seismicity normal faulting and the geomorphological development of the gulf of corinth greece the corinth earthquakes of february and march 1981 three major destructive earthquakes of m s 6 7 6 4 6 4 occurred in the eastern part of the gulf of corinth in february and march 1981 associated normal faulting was observed on both the north and the south sides of the gulf examination of teleseismic local seismic surface faulting and geomorpbological data suggests that the first and second of these shocks activated major north dipping normal faults these faults control the topography and bathymetry and are related to the recent uplift and subsidence of the coastline it is probable that the first earthquake occurred on a faultwhich outcrops underwater and the second on a fault which is visible on land it appears that the third shock activated an antithetic normal fault dipping southwards on the north side of the gulf and that the overall structure of the gulf of corinth graben is asymmetric the northern antithetic fault clearly demonstrates the geomorphological changes associated with developing young normal faulting in addition we suggest that observations of recent coastline movement provide a powerful tool for identifying major active fault systems and predicting their historical role in the paleogeography of an area

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

natural fractures in a united kingdom shale reservoir analog cleveland basin northeast england faults and fractures within the well exposed lower jurassic cleveland ironstone and whitby mudstone formations may provide insights into the tectonic history of gas prospective mississippian shale in northern england subvertical opening mode fractures occur throughout the cleveland basin bed parallel fractures some of which contain blocky calcite fills occur preferentially within well bedded clay rich mudstones of the cleveland ironstone and whitby mudstone formations at jet wyke and port mulgrave subvertical fractures display abutting or curving parallel relationships with under and overlying bed parallel fractures together these observations suggest that bed parallel fractures at times acted as free surfaces some bed parallel fractures curve toward and branch from calcite filled fault slip surfaces indicating that bed parallel fracturing and normal faulting were synchronous occurring within a regional stress field with vertical maximum principal stress this apparent paradox can be explained by normal compaction followed by cementation and coupling between pore pressure and minimum horizontal stress driven by poroelastic deformation or incipient slip along critically stressed normal faults causing elevation of horizontal stress in excess of the vertical stress within clay rich units propagation of bed parallel fractures was enhanced by dilatational strains adjacent to normal fault planes bed parallel fractures have not been observed within more rich units at the top of the whitby mudstone formation at whitby east cliff or within well bedded clay rich shale at saltwick nab this observation is consistent with the lack of normal faulting at saltwick nab and the whitby mudstone formation having been drained by structural and or stratigraphical juxtaposition against permeable middle jurassic sandstones at both these localities

the structural development of the wessex basin the mesozoic and cenozoic structures of southern england form part of a system of disturbances which extends across the channel into northern france they are reviewed in the light of published data from south dorset basin development started with permo triassic rifting and is believed to have continued through the jurassic and early cretaceous with intermittent growth on deep seated listric normal faults probably associated with roll over anticlines this regime had ceased by the aptian and the basin passed through a period of relative stability in the late cretaceous followed by tectonic inversion and in the miocene by northwards compressive movement along the former normal faults this partially restored the earlier separative displacement at depth and probably accentuated pre existing roll over anticlines it was expressed in the surficial upper cretaceous palaeogene sequence as monoclinal flexuring the early rifting and the change from overall n s crustal stretching to compression may reflect plate tectonic events in the north atlantic region

a statistical study of gravity waves in the polar regions based on operational radiosonde data gravity waves in the lower polar stratosphere are examined using operational radiosonde observations gathered from 33 stations over a period of 10 years both the potential and kinetic energies of the gravity waves vary annually and reach maxima in winter in the arctic and in spring in the antarctic in the antarctic spring a region of large gravity wave energy propagates downward following the movement of a zone of high static stability associated with southern hemispheric warming moreover the enhanced energy region and the high stability zone coincide in the horizontal plane and move gradually from 135 e 50 s to 45 w 70 s over the south pole the vertical and horizontal directions of wave propagation are examined using hodograph analysis in the vertical most gravity waves transfer energy upward in the arctic while the percentage of downward energy propagation is relatively high in winter and spring in the antarctic horizontally gravity waves propagate westward relative to the mean wind in the arctic while in the antarctic the dominant direction varies from station to station the correlation between gravity wave energy in the lower stratosphere and the mean wind is also examined in the arctic gravity wave energy is highly correlated with the surface wind though in the antarctic it correlates with the stratospheric wind these results suggest that gravity waves observed in the arctic are forced by topography whereas in antarctica some sources may exist in the stratosphere one such source candidate is likely to be the polar night jet

5 9 mw 18th june 2010 earthquake and fault segment linkage at andaman a study based on macroseismic survey gps geodesy and coulomb stress changes abstract 18th june 2010 5 9 mw earthquake at north andaman triggered along nw se pre existing fault with reverse fault mechanism macroseismic survey and gps geodesy reveal maximum damages following ne sw trend due to normal fault mechanism coulomb stress modeling for post and inter seismic earthquakes after the 2004 mega earthquake show different stages of fault segment linkage at north andaman the present earthquake has been explained as co shock due to asiesmic soft linkage of fault propagation

trapped waves in the edge region of stratospheric polar vortices 1 a global distribution and seasonal variability of short period 2 days disturbances in the lower and middle stratosphere are investigated using 6 hourly european centre for medium range weather forecasts reanalysis data over 15 years 1979 1993 two dimensional spectral analysis and a recently developed lagrangian mean diagnostic are used for the analysis it is shown that the short period disturbances are most active around the polar night jet in each winter hemisphere they have a wavelike structure in the longitudinal direction with typical zonal wavelengths of 1 700 2 000 km i e zonal wave number 10 12 and a latitudinally evanescent structure with a half width of about 1 500 km suggesting that they are waves trapped in the edge region of the polar vortex where the latitudinal gradient of isentropic potential vorticity is maximized the trapped waves have a nearly barotropic structure over a depth greater than 10 km because the polar vortex in the northern hemisphere is much deformed and not symmetric around the pole dynamical characteristics of the trapped waves in the southern hemisphere alone are investigated by applying a lag correlation analysis to the reanalysis data the characteristics of trapped waves are fairly dependent on the state of the polar vortex such as zonal wind speed and its vertical shear they have a significant westward intrinsic phase velocity from june through october when the polar vortex is most stable this indicates that the trapped waves during this period have their own dynamics contrary to the filaments being passively advected by the large scale flow

gravity wave generation around the polar vortex in the stratosphere revealed by 3 hourly radiosonde observations at syowa station intensive radiosonde observations were performed at syowa station 69 0 s 39 6 e over about 10 days in each of march june october and december 2002 to examine inertia gravity wave characteristics in the antarctic lower stratosphere based on the 3 hourly observation data two dimensional i e vertical wavenumber versus frequency spectra of wind fluctuations were examined utilizing a double fourier transform method clear signals of gravity waves whose phases propagate upward suggesting downward energy propagation are detected in june and october when the polar night jet pnj was present on the other hand downward phase propagation i e upward energy propagation components are dominant in all months there is a spectral peak around the inertial frequency in a wide range of vertical wavenumbers in december when the background wind was weak whereas large spectral densities are distributed over lower frequency regions in june and october these spectral characteristics are consistent with the results obtained using a gravity wave resolving global circulation model gcm by sato et al dynamical characteristics are examined separately for upward and downward propagating gravity waves in june using a hodograph analysis method as a result it is found that upward and downward propagating wave packets observed simultaneously in the same height regions have similar horizontal wavelengths and phase velocities this fact suggests that these gravity waves are generated from the same source with a similar mechanism when the wave packets were observed both the local rossby number and the residual in the nonlinear balance equation estimated using ncep ncar reanalysis data are large around the pnj situated slightly to the lower latitudes of syowa station therefore it is likely that the observed inertia gravity waves are generated by a spontaneous adjustment around the geostrophically unbalanced pnj and propagate toward syowa station the possibility of spontaneous gravity wave generation around the pnj is confirmed by comparison with the gcm simulation by sato et al

kinematic analysis of faults in a physical model of growth faulting above a viscous salt analogue abstract syn sedimentary faults overlying an extended ductile layer within a sand model provide an analogue for studying some aspects of the geometry and kinematics of basin scale extensional listric faults associated with salt rollers the displacement analysis techniques used to examine displacement variations over fault surfaces within the sand model show that displacement varies in a regular and predictable manner deviations from simple fault displacement patterns are due to transfers of displacement onto adjacent synthetic faults aggregation of the displacements on adjacent synthetic faults produces more regular patterns of displacement distribution and demonstrates the geometric coherence of the aggregated faults rapid upward decreases in displacement on the model faults are due to fault growth during sedimentation elsewhere in the model post sedimentary faulting is associated with very low upward displacement gradients and pre and syn faulting sedimentation are readily distinguished on cross sectional fault traces in three dimensions a non horizontal line separating the pre faulting and syn faulting sequences tracks the lateral extent of a fault through time backstripping of fault displacements by subtracting the fault displacement of a sedimentary horizon from the displacements of underlying horizons gives the displacement distribution on a fault surface at the time of deposition of the backstripped horizon backstripped fault displacement distributions also allow examination of the general fault structure through time backstripping of fault displacements on one of the larger faults within the model and on an associated hanging wall synthetic splay shows that the two structures originated as a relay zone which was breached by lateral propagation of one of the overlapping faults which form the relay zone the backstripping technique allows determination of the geometrical changes during growth of a fault system

displacement geometry in the volume containing a single normal fault fault displacements measured in coal mines and from seismic data are used to develop a model describing the near field displacements associated with an ideal single normal fault displacement on a fault surface ranges from a maximum at the center of the fault to zero at the edge or tip line the tip line is elliptical with the shorter axis of the ellipse parallel to the displacement direction contours of equal displacement form concentric ellipses centered on the point of maximum displacement displacement gradients vary with fault size and with mechanical properties of host rock fault radius to maximum displacement ratios range from 5 to 500 plotting of displacement contour diagrams and knowledge of displacement gradients are useful in interpreting seismic reflectio data both for quality control of interpretations and for quantitative extrapolation of limited data displacements associated with faulting decrease systematically with increasing distance along the normal to the fault surface this decrease is seen as reverse drag in both hanging wall and footwall hanging wall rollover and tilting of the reflectors cannot be used to distinguish listric from planar normal faults even where fault block rotation can be demonstrated neither listric fault geometry nor a flat detachment surface is geometrically necessary because faulting is accommodated by ductile deformation rigid fault bounded blocks cannot exist except in some special circumstances related to a free surface the displacements within the rock volume affected by a single fault are not simply related to regional extension apparent horizontal extension by faulting varies from one layer to another and a significant proportion of the extension in a basin may be due to ductile deformation

general aspects of a t213l256 middle atmosphere general circulation model 1 a high resolution middle atmosphere general circulation model gcm developed for studying small scale atmospheric processes is presented and the general features of the model are discussed the gcm has t213 spectral horizontal resolution and 256 vertical levels extending from the surface to a height of 85 km with a uniform vertical spacing of 300 m gravity waves gws are spontaneously generated by convection topography instability and adjustment processes in the model and the gcm reproduces realistic general circulation in the extratropical stratosphere and mesosphere the oscillations similar to the stratopause semiannual oscillation and the quasi biennial oscillation qbo in the equatorial lower stratosphere are also spontaneously generated in the gcm although the period of the qbo like oscillation is short 15 months the relative roles of planetary waves large scale gws and small scale gws in maintenance of the meridional structures of the zonal wind jets in the middle atmosphere are evaluated by calculating eliassen palm diagnostics separately for each of these three groups of waves small scale gws are found to cause deceleration of the wintertime polar night jet and the summertime easterly jet in the mesosphere while extratropical planetary waves primarily cause deceleration of the polar night jet below a height of approximately 60 km the meridional distribution and propagation of small scale gws are shown to affect the shape of the upper part of mesospheric jets the phase structures of orographic gws over the south andes and gws emitted from the tropospheric jet stream are discussed as examples of realistic gws reproduced by the t213l256 gcm

the estimation of fault slip from map data the separation pitch diagram although an essential feature of faults is that they produce a relative movement of two blocks the total or net slip is known only for a very small percentage of faults this note proposes a diagram for the graphical determination of net slip from the strike separation of markers recorded on geological maps with or without knowledge of the net slip direction the strike separation of one marker allows the drawing of a solutions line on the diagram depicting the range of slip vectors compatible with the measured separation the net slip vector can be obtained by either the intersection of two or more solutions lines or from a single solutions line if the direction of slip is independently known the diagram gives a visual appreciation of the effects of data uncertainty on the estimate of net slip and is a useful device for the representation of the kinematic characteristics of a collection of faults the use of the diagram is illustrated with examples from the south wales coalfield and the moine thrust zone

models of single stage concomitant potassium argon exchange an interpretation of discordant whole rock k ar data from hydrothermally altered igneous rocks of the south pennine orefield u k abstract a model of single stage concomitant potassium and argon exchange is advanced to explain the existence of rectilinear isochrons in potassium argon correlation diagrams produced from suites of altered rocks negative isochron intercepts are shown to be a consequence of fractional argon loss which exceeds potassium loss and it is demonstrated that no information of immediate geological significance can be obtained from the gradient of such an isochron bounds to the primary formation age and age of exchange event may be established using extreme values of the observed potassium content and from estimates based on the inferred petrology and chemistry of the unaltered rock and or its alteration products ten carboniferous igneous units from the south pennine orefield involving thirty eight independent samples are investigated by means of the model and eight of the units are consistent with a model of potassium and argon exchange occurring in earliest mesozoic times ca 200 ma it is argued that this conclusion augments the already substantial body of evidence for an identifiable widespread igneous and hydrothermal province associated with early rifting processes in the north atlantic

selective reverse reactivation of normal faults and deformation around reverse reactivated faults in the mesozoic of the somerset coast abstract normal faults exposed in the triassic jurassic limestones and shales of the somerset coast were formed during the mesozoic development of the bristol channel basin reverse reactivation of some of these normal faults occurred during late cretaceous to early tertiary north south contraction the contraction is also evident from thrusts and conjugate strike slip faults preferential reactivation of the normal faults is attributed to 1 decreased fault plane friction 2 domino block rotation 3 displacement magnitude and 4 fault connectivity the geometries of overlapping and underlapping zones in reactivated fault zones are dependent on the existing structural geometry two distinctive styles of displacement accommodation occur between reverse reactivated normal faults 1 formation of a network of strike slip faults conjugate about nne ssw and 2 oblique steeply dipping reverse faults interaction between strike slip and an existing fault is dependent on whether the normal fault was reactivated the range of structures related to the north south contraction has been incorporated into a single deformation model controlled by the northwards movement of the hanging wall of the quantock s head fault pure dip slip movement occurred in the centre of its curved fault trace with a sinistral component at the western tip and a dextral component of displacement and strike slip block rotations occurred at the eastern tip shortening of these blocks was achieved through development of a strike slip fault network and nw striking thrusts in an underlap zone loading of the footwall by the hanging wall block modified the local stress system to allow formation of oblique steeply dipping reverse faults

tectonic evolution of the northumberland basin the effects of renewed extension upon an inverted extensional basin the northumberland sedimentary basin has a history of repeated extensional and contractional tectonic phases and a study of the deformation interference pattern and sedimentary record allows the identification of the tectonic state through time initial rifting is represented by a thick dinantian sedimentary fill but carboniferous extension is thought to have ceased by the early namurian in order to explain the development of certain facies patterns during the westphalian thermal subsidence phase of the evolution of the northumberland basin some syn depositional extensional fault movements are required at other times in the westphalian compaction induced subsidence was the dominant control on facies distribution a single phase of e w to se nw variscan compression commenced during or after late westphalian times and ceased prior to the intrusion of the whin sills and dykes subsequent permo mesozoic extension with a right lateral shear component re activated pre existing normal fault lines these later structures may be interpreted as being listric in form shallowing onto decollement surfaces within the carboniferous basin fill and overlie the buried faulted margin at the southern side of the basin

structural evolution of the witch ground graben the witch ground graben is a nw se trending extensional basin in the central part of the northern north sea lying between the moray firth and the viking graben ne sw extension occurred from triassic to cretaceous times extension took place on listric normal faults along the sw margin with downthrow to the ne giving rise to the asymmetry of the basin one of the principal phases of fault controlled subsidence occurred in the lower cretaceous from the valanginian to albian compilation of biostratigraphic data from this interval shows the development of an increasing number of stratigraphic breaks across the basin from sw to ne these breaks increasing in time span also in this direction this is a result of rotation of the subsiding fault block on the listric extensional faults the rotation is recorded in dipmeter data and occurred in several distinct episodes the triassic the volgian and the valanginian to aptian in reconstructing a cross section of the basin the interpreted fault curvature is constrained by the observed rotation of bedding surfaces and the amount of extension across the listric faults is constrained by the observed basin subsidence a depth to decollement for the faults of 4 km below sea level and an extension across the basin of 40 are estimated

40ar 39ar ages from the narragansett basin and southern rhode island basement terrane their bearing on the extent and timing of alleghenian tectonothermal events in new england pennsylvanian sedimentary rocks record the effects of progressive barrovian metamorphism and polydeformation in the narragansett basin of rhode island whole rock phyllite samples from low grade portions of this terrane display internally concordant 40 ar 39 ar age spectra with plateau ages of 248 to 258 m y four samples biotite from higher grade rocks records plateau ages of 240 to 248 m y eight samples similar 40 ar 39 ar biotite ages are displayed westward across the southern rhode island basement terrane 239 to 250 m y nine samples although coexisting hornblende records slightly older plateau ages of 255 m y two samples the 40 ar 39 ar plateau ages are interpreted to date times of post metamorphic cooling through temperatures required for argon retention in the various mineral phases examined the ages suggest that a distinct late paleozoic alleghenian thermal event affected much of southern rhode island together with the depositional ages of the variably metamorphosed pennsylvanian rocks westphalian b stephanian a or b the 40 ar 39 ar data permit calibration of the sequence of alleghenian tectonothermal events recorded in the narragansett basin the controls suggest a permian event lasting about 40 to 50 m y between initial barrovian regional metamorphism and synchronous d 1 d 2 ductile deformation between 295 and 275 m y and post d 3 cooling below argon retention temperatures between 250 and 240 m y

basin inversion by distributed deformation the southern margin of the bristol channel basin england several models of basin inversion described in the literature are tested in a study of triassic and early jurassic strata exposed along the southern margin of the bristol channel basin in somerset england that has been exhumed by 95 of them are still in net extension despite widespread kinematic evidence for reverse reactivation when coupled with the general absence of thin skinned thrusts and the widespread occurrence of regional contractional folds it appears that none of three main inversion models the fault reactivation model the thin skinned model and the buttress model are by themselves applicable we erect a new model of basin inversion the distributed deformation model which consists of three stages of basin inversion stage one involved early partial reactivation of large displacement steep normal faults stage two was dominated by folding wherein fault blocks underwent oblique non coaxial shortening by map scale folding accompanied by formation of outer arc normal faults minor cleavage and neoformed thrusts stage three involved reverse reactivation of outer arc normal faults and activation of oblique and strike slip faults that partitioned deformation into compartments

dem based morphometry of range front escarpments in attica central greece and its relation to fault slip rates in this paper we apply current geological knowledge on faulting processes to digital processing of digital elevation models dem in order to pinpoint locations of active faults the analysis is based on semiautomatic interpretation of 20 and 60 m dem and their products slope shaded relief in northern eastern attica five normal fault segments were recognized on the 20 m dem all faults strike wnw ese the faults are from west to east thriassion thfs fili fifs afidnai affs avlon avfs and pendeli pefs and range in length from 10 to 20 km all of them show geomorphic evidence for recent activity such as prominent range front escarpments v shaped valleys triangular facets and tilted footwall areas however escarpment morphometry and footwall geometry reveal systematic differences between the bexternalq segments pefs thfs and avfs and the binternalq segments affs and fifs which may be due to mechanical interaction among segments and or preexisting topography in addition transects across all five escarpments show mean scarp slope angles of 22 18f0 78 for both carbonate and metamorphic bedrock the slope angle equation for the external segments shows asymptotic behaviour with increasing height we make an empirical suggestion that slope angle is a function of the long term fault slip rate which ranges between 0 13 and 0 3 mm yr the identified faults may rupture up to magnitude 6 4 6 6 earthquakes the analysis of the 60 m dem shows a difference in fault patterns between western and northern attica which is related to crustal rheology variations d 2004 elsevier b v all rights reserved

late brittle deformation in a caledonian ductile thrust wedge new evidence for gravitational collapse in the moine thrust sheet sutherland scotland abstract in the ductile regions of orogenic wedges late brittle structures formed at shallow crustal depths have received little attention however they are important as they of ten record the final stages in deformational history during uplift and erosion of the orogen in the moine rocks of sutherland late caledonian brittle folds and low angle faults post date ductile structures formed during wnw nw directed thrust movements earlier in the same orogenic event in the western moine nappe the late structures display geometries which indicate that they formed during regionally ese directed extensional movements down the dip of the pre existing regional foliation these late structures are correlated with similar wnw directed extensional low angle faults recognised in the moine thrust zone south of the assynt culmination both are thought to have formed in response to late caledonian gravity induced thinning of the moine thrust wedge and both pre date devonian extension associated with the formation of the west orkney basin along strike changes in the location and sense of extensional movements north and south of the assynt culmination are explained by changes in the pre existing structural geometry of the caledonian ductile thrust nappes within the moine hence earlier deformation patterns are thought to exert important controls over later events in an evolving orogenic wedge

paleostress inversion a multi parametric geomechanical evaluation of the wallace bott assumptions wallace 1951 and bott 1959 were the first to introduce the idea that the slip on each fault surface has the same direction and sense as the maximum shear stress resolved on that surface however this simplified hypothesis is questionable since fault mechanical interactions may induce slip reorientations earlier numerical geomechanical models confirmed that the slickenlines slip vectors are not necessarily parallel to the maximum resolved shear stress but are consistent with local stress perturbations this leads us to ask as to what extent the wallace and bott simplifications are reliable as a basis hypothesis for stress inversion from fault slip data here a geomechanical multi parametric study using a 3d boundary element method covering i fault geometries such as intersected faults or corrugated fault surfaces ii the full range of andersonian state of stress iii fault friction iv fault fluid pressure v half space effect and vi rock properties is performed in order to understand the effect of each parameter on the misfit angle between geomechanical slip vectors and the resolved shear stresses it is shown that significant misfit angles can be found under specific configurations invalidating the wallace and bott assumptions even though fault friction tends to minimize the misfit we therefore conclude that in such cases stress inversions based on fault slip data should be interpreted with care

the influence of differential sedimentary loading and compaction on the development of a deltaic rollover abstract three dimensional seismic data and wireline logs from the western niger delta were analyzed to reveal the sedimentary and tectonic history of a major deltaic growth fault depocenter comprising a kilometer scale rollover anticline the seismic units of the rollover show a non uniform thickness distribution with their respective maximum near the main bounding growth fault on the landward side of the system this wedge shaped sediment storage architecture ultimately reflects the non uniform creation of accommodation space in the study area that was controlled by 1 the differential compaction of the hanging wall and footwall strata 2 the lateral variation of fault induced tectonic subsidence above the listric master fault and possibly 3 local subsidence related to the subsurface movement of mobile shale reacting to loading and buoyancy a sequential three dimensional decompaction of the interpreted deltaic rollover units allowed to reconstruct and measure the compaction development of the rollover succession through time documenting that sediment compaction contributed per depositional interval to between 25 and 35 of the generation of depositional space subsequently filled by deltaic sediments the incremental decompaction of sedimentary units was further used to quantify the cumulative amount of accommodation space at and around the studied rollover that was created by fault movement shale withdrawal regional tectonic subsidence isostasy and changes in sea level if data on the regional subsidence and eustasy are available the contribution of these basinwide controls to the generation of depositional space can be subtracted from the cumulative accommodation balance which ultimately quantifies the amount of space for sediments to accumulate created by fault movement or shale withdrawal this observation is important in that it implies that background knowledge on subsidence stratigraphic age and sea level changes allows to reconstruct and quantify fault movement in syn tectonic deltaic growth successions and this solely based on hanging wall isopach trends independent of footwall information

energy enhancements of gravity waves in the antarctic lower stratosphere associated with variations in the polar vortex and tropospheric disturbances 1 gravity waves in the antarctic lower stratosphere are examined using original operational radiosonde data obtained at syowa station 69 0 s 39 6 e with fine vertical resolution in the lower stratosphere the temporal variation in gravity wave energy depends on height in the height region of 13 15 km just above the tropopause the seasonal variation in gravity wave energy is not evident the wave energy is rather enhanced when the absolute value of potential vorticity in the upper troposphere becomes small over syowa station this fact implies that tropospheric disturbances affect the dynamical processes of gravity waves there however the gravity wave energy in the height region of 15 25 km shows clear seasonal variation having a maximum in spring the time variation in gravity wave energy is examined in detail in terms of the polar vortex by using the equivalent latitude coordinate energy enhancements occur when the edge of the polar vortex approaches syowa station and the enhancements are especially large when the polar vortex breaks down in spring these results suggest that height variation in the background atmosphere leads to the difference of wave characteristics between the two height regions the enhancements of wave energy are partly explained as modification of the wave structure by the background wind speed and the static stability but it is also likely that enhancements of wave activity contribute to the energy enhancement at the edge of the polar vortex in spring

is lithostatic loading important for the slip behavior and evolution of normal faults in the earth s crust normal faults growing in the earth s crust are subject to the effects of an increasing frictional resistance to slip caused by the increasing lithostatic load with depth we use three dimensional 3 d boundary element method numerical models to evaluate these effects on planar normal faults with variable elliptical tip line shapes in an elastic solid as a result of increasing friction with depth normal fault slip maxima for a single slip event are skewed away from the fault center toward the upper fault tip there is a correspondingly greater propagation tendency at the upper tip however the tall faults that would result from such a propagation tendency are generally not observed in nature we show how mechanical interaction between laterally stepping fault segments significantly competes with the lithostatic loading effect in the evolution of a normal fault system promoting lateral propagation and possibly segment linkage resultant composite faults are wider than they are tall resembling both 3 d seismic data interpretations and previously documented characteristics of normal fault systems however this effect may be greatly complemented by the influence of a heterogeneous stratigraphy which can control fault nucleation depth and inhibit fault propagation across the mechanical layering our models demonstrate that although lithostatic loading may be an important control on fault evolution in relatively homogeneous rocks the contribution of lithologic influences and mechanical interaction between closely spaced laterally stepping faults may predominate in determining the slip behavior and propagation tendency of normal faults in the earth s crust

supracrustal faults of the st lawrence rift system quebec kinematics and geometry as revealed by field mapping and marine seismic reflection data abstract the st lawrence rift system from the laurentian craton core to the offshore st lawrence river system is a seismically active zone in which fault reactivation is believed to occur along late proterozoic to early paleozoic normal faults related to the opening of the iapetus ocean the rift related faults fringe the contact between the grenvillian basement to the nw and cambrian ordovician rocks of the st lawrence lowlands to the se and occur also within the grenvillian basement the st lawrence rift system trends ne sw and represents a se dipping half graben that links the nw se trending ottawa bonnechere and saguenay river grabens both interpreted as iapetan failed arms coastal sections of the st lawrence river that expose fault rocks related to the st lawrence rift system have been studied between quebec city and the saguenay river brittle faults marking the st lawrence rift system consist of ne and nw trending structures that show mutual crosscutting relationships fault rocks consist of fault breccias cataclasites and pseudotachylytes field relationships suggest that the various types of fault rocks are associated with the same tectonic event high resolution marine seismic reflection data acquired in the st lawrence river estuary between rimouski the saguenay river and forestville identify submarine topographic relief attributed to the st lawrence rift system northeast trending seismic reflection profiles show a basement geometry that agrees with onshore structural features northwest trending seismic profiles suggest that normal faults fringing the st lawrence river are associated with a major topographic depression in the estuary the laurentian channel trough with up to 700 m of basement relief a two way travel time to bedrock map based on seismic data from the st lawrence estuary and comparison with the onshore rift segment suggest that the laurentian channel trough varies from a half graben to a graben structure from sw to ne it is speculated that natural gas occurrences within both the onshore and offshore sequences of unconsolidated quaternary deposits are possibly related to degassing processes of basement rocks and that hydrocarbons were drained upward by the rift faults

growth and linkage of a complex oblique slip fault zone in the pearl river mouth basin northern south china sea abstract oblique slip faults are ubiquitous in sedimentary basins but have been largely neglected relative to their dip slip counterparts case studies of oblique slip faults are very limited in this study we used 3d seismic data tied to well control to investigate the geometry kinematic characteristics growth and linkage and tempo spatial evolution of a complex oblique slip growth fault zone in the pearl river mouth basin prmb of the northern continental margin south china sea scs the e w oriented 30 5 km long fault zone consists of two superimposed oblique slip fault systems the lower fault system is an integrated zig zag fault consisting of three ene wsw to e w striking right stepping sinistral en echelon fault segments which were hard linked by two nw se trending fault segments while the upper fault system is composed of nine wnw ese striking left stepping dextral en echelon component faults which had overlapping fault tips and were partly hard linked by breaching of the relay zones the lower and upper fault systems were activated in the eocene and the oligocene to pliocene which respectively correspond to the syn rift and post rift stages in the prmb the fault throws up to 288 m and activity rates up to 34 5 m ma of the upper fault system are overall much less than those of its lower counterpart reactivation of the lower syn rift fault system shows clear influence on the development of post rift en echelon fault segments a four stage evolution model of the oblique slip fault zone was presented

gravity wave characteristics in the lower atmosphere at south pole a 4 year 1993 1996 temperature and wind data set obtained from over 2000 high resolution balloon soundings at south pole is used to study gravity wave characteristics in the troposphere and lower stratosphere extensive analyses of energy density spectra and static stability are performed to present a comprehensive view of the gravity wave characteristics in the lower atmosphere at south pole our results show that the gravity waves are ubiquitous and often fairly strong at south pole even though the generation mechanisms are not clear gravity wave characteristics are in general similar to those obtained at other high latitude southern hemisphere stations potential energies vary between about 0 5 j kg and 5 j kg with season and altitude variations in kinetic energies are not well correlated with potential energy variations and range from 1 j kg to 11 j kg we observe significant seasonal variations of the slope and magnitude of the vertical wavenumber spectrum of temperature fluctuations especially in the stratosphere in general the gravity waves in the stratosphere are stronger weaker in austral spring fall wave activity in the troposphere has little seasonal dependence stability analysis shows that instabilities are more likely to occur in the troposphere than in the stratosphere the probability of wave instability is 13 7 in the troposphere and 5 4 in the stratosphere this is due to the less stable stratification in the troposphere where the buoyancy period averages 8 3 min compared to 4 9 min in the stratosphere dynamic shear instability is more likely to occur than convective instability 11 versus 2 6 in the troposphere and 4 7 versus 0 7 in the stratosphere due to the prevailing strong wind shear the instability probabilities vary seasonally with the austral winter exhibiting the highest probability of instabilities dynamic and convective instabilities combined in both the troposphere and stratosphere

dips of normal faults in british coal measures and other sedimentary sequences fault dip measurements n 3291 from 122 faults in british coalfields are presented two classes of normal fault are recognized a gently dipping 55 post coalification tectonic faults formed at depths of about 2 5 km which comprise 90 of the faults analysed dip data from the steeply dipping faults are variable standard deviation 9 both on single faults and between faults and 70 is a better approximation of fault dip than the commonly accepted value of 60 data on tectonic normal faults with comparable depths of formation using the modified griffith fracture criterion the dips of faults at varying depths up to 4 km are calculated for both unsaturated dry and saturated rocks the dips of normal faults are expected to vary from 90 at the surface to 60 at 3 4 km and this variation is consistent with the limited field data available the coalfield data are consistent with fault formation at standard hydrostatic pore fluid pressures at depths of about 2 5 km below depths of a few kilometres normal faults are expected to flatten out gradually to a dip of 45 but such flattening is not necessarily an indication of an underlying detachment

development of rift basins illustrated by the structural evolution of the oseberg feature block 30 6 offshore norway the mesozoic tilted fault block in norwegian north sea block 30 6 containing the giant oseberg oil and gas field is used to illustrate basin development during the jurassic and cretaceous there is seismic evidence for an early rifting phase in the northern viking graben on which the jurassic cretaceous rifting phase early bathonian to berriasian is overprinted the oseberg structure is representative of other fault blocks bordering the northern viking graben axis planar normal faults and listric faults which were restricted to the rifting phase dominate both fault types exhibit syn fault sedimentation listric faulting is recognized on seismic sections by the differential tilting reverse drag antithetic faulting and a wedge shaped syn rift reflector package the initiation of rifting is dated by baselap onto pre rift reflectors and cessation is dated by an unconformity beneath the generally onlapping post rift sediments steeply dipping planar normal faults often active along previously established fault zones played a significant part in the post rift development of the basin the last movement on planar normal faults in the oseberg fault scarp becomes younger away from the rift axis and this produced the complex fault scarp visible on many seismic lines the topography defined by the post rift unconformity is a composite surface which formed in response to subsidence processes it is not the result of orogenic events such as the kimmerian 9orogeny9 footwall uplift associated with planar normal faults caused local unconformities in complex fault scarps and on fault block crests

extensional failure and hydraulic valving at minas da panasqueira portugal evidence from vein spatial distributions displacements and geometries abstract at panasqueira portugal exceptional exposure and demonstrable vein connectivity allow robust characterisation of brittle elastic failure mechanisms in intrusive related environments extensional failure was driven by cycles of fluid injection hydraulic valving and vein growth under conditions with v 1 and differential stress

hydrothermal fluid origins in a fluorite rich mississippi valley type district combined noble gas he ar kr and halogen cl br i analysis of fluid inclusions from the south pennine ore field united kingdom the south pennine peak district ore field united kingdom is host to several fluorite rich mississippi valley type deposits and was chosen for study as an analogue to the illinois kentucky fluorspar district united states the study was undertaken to test the idea that the large scale carbonate dissolution and fluorite rich mineralogy characteristic of both districts may require a magmatic source of hf the data also provide constraints for water rock interactions and potential fluid sources relevant to the local geology of the south pennine ore field samples were studied from two of the largest and most economically important deposits within the south pennine ore field the hucklow edge and dirtlow rakes in vacuo crushing of irradiated calcite samples released inclusion fluids that were analyzed for noble gas isotopes ar ar kr and the halogens cl br i this was achieved simultaneously by noble gas mass spectrometry ar ar methodology and was combined with fluid inclusion thermometric salinity data to determine noble gas concentrations in addition he isotope analyses were obtained from unirradiated fluorite the he he ratio of the pennine ore fluids 0 1 ra where ra atmospheric he he ratio of 1 4 10 is significantly lower than the maximum value recorded in the illinois kentucky fluorspar district 0 35 ra kendrick et al 2002 this volume indicating a crustal fluid source and supporting existing basinal brine models the low ar ar ratios with most 50 to 60 percent halite dissolution water br cl mol ratio 0 57 0 92 10 the salinity of fluids included in the main stage of the hucklow edge mineralization avg of 22 wt nacl equiv places an upper limit on the extent of meteoric recharge at 15 vol percent a secondary vein present at hucklow edge has a lower salinity of 40 m y a time scale compatible with models in which fluids were derived from small local basins such as the widmerpool and edale gulfs

patterns of displacement along large normal faults implications for basin evolution and fault propagation based on examples from east africa seismic reflection data across six boundary faults from east africa have revealed information about the way boundary faults develop with respect to the synkinematic basin fill previous models of basin fill assume that lateral fault propagation and deposition occur simultaneously which gives rise to along axis onlap of the basin fill onto the prerift basement propagating basin model seismic reflection data from boundary faults in east africa show only rare evidence for along axis broadening of the basins instead the basin margins appear to be fixed from a very early stage in the basin history nonpropagating basin model depocenters shift not by gradual lateral propagation but by abrupt changes in location such observations indicate that boundary fault propagation to near maximum length occurs rapidly during the very early stages of rifting probably by linkage of numerous small faults displacement then builds following the b value earthquake model along the fault during basin development out of phase with the main propagation phase mature fault systems may have experienced several phases of jumps in fault length or the location of fault activity major boundary faults exhibit three basic patterns of evolution these patterns of evolution can have many variants and include 1 simple displacement where maximum displacement is approximately at the center of the fault and decreases gradually toward the fault tips 2 variable along strike displacement that incorporates linkage of in line or en echelon relatively large displacement faults of similar age leaving transverse anticlines and synclines and 3 asymmetric propagation where one tip of a fault remains more or less fixed while the other tip propagates a relatively long distance asymmetric propagation can occur smoothly and gradually or alternatively there can be a jump in the location of the fault and a new fault of different age can form along strike from the older fault eventually the new fault propagates and links with the older fault segment reactivating the older fault to some extent addition ally long lived faults may be composites of fault types 1 3

the geometrical evolution of normal fault systems abstract the purpose of this paper is to examine the kinematic behaviour of normal fault systems and see what general conditions govern their geometrical evolution we pay particular attention to seismological and surface data from regions of present day active normal faulting as the instantaneous three dimensional geometry at the time of fault movement is better known in active regions than in areas where the faults are now static most normal faults are concave upward or listric this shape can be produced by geometric constraints either because the faults reactivate curved thrusts or because they must be curved to accommodate rotations another effect which will produce curved faults is the variation of rheology with depth brittle failure at shallow depths produces less fault rotation than does distributed creep in the lower part of the crust an important geometric feature of normal faulting is the uplift of the footwall the amount of such uplift is related not only to the elastic properties of the lithosphere but also to the throw and dip of the fault a striking feature of active normal faults is that they occur in groups in which all the faults dip in the same direction this behaviour arises because the faults cannot intersect if they do one must cease to be active the rotation which such fault systems produce reduces the dip of the faults until a new steeply dipping fault is formed once a new fault cuts pre existing faults the earlier faults become locked and a new set of faults must propagate rapidly across the whole region involved many of these geometric constraints also apply to thrust faulting

structural controls on upper palaeozoic sedimentation in south east wales marked thickness changes in early dinantian courceyan chadian sediments occur across the cardiff cowbridge anticline a major east west variscan fold in the vale of glamorgan they resulted from differential subsidence over an active concealed basement fault zone the vale of glamorgan axis which is coincident with the hinge of the anticline the latter formed in response to inversion on this basement fault a caledonian ancestry for the vale of glamorgan axis is indicated by pronounced upper old red sandstone overstep across it across the severn estuary between south wales and the bristol mendips region there is a significant offset of isopachs and facies belts in both the courceyan chadian and arundian sequences it is suggested that these result from intra carboniferous dextral strike slip along a major fault zone underlying the severn estuary the severn estuary fault zone and that the vale of glamorgan axis was a synthetic structure developed in conjunction with this strike slip movement by inference the severn estuary fault zone shares a common history with the vale of glamorgan axis extending back to the devonian and possibly earlier late dinantian holkerian facies distribution reflects uplift and emergence on the north south usk anticline and malvern lineament continued uplift is recorded in silesian sequences in south east wales and the bristol mendips area the orientation of structures bordering the severn estuary is consistent with their development in a right lateral strike slip zone

the role of fault reactivation and growth in the uplift of western fennoscandia new structural data published aft data and topographic data suggest that the latest cretaceous cenozoic uplift of western norway was associated with normal reactivation of the more trondelag fault complex reactivation focused along the base of today9s topographic rise with maximum displacements in the order of 2 3 km structural and aft data indicate that reactivation occurred along a displacement gradient with least normal displacement in the ne and increasing displacements towards the sw reactivation commenced in connection with the triassic to earliest cretaceous phases of rifting on the norwegian margin and probably continued through most of the tertiary the late cretaceous to cenozoic topographic development of the scandes mountains followed structurally induced templates such as those described from other areas of active normal faulting a fault model for the cenozoic uplift of the norwegian mainland provides a framework for provenance erosion and transport of sediments eventually deposited in the offshore post rift basins in the latest cretaceous palaeogene and neogene the asymmetric topographic profile of fennoscandia is reflected in the aft data and suggests that lithospheric flexure places a first order control on the shape of the scandes mountains and the central fennoscandian craton

morphotectonic analysis of the lunigiana and garfagnana grabens northern apennines italy implications for active normal faulting abstract this work integrates existing structural geology data with new detailed geomorphic analyses of the fluvial network to characterize active and potentially seismogenic faults bordering the lunigiana and garfagnana basins in the northern apennines of italy these two basins are nw se oriented asymmetric grabens bordered by several normal faults with a poorly known but probable recent slip history several strong earthquakes m 5 0 6 5 have occurred in the area in the last millennium demonstrating that this is one of the most seismically active areas of the northern apennines however the lack of reliable instrumental data for strong earthquakes generally low deformation rates and poor exposures of faulted quaternary sediments render the characterization of active seismogenic faults problematic here we quantify the relationships between faults and watershed scale geomorphology using 10 m digital topography to extract channel and basin metrics such as steepness concavity and stream length gradient indices of modeled river longitudinal profiles in particular convex segments of longitudinal profiles knickpoints are investigated in the spatial context of suspected active faults several knickpoints arise locally from juxtaposed rock types of different erodibility however many others mapped along major normal faults have a clear tectonic origin in fact the height of the footwall knickpoints the closest to the fault trace varies along strike the fault increasing toward the fault center and tapering off toward the fault tips mimicking the expected displacement profile of a fault in these cases we consider the knickpoint height as a proxy of the fault throw accumulated by the youngest fault activity probably during the late quaternary the along strike distribution of knickpoint heights helps in defining the likely segmentation pattern of the fault system the identified active normal fault segments have lengths ranging from 9 5 to 28 5 km the inferred late quaternary throw rate ranges from 0 3 to 0 8 mm a however the absence of any offset datable material limits our ability to assign precise numeric ages and rates of offset to the faulting

longitudinally dependent ozone increase in the antarctic polar vortex revealed by balloon and satellite observations the horizontal structure of processes causing increases in ozone in the antarctic polar vortex was examined using data measured in 2003 from an ozonesonde observation campaign at syowa station 39 68e 69 08s and from the improved limb atmospheric spectrometer ii ilas ii onboard the advanced earth observing satellite ii the ilas ii data are daily and distributed uniformly at 14 points in the zonal direction mostly at polar latitudes the antarctic ozone hole that developed in 2003 was one of the largest recorded the period of focus in this study is 26 september through 24 october when a strong polar vortex was situated in the stratosphere an ozone mixing ratio contour 1 0 ppmv moved downward near a height of 20 km during the period of focus this increase in ozone is likely to result from downward transport of ozone rich air originating from lower latitudes by brewer dobson circulation first the descent rate of the mixing ratio contour was estimated by taking the geometric height as the vertical coordinate for the deep vortex interior around 20 km a significant longitudinal dependence was observed an analysis using ecmwf operational data shows that this dependence can be approximately explained by longitudinally dependent vertical movements of the isentropes caused by a zonal wavenumber 1 quasi stationary planetary wave with amplitude and phases varying on a seasonal time scale next the descent rate was calculated around 500 k around 20 km by taking the potential temperature isentrope as the vertical coordinate the longitudinal dependence was still present using this coordinate meaning that the ozone mixing ratio and its increase are not constant on the isentropic layer even in the interior of the polar vortex a backward trajectory analysis showed that air parcels with large ozone mixing ratios were mostly transported from the polar vortex boundary region this result suggests that lateral transport mixing is important even before the breakup of the polar vortex results from a tracer tracer correlation analysis of o3 and long lived constituent n2o were also consistent with this inference the contribution of lateral mixing to the increase in ozone was estimated at about 17 6 4 that of the brewer dobson circulation around 20 km using the calculated descent rates the results of this study also imply that lagrangian downward motions in the vortex interior are not correctly estimated without accounting for lateral mixing even if the polar vortex is dynamically stable

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

wintertime temperature maximum at the subtropical stratopause in a t213l256 gcm 1 a wintertime temperature maximum can be observed at the subtropical stratopause but does not appear in the radiative equilibrium temperature distribution this structure was well simulated using a high resolution general circulation model and examined in detail the stratopause temperature is latitudinally maximized in the winter subtropics because of a strong downwelling of the meridional circulation from summer tropics to winter subtropics passing above the stratopause its strong meridional flow consists of two parts a strong poleward flow in the winter subtropics with nearly vertically aligned contours of absolute angular momentum m and a strong cross equatorial flow toward winter hemisphere above the tropical stratopause with nearly horizontally aligned m contours the strong poleward flow in the winter subtropics is driven by a large eliassen palm e p flux convergence in a small absolute vorticity region the large e p flux convergence is due to extratropical planetary waves and asymmetric inertial instability on the other hand the strong cross equatorial flow is induced along the m contour to satisfy mass continuity with the strong poleward flow in the winter subtropics and exists in the easterly phase of s sao with a small latitudinal gradient of m the easterly of s sao during its mature phase acts as a corridor for cross equatorial meridional circulation while cross equatorial meridional circulation contributes to driving the easterly of s sao in its development phase

gravity waves appearing in a high resolution gcm simulation global characteristics of gravity waves in the lower stratosphere are examined using a gcm with high resolution in both the horizontal t106 corresponding to about 120 km and the vertical 600 m the bottom boundary condition of the model is that of an aquaplanet with perpetual february sea surface temperature the simulated gravity waves are in good agreement with mesosphere stratosphere troposphere mst radar observations at a middle latitude on the gravity wave structure and on the frequency spectra as a function of height the frequency spectra of simulated wind and temperature fluctuations are also examined as a function of latitude large values of spectral density are observed at frequencies higher than the inertial frequency f in a weak wind region around 20 km which is consistent with the characteristics of internal gravity waves an isolated peak is observed near f for horizontal wind spectra at latitudes higher than 108 while the energy is distributed in a wide range of frequency at lower latitudes where f approaches zero further analysis is performed of those fluctuations having periods shorter than 24 h and those having vertical wavelengths smaller than 5 km these are frequently analyzed as gravity waves using observation data the distribution of energy and momentum fluxes in the latitude height section is examined the result indicates that short period waves mostly propagate upward and poleward from the equatorial region the wave energy reaches about 508 lat at the 27 km altitude a negative positive maximum of vertical flux of meridional momentum y9w9 is seen above the subtropical jet in the northern southern hemisphere for small vertical scale gravity waves this is consistent with the preferred equatorward propagation of the wave indicated by a statistical analysis based on mst radar observations the ratio of potential to kinetic energy maximizes over the equator and decreases poleward the eliassen palm flux divergence associated with gravity waves is decelerative above the subtropical jet albeit small

tectonics of slow spreading mid ocean ridges and consequences of a variable depth to the brittle ductile transition geophysical evidence especially microearthquakes that extend into the upper mantle beneath the inner floor of the mid atlantic and gorda ridges indicates that the axial magma chamber episodically freezes beneath slow spreading ridges freezing of the axial magma chamber will result in a variable thermal structure that has important tectonic consequences most importantly large near axis faults will intersect as the brittle ductile transition deepens causing some of the faults to become locked the topographic effect of fault locking will be a variation in the width of the inner floor from narrow 10 km when a magma chamber is absent the deep microearthquakes also imply that faults at slow spreading ridges extend into the upper mantle the nature of these faults at depth is unknown but the following hypotheses are presented 1 the faults may be planar and pass downward into aseismic ductile shear zones and 2 the faults may sole into a flat detachment fault defining a sharp boundary between brittle faulting and homogeneous ductile flow such low angle normal faults are common in continental extensional domains large scale tilting 50 70 is probably common at slow spreading ridges and implies either listric faulting or rotation of planar faults and fault blocks similar to toppling dominoes calculations of temperatures at the brittle ductile transition are made assuming olivine and diabase rheologies for the mantle and crust respectively the temperature is approximately 800 c when the transition is at 8 km depth and approximately 600 when the transition is at 2 km depth the strength of the lithosphere varies dramatically with the rise and fall of the brittle ductile transition as magma chambers form and subsequently freeze strong lateral temperature gradients will be present when a magma chamber is formed resulting in localization of faulting within thin weak crust above the chamber when the magma chamber freezes lateral temperature gradients will be small and the strength of the lithosphere will be similar over a wide area this results in active faulting occurring over a width of as much as 60 km some ophiolites possibly provide insights to the tectonic processes at slow spreading ridges the entire crustal section of the josephine ophiolite was tilted by approximately 50 prior to deposition of overlying pelagic sediments this tilting probably took place by faulting suggesting that oceanic faults extended into the upper mantle possible oceanic faults have been identified in the josephine ophiolite but their oceanic origin cannot be established beyond doubt

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

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

impacts of data sampling on the interpretation of normal fault propagation and segment linkage abstract throw distance t d and throw depth t z plots are widely used by researchers and industry to examine the growth of normal faults this study uses high quality three dimensional 3d seismic and outcrop information to review the effect of data sampling on the interpretation of normal fault growth the results show that the accuracy of t d and t z data and of resulting fault slip tendency and leakage factor analyses are dependent on the sampling strategy followed by interpreters and field geologists i e on a sampling interval fault length ratio for discrete structures in particular this work demonstrates that significant geometric changes in t d plots occur when a module error ei for the ratio is larger than 6 9 for faults of all scales and growth histories this implies that a minimum number of measurements should be gathered on discrete faults to produce accurate t d and t z plots and that the number of measurements is dependent on fault length with no prior knowledge of fault segmentation a value of 0 05 should be applied when interpreting faults to fulfil the pre requisite of a i

accuracy evaluation of both wallace bott and bem based paleostress inversion methods abstract four decades after their introduction the validity of fault slip inversion methods based on wallace 1951 and bott 1959 hypothesis which states that the slip on each fault surface has the same direction and sense as the maximum resolved shear stress is still a subject of debate according to some authors this hypothesis is questionable since fault mechanical interactions induce slip reorientations as confirmed by geomechanical models this leads us to ask as to what extent the wallace bott simplifications are reliable as a basis hypothesis for stress inversion from fault slip data in this paper we compare two inversion methods the first is based on the wallace bott hypothesis and the second relies on geomechanics and mechanical effects on fault heterogeneous slip distribution in that context a multi parametric stress inversion study covering i the friction coefficients ii the full range of andersonian state of stress and iii slip data sampling along the faults is performed for each tested parameter the results of the mechanical stress inversion and the wallace bott wb based stress inversion for slip are compared in order to understand their respective effects the predicted discrepancy between the solutions of both stress inversion methods based on wb and mechanics will then be used to explain the stress inversions results for the chimney rock case study it is shown that a high solution discrepancy is not always correlated with the misfit angle and can be found under specific configurations r geometry invalidating the wb solutions we conclude that in most cases the mechanical stress inversion and the wb based stress inversion are both valid and complementary depending on the fault friction some exceptions i e low fault friction simple fault geometry and pure regimes that may lead to wrong wb based stress inversion solutions are highlighted

three dimensional structure of mass weighted isentropic time mean meridional circulations abstractthe present study develops a diagnostic framework for investigating the three dimensional 3 d structure of mass weighted isentropic time mean t mim meridional circulations and conducts a preliminary analysis of the winter hemispheres the t mim meridional velocity can unfold in the zonal direction time averaged two dimensional 2 d mass weighted isentropic zonal means furthermore the t mim velocity can be decomposed into the unweighted isentropic time mean utm velocity and the temporal eddy correlated transport velocity the so called bolus velocity the bolus velocity greatly contributes to the 2 d extratropical direct circulation in the troposphere and to the brewer dobson circulation in the stratosphere the 3 d bolus velocity seems to reflect the geographical distributions of baroclinic instability wave activity in the boreal winter both low level equatorward flows and upper level poleward flows are located around the north pacific and north atlantic storm tracks in the austral w

atmos atlas 3 observations of long lived tracers and descent in the antarctic vortex in november 1994 observations of the long lived tracers n2o ch4 and hf obtained by the atmospheric trace molecule spectroscopy atmos instrument in early november 1994 are used to estimate average descent rates during winter in the antarctic polar vortex of 0 5 to 1 5 km month in the lower stratosphere and 2 5 to 3 5 km month in the middle and upper stratosphere descent rates inferred from atmos tracer observations agree well with theoretical estimates obtained using radiative heating calculations air of mesospheric origin n2o 5 ppbv was observed at altitudes above about 25 km within the vortex strong horizontal gradients of tracer mixing ratios the presence of mesospheric air in the vortex in early spring and the variation with altitude of inferred descent rates indicate that the antarctic vortex is highly isolated from midlatitudes throughout the winter from approximately 20 km to the stratopause the 1994 antarctic vortex remained well isolated between 20 and 30 km through at least mid november

displacement gradients on fault surfaces abstract the maximum displacements and the dimensions of single faults are systematically related and the variation in displacement from a maximum at the centre of a fault to zero at an elliptical tip line loop is described by a simple theoretically derived expression these relationships are used to examine the theoretical ranges and distributions of rates of change of displacement on fault surfaces the dimensions and maximum displacement of a fault can be estimated from a limited number of displacement gradient measurements estimates are further constrained by a knowledge of the effective shear modulus of the rocks containing a fault an understanding of displacement gradients can be applied to problems commonly encountered in mining operations and in the interpretation and use of seismic reflection data in addition to field problems a comparison of theoretical displacement gradients with measured displacement gradients from british coalfield faults shows that i fault surface ellipticities are between 1 5 and 2 5 and ii gross displacement gradients expressed as the ratio of maximum displacement long axis radius of the fault ellipse range from 0 02 to 0 002 the measured displacement gradients indicate that the shear moduli of the faulted rocks range from 3 to 11 gpa which is within the known range for coal measure rocks displacement gradients along an array of fault segments are similar to those of single faults for analysis of displacement gradients it is necessary to sum the discontinuous and continuous components of displacement in extreme cases all the displacement may be accommodated by continuous deformation

displacement field in contraction driven faults we investigate the distribution of strain and deformation in the host sediment that arises once a contraction driven shear fault has localized and propagated under a zero lateral strain condition numerical modeling of displacement distributions compares well with those measured using 3d seismic data the parameters that determine the displacement field for a single normal fault embedded in sediments are fault height overburden effective stress stiffness and residual friction angle or post peak strength proximity to the free boundary biases the displacement pattern which becomes asymmetric although the measured displacements and numerical predictions are similar the measured magnitude requires pronounced low stiffness of the sediment as well as low post peak shear strength this requirement suggests that sediments hosting contraction driven shear faults most likely have high porosity and high clay fraction and have undergone diagenetic reactions involving significant mineral dissolution the diagenetic evolution of the sediment and its current composition may explain the global scaling relationship between the measured displacement and fault height for polygonal fault systems

slip distributions on intersecting normal faults abstract slip distributions on normal faults often are asymmetric and display multiple local maxima numerically computed slip distributions from elastic models indicate that such irregular slip distributions can be caused by mechanical interaction between intersecting faults that produce local perturbations of the stress field resolved on the faults a three dimensional boundary element model based on the displacement discontinuity method has been used to analyze the mechanical interaction of faults that form y or t shaped intersections slip distributions are asymmetric with a steeper slip gradient toward the line of intersection multiple slip maxima occur depending on the angle between the faults but generally they are not located along the intersections nor at the fault centers examples of intersecting normal faults taken from oil reservoir seismic surveys and sandbox experiments have been used to confirm the application of the theoretical results despite considerable simplifications in terms of geometry and boundary conditions the computed slip distributions capture the characteristics of the observed slip distributions

interannual variability of the vertical descent rate in the antarctic polar vortex to investigate a descent rate in the antarctic polar vortex we analyzed the long lived trace gas data derived from the halogen occultation experiment on board the upper atmosphere research satellite during the 6 year period from 1992 to 1997 by comparing the antarctic fall february and march and spring september and october methane profiles we estimated the middle stratospheric descent for each of the six winters large year to year variations are seen 1 2 1 8 km month 1 at 0 6 ppmv which consist of a biennial oscillation and a decreasing trend for the period analyzed the descent rate is larger in the even years 1992 1994 and 1996 than in the odd years 1993 1995 and 1997 dynamical fields for the 6 years are also analyzed using the united kingdom meteorological office assimilation data the differences between the even and odd years are clear in the midwinter in the even years the downward and poleward movement of the westerly jet occurs earlier the thermal wind relation infers that this event is associated with the development of a warm pool around the antarctic stratopause resulting from adiabatic heating due to the downward motion of air planetary wave activity over the winter season is more vigorous in the even years than in the odd years suggesting a close relationship between the mean flow and planetary waves

computations of diabatic descent in the stratospheric polar vortex a radiation model together with national meteorological center temperature observations was used to compute daily net heating rates in the northern hemisphere nh for the arctic late fall and winter periods of both 1988 1989 and 1991 1992 and in the southern hemisphere sh for the antarctic fall and winters of 1987 and 1992 the heating rates were interpolated to potential temperature surfaces between 400 k and 2000 k and averaged within the polar vortex the boundary of which was determined by the maximum gradient in potential vorticity the averaged heating rates were used in a one dimensional vortex interior descent model to compute the change in potential temperature with time of air parcels initialized at various values as well as to compute the descent in log pressure coordinates in the nh vortex air parcels which were initialized at 18 km on november 1 descended about 6 km by march 21 while air initially at 25 km descended 9 km in the same time period this represents an average descent rate in the lower stratosphere of 1 3 to 2 km per month air initialized at 50 km descended 27 km between november 1 and march 21 in the sh vortex parcels initialized at 18 km on march 1 descended 3 km while air at 25 km descended 5 7 km by the end of october this is equivalent to an average descent in the lower stratosphere of 0 4 to 0 9 km per month during this 8 month period air initialized at 52 km descended 26 29 km between march 1 and october 31 in both the nh and the sh computed descent rates increased markedly with height the descent for the nh winter of 1992 1993 and the sh winter of 1992 computed with a three dimensional trajectory model using the same radiation code was within 1 to 2 km of that calculated by the one dimensional model thus validating the vortex averaging procedure the computed descent rates generally agree well with observations of long lived tracers thus validating the radiative transfer model

gloria survey of the east pacific rise near 3 5 s tectonic and volcanic characteristics of a fast spreading mid ocean rise abstract a long range sidescan sonar gloria survey of an approximately 100 km square area of the east pacific rise crest between 3 s and 4 s extends results obtained in the same area by lonsdale 1977 using deep tow the axial linear volcano was found to be continuous over a distance of 75 km the presence of major inward and outward facing fault scarps was confirmed but the gloria data show several distinct differences between the two fault sets the inward dipping faults are more numerous more closely spaced and longer than the outward dipping ones and their dip slopes backscatter sound more extensively than those of the outward dipping faults moreover most of them appear to be formed within 2 km of the axis whereas the majority of the outward dipping faults begin to develop between 5 and 8 km from the axis these differences suggest that the two sets of faults have different origins the horizontal pattern of inward dipping faults is similar to those observed on other mid ocean rises at all spreading rates though the lengths and separations of the scarps are slightly and their throws considerably less than on slower spreading rises this common horizontal pattern suggests that inward dipping faults on all rises have a common mode of formation regardless of spreading rate horizontal tension is probably the dominant factor but an additional mechanism is needed to explain the polarization of fault dips that occurs in the region 2 8 km from the axis the similarity of major fault spacings on the east pacific rise to those on slower spreading rises suggests that faulting is invariant in space rather than time and that the lithosphere where these faults are formed about 2 km from the spreading axis has a similar small thickness for all spreading rates this is attributed to the regulating effect of hydrothermal circulation and plate cooling

seismic analysis of polygonal fault systems in the great south basin new zealand abstract polygonal fault systems pfs consisting of networks of layer bound normal faults are analyzed for eocene strata in the great south basin new zealand an advanced fault enhancement and skeletonization method is applied to delineate faults using 3d seismic data from the great south basin the process sharpens structural and stratigraphic discontinuities and smears the incoherent noise on coherence to obtain a skeletonized fault probability volume which can be directly used to extract and map fault geometries the characteristics of the polygonal faults in cross section planform and 3d space were studied the faults dip approximately 50 with displacements on a single fault ranging from tens of meters to a hundred meters the fault planform patterns are polygonal but also related to the regional horizontal stress anisotropy caused by slope changes of the basal unit the patterns vary from linear for high slopes rectangular for moderate slopes and polygonal for low slopes two preferred orientations may reflect the superposition of deep cretaceous trends on the polygonal system in the eocene strata a local concentric pattern with outward dipping normal faults is related to passive or active draping above a circular plutonic volcanic structure the genetic mechanism of the polygonal fault systems is interpreted to be related to volume loss and shear failure related to opal a ct transition within the sediments

graben hydrocarbon occurrences and structural style major hydrocarbon occurrences types of traps and structural styles have been synthesized from the sirte basin the suez and viking grabens and from other normal faulted regions hydrocarbons occur in a stacked succession of one or more basins pregraben graben fill and interior sag preservation of pregraben accumulations depends on late initiation of crustal arching and limitation of uplift to the graben shoulders furthermore a stable pregraben tectonic environment is required to ensure internal continuity of subsequent fault block closures hydrocarbon traps in the pregraben and graben fill sediments are primarily dependent on the multidirectional orientation of normal faults tilting of fault blocks and in many cases flexing or erosion parallel with block edges the fault pattern is dominated by longitudinal faults subparallel with the graben axis and secondarily by oblique faults the direction and degree of block rotation are influenced by fault profile planar or listric degree of extension fault pattern doglegs junctions terminations downwarping of the subsequent sag basin and isostatic adjustments between large blocks fold closures result from the upward termination of faults into forced folds which may be accentuated by drag during renewed faulting passive drape and differential compaction extend he folds to shallower depths because they form along block edges the flexures have trends that mimic the multidirectional fault patterns truncation traps are usually developed from the erosional retreat of fault scarps and they can also mimic the fault patterns where the sedimentary succession is complete an interior sag basin is superimposed across the graben its lower part is structured mostly by drape and differential compaction across the underlying graben fault blocks and fault block topography the upper part is usually an unsegmented syncline and hydrocarbon traps at this level include depositional buildups reefs turbidite mounds and salt diapirs or other structures caused by superimposed deformation unrelated to graben tectonics

response of unconfined turbidity current to normal fault topography turbidity currents descending the slopes of deep water extensional basins or passive continental margins commonly encounter normal fault escarpments but such large magnitude phenomena are hydraulically difficult to replicate at small scale in the laboratory this study uses advanced computational fluid dynamics numerical simulations to monitor the response of large natural scale unconfined turbidity currents 100 m thick and 2000 m wide at the inlet gate to normal fault topography with a maximum relief of nearly 300 m for comparative purposes the turbidity current is first released on a non faulted pristine slope of 1 5 simulation model 1 the expanding and waxing flow bypasses the slope without recognizable deposition within the vertical resolution limit of 2 m similar flow is then released towards the tip model 2 and towards the centre model 3 of a normal fault escarpment in both of these latter models the sand carried by flow tends to be entrapped in four distinct depozones an upslope near gate zone of flow abrupt expansion and self regulation a flow transverse zone at the fault footwall edge a flow transverse zone at the immediate hangingwall and a similar transverse zone near the crest of the hangingwall counter slope where some of the deposited sand also tends to be reshuffled to the previous zone by a secondary reverse underflow the near bottom reverse flow appears to be generated on a counter slope of 1 1 increased to 2 by deposition the kelvin helmholtz interface instability plays an important role by causing three dimensional fluctuations in the flow velocity magnitude and sediment concentration the thick deposits of large single surge flows may thus show hydraulic fluctuations resembling those widely ascribed to hyperpycnal flows the study indicates further that the turbiditic slope fans formed on such fault topographies are likely to be patchy and hence may differ considerably from the existing slope fan conceptual models when it comes to the spatial prediction of main sand depozones this article is protected by copyright all rights reserved

the kinematics of the plate boundary zone through new zealand a comparison of short and long term deformations summary surveys of shear strain rates derived from repeated triangulation cover about one quarter of the area of the plate boundary zone through new zealand and are well distributed within it using a method developed by haines relating shear strains to the total strain and velocity fields the dilatational and rotational strain rates and the velocities within the deformed zone are derived the plate boundary zone is shown to be two dimensional for the most part in that gradients of the velocity along the length of the zone are small or zero the shear strain rates are not uniform however they reach a maximum along a central axis and decrease gradually to zero toward the sides nor are the two independent components of strain one involving shortening or extension perpendicular and the other shear parallel to the zone equally developed everywhere there is a clear geographic separation with shortening developed over the subduction thrust and shear developed behind in a zone of wrench faulting time variations in the strain field in part of the region above the subduction interface are related to changes in the degree of coupling across the interface a velocity field is computed the relative velocity of the two plates from this data agree very well with that derived from seafloor spreading data these strain and velocity fields derived from geodetic studies give the short term kinematics of the plate boundary zone the long term kinematics of the zone are estimated from 1 uplift and subsidence data which are related to changes in crustal thickness and hence to dilatational strain and 2 variation in the declination of primary magnetization in rocks of known age related to the rotational strain the rate of rotational strain has increased in time from about 2 to 3 myr 1 10 myr ago to about 9 myr 1 today the increase can be understood as a secondary effect of a developing compressional component increasing the coupling between the plates so that more of the motion parallel to the zone is accommodated by distributed shear and less by aseismic slip the rates of strain averaged over the last 1 myr or so and at a scale length of a few tens of kilometres are closely similar in distribution and magnitude to the strain rates derived from short term kinematics while therefore at scale lengths of a few hundred metres or so faulting is very important and the deformation is discontinuous with unstrained blocks faulted with large but uncertain slip against adjacent blocks the deformation at these longer scale lengths is continuous and regular the two consequences of this study are that 1 strain from geodetic data can be directly related to the average long term deformation and therefore can be an important tool in the study of deformation in regions of current tectonic activity and 2 at scale lengths of a few tens of kilometres the deformation of a region can be described as the deformation of a continuum and we can ignore the effects of faulting

influence of tropical convection on the southern hemisphere ozone maximum during the winter to spring transition 1 during the southern hemisphere sh winter a zonally asymmetric maximum in column ozone develops south of australia which amplifies from august through october this ozone maximum lies in the band 50 60 s and extends from the southern indian ocean to the eastern pacific it is proposed that the location of the ozone maximum is due to the geographical distribution of outflow from tropical convection in the upper troposphere and lower stratosphere utls which is concentrated over the southern indian ocean this southward flow of tropical air creates subtropical anticyclones in the utls and provides the angular momentum for the entrance to the australian westerly jet the ozone rich troughs in synoptic waves breaking on the jet contribute to the monthly mean ozone maximum poleward of the jet as indonesian convection contracts zonally and shifts eastward during sh spring so do the australian jet and ozone maximum in addition extratropical planetary waves become more active from august through october convective outflow surges lead to amplification of subtropical anticyclones which often extend into the lower stratosphere and merge with stalling planetary wave ridges amplification of these ozone rich ridges over the high latitude south pacific contributes to the eastward shift of the ozone maximum the utls over the southern indian ocean appears to be a sensitive region where tropical convection can influence extratropical planetary waves via excitation of subtropical anticyclones and propagation of rossby wave activity through the connecting westerly waveguide

kar ages of clay size concentrates from the mineralisation of the pedroches batholith spain and evidence for mesozoic hydrothermal activity associated with the break up of pangaea abstract the k ar ages of 32 clay concentrates extracted from samples of ore gangue and wallrock associated with mineralisation in the pedroches batholith lie in the range 119 285 ma although some of the mineralisation is of permian age more than half of the ages lie between 210 and 230 ma and indicate a hydrothermal event at this triassic time a comparison with age data for mineralisation and certain anorogenic magmatism in other areas of the north atlantic reveals a consistent pattern of a major event at ca 210 230 ma and a minor event at ca 160 ma with little cretaceous or tertiary activity it is proposed that the ca 210 230 ma event was related to an initial rapid fracturing of the crust associated with the break up of pangaea which was related with an increase in the geothermal gradient and penetration of the deep crust by surface waters which returned via both new and rejuvenated fissure systems

localization of bedding plane slip and backthrust faults above blind thrust faults keys to wrinkle ridge structure a mechanically based model for wrinkle ridge development is developed that combines wrinkle ridge morphologies regional topographic offsets suggestive of subsurface thrust faults and folding of near surface layers this model provides explicit relationships between observed morphologic elements characteristic of wrinkle ridges and plausible mechanisms in the subsurface a key component that is absent in previous qualitative fault based scenarios for these structures as developed in this paper wrinkle ridges are the surface expression of anticlines that grow above a blind thrust fault as a result of both flexural slip folding of near surface strata and the nucleation and growth of echelon arrays of backthrust faults calculations of displacements both horizontal shortening and vertical uplift and coulomb stress change related to slip along blind thrust faults in the model demonstrate physically important spatial inhomogeneities in these quantities with revealing and useful implications 1 the ratio of shortening due to folding at the surface to the shortening due to faulting at depth is characteristically small for coupled wrinkle ridge blind thrust fault systems and decreases with increasing fault depth the depth of the blind thrust fault s upper tip thus profoundly influences the surface strains 2 folding and uplifted topography forming the topographic ridge are produced above the area of the slipping blind thrust fault plane horizontal and vertical deformation at the surface extend over several ridge widths or a total of at least 50 km for a 10 km wide ridge implying that topographic profiles and geologic studies must extend sufficiently far from the wrinkle ridge to fully characterize the surface deformation 3 calculations of coulomb stress changes suggest that fault slip can localize both bedding plane slip in overlying strata and new backthrust faults that propagate upward to become wrinkles on the trailing side of the ridge initiation of bedding plane slip in association with slip along the blind thrust fault likely determines whether the resulting surface structure becomes a wrinkle ridge or a lobate scarp wrinkle ridge spacing may also be related to stress changes associated with slip along the underlying blind thrust fault

relay zones between mesoscopic thrust faults in layered sedimentary sequences abstract we examine the geometry formation and destruction of relay zones in well bedded sedimentary sequences containing thrust fault segments with maximum observed displacements of 0 64 8 m contractional extensional and neutral relay zones are distinguished based on the stepping sense of the interacting fault segments and the orientation of the associated fault slip vectors large displacement gradients 0 17 1 0 in relay zones are mainly accommodated by folding with aggregate displacements maintained across segment boundaries and a significant component of the fault slip converted to fold related shortening folds in contractional relay zones verge in the direction of hanging wall motion with the steeper limb defining a parallelogram shaped zone between thrusts fault segment lengths are established after minimal displacement and folds in relay zones grow between segments as displacement accrues on the thrusts with increasing displacement upper and lower thrust tip lines in contractional and extensional relay zones are fixed at stratigraphic boundaries while the lateral thrust tip lines may propagate in a strike parallel direction upper and lower tip lines may eventually propagate to bypass relay zones that formed early in the fault growth history contractional relay zones remain intact at higher displacements than extensional relay zones

identifying fault segments from 3d fault drag analysis vienna basin austria abstract the segmented growth of the markgrafneusiedl normal fault in the late miocene clastic sediments of the central vienna basin austria was investigated by construction of a detailed three dimensional 3d structural model using high resolution 3d seismic data the fault surface and marker horizons in the hanging wall and the footwall of the markgrafneusiedl fault were mapped and orientation displacement and morphology of the fault surface were quantified individual fault segments were identified by direct mapping of the deflection of the marker horizons close to the fault surface correlating the size of the identified segments with the magnitude of fault drag and displacement distribution showed that fault evolution progressed in several stages the proposed method allows the detection of segments that are not recorded by the magnitude of displacement or fault morphology most importantly detailed mapping of marker deflections in the hanging wall could help to constrain equivalent structures in the footwall which may represent potential hydrocarbon traps

palaeomagnetic evidence for the age of the cumbrian and manx hematite ore deposits implications for the origin of hematite mineralization at the margins of the east irish sea basin uk examples of epigenetic hematite mineralization located at the margins of the east irish sea basin have been sampled for palaeomagnetic investigation to establish the timing of ore formation samples collected from 10 sites in cumbria are dominated by hematite of near pure composition and characterized by dual polarity and in part dual component magnetizations that yield palaeopoles nine sites between 50 n 130 e and 50 n 150 e in contrast samples recovered from seven sites on the isle of man have more varied mineralogical compositions that include ferromagnets with lower unblocking temperatures manx hematite mineralization also exhibits dual polarity but magnetizations yield steeper inclinations with palaeopoles lying between 55 n 130 e and 70 n 150 e steeper directions probably reflect minor tilting of the manx block following hematite emplacement correlation of poles with the european apparent polar wander path indicates that these ore deposits formed during the middle triassic results show that hematite mineralization sited at the margins of the east irish sea basin is essentially contemporaneous and establishes for the first time an underlying temporal relationship between these geographically dispersed ore bodies dating places the mineralization within a broader extensional geotectonic regime associated with the early rifting of pangaea in the north atlantic the context implies a causal link between crustal extension development of ore forming fluids within the evolving east irish sea basin and subsequent migration of fluids to basin margins where iron was precipitated as hematite supplementary materials locations and details of palaeomagnetic sample sites and a tabulation of selected reference palaeomagnetic poles defining the triassic and early jurassic segment of the apparent polar wander path for the european sector of the eurasian plate are available at www geolsoc org uk sup18691

listric normal faults an illustrated summary movement along listric normal faults is instrumental in formation of several types of structural traps e g rollover anticlines and upthrown fault block closures this type of fault may occur where brittle rocks overlie ductile rocks in an extensional regime the extensional regime may be locally derived within a broader stress regime of another type as evidenced by transtension associated with strike slip movement and arched strata in a compressive setting the flattening of the fault reflects an increase in ductility of the rocks with depth and in some cases deformation of the fault due to compaction or tilting of the upthrown block the dip angle may vary along the strike of the fault in response to changes in throw in cross section a listric fault may consist of relatively short en echelon fault segments this geometry may be particularly characteristic of growth faults sedimentary faults may sole in ductile strata or they may represent the brittle part of a fault flow system fault patterns commonly are characterized by bifurcation some of which may occur near the ends of individual faults comprising a zone although unequivocal recognition of listric normal faults requires unusually extensive outcrop data close subsurface control or high quality seismic data their presence is suggested indirectly by such features as increasing dip either depth toward the controlling fault reverse drag thick progradational sandstone overlying ductile strata and in some cases arcuate fault patterns basins or uplifts listric normal faults form during rifting drifting and evolution of passive continental margins with concomitant basinal development the basement is offset by listric faults as a fundamental element in the development of other types of basins including those which formed during postorogenic extension they also occur as secondary extensional features in an overall compressive stress regime due to plate convergence and during transform or strike slip faulting modified journal abstract

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

time variations of descent in the antarctic vortex during the early winter of 1997 1 we analyzed long lived chemical constituents observed by the improved limb atmospheric spectrometer ilas on board the advanced earth observing satellite adeos to study the stratospheric descent in the southern hemisphere polar vortex the ilas n2o distribution inside the polar vortex exhibited clear downward motion in february to june 1997 average descent for the 5 months is estimated to be 2 1 1 7 km month 1 in the middle stratosphere in late april to june when planetary waves are relatively active the vertical velocity displays time variations with a period of about 10 days these time variations also synchronize with both time variations of the temperature time change t and the eliassen palm flux divergence df in high latitudes moreover a correlation coefficient map in the latitude height cross section between the vertical velocity and the temperature time change reveals an interesting four box pattern suggesting warming below 10 hpa and cooling above 10 hpa in the polar region 70 90 s and an opposite distribution in midlatitudes 40 70 s when large descent is observed inside the polar vortex it is just like the meridional circulation in response to df induced by planetary waves which was first illustrated by matsuno s stratospheric sudden warming theory

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

potassium and argon loss patterns in weathered micas implications for detrital mineral studies with particular reference to the triassic palaeogeography of the british isles abstract potassium argon ages are reported for 16 muscovite and 14 biotite samples separated from triassic sandstones of the manx furness carlisle solway firth and lough neagh arran basins disturbance of the k ar isotopic system in these minerals during weathering erosion transport and lithification is discussed and loss of potassium shown to be as important a parameter as argon loss published data from tropical weathering profiles are used to establish the pattern of loss for these two elements during the formation of clay minerals from biotite the data being displayed in a potassium argon loss diagram the loss curve so produced is then used to interpret our new biotite data and previously published age data for detrital biotite from the cheshire basin the limit of interdigitation of northerly and southerly derived materials in the irish sea basins is shown to lie north of the fylde district of lancashire age data from detrital muscovite are used to establish a potassum argon loss curve for muscovite the features of the two curves are markedly similar little effect on the apparent k ar age is observed until about 20 loss of potassium occurs at this point massive argon loss takes place with little loss of potassium due to either potassium stabilisation or structural expansion the suitability of micas as k ar chronometers may be a consequence of the correlated potassium argon loss rather than intrinsic high argon retentivity if both mica curves are applied to detrial micas of the namurian millstone grit series a source area of age of ca 900 ma is indicated for both muscovite and biotite indicating a probable pre cambrian age source area probably in scandinavia

new discovery and geological significance of late silurian carboniferous extensional structures in tarim basin abstract late silurian carboniferous extensional structures have been discovered after careful interpretation of seismic reflection data in western manjiaer sag central tarim basin in central asia the extensional structures comprise numerous small normal faults in nearly n s strike direction groups of normal faults in profile show features suggestive of negative flower structures and small horst graben structures based on growth index calculation these extensional structures formed in the late silurian period continued activity in the devonian and carboniferous and then ceased at the end of carboniferous the peak stage of normal fault activity occurred in late silurian late silurian carboniferous normal faults also developed in the tazhong and tabei areas which implies that tarim basin were under regional extensional tectonic setting during that periods the extensional structure in southern tarim resulted from the post orogeny stress relaxation of the kunlun early paleozoic orogenic belt and those in northern tarim resulted from the paleozoic back arc rifting which led to the opening of south tianshan ocean