scale dependence of strike and dip in sedimentary basins implications for field measurements and integrating subsurface datasets abstract the measured orientation of geological surfaces such as bedding or fracture planes varies with scale of observation this can be demonstrated by comparing representative orientation of an outcropping surface at centimeter decameter and kilometer scale it can also be verified by tracking variation of dip vectors while generalizing structure maps of subsurface horizons stored as numeric grids the challenge of obtaining meaningful orientation information from outcrops is well known but in practice field geologists intuitively extract orientation information that suits their purposes rather than explicitly recording the scale of observation or even measurement process there is an analogous problem when subsurface structural maps in sedimentary basins made from kilometer scale areas of reflection seismic interpretation are integrated with wells containing image logs that yield strike and dip information at a scale of tens of centimeters in the absence of upscaling guidelines maps are often tied to the correct depth but not to the structural orientation measured in piercing wells the solution at outcrop and wells is to explicitly determine the scale dependent structure then use information at the appropriate length scale as required complete description of strike and dip requires a length scale parameter in addition to the orientation values

balanced section in thrust belts part 1 construction balanced geological cross sections are an important aid to understanding thrust belt structures and to estimating their hydrocarbon bearing potential two approaches to section balancing have been taken in the past construction of retrodeformable sections from raw data and modification of previous interpretations after an evaluation procedure these approaches may be unified by use of a langrangian grid projection of datum locations dips and stratigraphic thicknesses onto the section plane is performed directly by calculation or graphically using plunge lines spline interpolation and parallel fold modeling are the simplest ways of filling gaps in the sectional data but isogon interpolation yields rheologically more realistic results faults are interpolated using cutoff geometries as constraints fault tips are located from distance displacement plots whereas the depth to detachment is obtained by a modified chamberlin construction interpolations made on the section are directed back to the geologic map via plunge lines although these techniques of section construction do not guarantee a balance especially when complexities such as growth structures diapirs or strike slip faults are present they eliminate many potential errors

patterns of imbricate thrusting through the use of seismic reflection profiles satellite images and balanced kinematic models we describe patterns that help to identify imbricate structures and define the sequence of thrusting in fold and thrust belts measures of folding shear strains are employed to define break forward systems in which younger deeper faults refold overlying thrust sheets in contrast break backward sequences form a wide range of viable geometries that are not expected to conserve these folding strains thus measures of folding shear strains provide a means to define thrusting sequence we also explore map view patterns of imbricate thrusting by using three dimensional models and stereoscopic satellite images we present an example from the peruvian andes in which these map patterns are combined with seismic reflection profiles to define a complex imbricate system with components of both break forward and break backward thrusting these integrated methods provide new tools for understanding the deformational histories of fold and thrust belts including the definition of complex structural closures with opportunities for hydrocarbon reservoir duplication

surface cyclolysis in the north pacific ocean part ii piecewise potential vorticity diagnosis of a rapid cyclolysis event abstract employing output from a successful numerical simulation piecewise potential vorticity inversion is used to diagnose a rapid surface cyclolysis event that occurred south of the aleutian islands in late october 1996 the sea level pressure minimum of the decaying cyclone rose 35 hpa in 36 h as its associated upper tropospheric wave quickly acquired a positive tilt while undergoing a rapid transformation from a nearly circular to a linear morphology the inversion results demonstrate that the upper tropospheric potential vorticity pv anomaly exerted the greatest control over the evolution of the lower tropospheric height field associated with the cyclone a portion of the significant height rises that characterized this event was directly associated with a diminution of the upper tropospheric pv anomaly that resulted from negative pv advection by the full wind this forcing has a clear parallel in more traditional synoptic dynamic perspectives on lower tropospheric development which emphasize di

the 3d reconstruction of geological structures based on remote sensing data example from the anaran anticline lurestan province zagros fold and thrust belt iran abstract this work presents a methodological workflow for the 3d reconstruction of geological surfaces at regional scale based on remote sensing data and geological maps this workflow was tested on the reconstruction of the anaran anticline located in the lurestan province iran the remote sensing dataset used is a combination of aster and spot images as well as a high resolution digital elevation model the aster images were processed using the optimum index factor technique and pansharpened with the spot technique for an easier 3d mapping structural dip data were acquired through analysis of the 3d mapped geological traces and analysed to divide the structure into cylindrical domains related plunge line orientation was used to project data along the structure covering those areas where little or no information was available following the dip domain concept a selected horizon is reconstructed and manually adjusted to the mapped traces the reconstruction of the anaran anticline demonstrates the applicability of this workflow when attempting to remotely reconstruct a reliable geological surface the reconstructed surfaces clearly show the geometry of the ilam and asmari top horizons and the main faults affecting the anticline allowing a consistent structural interpretation of the deeper structures

crustal shortening in the palmyride fold belt syria and implications for movement along the dead sea fault system an edited version of this paper was published in tectonics by the american geophysical union agu copyright 1990 agu see also http www agu org journals tc http atlas geo cornell edu syria chaimov tectonics 1990 html

potential vorticity diagnosis of the severe convective regime part ii the impact of idealized pv anomalies abstract idealized numerical experiments are conducted to understand the effect of upper tropospheric potential vorticity pv anomalies on an environment conducive to severe weather anomalies are specified as a single isolated vortex a string of vortices analogous to a negatively tilted trough and a pair of string vortices analogous to a position error in a negatively tilted trough the anomalies are placed adjacent to the tropopause along a strong upper level jet at a time just prior to a major tornado outbreak and inverted using the nonlinear balance equations in addition to the expected destabilization beneath and adjacent to a cyclonic pv anomaly the spatial pattern of the inverted balanced streamfunction and height fields is distorted by the presence of the horizontal pv gradient along the upper tropospheric jet stream streamfunction anomalies are elongated in the cross jet direction while height and temperature anomalies are elongated in the along jet direction the amplitude of the inverted

geometric analysis of fold development in overthrust terranes abstract fault bend folding fault propagation folding and detachment or decollement folding are three distinct scenarios for fold thrust interaction in overthrust terranes simple kink hinge models are used to determine the geometric associations implicit in each scenario bedding maintains constant thickness in the models except in the forelimb of the fold the forelimb is allowed to thicken or thin without limit the models address individual folds and the calculated fold geometries are balanced structures each mode of fold thrust interaction has a distinct set of geometric relationships final fold geometry is adequate in itself to discern many fault bend folds this is not the case for fault propagation and detachment folds these two fold forms have very similar geometric relationships some knowledge of the nature of the underlying thrust or decollement zone is usually needed to distinguish between them the geometry of a fold is altered in a predictable fashion by transport through an upper ramp hinge and by fault parallel shearing of the structure the shearing results in a tighter fold whereas transport through the ramp hinge produces a broader fold the viability of the geometric analysis technique is demonstrated through its application to a pair of detachment folds from the canadian cordillera the geometric analysis is also used to evaluate cross sections through subsurface structures in an example from the turner valley oil field the analysis indicates how the interpretation should be altered so as to balance the cross section the analysis reveals hidden assumptions and specific inconsistencies in structural interpretations

investigating the mechanisms associated with the evolutions of twin extratropical cyclones over the northwest pacific ocean in mid january 2011

late mesozoic cenozoic evolution of the sanjiang basin in ne china and its tectonic implications for the west pacific continental margin abstract this study uses new seismic reflection profiles and exploratory well data to analyze the structural characteristics and evolution of the sanjiang basin in eastern heilongjiang ne china the basin sequence was divided into six stratigraphic units representing discrete middle upper jurassic lower cretaceous upper cretaceous eocene oligocene miocene and quaternary phases of development the sanjiang basin initiated as a passive marginal rift flank to the southern mongol okhotsk ocean during the middle jurassic and primary basin growth was terminated by orogenic deformation related to the mongol okhotsk suture to the north and the accretion of the nadanhada terrane to the east middle upper jurassic strata are controlled by half graben structures active during this phase of basin growth and are limited largely to the west suibin sub basin the wider basin experienced renewed rifting and large scale sag caused by back arc extension along the eurasian continental margin in the early cretaceous terminating during the late cretaceous in a phase of intense compression at the contemporary andean type continental margin this produced a series of thrust folds through the lower and upper cretaceous successions and led to the development of a regional scale erosional unconformity minor subsequent cenozoic extension is attributed to back arc extension along the west pacific continental margin with eocene oligocene miocene and quaternary deposits unconformably overlying the mesozoic sequences in half graben and extensional fault demarcated depocenters most prominently in the east qianjin sub basin

bronx river diversion neotectonic implications nearly all of the rivers draining the manhattan prong physiographic subprovince in new york city and vicinity flow southwestward in wide ne sw trending strike valley lowlands underlain by the cambro ordovician inwood marble for most of its course the bronx river flows in such a strike valley lowland however just at the point where the nw se trending mosholu fault offsets this marble lowland the bronx river leaves the lowland and flows southward across the more resistant gneisses and schists of the hartland formation in the narrow n s trending snuff mill gorge schuberth 1968 advocated that the bronx river started to erode the snuff mill gorge in miocene time 15 million years ago by finding a weak zone in the schist along a n s trending fault by contrast kemp 1897 made a convincing case for a postglacial age possibly 13 000 years ago for the bronx river s diversion into the snuff mill gorge subsurface data demonstrate that valley fill sediments ne of the point of diversion include a clay overlying a probable till we infer that this clay was deposited in a lake which formed when the bronx river s former path to the sw was blocked we infer that the mechanism of blockage was neotectonic uplift of the east 204th street bulge a bedrock barrier situated on the footwall block of the nw trending oblique slip mosholu fault at the exact point where the bronx river was diverted given the history of time separated seismic activity in new york city the possibility that a damaging earthquake will affect this densely populated area should not be ruled out

structural analysis of seismically mapped horizons using the developable surface model a new method for the analysis of folding of seismically mapped horizons is described based on a model of developable surfaces the local geometrical properties are determined by analyzing the variation of dip and strike along linear strips on the surface by considering strips in different directions a plunge line the approximation to the generatrix of a developable fold is identified as the direction associated with the least variation of surface attitude the map pattern obtained by analyzing the plunge and trend of plunge lines across an area allows the identification of domains where folding accords with a developable geometry such domains are recognized from straight plunge lines defining convergent or parallel patterns deviations from these patterns correspond to regions of structural complexity associated with ductile or brittle straining of the horizon we suggest that plunge line analysis may offer a useful technique for automatic fault recognition

seismic data geometry evolution and shortening in the active sulaiman fold and thrust belt of pakistan southwest of the himalayas surface and subsurface data from the sulaiman fold and thrust belt are integrated to analyze the deep structure tectonic shortening and kinematics of the sulaiman fold and thrust belt at the western margin of the indian subcontinent seismic reflection data show that nearly all the 10 km thick sequence of dominantly platform 7 km and molasse strata is detached at the deformation front these strata thicken tectonically to about 20 km in the hinterland without significant thrust faults in the foreland a balanced structural cross section suggests that structural uplift in the sulaiman fold and thrust belt is a result of a thin skinned passive roof duplex style of deformation the duplex sequence consists of jurassic and older strata it is separated from the roof equence by a passive roof thrust in thick cretaceous shales that has a backthrust sense of displacement over foreland propagating duplexes the roof sequence with incipient out of sequence thrusting is intact for about 150 km northwards where it emerges along a passive backthrust sequential restoration of the balanced section reveals a series of structural and geometrical features including 1 development of low amplitude broad concentric detachment folds sui and loti at the tip of the decollement 2 increase in amplitude of a detachment fold to a critical level for development of ramp and duplex structures and 3 out of sequence thrusting to create required critical taper for an outward translation of the foreland fold and thrust belt a balanced structural cross section 349 km long from the sulaiman fold and thrust belt restores to an original length of 727 km suggesting a maximum of 378 km of shortening since 21 ma in the cover strata of the indian subcontinent calculation of displacement rates over the sulaiman fold and thrust belt 18 mm yr added to the resolved rate of the chaman fault vector for the component parallel to the plate convergence direction 15 mm yr are close to the current india asia plate convergence rate 37 mm yr

the impact of extratropical transition on the downstream flow an idealized modelling study with a straight jet the interaction of a tropical cyclone undergoing extratropical transition et with the midlatitude synoptic scale flow is investigated using full physics numerical experiments with idealized initial conditions the emphasis is on the impact on the midlatitude flow downstream of the et event the midlatitude flow is represented by a balanced straight jet stream as the tropical cyclone approaches the jet a ridge trough couplet and a distinct jet streak form in the upper level flow a midlatitude cyclone develops rapidly downstream of the et system and the further evolution is characterized by downstream baroclinic development based on hovmoller diagrams the upper level development is interpreted as the excitation and subsequent dispersion of a rossby wave train on the potential vorticity gradient associated with the jet the characteristics of this wave train are sensitive to the structure of the jet and to moist processes in the midlatitudes the tropical cyclone undergoing et acts as a sustained forcing for the wave train and the structure of the et system impacts the development most significantly one to two wavelengths downstream of et piecewise inversion of potential vorticity complemented by the partitioning of the flow into its rotational and divergent parts is applied to assess the impact of the et system quantitatively both the cyclonic circulation and the outflow of the tropical cyclone are important contributors to the formation and amplification of the ridge trough couplet the outflow anomaly reduces the eastward motion of the ridge trough couplet significantly and thus promotes phase locking between the tropical cyclone and the upper level pattern copyright 2008 royal meteorological society

comments on the evolution and dynamical role of reduced upper tropospheric potential vorticity in intensive observing period one of fastex abstract the existence and production of reduced upper tropospheric potential vorticity rupv by heating is considered an objective technique is used that identifies anomalies of pv arising from a particular physical process here latent heat release the evolution of two rupv anomalies and a related diabatically increased lower tropospheric pv ilpv anomaly occurring during intensive observing period one of the cyclones from the fronts and atlantic storm track experiment fastex is examined using model analyses sounding data and trajectory calculations three distinct airflows are identified emanating from the ilpv anomaly each with a different evolution results show that rupv anomalies exist in the atmosphere and in a weaker form in numerical models the dynamical role of rupv anomalies is examined using a nonlinear balance pv inversion and reruns of the u k meteorological office limited area model this shows that instantaneously the flow and temperature perturbations associated with rupv an

dynamics of rossby wave packets in a quantitative potential vorticity potential temperature framework abstractrossby wave packets rwps have been associated with increased atmospheric predictability but also with the growth and propagation of forecast uncertainty to address the important question of under which conditions rwps imply high and low predictability a potential vorticity potential temperature pv framework is introduced to diagnose rwp dynamics finite amplitude rwps along the midlatitude waveguide are considered and are represented by the synoptic scale wavelike undulations of the tropopause the evolution of rwps is examined by the amplitude evolution of the individual troughs and ridges troughs and ridges are identified as pv anomalies on levels intersecting the midlatitude tropopause by partitioning the pv tendency equation individual contributions to the amplitude evolution are identified a novel aspect is that the important role of the divergent flow and the diabatic pv modification is quantified explicitly arguably prominent upper tropospheric divergent flow is associated

a diagnostic case study of mei yu frontal retreat and associated low development near taiwan abstractafter advancing southward across taiwan and becoming quasi stationary a mei yu front moved north again and led to a second period of significant rainfall during 13 14 june 2012 associated with this frontal retreat a meso scale low pressure developed to the southwest of taiwan in the proximity of organized mesoscale convective systems mcss along and south of the front over the northern south china sea in this study using mainly the european centre for medium range weather forecasts gridded analyses the physical mechanisms of this frontal retreat are investigated and diagnosed with a focus on the initial retreat and the role played by the deepening frontal low the diagnoses employing the vorticity equation and frontogenetical function both indicate that the appearance of southerly winds and thus the retrogression of cold air north of the front was the cause of the initial frontal retreat consistent with earlier studies the potential vorticity diagnosis using the piecewise inversion te

potential vorticity diagnosis of the severe convective regime part i methodology observational and modeling studies have shown that shear and instability are powerful predictors of the likelihood of severe weather and tornadoes to the extent that upper tropospheric forecast errors can be described as potential vorticity pv anomalies on the forecasted pv field knowing and being able to quantify the effects of such errors on shear and instability would allow forecasters to anticipate the effects of those errors on the likely mode of severe weather to test the sensitivity of the severe convective environment to pv fluctuations a pv inversion framework is adopted that utilizes nonlinear balance the observed pv field is modified in a way that mimics realistic perturbations of trough intensity location or shape soundings including moisture profiles are reconstructed from the balanced geopotential height field assuming that air parcels conserve mixing ratio while their isentropic surfaces are displaced upward or downward by the addition of anomalous pv unperturbed balanced soundings agree reasonably well with full unbalanced soundings and differences are attributable to departures from nonlinear balance in areas of strong vorticity or acceleration balanced vertical wind profiles do not include the effects of friction so the vertical shear of the balanced wind departs unacceptably from total shear within the lowest 1 km of the troposphere the balanced wind perturbations are added to the total analyzed shear profile to estimate the effect of pv perturbations on shear and storm relative helicity by this process the importance of typical or hypothesized upper tropospheric forecast errors may be addressed in an idealized case study or operational context

mesoscale convective vortex formation in a weakly sheared moist neutral environment abstract idealized simulations of a diabatic rossby vortex drv in an initially moist neutral baroclinic environment are performed using the fifth generation national center for atmospheric research pennsylvania state university ncar psu mesoscale model mm5 the primary objective is to test the hypothesis that the formation and maintenance of midlatitude warm season mesoscale convective vortices mcvs are largely influenced by balanced flow dynamics associated with a vortex that interacts with weak vertical shear as a part of this objective the simulated drv is placed within the context of the bow echo and mesoscale convective vortex experiment bamex field campaign by comparing its tangential velocity radius of maximum winds cape and shear with the mcvs observed in bamex the simulations reveal two distinct scales of development at the larger scale the most rapidly growing moist baroclinic mode is excited and exponential growth of this mode occurs during the simulation embedded within the

effective stratification for pseudoadiabatic ascent effective stratification can be interpreted as the resistance to upward motion of saturated air parcels experiencing condensation previously published expressions for effective stratification conflict with each other and the most widely distributed expression contains an o 1 error a derivation of effective stratification is presented that exposes its physical interpretation and that reveals the origin of the flaw in the incorrect derivation

use of fault cut offs and bed travel distance in balanced cross sections abstract successful hydrocarbon exploration in foreland fold thrust belts requires the preparation of numerous fully balanced cross sections each section must be compatible with neighboring sections line balancing on many sections is preferable to balancing on single sections a series of balanced sections must also be volume balanced if constructed properly an often overlooked basic principle is that the fault cut off angle on both hangingwall and footwall and the angle and distance that a fault travels within a bed will not change significantly during thrusting under simple shear motion assuming no significant interbed slippage the section must be geometrically correct if it is to have a chance of being geologically correct

displacement and deformation associated with a lateral thrust termination southern golden gate range southern nevada u s a abstract the golden gate thrust offers an excellent opportunity to study displacement and deformation at a lateral thrust tip slip across this e vergent thrust is uniformly about 2 4 km for the southern 2 km of exposed strike length and dies out to zero in the northern 5 km constant displacement and uniform hangingwall structure along the southern one third of exposed strike length suggest that along strike displacement variation and consequent deformation are localized near the lateral tip structures located at and north of the lateral tip are consistent with transpression and later uplift as slip accumulated on the thrust fold and fault orientations and calcite twinning strain record possible transpression north of the lateral tip e w striking normal faults at the thrust tip record extension that is interpreted to be the result of the uplift and translation of a structurally continuous rigid block located north of the normal faults this block is connected to and was uplifted with the crest of the hangingwall anticline and was separated by the normal faults from thrust related folding to the south the main hangingwall structure is an anticline that in southern exposures trends n s parallel to the thrust but bends westward and opens into a box fold to the north the hangingwall anticline superficially resembles a classic fault propagation fold formed by a migrating ductile bead however we are forced to reject the ductile bead hypothesis for the fold because 1 the geometry of the hangingwall anticline far from the thrust tip cannot have evolved from the geometry at the thrust tip and 2 twinned calcite strain data from along the thrust suggest that strain was homogeneous and coaxial rather than inhomogeneous and progressively non coaxial as predicted for a migrating ductile bead the three dimensional structural and kinematic relations at the lateral tip of the golden gate thrust appear to be the result of deformation around a pinned tip although the reason that the tip was pinned at its present location is unclear we interpret the thrust to have propagated relatively quickly to its ultimate extent with little initial displacement indicating that it was easier to fault the rocks than to fold them

projection of dip data in conical folds onto a cross section plane the projection of dip data onto a section plane can be a source of errors in the relative and absolute position of data depending on the choice of projection vectors to properly transfer data in conical folds onto a plane of section a best fitting cone must be defined for the fold dip data must be projected along the best fit cone generatrices which are defined individually for each dip measurement according to its orientation for individual dip measurements on bedding in a conical fold their corresponding generatrix can be defined as the line of tangency between bedding and the conical fold dip measurements on bedding not fitting an ideal conical geometry must be corrected before a valid generatrix can be calculated graphical procedures to obtain generatrices for individual dip data are discussed and a new analytical method is proposed to calculate generatrices for dip measurements on bedding not fitting an ideal conical geometry the maximum projection distance within conical folds is discussed and a way to estimate the natural extent of conical folds is defined the proposed methods are illustrated with data from a conical syncline in ne spain

using piecewise potential vorticity inversion to diagnose frontogenesis part i a partitioning of the q vector applied to diagnosing surface frontogenesis and vertical motion abstract the technique of piecewise potential vorticity pv inversion is used to identify the nondivergent wind fields attributed to upper middle and lower tropospheric pv anomalies in addition to the irrotational wind with the goal of diagnosing the respective wind fields frontogenetic potentialities frontogenesis is diagnosed using a piecewise separation of the q vector into parts associated with the partitioned wind field partitioned geostrophic q vectors are used to diagnose the vertical motion attributed to the upper middle and lower tropospheric pv anomalies insight gained from this new diagnostic technique is demonstrated by examining a particular case of extratropical marine cyclogenesis resulting from the interaction of an upper tropospheric short wave trough with a surface thermal wave in the early stages of development the largest contributor to surface frontogenesis was associated with winds attributed to the lower tropospheric thermal wave as the cyclone matured the contribut

kinematic 3 d retro modeling of an orogenic bend in the south limon fold and thrust belt eastern costa rica prediction of the incremental internal strain distribution the south limon fold and thrust belt in the back arc area of southern costa rica is characterized by a 90 curvature of the strike of the thrust planes and is therefore a natural laboratory for the analysis of curved orogens the analysis of curved fold and thrust belts is a challenge because of the varying structural orientations within the belt based on seismic reflection lines we created a 3 d subsurface model containing three major thrust faults and three stratigraphic horizons 3 d kinematic retro deformation modeling was carried out to analyze the spatial evolution of the fold and thrust belt the maximum amount of displacement on each of the faults is from hinterland to foreland thrust 1 800 m thrust 2 600 m thrust 3 250 m the model was restored sequentially to its pre deformational state the strain history of the stratigraphic horizons in the model was calculated at every step this shows that the internal strain pattern has an abrupt change at the orogenic bend contractional strain occurs in the forelimbs of the hanging wall anticlines while a zone of dilative strain spreads from the anticline crests to the backlimbs the modeling shows that a nne directed transport direction best explains the structural evolution of the bend this would require a left lateral strike slip zone in the north to compensate for the movement and thereby decoupling the south limon fold and thrust belt from northern costa rica therefore our modeling supports the presence of the trans isthmic fault system at least during the plio pleistocene

imbalance in a mesoscale vortex within a midlatitude continental mesoscale convective system abstract the authors examine the degree of hydrostatic and gradient balances in a mesoscale convective vortex mcv in the stratiform region of a mesoscale convective system mcs that crossed oklahoma on 1 august 1996 results indicate that the mcv was partially unbalanced because the cool layer at the base of its core was too cool and too shallow to balance the tangential winds about the mcv s axis the apparent imbalance may have been due to strong unsteady forcing on the vortex insufficient or unrepresentative data approximations used in the analysis or reasons that are unknown

computer synthesis of balanced structural cross sections by forward modeling forward modeling by computer generates unlimited intermediate balanced cross sections but even the simplest forward modeling casts doubts on many assumptions about fault processes geometric and mechanical problems must be resolved before more sophisticated modeling is feasible simple models of faulted and folded terranes suggest the following 1 fault geometry may lead to erroneous interpretations of fault chronology 2 fault duplexes generate many structures that are arcuate in profile or plan ranging in scale from hanging wall drag folds to strike slip continental margins 3 thrusts may be generated downward with ramping controlled by overburden distributed in the hanging wall 4 most folds can be generated by a finite number of faults calculated depths of detachment of concentric folds are generally misleading 5 blind thrusting within an envelope of high fluid pressure reduces mechanical problems inherent in models that restrict high fluid pressures to a basal decollement blind normal faults also occur blind thrusting may be the predominant mode of compression in layered rocks

using tropopause maps to diagnose midlatitude weather systems the use of potential vorticity pv allows the efficient description of the dynamics of nearly balanced atmospheric flow phenomena but the distribution of pv must be simply represented for ease in interpretation representations of pv on isentropic or isobaric surfaces can be cumbersome as analyses of several surfaces spanning the troposphere must be constructed to fully apprehend the complete pv distribution following a brief review of the relationship between pv and nearly balanced flows it is demonstrated that the tropospheric pv has a simple distribution and as a consequence an analysis of potential temperature along the dynamic tropopause here defined as a surface of constant pv allows for a simple representation of the upper tropospheric and lower stratospheric pv the construction and interpretation of these tropopause maps which may be termed isertelic analyses of potential temperature are described in addition techniques to construct dynamical representations of the lower tropospheric pv and near surface potential temperature which complement these isertelic analyses are also suggested case studies are presented to illustrate the utility of these techniques in diagnosing phenomena such as cyclogenesis tropopause folds the formation of an upper trough and the effects of latent heat release on the upper and lower troposphere

rossby wave packets on the midlatitude waveguide a review abstractrossby wave packets rwps are rossby waves for which the amplitude has a local maximum and decays to smaller values at larger distances this review focuses on upper tropospheric transient rwps along the midlatitude jet stream their central characteristic is the propagation in the zonal direction as well as the transfer of wave energy from one individual trough or ridge to its downstream neighbor a process called downstream development these rwps sometimes act as long range precursors to extreme weather and presumably have an influence on the predictability of midlatitude weather systems the paper reviews research progress in this area with an emphasis on developments during the last 15 years the current state of knowledge is summarized including a discussion of the rwp life cycle as well as rossby waveguides recent progress in the dynamical understanding of rwps has been based in part on the development of diagnostic methods these methods include algorithms to identify and track rwps

a diagnostic study of a retreating mei yu front and the accompanying low level jet formation and intensification abstract during 7 8 june 1998 an organized mesoscale convective system mcs formed within the mei yu frontal cloud band and moved northeastward to produce heavy rain over the island of taiwan during this period the section of the mei yu front east of taiwan moved northward most significantly for about 300 km over 12 h meanwhile a low level jet llj developed within the environmental southwesterly flow to the south of the mei yu front and the mcs observations revealed that the front retreated as low level meridional wind components over the postfrontal region shifted from northerly to southerly using european centre for medium range weather forecasts ecmwf analyses with piecewise potential vorticity pv inversion technique and other methods a diagnostic study was carried out to investigate the northward frontal movement and the formation of the llj results indicated that diabatic latent heating from the mcs large enough in scale generated positive pv and height fall at low levels the enha

potential vorticity diagnosis of the severe convective regime part iii the hesston tornado outbreak nonlinear balance potential vorticity pv inversion is used to diagnose the sensitivity of the severe convective parameter space to the amplitude of a subsynoptic scale pv anomaly on 13 march 1990 a day on which a significant tornado outbreak impacted the great plains pv surgery is used to both amplify and remove the pv anomaly and the contemporaneous impact on various convective parameters is subsequently quantified by using piecewise pv inversion to compute the changes in those parameters attributable to each pv alteration it is found that amplifying the anomaly increases the cape by amounts typically ranging from 20 to 30 within the atmospheric columns experiencing the maximum pv increase ascent is increased slightly downshear of the pv anomaly consistent with extant conceptual models governing synoptic scale forcing for vertical motion amplifying the pv anomaly increases deep layer shear over the southern half of the outbreak region and reduces storm relative helicity over the northern half primarily through changes in the estimated storm motion vector removing the anomaly produces complementary changes of the opposite sign thresholds of several commonly used convective parameters are chosen on the basis of prior empirical studies and the horizontal displacement of these threshold contours produced by the pv alterations reveals that relatively modest subsynoptic scale pv changes would not likely change the predominant convective mode during the hesston outbreak

synoptic and dynamic aspects of an extreme springtime saharan dust outbreak in march 2004 a large scale strong and persistent outbreak of saharan dust on to the adjacent tropical and subtropical atlantic ocean was observed in satellite imagery surface observations show that the event was accompanied by unusual weather conditions across large parts of north africa including low temperatures and strong winds over the sahara extreme precipitation in libya and a heat wave on the guinea coast the dust outbreak was associated with an unseasonally southerly position of the intertropical convergence zone and a delayed northward progression of the african monsoon the dust front was initially related to a density current caused by strong evaporational cooling along a precipitating cloud band that penetrated into the northern sahara ahead of an upper level trough at later stages massive upper level convergence sinking low level divergence and an explosive anticyclogenesis over northwest africa caused strong northerly flow and a quick spreading of the dust front to the south and west the strong pressure gradients over north africa were further enhanced by the formation of a cyclone ahead of the upper trough a dynamical analysis based on potential vorticity pv theory provides new insights into the generation of north african harmattan surges using a pv inversion it is shown that the explosive anticyclogenesis was caused largely by unbalanced dynamics related to the density current divergent outflow from the precipitation over libya and inertial instability in the entrance region of the strong subtropical jet and tropical plume along the eastern side of the upper trough these processes enhanced the effects of the balanced advection of negative vorticity and cold air by the large scale wave moreover we show the importance of an explosive cyclogenesis event over the central north atlantic for the amplification of the downstream wave associated with the penetration of the cold front into north africa copyright 2006 royal meteorological society

quantifying and correcting errors derived from apparent dip in the construction of dip domain cross sections this paper deals with the errors introduced in the construction of cross sections due to the use of apparent dips and thicknesses when projecting data onto the plane of section these errors are analyzed under the perspective of cross sections constructed with the dip domain method a method to evaluate variations of unit thicknesses due to distortion during projection is presented and modifications to the dip domain method are proposed to account for them including the use of apparent bisectors methodology is discussed for inclined section planes and the equations to calculate apparent thickness on inclined sections are presented an analytical definition of cylindrical folding is also derived

reexamining the dynamics of short scale diabatic rossby waves and their role in midlatitude moist cyclogenesis abstract as a step toward a more comprehensive study of the physical processes that underlie explosive cyclogenesis a two dimensional semigeostrophic model with a now standard parameterization of latent heat release is used to diagnose the structure energetics and propagation characteristics of short scale diabatic normal modes in a moist baroclinic atmosphere with the eady basic state upon revisiting the inviscid problem it is found that when a thermodynamically consistent vertical profile of latent heat release is used the short wave cutoff vanishes and growth rates become independent of zonal wavelength for zonal wavelengths shorter than approximately 1900 km the destabilized short scale modes identified previously as diabatic rossby waves owe their existence to the continuous generation of potential vorticity by moist processes associated with warm air advection rising motion and latent heat release to determine if these short scale diabatic rossby wave modes continue to grow at small

geophysical testing of balanced cross sections of fold thrust belts with potential field data an example from the fleurieu arc of the delamerian orogen south australia abstract the delamerian south australia and ross antarctica orogens once formed a continuous chain along the paleo pacific margin of gondwana correlations between the two are based on many characteristics including style of shortening and deformation constraining structural features in one of these orogens impacts on interpretations of tectonic processes for the other balanced cross sections have provided crucial information on the internal architecture of the delamerian orogen south australia and form a key piece of evidence in some widely circulated models for the deformational style these sections have not been constrained by geophysical investigations which can provide significant information about the subsurface geometry we present magnetic forward models for two balanced cross sections of the fleurieu arc in the delamerian orogen the forward models require a larger volume of magnetic basement at shallower depths than predicted by balanced sections requiring a revision of currently proposed shortening mechanisms the shortening mechanism inferred from the models requires less imbrication of upper crustal units and more folding above thrusts that involve both basement and cover sequences this style of shortening compares favorably with published observations from the ross orogen in antarctica

observations and tectonic setting of historic and instrumentally located earthquakes in the greater new york city philadelphia area a catalog of 383 earthquakes in southeastern new york southwestern connecticut northern new jersey and eastern pennsylvania including metropolitan new york city and philadelphia is compiled from historical and instrumental data from 1677 through 2006 a magnitude felt area relationship is used to calculate the equivalent magnitude mblg prior to the advent of abundant instrumental data in 1974 revised locations are computed for a number of historic earthquakes most hypo centers are concentrated in older terranes bordering the mesozoic newark basin in the reading manhattan and trenton prongs and in similar rocks found at a shallow depth beneath the coastal plain from south of new york city across central new jersey historic shocks of mblg 3 and larger were most numerous in the latter zone the largest known event mblg 5 25 occurred just offshore of new york city in 1884 many earthquakes have occurred beneath the 12 km wide ramapo seismic zone rsz in the eastern part of the reading prong where station coverage was the most ex tensive since 1974 the southeastern boundary of the rsz which is nearly vertical extends from near the surface trace of the mesozoic ramapo fault to depths of 12 15 km because the mesozoic border fault dips about 50 60 southeast earth quakes of the rsz are occurring within middle proterozoic through early paleozoic rocks which faults within the rsz are active is unclear well located activity in the manhattan prong since 1974 extends to similar depths but cuts off abruptly at all depths along a northwest striking boundary extending from peekskill new york to stamford connecticut that boundary which is subparallel to brittle faults farther south is inferred to be a similar fault or fault zone those brittle features may have formed between the newark hartford and new york bight basins to accommodate mesozoic extension the great valley in the northwestern part of the study region is nearly devoid of known earthquakes while few focal mechanism solutions and in situ stress measurements of high quality are available the maximum compressive stress is nearly horizontal and is oriented about n64 e similar to that in adjacent areas the catalog is likely complete for events of mblg 5 since 1737 3 5 since 1840 and 3 0 since 1928 extrapolation of the frequency magnitude relationship indicates that an event of mblg 6 0 is expected about once per 670 yr online material observations and tectonic setting of historic and instrumentally located earthquakes in the greater new york city philadelphia area

topological constraints on imbricate thrust networks examples from the mountain city window tennessee u s a abstract the geometry of thrust belts is best described in three dimensions as a network of linear geometric elements trailing branch lines where two thrusts diverge leading branch lines where two thrusts converge tip lines where thrust displacement vanishes and cutoff lines where a stratigraphic horizon intersects a thrust plane there are a number of topological constraints in three dimensions on the interrelationship of these linear elements these constraints provide a method of deciphering the three dimensional structure of an area from the geologic map pattern alone if topography or structural culminations and depressions create significant structural relief the mountain city window tennessee is an example of an imbricate thrust network which reveals its topology on the map pattern because of the presence of culminations the analysis of linear elements in this area allows the regional structural geometry to be described and also two kinematically distinct types of imbricate thrust systems to be characterized namely hinterland and foreland dipping duplexes the doe ridges culmination is a hinterland dipping duplex characterized by leading branch lines in a common roof thrust with the branch lines arranged in the same order hinterland to foreland as in the undeformed state the limestone cove culmination is a foreland dipping duplex characterized by trailing branch lines in a common roof thrust with the branch lines reversed in order hinterland dipping duplexes are the common and well known type foreland dipping duplexes are formed by successive trailing branch lines moving up off the lower flat horizon onto the ramp at which the imbricate slices are formed

displacement distance methods in the analysis of fold thrust structures and linked fault systems a new method for analysing the internal strain in thrust sheets is described the displacement distance diagram can be used to quantify the relative shortening or relative stretch between the hangingwall and footwall beds of a thrust and is a useful way of analysing commonly occurring fold thrust structures the stretch is a function of the relative rates of thrust propagation and thrust slip the cumulative displacement distance diagram described here can be used to calculate the absolute shortening or extension when this is accommodated above a single decollement in a linked fault system this method offers a useful way of analysing duplex structures and large scale foreland thrust zones as well as extensional fault systems and can be used as an alternative to or in conjunction with balanced cross sections both methods can be used to quantify the variation in shortening above a single detachment zone this variation may be mechanically significant reflecting lithological control on thrust or normal fault growth

a case study of downstream baroclinic development over the north pacific ocean part i dynamical impacts abstract the impact of eddy energy growth and radiation from a western north pacific cyclone on the intensity of an eastern north pacific cyclone a few days later is examined associated with the western cyclone is an upstream ridge and trough couplet initially over siberia on 8 march 1977 the amplitude of this couplet is perturbed in 5 day numerical simulations of the two marine cyclones balanced initial conditions are created by potential vorticity inversion the magnitude of the upper level couplet governs much of the subsequent growth of eddy energy in the western cyclone as well as the propagation of eddy energy between the two cyclones this culminates in measurable changes in the maximum intensity of the eastern surface cyclone the broader question of the sensitivity of this cyclone to upstream perturbations is also briefly addressed

paleostress pattern and salt tectonics within a developing foreland basin north western subhercynian basin northern germany analysing the paleostress field in sedimentary basins is important for understanding tectonic processes and the planning of drilling campaigns the subhercynian basin of northern germany is a perfect natural laboratory to study the paleostress field in a developing foreland basin the simple layer cake geometry of the basin fill is dominated by several piercing and non piercing salt structures we derived the paleostress field from the orientation of fracture sets faults slickensides and stylolites on a regional scale the basin fill is characterized by a horizontal compressional paleostress vector that is mainly nne ssw oriented which reflects the late cretaceous inversion phase in central europe we show that the local paleostress field is distinctly perturbated due to the salt structures along the edge of the salt pillows the maximum horizontal paleostress vector is deflected by up to 90 from the regional trend in the case of the elm salt pillow it forms a radial pattern restoration of balanced cross sections demonstrates at least 9 of the shortening of the north western part of the subhercynian basin was achieved by folding the salt structures in the north western subhercynian basin are the result of varying stress conditions initial extension in the triassic caused first salt movements that prevailed during the jurassic and early cretaceous most important is the late cretaceous contractional phase that shortened the diapirs and led to the formation of the salt pillows between diapirs due to detachment folding we derive four main controlling factors for such salt dominated contractional basins 1 the wedge shape basin fill is the product of the dynamic load at the southern margin of the basin 2 a basal salt layer fed the diapirs and acted as a detachment horizon during the later shortening 3 detachment folding was the dominating deformation mechanism during contraction and 4 the pre existing diapirs controlled the position of the detachment folds

least squares restoration of tertiary thrust sheets in map view tajik depression central asia the tajik depression located west of the pamirs and south of the tien shan is a compressional intermontane basin bounded by basement overthrusts and filled with mesozoic and cenozoic sediments the internal structure is typical of a thin skinned tbld and thrust belt kinematic data available in the literature suggest that indentation of the pamirs into asia durino the cenozoic collision of india and asia has been accommodated in various ways within the depression including westward extrusion thickening combined with wrenching along n s tblds and thrusts and counterclockwise rotations these various detbrmation processes can be analyzed and quantified by reconstruction of the predeformed state of the depression however the combina tion of thrusting wrenching and block rotations implies a nonplane deformation which cannot be restored properly using balanced cross sections alone we have therefore developed a numerical method for restoration of stratigraphic surfaces designed for regions of nonplane compressional tectonics the deformed region is represented in map view as a mosaic of fault bounded blocks overlapping each other along the faults blocks are separately unfolded and then numerically packed together by least squares minimization of overlaps yielding fields of finite horizontal translations and rotations about vertical axes to analyze the deformation postdating the collision of india and asia we have restored a stratigraphic surface at the base of the cenozoic first in order to test the numerical method we restored a map that had previously been restored by a purely manual method restoration of a second map drawn from newly available subsurface data leads to geometrical inconsistencies overlaps and gaps which cannot be reduced remain in the restored state after correction of these inconsistencies restoration yields a complex mode of deformation for the depression individual thrust slices have undergone counterclockwise rotations about verti cal axes the magnitudes increasing from west to east up to a maximum of 40 o near the pamirs horizontal shortening is 150 km 35 in the center of the depression and 240 km 85 in the northeastern part between the pamirs and the tien shan strike slip motions commonly not revealed by balancing cross sections are associated with thrusting on faults striking n s inde pendent paleomagnetic data and slip directions on small scale faults provide positive checks on the results of our restoration

the march 1993 superstorm cyclogenesis incipient phase synoptic and convective scale flow interaction and model performance abstract the incipient stages of the 12 14 march 1993 superstorm ss93 cyclogenesis over the gulf of mexico are examined noteworthy aspects of ss93 include 1 it is the deepest extratropical cyclone ever observed over the gulf of mexico during the 1957 96 period and 2 existing operational prediction models performed poorly in simulating the incipient cyclogenesis over the northwestern gulf of mexico a dynamic tropopause dt analysis shows that ss93 is triggered by a potent potential vorticity pv anomaly as it crosses extreme northern mexico and approaches the gulf of mexico the low level environment over the western gulf of mexico is warmed moistened and destabilized by a persistent southerly flow ahead of the approaching pv anomaly ascent and a lowering of the dt associated with a lowering of the potential temperature ahead of the pv anomaly contributes to further destabilization that is realized in the form of a massive convective outbreak an examination of the national centers for envi

book review the techniques of modern structural geology volume 2 folds and fractures john g ramsay and martin i huber academic press london 1987 xi 309 398 pp price stg17 50 us 34 50 paperback

the balanced dynamical nature of a rapidly intensifying oceanic cyclone abstract aided with a numerical simulation the authors diagnose the synoptic scale evolution of an intense extratropical cyclone over the western atlantic ocean from the perspective of balanced dynamics using potential vorticity inversion techniques the authors show that even during the period of largest growth rate early in the life cycle the balance equations capture much of the nondivergent wind irrotational wind and height tendency fields the structure of the cyclone evolves from a maximum amplitude at the tropopause to a maximum amplitude at the surface as the system moves offshore the vertical phase structure remains slightly upshear tilted throughout less than one quarter wavelength cyclogenesis is interpreted in terms of a baroclinic wave propagating through a varying basic state in which surface development is rapid because of the sudden response of the wave structure to a changing environment the mature cyclone structure strongly resembles cases of continental cyclones except that t

balancing deformation in nw borneo quantifying plate scale vs gravitational tectonics in a delta and deepwater fold thrust belt system abstract recent gps measurements demonstrate that nw borneo undergoes 4 6 mm of plate scale shortening a year which is not accommodated by plate scale structures the only geological structure in nw borneo described to accommodate on going shortening is the baram delta system located on the outer shelf to basin floor delta toe fold thrust belts are commonly thought to be caused by margin normal compressional stresses generated by margin parallel upslope gravitational extension the baram delta system is divided into three neotectonic provinces 1 an inactive onshore and inner shelf region of inversion superimposed on an older extensional deltaic province 2 an outer shelf region of present day deltaic extension and 3 a compressional delta toe however it is uncertain whether compression in the delta toe area is purely driven by gravity i e shortening is less than upslope extension or if there is a component of regional shortening involved which can only be demonstrated if shortening is greater than upslope extension in order to quantify the balance between the shortening related to the upslope gravitational extension and the shortening related to the regional geodynamic framework in the baram delta system we have used a geomechanical code based on the finite element method and conservation of mass and momentum dynel 2d this enabled us to reconstruct the tectonic evolution of the delta and to demonstrate for the first time that the total shortening observed in the delta toe does not balance against the active extension in the delta top with the system exhibiting 1 8 shortening overall or 2 0 km this additional shortening is therefore attributed to plate scale shortening across nw borneo produced by far field compression using a convergence rate of 4 mm y 1 demonstrated by gps measurements the delta toe has accommodated far field compression only in the last 0 5 my

a study of cyclone mesoscale structure with emphasis on a large amplitude inertia gravity wave abstract an analysis is presented of prominent mesoscale structure in a moderately intense cyclone with emphasis on a long lived large amplitude inertia gravity wave igw that moved through the northeastern united states on 4 january 1994 available national weather service wsr 88d doppler radar and wind profiler observations are employed to illustrate the rich time dependent three dimensional structure of the igw as the igw amplified peak crest to trough pressure falls exceeded 13 hpa 30 min 1 it also accelerated away from the cyclone reaching a peak forward speed of 35 40 m s 1 across eastern new england the igw was one of three prominent mesoscale features associated with the cyclone the others being a weak offshore precursor warm frontal wave and an onshore band of heavy snow snow bomb in which peak hourly snowfalls of 10 15 cm were observed none of these three prominent mesoscale features were well forecast by existing operational prediction models particularly with regard to preci

the structure of mountain fronts commonly the part of a mountain front which is visible at the surface consists of foreland dipping thrust belt rocks elevated above their regional structural position and overlain more or less conformably by molasse several explanations for their geometry are possible 1 major detachments exist within or beneath the molasse resulting in transport of the foreland basin examples of this geometry come from the swiss molasse plain the southern pyrenees and the mackenzie mountains of canada 2 displacement is lost on major backthrusts beneath the frontal monocline examples cited here are the rockies of alberta the sulaiman ranges of pakistan the mackenzies and the andes in peru 3 thrust sheets travelled over an old land surface and syntectonic molasse contemporaneously offlaps the topographic high of the thrust front this phenomenon occurs along the alpine thrust front in haute provence 4 the frontal fold represents deformation above a large scale thrust tip no unequivocal example of tip line strain at this scale has been recorded although this type of deformation may occur in the brooks range of alaska in many areas mountain fronts show a combination of these idealized geometries

models of strain variation in nappes and thrust sheets a review abstract strain within nappes and thrust sheets can be modelled using simple boundary conditions an original rectangular prism of material resting on a thrust plane is considered to be subject to various pure and simple shear components operating parallel to the thrust deformation gradient tensors are determined for the models and solutions found for the principal strains a two dimensional model considers heterogeneous simple shear combined with a stretch in the direction of shear simple shear zones arise as a special case where 1 recumbent fold nappes characteristic of gravitational collapse can be modelled with 1 and thrust sheets with layer parallel shortening and folding with differential transport of nappes gives rise to additional wrench type shears solutions for the principal strains in this type of model are found and used to interpret side wall ramps and steep zones parallel to nappe movements by including a stretch in the transport direction these differential transport models produce prolate strains 1 and oblate strains finally a brief consideration of bending strains produced in a sheet passing over a ramp indicates reversals in the shear direction during the strain history these predict possible crenulation of early thrust fabrics at ramps

interpretation validation on vertically exaggerated reflection seismic sections abstract reflection seismic data is usually displayed with a vertical exaggeration factor in the range 2 6 irrespective of whether it is time or depth domain data this vertical exaggeration gives certain advantages to stratigraphic and structural interpretation and is sometimes a prerequisite to view long wavelength structures however vertical exaggeration distorts geological structures affecting dip curvature line length cross sectional area volume and angular relationships reflection seismic can be assigned a vertical exaggeration heterogeneity factor based on the extremes of seismic velocities in the absence of appreciable poorly compacted units and bathymetry and generally on depth domain data vertical exaggeration is relatively homogeneous analytical solutions are derived to quantify the distortion of angular relationships curvature and bed thickness under homogeneous vertical exaggeration modelled extensional and compressional geometries give acceptable area balance restorations using vertical shear under homogeneous vertical exaggeration these vertically exaggerated restorations are neither admissible nor viable because the deformed and restored state sections are unrealistic given low heterogeneity of vertical exaggeration and relatively simple structure that typifies many extensional geometries and some thrust geometries aspect ratios of 1 1 are not definitively required for section validation by restoration

dynamics of a local alpine flooding event in october 2011 moisture source and large scale circulation alpine heavy precipitation events often affect small catchments although the circulation pattern leading to the event extends over the entire north atlantic the various scale interactions involved are particularly challenging for the numerical weather prediction of such events unlike previous studies focusing on the southern alps here a comprehensive study of a heavy precipitation event in the northern alps in october 2011 is presented with particular focus on the role of the large scale circulation in the north atlantic european region during the event exceptionally high amounts of total precipitable water occurred in and north of the alps this moisture was initially transported along the flanks of a blocking ridge over the north atlantic subsequently strong and persistent northerly flow established at the upstream flank of a trough over europe and steered the moisture towards the northern alps lagrangian diagnostics reveal that a large fraction of the moisture emerged from the west african coast where a subtropical upper level cut off low served as an important moisture collector wave activity flux diagnostics show that the ridge was initiated as part of a low frequency large scale rossby wave train while convergence of fast transients helped to amplify it locally in the north atlantic a novel diagnostic for advective potential vorticity tendencies sheds more light on this amplification and further emphasizes the role of the ridge in amplifying the trough over europe operational forecasts misrepresented the amplitude and orientation of this trough for the first time this study documents an important pathway for northern alpine flooding in which the interaction of synoptic scale to large scale weather systems and of long range moisture transport from the tropics are dominant moreover the trapping of moisture in a subtropical cut off near the west african coast is found to be a crucial precursor to the observed european high impact weather

wavelet analysis and the governing dynamics of a large amplitude mesoscale gravity wave event along the east coast of the united states detailed diagnostic analyses are performed upon a mesoscale numerical simulation of a well observed gravity wave event that occurred on 4 january 1994 along the east coast of the united states the value of using wavelet analysis to investigate the evolving gravity wave structure and of using potential vorticity pv inversion to study the nature of the flow imbalance in the wave generation region is demonstrated the cross stream lagrangian rossby number the residual in the nonlinear balance equation and the unbalanced geopotential height field obtained from pv inversion are each evaluated for their usefulness in diagnosing the flow imbalance all of these fields showed clear evidence of strong imbalance associated with a middle to upper tropospheric jet streak and tropopause fold upstream of the large amplitude gravity wave several hours before the wave became apparent at the surface analysis indicates that a train of gravity waves was continuously generated by geostrophic adjustment in the exit region of the unbalanced upper level jet streak as it approached the inflection axis in the height field immediately downstream of the maximum imbalance associated with the tropopause fold a split front in the middle troposphere characterized by the advance of the dry conveyor belt above the warm front was overtaken by one of these propagating waves during this merger process a resonant interaction resulted which promoted the rapid amplification and scale contraction of both the incipient wave nonlinear wave development and the split front frontogenesis the gravity wave and front aloft became inseparable following this merger the situation became even more complex within a few hours as the vertical motion enhanced by this front wave interaction acted upon a saturated potentially unstable layer to produce elevated moist convection an analysis of the temporal changes in the vertical profile of wave energy flux suggests that moist convective downdraughts efficiently transported the wave energy from the midlevels downward beneath the warm front surface where the wave became ducted however pure ducting was not sufficient for maintaining and amplifying the waves rather wave cisk conditional instability of the second kind was crucial this complex sequence of nonlinear interactions produced a long lived large amplitude gravity wave that created hazardous winter weather and disrupted society over a broad and highly populated area although gravity waves with similar appearance to this large amplitude wave of depression occasionally have been seen in other strong cyclogenesis cases involving a jet streak ahead of the upper level trough axis it is unknown whether other such events share this same sequence of interactions

palinspastic restoration of a post taconian successor basin deformed within a transpressive regime northern appalachians restoration of transpressional orogens requires a three dimensional analysis of the strain state in order to take into account both the pure shear and simple shear components of the deformation and assess their relative contribution throughout the deformation history restoration of the post taconian successor basin the gaspe belt located within the external part of the acadian orogen in the canadian appalachians was performed by using a step by step method based on the successive removal of strain increments the pure shear component contributed 70 of the total strain during the first stages of the deformation whereas the simple shear component contributed 30 of the total strain during the last stages three retrodeformation steps are defined starting with restoration of the last deformation stage and working back to the first deformation stage the first step is to restore slip along acadian strike slip faults the second step is to restore shortening related to the horizontal extension during the acadian regional simple shear event finally the third step is to restore vertical extension related to the pure shear event by removing slip along the reverse faults unfolding and removing internal strain associated with cleavage development retrodeformation of the simple shear component of the transpressive deformation during the first two steps is performed on a horizontal view of the gaspe belt basin which contains the horizontal extension direction and which is perpendicular to the acadian nw se directed compression likewise restoration of the pure shear component is performed in vertical sections which contain the vertical extension and which are perpendicular to the acadian nw se directed compression the palinspastic map presented here is a much more appropriate base map for the basin and allows for a more realistic paleogeographic interpretation of the gaspe belt

deformation and displacement of the jura cover on its basement abstract the sedimentary cover of the internal jura displaced over its basement conforms well with the model of a thin skinned thrust sheet the wedge shaped sheet which includes a thick sequence of molasse deposited ahead of the alpine front slid over the basement cover interface the alpine crustal thrust sheets created a load at the south east end of the overthrust european plate molasse was deposited on the bent plate and the internal part of the basin was progressively affected by thrusting this process also induced deformation and displacements in the foreland gravity spreading in the internal molasse and a forward motion by rigid slipping movement led to a horizontal push causing deformation by indentation in the internal jura in the plateaux of the external jura there is very little extension in the cover and minimal shortening in the basement this shortening induced a decollement under the plateaux over the bresse graben gravity sliding occurred in the form of huge landslides these contrasts in the origin of the jura structures along a median cross section from thonon to arbois are shown by geophysical data construction of a balanced cross section and calculations of realistic mechanical models for the bending of the foreland plate and for the motion of the cover sheet

piecewise frontogenesis from a potential vorticity perspective methodology and a case study output from a numerical simulation by the university of wisconsin nonhydrostatic modeling system is used to investigate the evolution of the surface frontal structure of an intense winter cyclone that occurred off the east coast of north america using the model data as input to the piecewise potential vorticity pv inversion method developed by davis and emanuel the total surface frontogenesis is partitioned into contributions from discrete pv anomalies these contributions are calculated using the nondivergent balanced winds associated with pv anomalies in the upper interior and surface layers as well as the balanced irrotational winds in what is termed piecewise frontogenesis the cyclone of interest developed into a nearly stationary well occluded storm characterized by a cutoff pv anomaly at the tropopause and near surface frontogenesis concentrated in the warm frontal zone during the open wave stage of the cyclone life cycle this frontogenesis was produced largely by the balanced flow particularly that portion of it associated with the upper level pv anomaly throughout the remainder of the cyclone life cycle the upper level contribution to the frontogenesis retained a distribution similar to that of the total frontogenesis after the cyclone occluded however the frontogenesis forced by the unbalanced portion of the flow became increasingly significant despite the persistent smallness of the unbalanced winds in fact a substantial portion of the lower tropospheric frontogenesis observed in the occluded quadrant including that along a developing bent back front was eventually associated with the unbalanced flow these results suggest a potentially significant role is played by unbalanced motions in the development and maintenance of lowertropospheric frontal structure in midlatitude cyclones

roof sequence response to emplacement of the wills mountain duplex the roles of forethrusting and scales of deformation abstract this paper focuses on the behavior of a roof sequence in the appalachian plateau of west virginia u s a and emplacement of the wills mountain duplex with 17 5 km of displacement unlike the plateau along strike in pennsylvania and new york where forethrusting was previously documented this roof sequence lacks an underlying salt dominated roof decollement kinematic analyses reveal that the roof sequence in the west virginian plateau accommodated about two thirds of the 17 5 km of shortening by the adjacent wills mountain duplex as a forethrusting kinematic response the remaining shortening imbalance of about 5 km between the duplexes and younger roof sequence rocks is accommodated by additional forethrusting further into the foreland and local compensation this kinematic response matches that along strike in the central appalachians despite the loss of the salt decollement we interpret that an ordovician shale dominated formation was sufficiently weak to substitute for the salt horizon thus a weak mechanical unit rather than specifically a salt decollement is a necessary prerequisite for forethrusting a contributing factor to forethrusting may be the subvertical front of the wills mountain duplex which inhibited other responses by the roof sequence mesoscale and smaller processes including grain to grain pressure solution twinning and cleavage formation account for over 75 of the shortening in the roof sequence and if ignored would result in an erroneous interpretation of backthrusting or local compensation this result suggests that failure to consider all deformation scales could lead to incorrect kinematic conclusions in other tectonic systems

influence of balanced motions on heavy precipitation within a long lived convectively generated vortex abstract the forcing of heavy precipitation within a long lived convectively generated mesoscale vortex mcv is investigated with the aid of diagnoses from rapid update cycle gridded analyses organized convection within the mcv followed a distinct diurnal cycle which featured organized mesoscale convective systems mcss that matured overnight near the mcv center on successive days the mcv was typically most intense in the middle troposphere but intensified within the lower troposphere during the episodes of organized nocturnal convection the lower tropospheric vertical shear was an important organizing factor in mcs development and sustenance in the sense that its interaction with the cold temperature anomaly beneath the mcv center determined where balanced lower tropospheric ascent occurred from trajectory analyses we estimate that balanced ascent accounted for approximately half of the total vertical displacement of the thermodynamically unstable air that eventually composed elevated saturated

on the lag time between internal strain and basement involved thrust induced exhumation the case of the colombian eastern cordillera abstract thrust sheets accumulate internal strain before they start moving along discrete fault planes however there are no previous studies evaluating the time difference between initiation of strain and fault displacement in this paper we use observations from the eastern cordillera of colombia to evaluate this interval we utilize multiple thermochronometers and paleothermometers to refine the timing of deformation based on these new data we build time temperature path estimates that together with geometric outcrop based structural analysis and fluid inclusions allow us to assign relative timing to features associated with strain such as cleavage veins and certain types of fractures and compare that with the timing of thrusting we find that cleavage was only formed close to maximum paleotemperatures almost coeval with the onset of thrust induced denudation by the late oligocene the corresponding structural level of fold related veins suggest that they were formed later but still when the country rocks were at temperatures higher than 160 c mostly during the early miocene and still coexisted with the latest stages of cleavage formation our data show that the main period of strain hardening was short probably a few million years and occurred before first order basement thrusting was dominant but was associated with second order folding

numerical simulations of the genesis of hurricane diana 1984 part i control simulation abstract the complete transformation of a weak baroclinic disturbance into hurricane diana is reproduced by numerical simulations using the fifth generation pennsylvania state university national center for atmospheric research mesoscale model three distinct phases of the evolution are evident first baroclinic and barotropic development strongly modified by the effects of latent heating occurs during the latter part of this phase the low level circulation is strengthened through the axisymmetrization of remote potential vorticity anomalies that are generated by condensational heating and then advected toward the incipient storm the axisymmetrization process evinces properties of both nonlinear discrete vortex merger and vortex rossby wave dynamics the transformation from cold core to warm core vortex occurs in this development stage in the second phase lasting 10 12 h little deepening occurs spiral bands of convection begin to form and the core of the storm moistens eventually reaching 95

fault related folding a review of kinematic models and their application abstract folding that is directly related to fault activity is an important deformation feature that occurs all over the world in mountain belts accretionary wedges fold and thrust belts and intra plate settings in either strike slip compressional or extensional regimes due to their widespread occurrence knowledge about the development of these structures is important to a broad spectrum of geoscience sub disciplines such as structural geology seismology geomorphology petroleum geology and quaternary geology fault related folding has been analyzed intensively over the last 140 years for the sake of this review we divide the folds according to the way the faults and the folds form that is into detachment fault bend and fault propagation folds all fault related folds are caused by changes in fault parameters the simplest method to produce folds is to transport material along faults that have stepped flat ramp flat geometries fault bend fold alternatively the slip can decrease along the length of the fault and depending on whether the fault remains within a detachment layer or steps up through mechanical stratigraphy either a detachment fold or a fault propagation fold is formed respectively detachment folding was first investigated in the early 20th century whereas the full significance of fault propagation folds was recognized quite late in the 1980s seminal work on fault related folding was carried out in the 1930s but quantitative kinematic models have only been available in the last 30 years these models are extremely valuable because they allow a comprehensive understanding of the evolution of fault related folds and lead to more accurate predictions of the sub surface structure from the mid 1990s onwards numerical simulations have been used to identify how fault parameters such as dip and fault bend angle propagation to slip ratio and shape of the trishear zone influence the geometry of the related folding this is directly applicable to the analysis of the shape of anticlines produced however this does not mean that fold geometry is uniquely related to fault geometry on the contrary different kinematic approaches can lead to a similar fold shape

kinematic modeling of cross sectional deformation sequences by computer simulation we derive a kinematic algorithm which permits simulation of postulated cross sectional deformation sequences in sedimentary rocks affected by faulting fault related folding and simple shear the transformations are to a more deformed state and are formulated analytically in terms of the less deformed configuration forward modeling lagrangian description the medium is subdivided into domains of constant dip and homogeneous displacement vector fields which are delimited by the axial planes of the fault inflections the displacement trajectory is of constant length for all the displaced particles throughout the medium and parallel to the underlying active fault segment as a consequence the deformation path is continuous but not smooth and causes an angular style of parallel folding except at the deformation front where the layer thickness is not conserved the inhomogeneity of the displacement vector field across axial planes introduces longitudinal and angular shear strains whereas the area of the medium remains constant these strains which are superposed on the externally applied simple shear make the mapping transformation unconformal we define the stratigraphic layering of the undeformed medium by an approximating body of finite quadrilateral elements evaluate the defined displacement functions for the grid nodes and graph the deformed mesh eventually we create with the algorithm synthetic deformation sequences for simple boundary conditions and try in a specific case study to match the resulting synthetics with the available observational and experimental data

growth of the central andean plateau by tectonic segmentation is controlled by the gradient in crustal shortening abstract crustal deformation orocline formation and growth of the central andean plateau as well as the mutual relations of these processes with climate are a matter of international debate earthquake focal mechanism fault kinematic paleomagnetic and cross section balancing data are paramount for understanding the morphotectonic evolution of this noncollisional orogen but collectively await an explanation in terms of a comprehensive kinematic model we offer such a model that approximates simple shear in plan view and that predicts the kinematics of first order fault zones in the southern central andes the model indicates that segmentation of the upper crust into rhomb shaped domains confined by transpressive ranges resulted from the decrease in crustal shortening with distance to the central bend of the andes an anastomosing network of kinematically coupled reactivated orogen parallel and newly formed ne trending deformation zones encompassing components of sinistral and dextral strike slip res

late cenozoic tectonic development of the intramontane alai valley pamir tien shan region central asia an example of intracontinental deformation due to the indo eurasia collision 1 the pamir indentor of the northwestern himalayan syntaxis is a first order feature demonstrating partly the northward extent of deformation due to the cenozoic indo eurasia collision the alai valley of kyrgyzstan at the northern end of the indentor is a strategically positioned e w trending intramontane basin that constrains the timing and extent of crustal deformation in this area of the collision zone to quantify the convergence accommodated across the alai valley during the late cenozoic we collected structural and stratigraphic field data reviewed existing soviet literature and analyzed migrated seismic reflection profiles to construct and restore two regional sections crosscutting the basin our study suggests that the development progressive closure and conversion of this formerly marine basin into a terrestrial intramontane basin result from two main deformation events 1 distributed north south contraction took place during the late oligocene early miocene accommodated one third to half of the total shortening and was followed by the formation of a regional erosion surface and 2 n s shortening resumed in the mid miocene and continues today during this second episode the thrust front migrated southward localized along the trans alai ranges and failed to reactivate earlier neogene structures horizontal shortening of about 35 across the alai valley implies relatively low strain rates and displacement rates of about 4 18 4 69 10 16 s 1 and 0 66 0 78 mm yr 1 respectively for the last 25 myr our study confirms other regional observations indicating that contractional deformation occurred far in the interior of the asian continent as early as the late oligocene

quick look techniques for evaluating two dimensional cross sections in detached contractional settings for more than 30 yr geologists and geophysicists have used balancing techniques to constrain their cross sectional interpretations in detached contractional settings the quality of the resulting interpretations commonly directly correlates to the quality of the data the balancing and interpretational experience of the interpreter and the time allotted for the interpretation we demystify the balancing process and present quick look techniques for quickly and effectively detecting and preventing common cross section balancing errors in detached contractional settings common balancing problems are highlighted through close scrutiny of hanging wall and footwall ramps and flats such analysis helps identify inconsistencies in the numbers of ramps and flats in the strata and stratal thicknesses in corresponding ramps and in displacement along the fault these techniques possess the additional advantages of being useful at any stage of the interpretational process for time or depth sections and being easily comprehensible by students geologists geophysicists and managers alike the quick look techniques however are not an all encompassing panacea they do not guarantee a unique and or correct cross sectional interpretation instead they serve to focus the interpreter s attention on potentially problematic areas in the cross section that might require explanation and or reinterpretation

numerical simulations of the genesis of hurricane diana 1984 part ii sensitivity of track and intensity prediction abstract the authors examine numerous simulations that probe the dynamics governing the intensification and track of tropical cyclone diana 1984 simulated in part i the development process is fundamentally dependent on a preexisting upper tropospheric trough ridge couplet this couplet focuses mesoscale vertical motion that in turn produces lower tropospheric potential vorticity pv anomalies which form the seed for the tropical storm removal of this trough ridge couplet from the initial conditions eliminates cyclogenesis the simulated rate of development of diana in the prehurricane phase depends principally on choices of cumulus parameterization boundary layer treatment sea surface temperature and grid spacing simulations with cumulus schemes that allow more grid scale precipitation on the 9 km grid exhibit unrealistic grid scale overturning and slower intensification primarily due to production of cyclonic vorticity anomalies at large radii use of an innermost nest with 3 km grid spacing

a potential vorticity diagnostic approach to upper level frontogenesis within a developing baroclinic wave the process of tropopause folding is studied in the context of the life cycle of baroclinic waves previous studies of upper level frontogenesis have emphasized the role of the vertical circulation in driving stratospheric air down into the midtroposphere here a potential vorticity based approach is adopted that focuses on the generation of a folded tropopause to facilitate comparison of the two approaches the diagnosis is applied to the upper level front previously simulated and studied by rotunno et al the potential vorticity approach clarifies the primary role played by the horizontal nondivergent wind in producing a fold and explains why folding should be a common aspect of baroclinic development between the trough and upstream ridge prolonged subsidence within a region of weak system relative flow generates a tropopause depression oriented at an angle to the large scale flow the large scale vertical shear then locally increases the slope of the tropopause eventually leading to a tropopause fold in contrast tropopause folding in the base of the trough is caused by the nondivergent cyclonic circulation associated with the surface thermal wave the winds associated with the thermal wave amplify the potential vorticity wave aloft and these winds which decrease with height rapidly generate a tropopause fold within the trough

quaternary tectonic faulting in the eastern united states abstract paleoseismological study of geologic features thought to result from quaternary tectonic faulting can characterize the frequencies and sizes of large prehistoric and historical earthquakes thereby improving the accuracy and precision of seismic hazard assessments greater accuracy and precision can reduce the likelihood of both underprotection and unnecessary design and construction costs published studies proposed quaternary tectonic faulting at 31 faults folds seismic zones and fields of earthquake induced liquefaction phenomena in the appalachian mountains and coastal plain of the 31 features seven are of known origin four of the seven have nontectonic origins and the other three features are liquefaction fields caused by moderate to large historical and holocene earthquakes in coastal south carolina including charleston the central virginia seismic zone and the newbury massachusetts area however the causal faults of the three liquefaction fields remain unclear charleston has the highest hazard because of large holocene earthquakes in that area but the hazard is highly uncertain because the earthquakes are uncertainly located of the 31 features the remaining 24 are of uncertain origin they require additional work before they can be clearly attributed either to quaternary tectonic faulting or to nontectonic causes of these 24 14 features most of them faults have little or no published geologic evidence of quaternary tectonic faulting that could indicate the likely occurrence of earthquakes larger than those observed historically three more features of the 24 were suggested to have had quaternary tectonic faulting but paleoseismological and other studies of them found no evidence of large prehistoric earthquakes the final seven features of uncertain origin require further examination because all seven are in or near urban areas they are the moodus seismic zone hartford connecticut dobbs ferry fault zone and mosholu fault new york city lancaster seismic zone and the epicenter of the shallow cacoosing valley earthquake lancaster and reading pennsylvania kingston fault central new jersey between new york and philadelphia and everona fault mountain run fault zone washington d c and arlington and alexandria virginia

a classification of thrust fronts variations in structural style at thrust fronts are examined to determine whether they represent different stages of typical thrust sheet development or unique events as orogenic stresses declined thrust fronts are classified as buried or emergent in which either the sole thrust died out in the subsurface or emerged to the synorogenic surface buried thrust fronts are subdivided into two types type 1 fronts end in broad zones of low strain type 2 fronts end in zones of high strain emergent thrust fronts may display significant horizontal displacement strongly emergent or limited displacements of about 1 km weakly emergent tip stick thrust fronts exhibit high strains and out of sequence thrusting different types of thrust fronts are linked by transitional tip li e anticlines and strike slip zones most thrust front types represent different stages of typical thrust sheet development but those in type 1 display atypical development unique to thrust fronts

a pv perspective on the vertical structure of mature midlatitude cyclones in the northern hemisphere development of extratropical cyclones can be seen as an interplay of three positive potential vorticity anomalies an upper level stratospheric intrusion low tropospheric diabatically produced potential vorticity pv and a warm anomaly at the surface acting as a surrogate pv anomaly this study based on the interim ecmwf re analysis era interim dataset quantifies the amplitude of the pv anomalies of mature extratropical cyclones in different regions in the northern hemisphere on a climatological basis a tracking algorithm is applied to sea level pressure slp fields to identify cyclone tracks surface potential temperatureanomalies duandverticalprofilesofpvanomalies dpvarecalculatedatthetimeofthecyclones minimumslpinaverticalcylinderaroundthesurfacecyclonecenter tocomparethecyclones characteristics they are grouped according to their location and intensity composite dpv profiles are calculated for each region and intensity class at the time of minimum slp and during the cyclone intensification phase in the maturestage allthree anomaliesare on averagelargerfor intense thanforweak wintercyclones e g 0 6 versus 0 2 potential vorticity units pvu 1 pvu 510 26 kk g 21 m 2 s 21 at lower levels and 1 5 versus 0 5 pvu at upper levels the regional variability of the cyclones vertical structure and the profile evolution is prominent cyclones in some regionsare moresensitiveto the amplitude ofa particularanomalythanin other regions values of du and low level dpv are on average larger in the western parts of the oceans than in the eastern parts results for summer are qualitatively similar except for distinctively weaker surface du values