extensional forced folding and decollement of the pre rift series along the rhine graben and their influence on the geometry of the syn rift sequences

the ufa indenter stratigraphic and geophysic evidences for an actual indentation of the southern urals by the east european craton study of the altitudes of the lowest part of the upper cretaceous eocene and aktschagylian quaternary stratigraphic ensembles known on the western slope of the southern urals evidences the existence of an east west elongated dome which follows the n53 latitude this ridge is superimposed at depth with the remnants of the sernovodsk abdulino aulacogen and with the belaya tear fault which support the existence of a recent rejuvenation of these old structures north of these disruptions the southern urals display a clear bent towards the east detailed microstructural studies show that this curvature is associated with a typical stress pattern which suggests the existence of an indentation of the fold belt by the east european craton the hypothesis of an ufa indenter is not supported by an equivalent east west deep fault north of the bend however a long n100 magnetic anomaly interpreted as a shear zone suggests that the indenter is a reality quaternary uplift and crustal thickening at its front as well as seismological data support our interpretation it is not stressed that the curvature of the urals observed at 56 latitude results solely from this recent indentation it is only assumed that the actual indentation is rejuvenating a former unevenness which existed before in the east european craton study of the inner part of the indenter shows that this type of structure is not necessarily rigid and undeformed some of the structures described on the urseis deep seismic line could be much younger than previously expected

sedimentologic and tectonic origin of an incised valley fill sequence along an extensional marginal lacustrine system in the basin and range province united states implications for predictive models of the location of incised valleys incised valleys in extensional lacustrine systems should be common and significant petroleum targets yet documentation and analysis of these systems are limited and hence so are predictive models for their location geologic mapping of the miocene pliocene humboldt formation in knoll basin northeastern nevada has revealed a significant incised valley system formed along the lacustrine margins of an extensional basin the valley formed during a relative lake level fall and incised into lacustrine shoreface and offshore sandstone and subsequently was filled with fluvial and eolian sediment as lake level rose the valley s location was tectonically influenced it is situated in the hinge zone of a syncline near the tip of the range bounding fault system folding of the syncline was broadly synchronous with incision and filling and it appears to have localized the valley along the topographically low hinge zone furthermore the large relative lake level change that produced the valley is only recorded in strata in the syncline area suggesting that the location and cause of incision was greatly influenced by tectonics thus the location of similar incised valleys in other extensional basins may be predictable if comparable tectonic features and processes are recognized our study suggests that the best locations to develop and preserve incised valleys are near the tips of normal faults during periods of overall high tectonic subsidence specific areas along basin bounding faults where tectonically influenced incised valleys are more likely to form include fault propagation folds synthetic relay ramps near transfer faults and areas that have large changes in fault slip although lake volume changes caused predominantly by climate change can be an important factor in producing incised valleys tectonically influenced incised valleys are likely to be larger better preserved and more petroleum prone compared to climate controlled incised valleys

testing thin skinned inversion of a prerift salt bearing passive margin eastern prebetic zone se iberia abstract detailed geologic mapping combined with well and seismic data from the eastern prebetic zone se iberia reveal extensional and contractional structures that permit characterization of passive margin development and its incorporation into a thin skinned fold and thrust belt the study area is represented by nw directed ene trending folds and thrusts faults locally disrupted by the nw trending matamoros basin and the active jumilla and la rosa diapirs these structures resulted from the thin skinned inversion of the proximal part of the eastern south iberian passive margin containing prerift salt here upper jurassic to santonian thick skinned extension controlled the accumulation of sediment over mobile prerift salt this in turn defined the style of salt tectonics characterized by monoclinal drape folds suprasalt extensional faults and diapirs the structural and sedimentological analysis suggests that during extension salt localizes strain thus decoupling sub and suprasalt deformation thick skinned extension controls suprasalt deformation as well as its location and distribution which changes over time salt also localizes strain during inversion the preexisting salt structures weaker than adjacent areas preferentially absorb the contractional deformation in addition the stepped subsalt geometry that results from thick skinned extension also controls the shortening propagation therefore the degree of strain localization depends on the thickness of the suprasalt cover and on the dip of subsalt faults relative to the thin skinned transport direction

the rhinegraben extension subsidence and shoulder uplift abstract we apply a numerical model of the thermal evolution of a continental lithosphere undergoing extensional deformation to the rhinegraben using reasonable parameters the results of computations are in agreement with the present configuration of the rift and of its shoulders as well as with their evolution since the oligocene contrasting evolutions are reconstructed in the northern and southern rhinegraben whereas the northern history is accounted for by a simple model of homogeneous stretching of the lithosphere the history of the southern rhinegraben cannot be explained without introducing two main periods of heterogeneous stretching the results are locally supported by structural analyses of extensional patterns factors of extension average 1 2 in the axial portion of the rhinegraben and 1 15 for the whole rift section suggesting that the total amount of e w extension reaches 6 km

extension related buttress like folds the western side of the gulf of suez rift egypt the wedge shaped st paul block western side of the gulf of suez rift exposes late cretaceous beds that are folded into transverse folds the block is bounded from the east and west by east and southeast dipping rift related normal faults respectively this study reveals that the transverse folds are extension related and formed due to the buttress like effect that was created during the movement along the rift related normal faults the more competent eocene hanging wall block of the n s striking fault buttressed against the moving less competent cretaceous hanging wall block of the ne sw striking fault a localized zone of shortening developed between the two fault trends causing the intervening wedge shaped block to be crumpled and folded into a series of kilometer scale gentle sse plunging folds the buttressing within block internal localized strain caused by the zigzag geometry of the ne sw striking fault and the effect of the minor cross fault explain the sse to ese plunges of the mesoscopic folds this study turns the attention to the buttress like effect as one of the mechanisms of extension related folds during rifting

kinematic and geometric analysis of fault related folds in a rift setting the dannemarie basin upper rhine graben france abstract the upper rhine graben urg developed in the alpine foreland from mid eocene to pliocene as part of the west european rift system the dannemarie basin occupies the sw termination of the urg and is bordered by the vosges fault zone west and the illfurth fault zone east we constructed a 3d model of faults and principal pre and syn rift stratigraphic surfaces using all available subsurface and surface geological and geophysical data the model shows 1 syn rift strata thinning across kilometre scale fault parallel monoclinal flexures associated with basin margin faults and 2 major basin margin faults terminating laterally into major flexures sequential cross section restorations show that these flexures accommodated deposition of over 1300 m of syn rift strata salt series which is 42 63 of the basin fill these folds are interpreted as syn rift fault propagation folds that developed above normal faults their geometry is replicated in a trishear numerical model using reasonable parameter values fold development was controlled principally by 1 reactivation of favourably oriented basement faults 2 the presence of a thick viscous layer principally triassic evaporites allowing decoupling between crystalline basement and competent jurassic cover and 3 a relatively slow deformation rate

high resolution observations and numerical simulations of easterly gap flow through the strait of juan de fuca on 9 10 december 1995 abstract this paper examines the three dimensional flow and dynamics of easterly gap flow through the strait of juan de fuca on 9 10 december 1995 using high resolution observations and model simulations the observations were obtained during the fourth intensive observing period during the second phase of the coastal observation and simulation with topography field experiment one of the most important data sources was the noaa p 3 aircraft which provided flight level data reflectivity and doppler winds as it flew down the strait of juan de fuca below 900 m the flow accelerated from 7 to 14 m s 1 at the entrance to the strait with a significant cross gap component and confluence over the eastern sections of the strait below 500 m the easterly flow approaching the western exit of the strait accelerated from 15 to 20 m s 1 as the 900 m deep easterly flow exited the gap it decreased in depth and accelerated to 25 m s 1 creating a shallow swath of diffluent winds below 300 m later in the event whe

nonlinear 3 d traveltime inversion of crosshole data with an application in the area of the middle ural mountains this paper deals with the problem of nonlinear seismic velocity estimation from first arrival traveltimes obtained from crosshole and downhole experiments in three dimensions a standard tomographic procedure is applied based on the representation of the crosshole area into a number of cells which have an initial slowness assigned for the forward modeling the raypath matrix is computed using the revisited ray bending method supplemented by an approximate computation of the first fresnel zone at each point of the ray hence using physical and not only mathematical rays since 3 d ray tracing is incorporated the inversion technique is nonlinear velocity images are obtained by a constrained least squares inversion scheme using both damping and smoothing factors the appropriate choice of these factors is defined by the use of appropriate criteria such as the l curve the tomographic approach is improved by incorporating a priori information about the media to be imaged into our inversion scheme th

a structural model for the seismicity of the arudy 1980 epicentral area western pyrenees france summary the western pyrenees presents a diffuse and moderate m 5 7 instrumental seismicity it nevertheless historically suffered from strong earthquakes i ix msk the seismic sources of these events are not yet clearly identified we focus on the arudy 1980 epicentral area m 5 1 and propose here the reactivation of early cretaceous normal faults of the iberian margin as a potential source the late cretaceous inversion of this basin first in a left lateral strike slip mode and then in a more frontal convergence resulted in a pop up geometry this flower structure attests of the presence of a deep crustal discontinuity the present day geodynamic arrangement suggests that this accident is reactivated in a right lateral mode this reactivation leads to a strain partitioning between the deep discontinuity that accommodates the lateral component of the motion and shallow thrusts rooted on this discontinuity these thrusts accommodate the shortening component of the strain the distribution of the instrumental seismicity fits well the structural model of the arudy basin whatever the compressive regional context the structural behaviour of the system explains too the extensive stress tensor determined for the arudy crisis if we interpret it in terms of strain ellipsoid indeed numerical modelling has shown that this concomitant activity of strike slip and thrust faulting results in an extensive component that can rise 50 per cent of the finite strain we identify too a 25 30 km long potential seismic source for the arudy area the size of the structure and its potential reactivation in a strike slip mode suggest that a maximum earthquake magnitude of 6 5 could be expected the extrapolation of this model at the scale of the western pyrenees allows to propose other potential sources for major regional historical earthquakes

imaging of fracture zones in the finnsjon area central sweden using the seismic reflection method in 1987 the swedish nuclear fuel and waste management co skb funded the shooting of a 1 7 km long high resolution seismic profile over the finnsjon study site using a 60 channel acquisition system with a shotpoint and geophone spacing of 10 m the site is located about 140 km north of stockholm and the host rocks are mainly granodioritic the main objective of the profile was to image a known fracture zone with high hydraulic conductivity dipping gently to the west at depths of 100 to 400 m the initial processing of the data failed to image this fracture zone however a steeply dipping reflector was imaged indicating the field data were of adequate quality and that the problem lay in the processing these data have now been reprocessed and a clear image of the gently dipping zone has been obtained in addition several other reflectors were imaged in the reprocessed section both gently and steeply dipping ones correlations with borehole data indicate that the origin of these reflections are also fracture zones the improvement over the previous processing is caused mainly by 1 refraction statics 2 choice of frequency band 3 f k filtering and 4 velocity analyses in addition to reprocessing the data some further analyses were done including simulation of acquisition using only the near offset channels channels 1 30 and the far offset channels channels 31 60 and determining the damping factor q in the upper few hundred meters based upon the amplitude decay of the first arrivals the data acquisition simulation shows the far offset contribution to be significant even for shallow reflectors in this area contrary to what may be expected a q value of 10 determined from observed amplitude decay rates agrees well with theoretical ones assuming plane wave propagation in an attenuating medium

using footwall structures to constrain the evolution of low angle normal faults controversy exists over the presence of normal faults that initiate and slip at low angles c 15 east on the island of elba italy indicates that the early stages of low angle faulting were synchronous with development of subsidiary high angle footwall faults these footwall structures controlled fault rock distribution and caused the development of flow folds similar to those produced in analogue studies of synchronous high and low angle faulting the current configuration of footwall structures indicates that the zuccale fault cannot have originally dipped greater than c 20 east and represents a primary low angle normal fault

seismic wide angle constraints on the crust of the southern urals a wide angle seismic reflection refraction data set was acquired during spring 1995 across the southern urals to characterize the lithosphere beneath this paleozoic orogen the wide angle reflectivity features a strong frequency dependence while the lower crustal reflectivity is in the range of 6 15 hz the pmp is characterized by frequencies below 6 hz after detailed frequency filtering the seismic phases constrain a new average p wave velocity crustal model that consists of an upper layer of 5 0 6 0 km s which correlates with the surface geology 5 7 km depths at which the velocities increase to 6 2 6 3 km s 10 30 km depths at which on average the crust is characterized by velocities of 6 6 km s and finally the lower crust from 30 35 km down to the moho which has velocities ranging from 6 8 to 7 4 km s two different s wave velocity models one for the n s and one for the e w were derived from the analysis of the horizontal component recordings crustal sections of poisson s ratio and anisotropy were calculated from the velocity models the poisson s ratio increases in the lower crust at both sides of the root zone a localized 2 3 anisotropy zone is imaged within the lower crust beneath the terranes east of the root this feature is supported by time differences in the sms phase and by the particle motion diagrams which reveal two polarized directions of motion velocities are higher in the central part of the orogen than for the siberian and eastern plates these seismic recordings support a 50 56 km crustal thickness beneath the central part of the orogen in contrast to moho depths of 45 km documented at the edges of the transect the lateral variation of the pmp phase in frequency content and in waveform can be taken as evidence of different genetic origins of the moho in the southern urals

interpretation of the reflections in the siljan ring area based on results from the gravberg 1 borehole abstract during 1985 about 80 km of surface multichannel seismic reflection data were collected across the meteorite impact in the siljan ring area in central sweden the area consists mainly of granitic and gneissic rock ranging in age from 1400 to 2000 million years with remnants of palaeozoic sedimentary rocks preserved by downfaulting after a meteorite impact at 360 ma thereby forming a circular ring about 40 km in diameter dolerite intrusions ranging in age from 850 to 1700 million years are also present the seismic data revealed several high amplitude laterally continuous sub horizontal reflections in the northern part of the structure the high amplitude reflections and a possible intermediate low velocity zone were contributing factors in choosing the site for the gravberg 1 deep earth gas test well drilling and vertical seismic profiling vsp found that the reflectors were associated with dolerite sills which had intruded into the granite and which range in thickness from a few metres up to 60 m and with a pre impact area extent of at least 800 km 2 studies of amplitude and frequency versus offset afvo show the observations are compatible with a model of simple granite dolerite granite layering

the late variscan control on the location and asymmetry of the upper rhine graben the nne trending upper rhine graben urg of the european cenozoic rift system developed from c 47 ma onwards in response to changing lithospheric stresses in the northwestern foreland of the alps the composite graben structure consists of three segments each c 100 km long and 30 40 km wide but flares to c 60 km near its southern and to c 80 km near its northern termination normal faulting induced a total extension of 5 8 km of the 1 2 km thick mesozoic sedimentary franconian platform and underlying variscan basement rocks however distribution of an up to 3 5 km thick sedimentary graben fill and cumulative displacements near eastern and western main border fault systems suggest that subsidence of the graben floor and shoulder uplift created strong cross sectional asymmetries cumulative w down displacements 3 km along strongly segmented transfer faults in the east contrast with e down displacements 600 km long zone that delimits the trailing edge of a sw moving lithospheric block in the urg area ne sw oriented seismic anisotropy at sublithospheric depths of c 60 80 km suggest active mantle flow in this direction as a possible driving force for the reactivation of pre graben lithospheric shear zones

an extreme cold surge over the greek peninsula summary this paper is devoted to the detailed description of an extreme cold surge that occurred 3 13 march 1987 over greece this event has been rated as the worst snowfall over the last 100 years and duc to its severily and persistence it paralysed the cconornic and communal life of greece for several days emphasis is given to the initiation phase of this event the structural evolution of the cold surge is analysed using both observations and model results model simulations pcrformed with the colorado state university regional atmospheric modelling system provided the necessary data to diagnose the mesoscale structure of the cold outbreak different mechanisms involved in the structural evolution ofthe cold surge are investigated the gustiness of the observed winds and their significant departure from geostrophy are related to the role of an important isallobaric wind the progression of this surge presented characteristics of a density current while near the eastern slopes of the mountain barriers of continental greece cold air damming occurred leading to an accelerated flow parallcl to the mountains heavy snowfall events over greece are often associated with cold air surges prop agating from northern and central europe through the balkans metaxas 1978 livada tselepidaki 1979 prezerakos and angouridakis 1984 these cold surges are accompanied with the passage of a fast moving cold front from the north towards the south very strong winds especially in the gaps between mountains in northern greece and over the aegean sea a sharp temperature decrease over the whole country and a sharp pressure rise the lifetime of these surges is normally from 1 to 3 days extending up to 10 days in exceptional cases their persistence can cause important problems in economic life since the result ing snowfall can prohibit road transportation on the main traffic routes greek forecasters call these cold fronts balkan fronts due to their origin in the frame of this study this terminology will be retained although the classical term cold surge will also be used interchangeably the forecast of the evolution of these fronts as well as the persistence of cold surges over greece is of great importance not only for the impact of snowfall on economic life but also for the safety of navigation in the aegean sea in gale force winds cold surges accompanied by severe weather phenomena have also been reported in the himalayan region nakamura and murakami 1983 over the usa e g bell and bosart 1988 colle and mass 1995 as well as over central america schultz et al 1997 all the aforementioned studies underlined the fact that cold surges are accompanied by strong lower tropospheric northerly winds sharp decreases in temperature and sharp pressure rises in these studies some interesting features accompanying cold surges were also ad dressed mainly cold air damming near mountain barriers as a result of the interaction of the synoptic scale flow with topography bell and bosart 1988 concluded that the component of the pressure gradient force parallel to the mountain was the primary cause for the appearance of an accelerated flow nearly parallel to the mountains colle and mass 1995 demonstrated that pressure ridging east of the mountain barrier caused ageostrophic northerly winds while cold avection of upslope flow led to the damming of cold air schultz et al 1997 showed that the extraordinary equatorial extent of a cold surge was aided by topographic channelling similar to cold air damming

fault propagation folding in extensional settings examples of structural style and synrift sedimentary response from the suez rift sinai egypt field data from the oligocene miocene gulf of suez rift demonstrate that coeval growth faults folds and transfer zones exerted a major control on synrift stratigraphic sequence development growth folds in the suez rift are related to steeply dipping normal faults that propagated upward resulting in broad upward widening monoclines in overlying strata folding during fault propagation was accommodated by layer parallel slip and detachment along mudstone horizons as well as by normal and rare reverse secondary faults that propagated away from the master fault the eventual propagation of the master fault through to the surface left the steep limb of the monocline and most of the secondary faults in the hanging wall this evolving structural style exerted a marked control on the geometry and stacking patterns of coeval synrift sediments synrift sediments display onlap and intraformational unconformities toward the growth monoclines and buried faults whereas they diverge into broadly synclinal expanded sections away from the growth monocline continued movement across buried faults resulted in the progressive rotation of the monoclinal limb and associated synrift sediments each successively younger sequence dipping basinward at a shallower angle than the previous one the resulting synrift geometries differ significantly from stratal geometries normally anticipated adjacent to normal faults along strike variations in facies stacking patterns are also commonly associated with decreasing displacement across faults and associated folds toward low relief transfer zones data from other rift basins indicate that fault propagation folds are not unique to the gulf of suez

monocline formation during growth of segmented faults in the taranaki basin offshore new zealand abstract precursor monoclines or fault propagation folds are commonly associated with normal faults many previous studies have analysed these structures at outcrop or in analogue models but there are few natural examples which have been studied in detail in 3d here we present the results of analysis of two monoclines imaged in a 3d seismic reflection survey in the taranaki basin offshore new zealand the monoclines formed in response to miocene recent extensional reactivation of underlying basement normal faults of cretaceous age the miocene structures have associated growth strata that allows their geometrical evolution to be established the two monoclines initiated at the same time 3 4 ma the smaller of the two monoclines has only limited associated faulting while the larger structure was cross cut by upward propagation of the basement fault as a segmented array of normal faults variations in fold amplitudes and fault displacements within the growth strata associated with the larger structure record the progressive transition from folding to faulting with folding limited to the relay zones between fault segments in the later stages of growth this structure demonstrates spatial and temporal complementary relationships between folding and faulting so that together they define a single kinematically coherent structure although the monoclines widen upwards with geometries consistent with the trishear model of forced folding there is also a positive correlation between monocline amplitude and wavelength measured along the length of the structure which suggests that the wavelengths of these structures increased as they grew

finescale vertical structure of a cold front as revealed by an airborne doppler radar abstract in the afternoon of 24 may 2002 a well defined and frontogenetic cold front moved through the texas panhandle detailed observations from a series of platforms were collected near the triple point between this cold front and a dryline boundary this paper primarily uses reflectivity and doppler velocity data from an airborne 95 ghz radar as well as flight level thermodynamic data to describe the vertical structure of the cold front as it intersected with the dryline the prefrontal convective boundary layer was weakly capped weakly sheared and about 2 5 times deeper than the cold frontal density current the radar data depict the cold front as a fine example of an atmospheric density current at unprecedented detail 40 m the echo structure and dual doppler inferred airflow in the vertical plane reveal typical features such as a nose a head a rear inflow current and a broad current of rising prefrontal air that feeds the accelerating front to rear current over the head the 2d cross fro

geodynamics of rifting and implications for hydrocarbon habitat abstract rifting activity is probably mainly governed by frictional forces exerted on the base of the lithosphere by the convecting sub lithospheric upper mantle combined with deviatoric tensional stresses developing over upwelling branches of the asthenospheric convection system and by far filed stresses controlling the interaction of lithospheric plates moving relative to each other mantle plumes rising from the deep mantle do not appear to be a major driving force of rifting therefore it is questioned whether a distinction between active and passive rifts is still justified lithospheric extension triggers by decompression partial melting of the lower lithosphere and upper asthenosphere magmatic processes contribute materially to thinning of the subcrustal lithosphere and probably also of the lower crust this could explain the frequently observed discrepancy between upper crustal extension by faulting and lower crustal attenuation as defined by refraction and deep reflection seismic data the duration of the rifting stage of palaeorifts and passive margins is highly variable depending on plate interaction crustal separation can be achieved after as little as 7 ma and as much as 280 ma of rifting activity the availability of crustal discontinuities does not appear to play a significant role in the time required for crustal separation to be achieved the structural style of rifts is controlled by the physical state of the lithosphere the mode and amount of its extension and the lithological composition of pre and syn rift sediments subsidence of rift basins is controlled by the balance between isostatic adjustment of the crust to lithospheric stretching and uplift induced by mechanical and thermal attenuation of the subcrustal lithosphere post rift basin subsidence is mainly governed by the decay of rift induced thermal anomalies densification of the lower crust and intra plate stresses provide overprinting effects in view of this it is unlikely that quantitative analyses of post rift basin subsidence give a direct measure of lithospheric extension tectonically active rifts palaeorifts and passive margin basins contain major hydrocarbon provinces their hydrocarbon charge can rely exclusively on pre rift syn rift or post rift sedimentary sequences or a combination thereof maturation of source rocks can be achieved during the syn and or post rift stage of basin evolution during rifting conductive and convective heat transfer accounts for elevated geothermal gradients these play an important role in the maturation of pre and syn rift source rocks thermal gradients decrease asymptotically during the post rift stage

tectonic implications of faulting styles along a rift margin the boundary between the rhine graben and the vosges mountains 1 seismic reflection data show the effects of the miocene strike slip environment on the boundary between the upper rhine graben urg and the vosges mountains vm the border fault zone exhibits three types of responses to the new nw se directed regional stress regime where it trends n s no new deformation is observed where it trends nne ssw transpression is evident and it develops into a few kilometers wide zone of intense deformation along the ne sw trending southern boundary of vm transpression intensifies with an increase in the perpendicular shortening component and the border fault zone turns into a reverse fault the uplift of the boundary relative to the graben is estimated to be no less than 1000 m near colmar and significantly more along the boundary with the dannemarie basin these estimates and kinematics considerations support the hypothesis that the vosges mountains are mostly a transpressional feature the rhine fault is mapped and suggested to be a lower miocene structure that was formed in response to the change in the regional stress regime

offset source vsp surveys and their image reconstruction zero offset source vsp surveys provide information about the subsurface only within the fresnel zone centered at the well offsetting the source location moves the reflection zones away from the well thus providing lateral cover conventional processing of this type of data gives rise to a distorted image of the subsurface using a simple ray tracing scheme this image may be reconstructed into the more familiar coordinate system of the surface seismic section this simple data independent mapping is based on the assumption of horizontal layering and requires a vertical velocity profile the technique of placing the source away from the borehole was first applied to the single offset source vsp survey however data from any survey geometry such as deviated well with rig source walkaway vsp etc can be mapped to the coordinate system defined by the appropriate seismic section to obtain the best results from this type of survey the target area must be defined and simple modeling techniques used to optimize the source location s these pre survey modeling methods may also be used to anticipate and hence avoid a number of problem areas which experience has highlighted the data from any vsp survey is the result of a realizable experiment and as such obeys the wave equation this implies that the wave equation may be used to migrate the data to its true subsurface location theoretically such a process is more secure than ray tracing techniques although its practice presents many difficulties

the owles iop2b lake effect snowstorm shoreline geometry and the mesoscale forcing of precipitation abstractlong lake axis parallel llap lake effect precipitation systems that form when the flow is parallel to the long axis of an elongated body of water frequently produce intense highly localized snowfall conceptual models of these llap systems typically emphasize the role of thermally forced land breezes from the flanking shorelines with low level convergence and ascent centered near the lake axis in reality other factors such as shoreline geometry and differential surface roughness can strongly influence llap systems here a wrf model simulation is used to examine the mesoscale forcing of lake effect precipitation over lake ontario during iop2b of the ontario winter lake effect systems owles field campaign in the simulation the large scale flow shoreline geometry and differential surface heating and roughness contribute to the development of three major airmass boundaries the first is a land breeze front that forms along a bulge in the south shoreline between st catharines ontario can

low level easterly winds blowing through the tsugaru strait japan part i case study and statistical characteristics based on observations abstract this study has investigated structures and diurnal variations of the easterly surface winds blowing throughout the east west passage comprising the tsugaru strait mutsu bay and circumjacent terrestrial gaps in northern japan during the summer months based on observational and reanalysis data a representative case study in june 2003 and supplemental statistical analyses are presented the cool easterly winds accompanied by clouds and fog are blocked by the central mountain range this condition increases an along strait sea level pressure slp gradient which induces strong winds in the west of the strait the along strait slp gradient is enhanced by the developed okhotsk high and by low pressure systems passing along the southern coast of japan or over the japan sea stronger weaker and easterly east northeasterly winds are observed during the nighttime daytime corresponding to the cool air intrusion from the east retreat from west differences in slp observed at meteorological obse

crustal structure of the middle urals based on reprocessing of russian seismic reflection data summary reprocessed russian seismic reflection data combined with existing russian geological maps and seismic interpretations provide the basis for a revised tectonic interpretation of the upper crust in the middle urals the main uralian fault muf the principal suture of the urals separating the east european craton to the west from accreted terranes to the east is found to penetrate to depths of at least 18 km and perhaps much deeper with a uniform eastward dip of 35 after migration as the muf appears to truncate reflections in both the foreland and hinterland of the urals it is arguably one of the youngest structural features of the orogen basement rocks of the east european platform underthrust the suture and comprise the deep crust a minimum of 30 km east of the surface expression of the muf the tagil volcanic arc complex greater than 1000 km in length along strike comprises at least the upper 10 km of the crust east of the muf this terrane shallows eastwards where it appears to be truncated by the west dipping serov mauk fault based on correlation with surface geology the hinterland of the urals east of the muf is characterized by a previously unrecognized zone of discontinuous mid crustal reflectivity at depths of 14 16 km that is discordant with upper crustal reflections this mid crustal zone of reflectivity is interpreted to represent either a major subhorizontal structural detachment or a zone of magmatic intrusion

tertiary tectonics of the dannemarie basin upper rhine graben and regional implications recently released seismic reflection data together with previous seismic and well data are used to describe the development of the dannemarie basin in the sw end of the upper rhine graben the dannemarie basin was formed during the main rifting phase of the upper rhine graben as an asymmetrical graben trending ne sw post rift tectonism shifted the depocenter southward and changed the overall shape of the basin miocene jura compression did not result in the formation of folds as in the adjacent mulhouse horst strike slip faulting was dominant in the post rift period and new faults were created most notably the north trending and transpressional belfort fault the boundary of the dannemarie basin with the vosges mountains is part of a restraining bend which may account for the uplift of the southernmost part of the vosges mountains

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

doppler radar observation of a land breeze cold front abstract during the early morning hours of ii january 1981 a very narrow intense band of snow which had formed along the leading edge of a land breeze cold front was viewed by cp 4 radar near muskegon michigan the front formed well inland and moved through the area from the northeast shortly after dawn the driving force for the land breeze was the large temperature contrast that existed between radiationally cooled air over the northern highlands of lower michigan and the relatively warm lake modified air near the shore of lake michigan the possibility that the observed snowband was associated with a mesoscale feature other than the land breeze is investigated an analysis of minimum temperatures in the great lakes region for 11 january 1981 shows that a strong temperature gradient existed over western lower michigan this gradient reached a maximum value well inland rather than at the lake shore radar observations show the band to be over 80 km long and only 4 km wide oriented roughly parallel t

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

formation of the convective lines off the mountainous coast of southeastern taiwan a case study of 3 january 2004 abstract convective lines frequently occurring off the mountainous coast of southeastern taiwan under weakly synoptically forced weather conditions are one of the most well known mesoscale phenomena in taiwan these lines usually develop close to the coast but frequently can also be observed well offshore while nearshore lines are better understood the formative processes of the offshore lines remain unclear the main objective of this study is to use various available observations e g doppler radar surface and sounding observations quikscat and ncep data collected over southeastern taiwan to investigate a specially chosen case on 3 january 2004 in an attempt to identify possible mechanisms leading to the formation of the offshore lines the studied line was formed 50 60 km away from the southeastern coast of taiwan and oriented south southwest to north northeast and approximately parallel to the coast detailed analyses of the event indicated that the formation of the line did not appear direc

integrated geological and geophysical studies in the sg4 borehole area tagil volcanic arc middle urals location of seismic reflectors and source of the reflectivity near vertical incidence reflection seismic data acquired in the tagil volcanic arc middle urals show the upper crust to be highly reflective two intersecting seismic lines located near the ongoing 5400 m deep sg4 borehole show that the main reflectivity strikes approximately n s and dips 35 55 to the east prominent reflections intercept the borehole at 1000 1500 2800 2900 3400 and between 4000 and 5400 m which correspond to intervals of low velocity low density low resistivity the surface projections of these reflections lie parallel to the strike of magnetic anomaly trends multioffset vertical seismic profile vsp data acquired in the sg4 borehole show a seismic response dominated by p to s reflected converted waves from the moderately east dipping reflectivity and from a set of very steep east dipping reflectors not imaged by the surface data modeling of the vsp data constrains the depth at which reflectors intercept the borehole and suggests that the p to s conversions are best explained by low velocity porous intervals rather than higher velocity mafic material the most prominent east dipping reflection on the surface seismic data is only imaged on vsp shots that sample the crust closer to the e w seismic line this discrepancy between the vsp and the surface seismic data is attributed to rapid lateral changes in the physical properties of the reflector surface and borehole data suggest that the low velocity low density low resistivity intervals are the most important source of reflectivity in the sg4 borehole area although lithological contrasts may also play a role drill cores from the these zones contain hydrothermal alteration minerals indicating interaction with fluids tectonic criteria suggest that they might represent imbricated fracture zones often bounding different lithologies and or intrusions some of them might also represent high porosity lava flows or pyroclastic units common in island arc environments

palaeozoic tectonic evolution of the middle urals in the light of the esru seismic experiments abstract a new compilation of deep seismic reflection data in combination with the results of recent geological and isotopic investigations provides the basis for significantly refined structural and evolutionary models of the middle urals many of the major structural boundaries observed at the surface e g main uralian thrust main uralian normal fault serov mauk fault prianitchnikova shear zone can be followed on the seismic reflection data to depths of 8 15 km only a few features can be traced through the horizontal to shallow dipping zones of middle crustal reflectivity that extend beneath much of the middle urals exceptions might be the deevo thrust and a newly discovered deep band of moderately dipping reflections beneath the west siberian basin that may represent the remnants of an ancient subduction zone the reflectivity of the lower crust and moho are similar beneath the hinterland of the urals and below the western part of the west siberian basin suggesting that in both places they have the same extensional origin accretion of various exotic terranes to the eastern margin of baltica during late palaeozoic time involved considerable shortening of the continental margin the accreted terranes e g tagil petrokamensk and alapaevsk arc complexes consist mostly of island arc material formed during mid and late palaeozoic time closely associated with the island arcs are several high grade metamorphic complexes e g salda and murzinka adui complexes that were exhumed during and after late palaeozoic convergence towards the end of the orogeny several north south trending strike slip faults e g sisert fault were active after the orogeny major periods of tectonism and magmatism in the middle urals resulted in the extrusion of the siberian trap basalts crustal stretching and or underplating and the formation of the west siberian basin the planet s largest intracontinental sedimentary basin finally a period of renewed thrust faulting often reactivating older faults led to the inversion of the mesozoic basins

seismic imaging of reflectors in the sg4 borehole middle urals russia the upper crust in the middle urals is known to be highly reflective however it is not clear whether the observed reflections originate from lithological boundaries or from fault zones the sg4 borehole located in the tagil synform of the middle urals drilled to 5354 m as of august 1995 presents one opportunity to study the source of this reflectivity the hole has penetrated several different lithologies as well as numerous tectonic or fracture zones the upper 5070 m consist of island arc rocks which have presumably been thrust on top of basalts to allow correlations between available surface seismic studies and the borehole observations vertical and offset seismic profile data were acquired in the borehole over the interval 520 m to 3940 m two shot points were used a near offset one at 135 m from the wellhead and a far offset one at 1845 m from the wellhead after processing the borehole seismic data show numerous reflecting horizons many reflections correlate with major fracture zones while others have no clear correlation with fracture zones nor lithological contrasts the interval between approximately 4450 m and 5100 m which is imaged below the bottom of the survey shows a layered reflective pattern that correlates with the lower part of a flysch unit which ends at 5070 m the basalts below appear to be relatively transparent a prominent east dipping reflector on a w e cdp line about 700 m north of the wellhead is not clearly imaged on the borehole seismic however in a pilot hole which deviates a few hundred metres in the northerly direction from the main hole a marked low velocity zone is observed at the corresponding depth for this reflector indicating its source to be from a fault zone that the fault zone is not clearly observed on the borehole seismic data is attributed to 3d effects

vertical seismic profile migration using the kirchhoff integral wave equation migration can form an accurate image of the subsurface from suitable vsp data the image s extent and resolution are determined by the receiver array dimensions and the source location s experiments with synthetic and real data show that the region of reliable image extent is defined by the specular zone of illumination migration is achieved through wave field extrapolation subject to an imaging procedure wave field extrapolation is based upon the scalar wave equation and for vsp data is conveniently handled by the kirchhoff integral the migration of vsp data calls for imaging very close to the borehole as well as imaging in the far field this dual requirement is met by retaining the near field term of the integral the complete integral solution is readily controlled by various weighting devices and processing strategies whose worth is demonstrated on real and synthetic data

decoupled extensional faulting and forced folding in the southern part of the roer valley graben belgium abstract during late oligocene incipient rifting the southern part of the roer valley graben was characterized by normal faulting and forced folding of its paleogene pre rift strata the 2d seismic data used in this study shows that these faults and forced folds were geometrically decoupled from faults or fault zones in the underlying triassic and older strata geometric decoupling consistently took place in an interval that comprises latest triassic to early jurassic soft claystones on top of triassic alternations of evaporites and claystones layers this mechanically weak interval probably inhibited the upward propagation of re activated underlying faults resulting in the formation of the observed forced folds monoclines in the overlying paleogene pre rift strata strain from the sub detachment faults was distributed along the mechanically weak interval towards detachment edges leading to the consistent presence of faults in the footwall domain of the supra detachment monoclines the mechanically weak interval was thereby able to maintain the kinematic coherency between geometrically decoupled under and overlying deformation throughout late oligocene rifting

transpressive inversion of a mesozoic extensional forced fold system with an intermediate decollement level in the basque cantabrian basin spain 1 in the basque cantabrian basin spain normal faulting and associated folding occurred during late jurassic to early cretaceous rifting cenozoic pyrenean thick skinned transpressive inversion in the western parts of the basin preserved the first order extensional architecture integration of geological maps and seismic profiles has permitted to fully constrain the style of extensional deformation and subsequent inversion in the western portion of the basque cantabrian basin extensional faults offset the paleozoic basement up to lower triassic rocks the presence of an efficient decollement level represented by triassic evaporites produced the decoupling between basement rocks and the upper triassic to middle jurassic prerift cover sequence extensional forced folding occurred in the cover driven by basement faulting and the migration of evaporites toward the hanging wall of the extensional faults with salt welds developing away from them upper jurassic to lower cretaceous syn rift sediments deposited synchronously with forced folding which led to the development of extensional growth geometries associated with both master faults and nearly transverse faults syn rift growth sequences are characterized by downlap and onlap relationships with the underlying prerift units interpreted as the result of along strike variations of master fault extensional displacement rate cenozoic pyrenean contraction generated the right lateral transpressive inversion of basement master faults and the almost dip slip reactivation of transverse extensional faults

development of extensional fault and fold system insights from 3d seismic interpretation of the enderby terrace nw shelf of australia abstract extensional fault related folding has been widely observed in rift systems that are characterised by basement involved fault reactivation on the enderby terrace nw shelf of australia oblique reactivation of a basement structure resulted in a depth branched fault system that consists of six splay faults in the cover stratigraphy extensional fault related folding is obvious and predominantly developed in the hangingwall of reactivated basement fault the mechanically weak locker shale not only plays an important role in displacement accommodation at the basement fault tip but also exerts a strong impact on flat development of the ramp flat ramp fault thereby controlling the location and geometry of the hangingwall anticline the kinematic evolution of these structures can be determined based on the well preserved stratigraphy of the hangingwall basins faults and folds deformation exhibits systematic lateral changes which provides clues for the kinematic evolution of the hangingwall folds that is i hangingwall synclines and anticlines formed as a result of fault propagation and linkage ii partial truncation of the anticline by adjacent fault segments due to lateral fault lengthening and interaction and iii complete truncation of the anticline by a planar fault that results in the abandonment of the curved fault plane in the footwall results of this study are applicable to other extensional fault and fold systems of similar origin and provide models for partially preserved outcrop deformation and poorly imaged seismic data interpretation

active tectonics of the southeastern upper rhine graben freiburg area germany the upper rhine graben has two plio quaternary depocentres usually interpreted as resulting from tectonic reactivation the southern basin near freiburg im breisgau germany contains up to 250 m of sediments beneath the younger alluvial deposits related to the current drainage system a former river network deeply entrenched in the substratum reveals a very low regional base level of early pleistocene age the offset of channels at faults allows us to infer a pleistocene reactivation of the syn rift fault pattern and the estimation of slip rates maximum vertical movements along the faults have not exceeded 0 1 mm yr since the middle pleistocene current activity is concentrated along the westernmost faults morphologic markers indicate late pleistocene reactivation of the rhine river fault and geophysical prospecting suggests a near surface offset of young sedimentary deposits the size of the fault segments potentially reactivated suggests that earthquakes with magnitude larger than mw 6 3mw 6 3 could be expected in the area with a return interval of about 8000 years extrapolated to the duration of the plio pleistocene the strain rate estimates reveal that the tectonic forcing may account for only one third to one half of the whole thickness of the plio pleistocene sediments of the basin fill thus other processes must be invoked to understand the growth of the plio pleistocene basin especially the piracy of the rhine river to the north during the early pleistocene could explain these effects

balancing sub and supra salt strain in salt influenced rifts implications for extension estimates the structural style of salt influenced rifts may differ from those formed in predominantly brittle crust salt can decouple sub and supra salt strain causing sub salt faults to be geometrically decoupled from but kinematically coupled to and responsible for supra salt forced folding salt influenced rifts thus contain more folds than their brittle counterparts an observation often ignored in extension estimates fundamental to determining whether sub and supra salt structures are kinematically coherent and the relative contributions of thin i e gravity driven and thick skinned i e whole plate stretching deformation to accommodating rift related strain is our ability to measure extension at both structural levels we here use published physical models of salt influenced extension to show that line length estimates yield more accurate values of sub and supra salt extension compared to fault heave before applying these methods to seismic data from the halten terrace offshore norway we show that given the abundance of ductile deformation in salt influenced rifts significant amounts of extension may be ignored leading to the erroneous interpretations of thin skinned gravity gliding if a system is kinematically coherent supra salt structures can help predict the occurrence and kinematics of sub salt faults that may be poorly imaged and otherwise poorly constrained

radar observations of the diurnally forced offshore convective lines along the southeastern coast of taiwan this study documents offshore convective lines along the southeastern coast of taiwan a frequent but poorly understood mesoscale phenomenon that influences coastal weather during the taiwan mei yu season doppler radar and surface observations were gathered from a specially chosen period 11 15 may 1998 when the offshore convective lines were active off the southeastern coast of taiwan these observations were used to show the basic character structure and possible formative processes of offshore convective lines the synoptic environment accompanying these events was found to be relatively undisturbed and featured uniformly prevailing southerly south southeasterly winds in the boundary layer with southwesterlies westerlies aloft examination of radar data during the study period indicates that the lines generally occurred 10 30 km offshore and were characterized by an elongated narrow zone 5 10 km wide of heavy precipitation the lines were oriented roughly parallel to the coastline and generally did not move significantly the intensity of the radar reflectivity associated with the lines exhibited a marked diurnal variation and was closely related to the coastal offshore flow developing at night detailed analyses of an event on 14 15 may 1998 further show the important physical link between the offshore flow and the development of the line the offshore line was found to be located near and immediately ahead of the seaward extent of the offshore flow particularly a very narrow zone 2 km of low level heavy precipitation 40 45 dbz coincided with regions of strong updrafts and convergence where the prevailing southerly onshore flow encountered the cool offshore flow nearshore this offshore flow induced convergence given a stable thermodynamic condition in the lowest 1 km in the inflow region was a crucial low level forcing that provided lifting to trigger moist deep convection in this case the line s precipitation tilt eastward was confined primarily to the warmer inflow side rather than feeding the offshore flow to the west of the line no consistent upshear tilt of updrafts throughout the storm layer was observed which is consistent with the presence of a strong westerly shear in the line s environment both of these observations explain a relatively strong weak modification of low level onshore offshore flow by precipitation additionally a combination of surface and doppler radar observations indicates that the leading edge of the offshore flow moved seaward very slowly at 0 7 m s 1 and possessed a frontal character with notable discontinuities in near surface wind and temperature instead of pressure and dewpoint temperature

the structure and evolution of gap outflow over the gulf of tehuantepec mexico abstract mesoscale model simulations are used to examine the structure and dynamics of a gap outflow event over the gulf of tehuantepec mexico that was associated with a surge of cold air along the eastern slopes of the sierra madre the simulated gap outflow winds emerged from chivela pass reached a maximum speed of 25 m s 1 and turned anticyclonically as they fanned out over the gulf northerly winds were also able to ascend the mountains east and to a lesser extent west of chivela pass indicating that the movement of cold air across the sierra madre was not confined to the pass a mesoscale pressure ridge was aligned along the axis of the gap outflow jet which was flanked to the west by an anticyclonic eddy and to the east by a weaker cyclonic eddy a model derived trajectory along the axis of the outflow jet traced an inertial path with anticyclonic curvature produced primarily by the coriolis acceleration the cross flow pressure gradient acceleration along this trajectory was negligible be

style and sequence of deformation during extensional fault propagation folding examples from the hammam faraun and el qaa fault blocks suez rift egypt kilometre scale fault parallel folds are identified adjacent to normal faults in the oligo miocene suez rift egypt and are interpreted to have formed in response to fault propagation folding above upward propagating blind faults the geometry scale and distribution of secondary structures within the folds and their cross cutting relationships with the master faults allow the style and sequence of deformation during fault propagation folding to be established and suggest that during the initial stages of folding the proto footwall underwent extension which was accommodated by layer parallel slip in encasing mudstone horizons and linked normal faulting and block rotation in carbonate and sandstone units the proto hanging wall also contains dominantly extensional normal faults although locally where the master fault had a convex into the footwall map view trace reverse faulting and fracturing occurred secondary structures adjacent to the master fault were not all active simultaneously but initiated and died at different stages during the evolution of the fault propagation fold the results of this study confirm many key predictions of numerical and physical analogue models but also highlight several important controls on the evolution of fault propagation folds in extensional settings which existing models cannot capture such as the influence of the map view trace of the propagating fault and lateral variations in cover stratigraphy lithology and strength on the style and magnitude of secondary deformation

extensional fault related folding northwestern red sea egypt the duwi and hamadat areas on the northwestern margin of the red sea rift system exhibit superb outcrop examples of kilometric scale extensional fault related folds in this area the nakheil and hamadat faults of the rift border fault system consist of a series of wnw and nw trending segments that link through breached relay ramps the fault hanging walls are characterised by a series of offset synclines with non linear axial traces sub parallel to the faults the synclines are doubly plunging and in the immediate hanging wall to the normal faults the strata dip sub parallel to the fault these folds result from along strike displacement variations on the individual fault segments together with extension related fault propagation folding as the faults propagated upwards through a highly anisotropic pre rift sedimentary section in the duwi area the axial traces of the synclines are offset and bend in the regions of relay ramps in the hamadat area the synclines associated with individual fault segments are separated by transverse hanging wall anticlines that formed where segment linkage occurred numerical simulations of extension related fault propagation folding using a trishear model produce geometries that closely match those of the duwi and hamadat folds the dimensions of these hanging wall synclines and their relationships to fault displacement variations indicate that they are formed by extensional fault propagation folding rather than by frictional drag along the fault surface

contrasting tectonic history of the arc continent suture in the southern and middle urals implications for the evolution of the orogen the main uralian fault has been considered the original arc continent suture for 2000 km along the uralide orogen the symmetry of the tectonic units across it suggested a consistent east dipping polarity for the palaeosubduction zone which together with its topographic and aeromagnetic signature supported the idea of a single suture however several characteristics vary at different latitudes in the middle urals it is a strike slip fault zone with moderately deformed and metamorphosed volcanic arc fragments in its hanging wall and low grade metamorphic rocks of the east european craton in its footwall here it has a prominent nnw trending magnetic signature which cross cuts north trending anomalies in its hanging wall and a pronounced reflection seismic signature that can be traced to the top of the middle crust at c 5 s twt in the southern urals it is a serpentinite melange zone of ambiguous kinematics with a weakly deformed and metamorphosed volcanic arc in its hanging wall and moderately metamorphosed to high pressure rocks of the east european craton in its footwall in this part of the orogen it has a weak reflection seismic character and a magnetic signature that parallels that of its hanging wall on the basis of an integrated analysis of these different data sets we suggest that the main uralian fault as it is currently defined is not a single entity but rather the original arc continent suture in the south and the western strand of a strike slip fault system that reworked the original suture in the middle urals

deep crustal structure of the rhine graben from dekorp ecors seismic reflection data a summary abstract results of two deep reflection seismic lines crossing the northern and southern part of the rhine graben which were recorded in 1988 by the french ecors and the german dekorp teams indicate that the asymmetry of this rift persists to the base of the crust the brittle ductile transition zone approximately coincides with the top of the lower crust ductile shear zones appear to affect the crust mantle boundary upper crustal extension by faulting accounts for a divergence of the graben flanks by 5 7 km whereas the crustal configuration of the rhine graben suggest an extension value of some 17 km

growth of normal faults in multilayer sequences a 3d seismic case study from the egersund basin norwegian north sea abstract we investigate the structural style and evolution of a salt influenced extensional fault array in the egersund basin norwegian north sea through analysis of 3d reflection seismic and well data analysis of fault geometry morphology throw distribution and syn kinematic strata reveal an intricate but systematic style of displacement and growth suggesting an evolution of 1 initial syn sedimentary fault growth contemporaneous with salt mobilization initiated during the late triassic 2 cessation of fault activity and burial of the stagnant fault tips and 3 subsequent nucleation of new faults in the cover above contemporaneous salt re mobilization initiated during the late cretaceous with downward propagation and linkage with faults stage 3 was apparently largely controlled by salt mobilization in response to basin inversion as reactivated faults are located where the underlying salt is thick while the non reactivated faults are found where salt is depleted based on the 3d throw analyses we conclude that a combination of basement faulting and salt re mobilization is the driving mechanisms behind fault activation and reactivation even though the sub and supra salt faults are mainly geometrically decoupled through the salt a kinematic coupling must have existed as sub salt faults still affected nucleation and localization of the cover faults

modelling and imaging the moho transition the case of the southern urals summary synthetic seismic modelling is used to test different possible structures and forming processes of the lower crust and moho one and two dimensional synthetic seismic modelling of the moho reflection is carried out to constrain the internal structure of a crust mantle transition a reflectivity algorithm was used to calculate the synthetic seismograms for models of the crust mantle transition consisting of gradient zones and layered sequences the synthetic seismograms for models consisting of laterally variable velocity structure were calculated by an explicit finite difference wave equation algorithm the laterally heterogeneous transition models can be achieved by assuming a moho with different degrees of variable topography or laterally discontinuous layering the effects of a low velocity surface cover on the seismic signature of deep signals is also analysed the seismic modelling coupled with stacked images of wide angle seismic reflection data constrain the case history of the moho transition beneath the southern urals a smooth gradational crust mantle transition gradient velocity depth function does not predict the seismic features observed in the shot records the coda of the pmp and the amplitude behaviour of this phase with offset are modelled with a 6 km thick transition zone which consists of approximately 600 m thick laterally variable layers with a bimodal velocity distribution the horizontal component stacks of the wide angle data feature arcuate events suggesting boudin like structures or a boundary with topographic relief high amplitude sub moho reflections support that the structural complexity of the crust mantle transition can be followed to the upper mantle suggesting eastward dipping structures indicating either remnants of an old subduction zone trapped crustal material within the mantle or active crust mantle interactions

cenozoic right lateral wrench tectonics in the western pyrenees spain the ubierna fault system abstract a study of macro and mesostructural deformation patterns of the southern margin of the cantabrian area western pyrenees spain has revealed a complex cenozoic tectonic framework right lateral tectonics reactivated inherited wnw ese striking faults which developed during late paleozoic and early triassic events and late jurassic to early cretaceous main rifting stage the ubierna fault represents the southern boundary of the mesozoic basin during the oligocene even eocene to present day deformation this fault and the ventaniella fault located to the south in the study area acted as right lateral slightly transpressive elements forming a 120 km long and 15 km wide overstep area here named ubierna fault system where the cumulative right lateral displacement exceeds 15 km the cenozoic tectonic framework of the ubierna fault system includes reactivation along the wnw ese faults development of negative and mostly positive flower structures branch faults strike slip duplexes and releasing and restraining bends ne sw to ene wsw striking reverse faults and contractional horsetail terminations and nnw sse striking normal faults and joints are produced by the wnw ese right lateral strike slip motion the extensional elements are well developed and deformation progression implied their incorporation in the strike slip system as right lateral faults forming part of strike slip duplexes the abundance of flower structures striking wnw ese and paralleling the main strike slip faults together with the overall uplift of the overstep area testifies for a slight compressional component at a regional scale the ubierna fault system represents the most prominent element of a cenozoic transpressional belt which incorporates the western portion of the basque cantabrian basin and the asturian massif area lateral transition between this transpressive belt and the dip slip belt located to the east occurs across an area experiencing along strike shortening which developed to accommodate the eastward extrusion of the transpressional belt

early synrift reservoir development on the flanks of extensional forced folds a seismic scale outcrop analog from the hadahid fault system suez rift egypt forced folds typically develop above the tips of propagating normal faults in rifts that contain thick prerift salt or mudstone sequences this structural style is associated with the deposition of wedge shaped synrift deposits that thin and onlap toward monoclinal growth folds overlying the vertically restricted fault tips subtle stratigraphic traps may develop on the flanks of these folds although because of limited seismic resolution and sparse well data the architecture thickness and distribution of these early synrift reservoirs are difficult to predict to improve our understanding of early synrift reservoir development on the flanks of forced folds we focus on seismic scale outcrop analogs along the hadahid fault system suez rift egypt our data indicate that forced folding dominated during early rifting and that the onset of folding was diachronous along strike fluvial systems incised the rotating monocline limbs leading to the formation of valley like erosional relief along the base synrift unconformity reservoir prone fluvial facies are only locally developed along the forced fold flank with their distribution related to the degree of sediment bypass downdip into the adjacent basin early synrift relief not filled by fluvial strata was backfilled by transgressive tidally influenced reservoir prone facies with carbonates being locally developed in areas of low clastic sediment supply further extension and fault tip propagation led to amplification of the forced folds and deposition of shallow marine to shelf parasequences that became thinner toward the growing folds although displaying greater strike continuity than the underlying fluvial or tidal reservoirs shoreface sandstone reservoirs amalgamate onto the flanks of the forced folds and may be absent toward the fold crest this seismic scale outcrop analog helps us better understand the subseismic stratigraphic architecture and facies distributions of early synrift reservoirs on the flanks of extensional forced folds observations from this and other well exposed outcrop analogs should help reduce subsurface uncertainty and risk when exploring for hitherto under explored subtle early synrift stratigraphic traps

high resolution seismic reflection profiles reveal fracture zones within a homogeneous granite batholith several countries are investigating the use of plutonic rock bodies for the ultimate disposal of radioactive waste material1 among criteria2 3 that must be met before a rock body is mined for a repository is that it must have a low in situ permeability as the permeability of most unfractured plutonic rocks is very low3 the problem reduces to finding those bodies which do not contain major connected fractures that would allow radioactive material to be transported by water to the biosphere we report here that a high resolution seismic reflection survey across the central region of an archaean granitic pluton which on the basis of other data might be defined as relatively homogeneous identifies major sub horizontal fracture zones at depth such fracture zones which could be a major hazard for the containment of radioactive wastes may therefore be detected before selection of a repository site by a combination of high resolution seismic reflection surveying and suitably located deep drilling

formation and maintenance of a long lived taiwan rainband during 1 3 march 2003 abstracttaiwan rainbands trs defined here as convective lines which form off the mountainous eastern coast of taiwan under weakly synoptically forced weather conditions are a well known mesoscale phenomenon but their formative processes remain the subject of debate this study uses surface and radar observations within the coastal zone of eastern taiwan and ncep reanalysis data to document a long lived tr with a lifetime of 36 h during 1 3 march 2003 to advance the current general understanding of mechanisms responsible for the tr s formation and maintenance detailed analyses indicate that the rainband was initiated by convergence that was produced as low level environmental northeasterly easterly onshore flow encountered topographically blocked northerlies that developed nearshore the northerly blocked flow was observed to weaken and subsequently dissipate because of changing synoptic pressure patterns that caused prevailing southeasterlies southerlies at low levels however colder nearshore ai

the 1993 superstorm cold surge frontal structure gap flow and tropical impact in the wake of the eastern united states cyclone of 12 14 march 1993 a cold surge originating over alaska and western canada brought northerlies exceeding 20 m s21 and temperature decreases up to 158c over 24 h into mexico and central america this paper addresses the multiscale aspects of the surge from the planetary scale to the mesoscale focusing on 1 the structure and evolution of the leading edge of the cold surge 2 the reasons for its extraordinary intensity and equatorward extent and 3 the impact of the surge on the tropics specifically on the strength of the trade winds and on the sea surface temperature in the eastern pacific the cold surge was initiated as a developing cyclone over the gulf of mexico and an upstream anticyclone east of the rockies caused an along barrier pressure gradient to form forcing topographically channeled northerlies along the rocky and sierra madre mountains to transport cold air equatorward on the mesoscale the leading edge of the cold surge possessed nonclassical frontal structure for example as the cold surge entered mexico the coldest air and the strongest wind arrived at about 900 hpa before affecting the surface suggestive of a tipped forward leading edge to the surge also satellite imagery and surface observations indicate that the leading edge appeared to be successively regenerated in the warm presurge air the cold surge had characteristics reminiscent of a kelvin wave a tipped forward cold front a pressure jump line a bore and a gravity current but none of these conceptual dynamical models was fully applicable associated with the cold surge gap winds up to 25 m s21 were observed in the gulfs of tehuantepec a tehuantepecer fonseca papagayo and panama owing to the strong cross mountain pressure gradient in the case of the tehuantepecer a rope cloud emanated from the isthmus of tehuantepec and turned anticyclonically consistent with an inertial oscillation on the synoptic and planetary scales the extraordinary equatorward extent of the cold surge was aided by topographic channeling similar to cold air damming by a low latitude upper tropospheric trough and by the lower branch of the secondary circulation associated with a confluent jet entrance region aloft the cold surge also impacted the tropical atmosphere and ocean by contributing to the strengthening of the northeast trade winds over the eastern pacific ocean and by inducing local cooling of the sea surface temperature in the gulfs of tehuantepec and papagayo by about 48 88c