trishear kinematic modeling of extensional fault propagation folding we present a new non linear 2 d numerical trishear model that is capable of modeling both symmetrical and asymmetrical trishear zones and a strain prediction approach based on the velocity field within the trishear zone a simple relationship exists between the shape factor r of the velocity field the hanging wall apical angle and footwall apical angle the implication of this relationship is that when dealing with a real deformed state cross section one can measure the hanging wall and footwall apical angles to determine the r value to specify the velocity field within the trishear zone for either the forward modeling or restoration the new trishear model can accurately reproduce the geometry of two experimental clay models and an extensional fault propagation fold from the gulf of suez predicted strain is greatest directly above the fault tip and decreases with distance from the fault tip as in the experimental models greater strain occurs in the hanging wall because of the greater velocity gradient there whereas the footwall is much less intensely deformed consequently secondary faulting and fracturing if present should be better developed along the fault tip line or in the hanging wall the orientation of fractures or minor faults can be predicted from the strain ellipses calculated from the trishear velocity field

fold related faults in the syrian arc belt of northern egypt abstract late cretaceous early tertiary syrian arc folds in northern egypt include both inversion and non inversion folds these folds are well exposed in northern sinai and the northern eastern desert but exist in the subsurface in the northern western desert in northern sinai the maghara yelleg and halal inversion folds are 45 50 km long similar size inversion folds with opposite vergence exist in the subsurface in the northern western desert and include the kattaniya mubarak alamein razzak and matruh basin folds smaller non inversion compressional folds include the falig and meneidret el etheili folds in northern sinai as well as the abu gharadig anticline in the subsurface in the northern western desert among others detailed surface and subsurface structural mapping made use of the excellent exposures and good 2d and 3d seismic data and led to the identification of the fault patterns of the inversion and non inversion syrian arc folds inversion folds have fault patterns that differ from the backlimb to the forelimb the backlimbs are pervasively dissected by long nw se oriented normal faults that were formed by the regional stress field on the contrary the forelimbs of inversion folds as well as the two limbs of non inversion folds are affected by the local stress in the folded areas and are dissected by three shorter fault sets a set of hinge transverse normal faults and two conjugate sets of hinge oblique faults that have oblique slip the hinge oblique faults dominate the steeper limbs of asymmetric non inversion folds

sar image statistics related to atmospheric drag over sea ice the possibility of using synthetic aperture radar sar data to distinguish sea ice regions with different atmospheric drag is explored both the amplitude of the radar return and statistics derived from sar image data are examined roughness statistics data from several pack ice areas are used in a backscatter model to predict the return from surfaces with measured drag coefficients the results suggest that the scattering coefficient for typical radar wavelengths is insensitive to the roughness elements responsible for the observed drag coefficient variations over pack ice free of major ridges for marginal ice zones where ice concentration and floe deformation contribute to atmospheric drag a simple model for the atmospheric boundary layer is used to provide qualitative relationships between drag coefficient and regional ice properties ice concentration floe size distribution floe edge density derivable from sar data simple algorithms to produce maps of ice concentration and edge density are outlined and applied to 23 5 cm sar digital image data

on the effective aerodynamic and scalar roughness length of weddell sea ice we study the effective aerodynamic roughness length z0 eff and scalar roughness length for temperature zt eff over different compact sea ice types in the antarctic weddell sea by aircraft measurements during two austral summer seasons z0 eff and zt eff are highly variable in the weddell sea ice area the averaged value of in all main sea ice areas was smaller than the averaged value of the ratio between the two roughness lengths was relatively small for new young sea ice with 2 but the ratio became significantly large for the multiyear pack ice with 227 for the pack ice area with sea ice concentration ranging between 95 to 100 we determined a median 4 1 10 03 m and a median 1 8 10 05 m in the new young sea ice area with sea ice concentration ranging between 98 and 100 we observed a median 10 04 m and a median 2 2 10 04 m these values of and differ from published observations conducted in a pack ice and new young sea ice area in the northern hemisphere such as the arctic most model parameterizations require the roughness lengths as constant values as boundary input parameters our study shows that by using the overline z 0 rm eff and values of this study instead of commonly used sea ice roughness length values the accuracy of parameterized heat and momentum fluxes in the weddell sea ice area can significantly be improved

origin dimensions and distribution of remobilized carbonate deposits in a tectonically active zone eocene thebes formation sinai egypt abstract determination of the distribution and mechanism for carbonate dominated mass transport sediments is often compromised by the scale and access to exposures consequently many studies lack the resolution to capture the heterogeneity and dimensions of mass transport deposits this study documents the size shape and stratal assemblage of remobilized carbonates in the eocene thebes formation in the hammam faraun fault block hffb of western sinai revealing the complexities of carbonate mass transport deposits at sub seismic scale present day pseudo three dimensional exposure of the thebes formation in a large fault block formed during the opening of the gulf of suez allowed for lateral and down dip measurement of slope and basinal facies in the field and from photos remobilized facies were digitized in the photos and evaluated using image analysis software a technique with a wide range of applications to outcrop studies of sedimentary architecture debris flow deposits in the lower section of the thebes formation comprises clasts with differing fossil assemblages a relative sea level rise at the start of upper thebes formation deposition resulted in basinal sediments comprising periodic incursions of high density turbidite grainstones encased within a background of planktonic foraminiferal wackestones foraminiferal assemblages of remobilized facies imply multiple sources on the carbonate platform demonstrating the effect of short lived tectonism on slope instability and deposition of mass transport deposits the results of the study confirm that tectonism associated with the syrian arc fold belt which altered the style of basin sedimentation between egypt and syria persisted into the eocene at least as far south as wadi araba in the western desert and hammam faraun in sinai in addition the shape size and extent of the two dominant remobilized facies debris flows and grainstone turbidites are influenced by their mud rich versus grainy compositions

a parameterization of the ice ocean drag coefficient 1 a parameterization of the ice ocean drag coefficient cw was developed through partitioning the oceanic drag force into three components 1 form drag on the floe edge 2 form drag on the ridge keel and 3 skin friction on the ice bottom through these quantities cw was expressed as a function of observable sea ice geometric parameters sensitivity studies were carried out to investigate the influence of varying sea ice conditions on cw the results revealed that cw increases first and then decreases with increasing ice concentration a similar to the observations of the air ice drag coefficient and which is mainly attributed to the nonmonotonic variation of the form drag on the floe edge with ice concentration moreover the form drag on the floe edge is always the dominant component having a proportion of more than 60 in sea ice with a large aspect ratio draft length 1 100 indicating the necessity of including this term in sea ice dynamic models particularly for the marginal ice zone miz the form drag on the ridge keel becomes dominant only when the ridging intensity is extremely high depth spacing 1 20 additionally a large value of cw cannot be caused only by the inclusion of form drag terms but also by large skin friction over rough ice bottoms finally for typical situations in the miz with moderate ridging intensity the parameterization will underestimate cw by approximately 30 for a rough ice bottom and by over 80 for a smooth ice bottom if no form drags are considered

groundwater dynamics in fossil fractured carbonate aquifers in eastern arabian peninsula a preliminary investigation abstract eastern arabian peninsula represents the main natural groundwater discharge area of the arabian platform fossil aquifer system in such settings connections between aquifers could strongly affect the flow dynamics water quality and availability as well as karst formation and landscape evolution geological structures such as folds and faults are central to aquifer connectivity yet their role on groundwater flow is poorly understood herein we perform mapping of exposed and buried structural features in the qatar peninsula using landsat sentinel 2 and alos palsar scenes correlated with field gpr and isotopic data to assess their role in aquifer connections and groundwater dynamics our results suggest that ene wsw oriented fold related faults act as vertical conduits along which artesian upward leakages from the deep aruma aquifer take place into the shallower main aquifer unit i e umm er radhuma and rus in southern qatar peninsula on the other hand downward leakage from the freshwater lens in the dammam aquifer take place in northern qatar peninsula the deep brackish and gaseous rich waters ascending along faults in south qatar peninsula in addition to degrading the water quality in the main aquifer unit enhance dissolution of carbonates and evaporites leading to strong karstification that produces abundant collapse features our findings suggest that structure controls can add significant complexity to recharge mechanisms and groundwater dynamics in fossil aquifers future large scale radar subsurface mapping will be essential to resolve the variability of the water heads in such areas and its correlation to structural discontinuities

geometric tests and their application to fault related folds in kuqa abstract for brittle rock deformation there are two main types of fault related folds found in foreland thrust belts i e fault bend folds and fault propagation folds the predicted angular function for the quantitative geometric relationships between fault shapes and fold shapes in fault bend folds and fault propagation folds have been tested in seismic profiles i e deep bashijiqike tugeerming kashangtokai east qiulitage deep east qiulitage and yakelike fault bend anticlines and bashijiqike yiqikelike and south yiqikelike fault propagation anticlines in the kuqa rejuvenated foreland thrust belt test results for the transformation from seismic time section into seismic depth section using the seismic velocity spectrum can be used to identify whether the interpreted structures are reasonable with geometric analysis and testing of the subsurface structures it is possible to predict the existence of the fault bend folds and fault propagation folds in the kuqa area this study provides convincing proof that the kuqa basin is a rejuvenated foreland basin

roughness variability of sea ice and snow cover thickness profiles in the ross amundsen and bellingshausen seas investigation of top and bottom surface roughness was carried out on snow and ice thickness profiles sampled on 57 floes in the ross amundsen and bellingshausen seas between may and september 1995 an objective classification scheme was used to group the studied sea ice floes according to the degree of deformation they had undergone different roughness criteria and methods were applied to the classified floes roughness variances and other properties such as fractal dimensions derived from fourier spectra depend critically on the deformational history of the floes under consideration the wavelet transform is presented as a new two dimensional method to find dominant structure lengths and at the same time localize them in the studied profiles finally air water and ice surface drag coefficients are calculated from the surface roughness characteristics air drag coefficients ranged between 1 1 and 1 7 103 and increased with increasingly deformed ice

fold accommodation faults fold accommodation faults are secondary faults that accommodate strain variations related to structural and stratigraphic position during fold evolution four main types of fold accommodation faults are commonly found out of syncline and into anticline thrusts form primarily because of an increase in bed curvature within fold cores although differential layer parallel strain at different scales also contributes to fault slip depending on the kinematic evolution of the major fold the thrusts may propagate along the steep or gentle limb of an asymmetric fold or along the hinge of symmetric folds wedge thrusts are primarily formed in competent units because of variations in penetrative layer parallel strain between adjacent units limb wedges occur as hanging wall and or footwall fault bend and fault tip folds whereas hinge wedges occur as multiple nested faults that tend to thicken the more competent units forelimb and backlimb thrusts form by a variety of mechanisms forelimb space accommodation thrusts are low displacement thrusts that resolve strain discontinuities resulting from increased curvature in fold cores forelimb shear thrusts form in the late stages of folding because of rotation and layer parallel extension on the steep forelimbs of folds most backlimb thrusts originate as out of syncline thrusts they may eventually link with forelimb thrusts to form forelimb backlimb thrusts back thrusts accommodate hanging wall strain during the formation of fault related folds they either form selectively in competent units or propagate through the section at the same rate as the main thrust although fold accommodation faults are secondary features they are important elements that define the geometry and size of structural traps in fold thrust structures accurate mapping of these structures is therefore critical in interpreting the structural geometry of fold and thrust belts shankar mitra holds the monnett chair and professorship of energy resources at the university of oklahoma he received his ph d in structural geology from johns hopkins university in 1977 he spent 19 years at arco research and exploration as senior and principal research geologist director of structural geology manager of geological research and senior exploration research advisor his primary research interests are in the development of structural concepts and methods and their application to exploration and production problems he is a recipient of aapg s wallace pratt and cam sproule awards

deformation and secondary faulting associated with basement involved compressional and extensional structures experimental clay modeling is used to study the geometry and evolution of deformation zones formed above basement faults the nature of deformation is compared for reverse faults dipping 30 45 and 60 vertical faults and normal faults dipping 60 and 75 basement faulting results in the formation of a sheared triangular deformation zone that widens upward in the cover units most of the deformation is focused within a central zone of secondary faults which propagate upward and eventually break through the entire section basal units exhibit steeper dips and higher fault densities whereas stratigraphically higher units exhibit gentler dips and lower fault densities the width of the deformation zone is generally greater for reverse faults with low dips the anticlinal axial surface typically dips in the same direction as the synclinal axial surface for low to moderate angle reverse faults however the axial surfaces dip in opposite directions for vertical faults and normal faults particle paths suggest a convex upward rotation within the deformation zone suggesting transfer of material across the extension of the master fault reverse faults are associated with secondary faults with reverse and thrust separations vertical faults are associated with mostly vertical and reverse secondary faults whereas normal faults are generally associated with normal separation of most secondary faults therefore the nature of secondary faults varies with structural position possibly within the same layer these results provide some key insights that are useful in the interpretation of macroscopic surface and subsurface basement involved structures

structural architecture and tectonic evolution of the yelleg inverted half graben northern sinai egypt abstract the gebel yelleg area includes a number of folds belonging to the northern sinai syrian arc structures detailed surface structural mapping and subsurface seismic and borehole data show that the gebel yelleg structures are related to late cretaceous early tertiary inversion of a jurassic asymmetric or half graben formed during the opening of neotethys the inversion structures include a large 45 km long asymmetric fold yelleg anticline with a steep flank overlying the southeastern main bounding fault of the inverted half graben as well as some right stepped en echelon folds overlying the northwestern bounding fault of the half graben the large inversion anticline is dissected by a large number of long nearly orthogonal normal faults whereas the en echelon folds are dissected by transverse normal faults and two sets of oblique slip faults inversion of the northern sinai extensional basins is related to africa eurasia convergence and was probably transpressional with a small component of dextral slip this study shows that the magnitude of inversion in the northern sinai fold belt decreases toward the southern boundary of the jurassic extensional province

convection in enceladus ice shell conditions for initiation 1 observations of enceladus by the cassini spacecraft indicate that this tiny saturnian moon is geologically active with plumes of water vapor and ice particles erupting from its southern polar region this activity suggests that tidal dissipation has become spatially localized perhaps due to a compositional rheological and or thermal anomaly in its ice shell here we examine the role that solid state convection may have played in enceladus prolific activity by creating a suitable rheological and thermal anomaly we find convection can only initiate in the pure water ice i shell of a differentiated enceladus if the ice grain size is less than 0 3 mm which is quite small but may be realistic if non water ice impurities and or tidal stresses keep grains from growing this grain size restriction becomes more severe for lower basal ice temperatures which implies that any ammonia present has not become strongly concentrated in a thin basal ocean while convection occurs for a maximally thick pure ice shell and underlying ocean convective heat flows are 7 11 mw m 2 for ice grain sizes of 0 1 0 3 mm compared with the 100 mw m 2 measured for enceladus south polar terrain from cassini cirs observations thus whereas solid state convection may be a prerequisite for enceladus geological activity the observed heat flow requires strong tidal dissipation within the convecting region and possibly that convection reaches the surface

structural models of faulted detachment folds faulted detachment folds represent a common structural style in several hydrocarbon producing fold and thrust belts including the zagros idaho wyoming utah carpathian and albanide belts and several deep water fold belts including the mississippi fan and per dido belts these structures form in units with high competency contrasts and display a transition in deformational behavior from detachment folding to progressive fault propagation with increasing shortening the structures first form by symmetric or asymmetric detachment folding with the fold wavelength controlled by the thickness of the dominant units volumetric constraints require the movement of material from the synclines to the anticlines contin ued shortening results in tighter folds with limb rotation by hinge migration limb segment rotation and internal shear rotation of limb segments between locked hinges results in thrust faults which propagate through deformation zones on the frontlimb and possibly the backlimb the faults may terminate both up and down section within brittle or ductile deformation zones eventually a through going fault connects one of the major faults with the basal detach ment variations in the structural geometry are related to the rela tive thickness and competency of the units and the mechanisms of deformation because faulted detachment folds superficially resem ble fault propagation folds their geometry can be misinterpreted in areas of poor data quality characteristic features for distinguish ing these structures include 1 smaller variations in anticlinal length during fold evolution 2 a more open and rounded fold geometry 3 complex and nonuniform variations in fault slip 4 a significant variation in deformational behavior among different units and 5 fold fault relationships indicating transition from folding to faulting such as footwall synclines and decapitated fold geometries

structural architecture and tectonic evolution of the maghara inverted basin northern sinai egypt abstract large ne sw oriented asymmetric inversion anticlines bounded on their southeastern sides by reverse faults affect the exposed mesozoic and cenozoic sedimentary rocks of the maghara area northern sinai seismic data indicate an earlier jurassic rifting phase and surface structures indicate late cretaceous early tertiary inversion phase the geometry of the early extensional fault system clearly affected the sense of slip of the inverted faults and the geometry of the inversion anticlines rift parallel fault segments were reactivated by reverse slip whereas rift oblique fault segments were reactivated as oblique slip faults or lateral oblique ramps new syn inversion faults include two short conjugate strike slip sets dissecting the forelimbs of inversion anticlines and the inverted faults as well as a set of transverse normal faults dissecting the backlimbs small anticline syncline fold pairs ornamenting the steep flanks of the inversion anticlines are located at the transfer zones between en echelon segments of the inverted faults

rejuvenation of the tethyan passive continental margin of northern sinai deformation style and age gebel yelleq area abstract detailed field mapping and structural analysis of the northeastern and southeastern parts of gebel yelleq the largest fold among the northern sinai folds indicate the presence of two ene oriented dextral wrench zones the northern meneidret el etheili wrench zone is represented by right stepped en echelon doubly plunging folds whereas throughgoing wrench faults characterize the southern minsherah wrench zone the steep southeastern flank of gebel yelleq asymmetric fold makes an acute angle with the wrench zones and is orthogonal to the nw se directed shortening direction indicated by mesostructures similar structural relations are evident in the other major folds of northern sinai gebels el maghara and halal a structural model is proposed for the deformation of northern sinai late cretaceous tertiary rejuvenation of the early mesozoic passive continental margin of the neotethys proceeded via right lateral wrenching in northern sinai and is related to the oblique convergence between africa arabia and eurasia during the closure of the neotethys as a result wrench zones developed above the early rift faults e g meneidret el etheili and minsherah wrench zones also nw se directed shortening related to and parallel to the convergence of africa arabia and eurasia deformed the blocks lying between the wrench zones through the development of ne sw oriented thrust faults at acute angles to the wrench zones these thrusts ruptured the precambrian basement and propagated upward through the overlying sedimentary cover as listric thrust faults forming large fault propagation folds in gebels yelleq el maghara and halal these thrusts underlie the steep southeastern flanks of these folds and are exposed in gebels el maghara and hamayir the depth to detachment of these thrusts progressively increases southward to a value underneath the gebel yelleq area close to the brittle ductile transition of the crust the deformation reached its zenith in the early late senonian and probably continued into the early miocene the northern sinai fold belt characterizes an unstable crustal block separated from a tectonically stable crustal block to the south in central and southern sinai by a belt of ene oriented closely spaced faults forming what is called the central sinai hinge belt

laser profiling of the ice surface topography during the winter weddell gyre study 1992 a laser profiler mounted on a helicopter was used to measure the surface topography of sea ice in the weddell sea the measurements were carried out during the cruise antarktis x 4 of r v polarstern as part of the winter weddell gyre study 1992 wwgs 92 the total length of the measured surface profiles amounts to 793 km the observed mean ridge heights and mean ridge spacings are fairly well correlated therefore the ridging intensity r1 which is the ratio of ridge height and spacing was used as a quantitative classifier in order to arrange the laser data into different groups at a cutoff height of 0 8 m the average ridge height and spacing are 1 16 m and 160 m at the lowermost range of ridging intensities r1 0 04 respectively the best fits to the observed ridge height distributions are achieved by negative exponentials at lower ridging intensities as a function of ridge height at the regime of highest ridging intensity as a function of the ridge height squared the distributions of ridge spacing are well described by a lognormal distribution function a simple model is used to estimate the average thickness hd and the areal fraction of ridged ice from the laser data the values of hd range from 3 1m with an areal coverage of 5 at the lowermost range of r1 to 3 7 m with an areal coverage of 31 at the uppermost range if the ridged ice is distributed as a uniform layer over a unit area the corresponding effective thickness values are 0 14 m and 1 16 m respectively mean ridge heights and spacings are determined for different cutoff heights in order to enable comparisons to other measurements the effect of ridges on the surface stress over the ice is estimated using the drag partition theory which is applicable to the regime of lowest ridging intensity the contribution of ice ridge form drag to the total wind drag for an average ridging intensity of 0 007 and a cutoff height of 0 8 m is about 35 to 40 at neutral stability if it is assumed that the aerodynamic roughness length z0 of the intervening ice surface varies between 3 3 10 4 m and 5 5 10 4 m the drag coefficient cdn ranges from 2 08 10 3 to 2 24 10 3 at a reference height of 10 m

atmospheric boundary layer structure and drag coefficients over sea ice this paper estimates the air sea drag coefficient for first year ice from recent aircraft measurements and reconciles the range of observed drag coefficients 103cd 1 2 3 7 referenced to 10 m for all sea ice types based on ice roughness and seasonal meteorology for the purpose of sea ice modeling it is necessary to define an effective drag coefficient which relates regional stress to regional wind because sea ice is heterogeneous on scales less than 20 km regional stress is influenced by the distribution of surface roughness the buoyancy flux from quasi periodic leads and external atmospheric conditions principally the inversion height 103cd is 1 3 1 5 for smooth ice but is much greater for nonflat surfaces for wind speeds greater than 5 m s and air temperatures below freezing the effective 103cd is 2 5 3 0 for nearly continuous pack ice such as first year ice in seasonal ice zones and central arctic basin the range of values of 103cd is 3 0 3 7 for unstable boundary layers typical of off ice winds in the marginal ice zone miz or even greater if the ice has been broken by a recent storm cd values at the lower end of these ranges are associated with low inversion heights these coefficients are confirmed by 103cd of 2 9 2 5 and 3 1 for first year sea ice calculated from gust probe data collected by the noaa p 3 aircraft interior to the inner miz in the bering sea during the marginal ice zone experiment mizex west in february 1983 and 103cd of 2 6 for the arctic calculated from arctic ice dynamics joint experiment aidjex aircraft data for february 1976 the effective drag coefficient with the presence of even a small concentration of sea ice is greater than the oceanic value as shown by a 103cd of 2 2 calculated from noaa p 3 gust probe data over a 40 km track of 0 4 ice concentration in the outer miz of the greenland sea in june 1984 during mizex 84 the relation of surface wind and stress to the geostrophic wind for shallow inversion heights typical of high latitudes is reviewed with a turbulent closure atmospheric boundary layer model the winter arctic is typified by low inversions 100 m low geostrophic drag coefficients and large geostrophic surface wind turning angles with low functional dependence on surface roughness seasonal ice zones are typified by a more modest influence of the inversion on boundary layer characteristics

control of extensional transfer zones on syntectonic and post tectonic sedimentation implications for hydrocarbon exploration the gulf of suez red sea rift system exhibits superb outcrop examples of extensional transfer zones and displays the control of these zones on syntectonic and post tectonic sedimentation hard and soft linkage transfer zones were identified at variable scales hard linkage transfer zones form inward and outward fault kinks whereas soft linkage transfer zones form relay ramps between overlapping rift parallel faults the two types of transfer zones invariably exerted fundamental control on the deposition of syn and post tectonic sediments flow direction of drainage systems and locations of sediment entry points as well as the intensity of erosion patterns of the structurally high sediment source areas this study highlights the close relationship between the transfer zones and hydrocarbon accumulations in clastic syntectonic reservoirs in rift basins

kinematic modelling of extensional fault propagation folding abstract many studies have shown that in extensional basins discrete faulting at depth is commonly linked to more distributed deformation in particular folding at higher levels such extensional fault propagation folds are particularly common where there is a distinct mechanical contrast between faulted basement and sedimentary cover outcrop and analogue modelling studies indicate that such folds form as upward widening zones of distributed deformation monoclines above discrete faults at depth with increasing displacement strain the folds are cut by faults as they propagate upwards into the cover to date however there has been little investigation into the kinematics of linked basement faulting and extensional fault propagation folding here we present a two dimensional kinematic model of linked basement faulting and fault propagation folding which is based upon trishear the model allows investigation of the influence of shear zone geometry and the rate of fault propagation upon the style of folds and the strains associated with them the evolution of linked basement faulting and folding predicted by the model is compared in detail to that observed in an analogue model the kinematic model reproduces well many of the features seen both in the analogue model and reported from outcrop and seismic studies