material properties to estimate fault geometries and loading conditions where only deflection of strata record these parameters

a plate flexure approximation to postseismic and interseismic deformation the rather large postseismic deformation that is associated with two dimensional dip slip faulting in the lithosphere is related to the bending of a free plate generated by dip slip faulting in the absence of gravity asthenosphere relaxation eventually permits the faulted lithosphere to assume the dihedral configuration of a faulted free plate for thrust faulting the faulted area is depressed into the asthenosphere and the flanks of the plate slope uniformly upward in the presence of gravity buoyancy forces act upon the plate and the ultimate t postseismic uplift is approximated y 0 2 by w1 exp y cos y sin y where w1 is an explicit function of the fault parameters and lithosphere properties y is the horizontal distance from the downdip end of the fault and is the flexural parameter for the lithosphere plate the relaxed asthenosphere response is the sum of the coseismic deformation unrelaxed astheriosphere response and this ultimate postseismic deformation the annual steady deformation associated with strain accumulation at a subduction zone is simply the relaxed asthenosphere response to virtual normal slip on the main thrust zone of an amount equal to the annual plate convergence from these relations we have estimated the deformation strain and uplift expected along the pacific coast of northern honshu the estimated deformation is about twice the observed deformation but the predicted geographical distribution of the deformation is similar to the observed deformation

on a possible connection between three major earthquakes in california and oil production abstract the 1983 coalinga m 6 5 the 1985 kettleman north dome m 6 1 and the 1987 whittier narrows m 5 9 earthquake sequences each occurred beneath major producing oil fields and caused an aftershock sequence whose epicentral extent coincides approximately with that of the overlying oil field despite this coincidence a causal relationship between these sequences and oil production has been discounted because the earthquakes were located at depths of the order of 10 km whereas oil production is confined to the topmost several km moreover because all three oil fields coalinga kettleman north dome and montebello are situated on anticlines that have undergone recent uplift as a consequence of horizontal tectonic compression of the crust natural earthquakes are not unexpected a mechanical connection between oil production and the earthquake sequence is suggested however by the observation that in each case the total seismic deformation was just that required to offset the force imbalance caused by oil production specifically for each of the three sequences m 0 2 m c where m 0 is the sum of the seismic moments is the modulus of rigidity m is the mass of the fluid removed due to oil production is the fraction of the upper crust that is seismogenic and c is the average upper crustal density in essence net extraction of oil and water reduces slightly the average density of the upper crust causing an isostatic imbalance the ductile lower crust deforms in response to this imbalance thus increasing the load on the seismogenic layer which fails seismically to thicken the crust so as to restore static equilibrium locally accordingly earthquakes near the base of the upper crust may be an expected outcome of major oil production from growing anticlines irrespective of the depths of the producing formations

morphotectonic analysis of the long term surface expression of the 2009 l aquila earthquake fault central italy using airborne lidar data abstract in this paper we present a morphotectonic study of the paganica san demetrio fault system psdfs responsible for the mw6 1 april 6 2009 earthquake l aquila central italy the discrepancy observed between the length of the seismologic geodetic modeled fault the limited size of the primary coseismic surface ruptures and the significant morphological expression of the psdfs stimulated a debate about the maximum rupture length of the psdfs and its capability to generate larger magnitude events to image the psdfs long term morphological expression and define its surface geometrical arrangement length number of fault splays and boundaries we took advantage of a high resolution airborne lidar dataset lidar topography substantially increased our confidence in detecting even subtle tectonic controlled morphologies we define the psdfs as a 19 km long fault system that displays a complex structural setting characterized by two different sectors 1 the paganica sector to the nw with a narrow deformation zone and 2 the san demetrio sector to se where the strain is accommodated by several fault splays dissecting a wider quaternary basin we also defined a first order hierarchy among the numerous fault splays across the psdfs the long term geomorphic expression of the psdfs suggests that it ruptured also involving the whole 19 km long structure besides rupturing only small sections as it occurred in 2009 this suggests a variable slip behavior empirical relations applied to this hypothesis allow up to m 6 6 earthquakes along the psdfs these results have a critical impact on the seismic hazard assessment of the area when compared with a m 6 1 event as the 2009

a new crustal fault formed the modern corinth rift abstract this review shows how collective analysis of morphotectonic elements on uplifting rift margins can constrain the mechanical behaviour of continents during early rifting this is shown for the modern corinth rift one of the fastest extending and most seismically active continental regions worldwide we reconstruct the growth of the normal fault system that accommodates most of the rift strain and the uplift of the rift margin it bounds from onset to present and at rift scale our approach allows first order inferences on the mechanics and evolution of the rift and can be used in other areas of early continental rifting we review and re assess known geologic evidence in the corinth rift and compile morphotectonic elements into a new map we analyse the rift topo bathymetry and the footwall relief river catchments and tectonic knickpoints in its uplifting margin we also review studies that constrain the growth of normal faults using morphotectonic elements in their footwall and propose a novel theoretical framework to reconstruct fault time evolution during early rifting we couple known and new data to derive fault displacement profiles in time and use the theoretical framework to infer the history of growth and linkage of rift border faults in turn constraining rift growth mechanics and evolution our rift scale morphotectonic investigation shows that the current rift bounding faults are kinematically coherent at depth and constitute a fault 80 km in length this composite master fault grew along strike from the rift centre linking and integrating individual fault segments that developed co linearly at earlier times the observed fault elastic flexure footwall relief wavelength and high uplift and slip rates throughout the rift margin suggest the border fault is steep and highly localized in strain and transects the entire seismogenic layer growing in a long term strong elastic lithosphere integration of previous and our new findings suggest the corinth rift evolved in two distinct extensional phases these extensional phases are delimited by the fast overwriting growth of the new rift forming fault that switched rift mechanics in a 300 kyr timespan and controls rift evolution thereafter the new rift forming fault enlarges the modern rift as an asymmetric half graben along and across strike superimposed onto the preceding 4 my distributed extension

the role of pre existing thrust faults and topography on the styles of extension in the gran sasso range central italy abstract structural analysis and field mapping together with simple geometrical and flexural elastic models document that two styles of quaternary extensional tectonics characterized the gran sasso range central apennines italy in the western part of the range extension took place on 10 15 km long range front normal faults with associated 600 1000 m high escarpments showing evidence of late glacial holocene activity this topography has been reproduced with a thin elastic plate subjected to the isostatic forces induced by the movement along high angle 55 65 planar normal faults in the eastern part of the belt extension occurred on shallow dipping normal faults 30 35 which reactivated progressively deeper pre existing thrusts in this area antithetic domino faults formed to accommodate the mechanical adjustment of the hanging wall over a variably dipping major fault surface the eastward increase in shortening due to the earlier compressional phase documented in the gran sasso belt by previous authors accounts for the more developed zones of weakness and high topographic relief in the eastern sector this setting could explain the different styles of extension and the more advanced northeastern limit of normal faulting in the eastern sector this work suggests that normal faults can originate either with low or high angle geometry in the upper crust according to the pre existing tectonic setting and that topography could be important in controlling the geometry and pattern of migrating normal faulting

crustal versus asthenospheric relaxation and post seismic deformation for shallow normal faulting earthquakes the umbria marche central italy case summary following a normal mode approach for a strati ed viscoelastic earth we investigate the eiects induced by shallow normal faulting earthquakes on surface post seismic vertical displacement and velocity at the surface when stress relaxation occurs in the crust or in the asthenosphere the modelled earthquake is a moderate one characteristic of some slowly deforming plate boundaries in the central mediterranean region we focus on the umbria marche central italy region where deep seismic re ection studies crop03 and the 1997 earthquake sequence clearly show a seismogenic layer decoupled from the lower crust by a sizeable transition zone accordingly the crust is subdivided into three layers an elastic upper crust a transition zone and a low viscosity lower crust the fault is embedded in the upper crust the layered viscoelastic structure of the crust and mantle imposes a pattern and scale on the modelled coseismic and post seismic deformation with a major contribution from the transition crustal zone and low viscosity lower crust stress relaxation in the mantle being negligible we show that signi cant vertical deformation rates of the order of 1 mm yr 1 could be expected for a shallow and moderate event such as the recent umbria marche earthquake for viscosity values of 10 19 and 10 18 pa s in the crustal transition zone and lower crust respectively

phosphate stromatolites from condensed cephalopod limestones upper jurassic southern spain upper jurassic phosphate stromatolites of the almola sierra southern spain encrust macrofossils and hardgrounds and form oncoids included within pelagic condensed fossiliferous limestones their accretion was determined by bacterially mediated precipitation of phosphate by the trapping and binding of fine siliciclastics and pelagic biomicrite and by the encrustation of benthonic foraminifera phosphorous trace elements and rare earth elements were concentrated from degraded organic matter and seawater by stromatolite building communities which mediated the formation of phosphate rich and fe al si rich organic gels under oxic conditions favouring the precipitation of amorphous mineral precursors acp and fe al si oxyhydroxides the observed ce enrichment for some stromatolites is explained by oxidative scavenging of ce4 from seawater by fe mn oxyhydroxides the bacterially mediated gels were able to migrate and fill the voids of the stromatolite structure and later changed to carbonate fluorapatite haematite and poorly crystalline fe rich clays under postoxic conditions phosphatization of trapped carbonate particles also occurred the phosphate stromatolites formed on a sediment starved pelagic swell during periods of no carbonate sedimentation and hardground development stromatolite lamination provides evidence for rhythmic alternation between bacterially mediated phosphogenesis sedimentation and erosion suggesting episodic changes in the sedimentary environment although some of the parameters that controlled phosphate precipitation associated with the stromatolites local high organic productivity sediment starvation moderate depth of deposition and physicochemical conditions were similar to those found in modern and ancient phosphogenic settings the palaeogeographical framework and the intensity of sedimentary processes were different to those of the world s major phosphorite deposits

m 6 earthquakes in southern california during the twentieth century no evidence for a seismicity or moment deficit abstract a broadly based report on seismic hazards in southern california wgcep 1995 concluded that the predicted seismicity exceeds that observed since 1850 a subsequent independent analysis argued that infrequent huge m 8 earthquakes are needed to explain the low rate of large earthquakes jackson 1996 frequency magnitude relationships and earthquake reporting suggest that the 1903 to 1997 catalog we present here with a b value of 1 0 and a rate of m 6 shocks of 0 42 to 0 49 yr 1 is nearly complete in contrast the 1850 to 1994 catalog used by wgcep is incomplete before the turn of the century and thus its reported seismicity rate of 0 32 m 6 shocks yr 1 is too low principally because the wgcep 1995 model results in b values of up to 4 0 for regions of lesser and blind faults the rate of m 6 shocks off the san andreas system predicted by the wgcep 1995 model is three times greater than that observed in this century because they obtained b 0 4 for m b 2 2 for m 7 3 on major faults their expected rate of m 7 san andreas shocks is twice as high as observed thus part of the seismicity and moment discrepancy identified by wgcep was caused by use of an incomplete catalog and part was caused by inappropriate b values we obtain a southern california moment release rate of 8 to 12 10 18 n m yr 1 which cannot be distinguished from the moment release estimated by fault slip or the moment accumulation inferred from plate motions or geodetically measured shear strain we thus find no evidence for a moment deficit significant aseismic moment release or for rare m 8 earthquakes off the san andreas fault system finally the number of m 6 earthquakes per decade does not depart significantly from a poisson process during this century and thus we find no evidence that the rate of seismicity is increasing now or at any other time since 1900