a gcm investigation into the nature of baroclinic adjustment abstract spindown experiments have been conducted using an atmospheric general circulation model to determine the nature and timescale of adjustment to a baroclinically neutral state the spindown was obtained by turning off the radiative cooling of the atmosphere a procedure the authors argue that retains all the relevant constraints on the atmospheric motions a further experiment with radiation and all other physical parameterizations turned off was performed for comparison the neutral state was characterized by increased static stability but little reduction in meridional temperature gradient in the main baroclinic zones however the zones were observed to narrow and were flanked by regions where the meridional temperature gradient was reduced significantly this pattern was repeated in the no physics spin down experiment but in the absence of surface friction and strong orographic drag the flow also appeared to be stabilized by enhanced barotropic shear the neutral states from these two expe

integrated seismic studies of the baltic shield using data in the gulf of bothnia region in the autumn of 1989 a co operative experiment involving 12 research institutions in northwestern europe collected 2268 km of deep seismic reflection profiles in the gulf of bothnia and the baltic

recording marine airgun shots at offsets between 300 and 700 km this paper demonstrates that under favorable conditions by using multichannel recording and subsequent stacking of adjacent records marine airgun shots have been detected at offset distances up

baroclinic eddies and the extent of the hadley circulation an idealized gcm study thehadleycirculationhaswidenedoverthepast30years thiswideninghasbeenqualitativelyreproduced in general circulation model gcm simulations of a warming climate comprehensive gcm studies suggest this widening may be caused by a poleward shift in baroclinic eddy activity yet the limited amplitude of the climate change signals analyzed so far precludes a quantitative comparison with theories this study uses two idealized gcms one with and one without an active hydrologic cycle to investigate changes in the extent of the hadley circulation over a wide range of climates the climates span global mean temperatures from 243 to 385k and equator to pole temperature contrasts from 12 to 100k baroclinic eddies control the extent of the hadley circulation across most of these climates a supercriticality criterion that quantifies the depth of baroclinic eddies relative to that of the troposphere turns out to be a good indicator of where baroclinic eddies become deep enough to terminate the hadley circulation the supercriticality depends on meridional temperature gradients and an effective stability that accounts for the effect of convective heating on baroclinic eddies astheequator to poletemperaturecontrastweakensortheconvectivestaticstabilityincreases convective heating increasingly influences the thermal stratification of the troposphere and the supercriticality consistent with the supercriticality criterion the hadley circulation contracts as meridional temperature gradients increase and it widens as the effective static stability increases the former occurs during el nino and may account for the observed hadley circulation contraction then the latter occurs during global warming

the fine scale structure of upper continental lithosphere from seismic waveform methods insights into phanerozoic crustal formation processes summary studies of the fine scale structure of the continental lithosphere using seismic coda associated with reflections from within the crust and the uppermost mantle have almost solely been based on the compressional wavefield observed at near vertical to wide angle incidence here the results from a full waveform analysis of both p and s wave coda obtained during a crustal scale wide angle refraction experiment from southwest ireland are presented the basic foundation for the study is a 2 d model for the p and s wave structure of the crust and its chemical composition based on traveltime inversion of first arrivals and reflections for the irish caledonides this sector of the caledonian orogenic belt straddles the boundary between the laurentian and avalonian tectonic plates along the iapetus suture zone the excellent quality and relatively broad frequency range e g 1 20 hz of the p and s wave coda permits finer structure in the upper 40 km of lithosphere to be resolved than would be possible using just primary seismic phases a series of 1 d waveform calculations are performed to systematically build a model for the fine scale structure of the 32 km thick crust and the uppermost mantle lithosphere petrophysical and geochemical data from felsic lower crustal xenoliths from central ireland place limits on the permitted velocity fluctuations additional constraints are imposed by vertical p wave reflections observed on contiguous offshore seismic reflection profiles the results indicate that the uppermost mantle to a depth of ca 40 km consists of a vertically stacked sequence of alternating high vp 8 0 km s 1 and low vp 7 25 km s 1 velocity layers each layer is about 500 m thick with a vp vs ratio 1 73 these layers are interpreted as a series of lens shaped mafic sill complexes intruded into the subcrustal lithosphere the fine structure within the lower crust consists of similar seismic velocity fluctuations vp 6 4 and 7 1 km s 1 but on a scale of 200 300 m thickness velocity variations within the lower crust are consistent with the petrophysical properties of metapelitic orthogneissic and psammitic lithologies from lower crustal xenoliths in central ireland and with similar exhumed sections of lower crust in southern europe these results support tectonic theories for the origin of the crust by tectonic accretion of predominantly sedimentary and volcaniclastic material derived from oceanic island arc and continental margin sources during the caledonian orogenic cycle a conceptual model for crustal accretion and growth involves partial melting of the accreted sedimentary wedge producing granites and a chemically differentiated crust during the late caledonian latest silurian early devonian the heat source that drove melting of the accreted sediments may have been provided by the interpreted mafic sills intruded into the uppermost mantle during oblique late caledonian sinistral collision of the laurentian and avalonian plates

the equilibration of short charney waves implications for potential vorticity homogenization in the extratropical troposphere in this paper the authors discuss the vertical distribution of the interior potential vorticity gradients in the extratropical troposphere in an idealized setting this structure is characterized by large positive gradients at the top of the boundary layer and a narrow homogenized region in the interior to understand this partial homogenization the authors have looked at how charney waves of different scales equilibrate it is shown that when the interior gradients of potential vorticity are small compared to the delta function at the ground the modes can equilibrate without eliminating the lower level shear as is the case in the eady model these neutral states can exist even though they violate the charney stern condition for stability the equilibration process also produces a concentration of the potential vorticity gradients at heights of the order of the rossby depth which can be regarded as a boundary to the interior mixing of potential vorticity the extent of interior potential vorticity mixing required for equilibration depends on the ratio between the boundary and interior potential vorticity gradients it is implicit in the analysis of previous authors that this ratio is close to 1 in midlatitudes which implies that an eady model with full homogenization of the interior potential vorticity gradients is not an appropriate paradigm for the midlatitude troposphere nevertheless it is argued that localized interior potential vorticity mixing could be sufficient for neutralizing the shortest waves

morphodynamic signatures of braiding mechanisms as expressed through change in sediment storage in a gravel bed river previous flume based research on braided channels has revealed four classic mechanisms that produce braiding central bar development chute cutoff lobe dissection and transverse bar conversion the importance of these braiding mechanisms relative to other morphodynamic mechanisms in shaping braided rivers has not yet been investigated in the field here we exploit repeat topographic surveys of the braided river feshie uk to explore the morphodynamic signatures of different mechanisms of change in sediment storage our results indicate that when combined the four classic braiding mechanisms do indeed account for the majority of volumetric change in storage in the study reach 61 total chute cutoff traditionally thought of as an erosional braiding mechanism appears to be the most common braiding mechanism in the study river but was more the result of deposition during the construction of diagonal bars than it was the erosion of the chute three of the four classic mechanisms appeared to be largely net aggradational in nature whereas secondary mechanisms including bank erosion channel incision and bar sculpting were primarily net erosional although the role of readily erodible banks in facilitating braiding is often conceptualized we show that bank erosion is as or more important a mechanism in changes in sediment storage than most of the braiding mechanisms and is the most important secondary mechanism 17 of total change the results of this study provide one of the first field tests of the relative importance of braiding mechanisms observed in flume settings

sediment residence time and connectivity in non equilibrium and transient geomorphic systems abstract growing empirical evidence shows that many geomorphic systems are in transient state or out of equilibrium with respect to the external driving forces the transient state is often related to the dis connectivity of the many constituent parts of geomorphic systems as a result of sediment storage along the sediment flow path from its source to the final sink the response time of geomorphic systems to external changes is thus dependent on the residence time of sediment in various storage compartments here i present a mathematical concept based on reservoir theory to model residence time of sediment using millennial scale sediment budgets the framework sheds light on the limitation of the sediment delivery ratio which is often used as a measure of sediment connectivity in geomorphic systems and provides analytical information on process type pace of sediment flux and connectivity of storage compartments along the sediment cascade the application of the reservoir theory to geomorphic systems under agricultural land use shows that sediment delivery ratios are linked to the virtual velocity of the eroded sediment the time since the onset of agricultural land use and the size of the studied basins with respect to the temporal evolution of sediment storages that temporarily remove sediment from the conveyor belt the framework aims to estimate the sediment residence time in storages which is linked to the effective time scale of disconnectivity reanalysis of a long term empirical sediment budget from central europe reveals that the response to agricultural land use which started 5000 years bp is mainly buffered by the long residence time of sediment on hillslopes in the order of 10 3 years which results in a delayed floodplain aggradation furthermore the framework was applied to paraglacial mountain systems that inherit striking evidences of pleistocene glacial erosion and still recover from the change from glacial to interglacial conditions as a consequence of the reduced lateral and longitudinal connectivity i show that paraglacial response times of sediment flux in mountain headwater in the canadian rocky mountains range in the order of 100 400 ka the results indicate that response times at the transition from glacial to interglacial conditions are much longer than the return interval of the major glaciations causing a transient behavior of mountain headwater basins during interglacial periods the presented reanalysis of millennial scale sediment budgets of agricultural and mountain geosystems provides an integrative framework to link paleo environmental reconstructions and the connectivity of transient geomorphic system to external changes

reflections from a mylonitized zone in central sweden dipping reflections imaged on a deep seismic reflection profile acquired within the baltic shield can be indirectly linked to strain induced acoustic impedance contrasts within a regional brittle ductile shear zone the singo shear zone measurements made at various scales and frequencies estimate rock velocity within the shear zone and correlate well with the ductile component of strain previously determined by structural analysis velocity measurements include some made on cored field samples at confining pressures of 0 4 gpa in a laboratory 10 mhz sensor frequencies and some made in situ using ultrasonic 54 khz sensors on exposures within the shear zone laboratory measurements show a 10 change in seismic anisotropy and a contrast of 0 5 km s 1 in bulk rock velocity between granitoid protolith and highly strained ultramylonite the in situ velocity measurements demonstrate that the velocity variations persist over considerable volumes including zones where strain and associated volume loss of silica remain elevated without mylonitization synthetic seismograms generated using a one dimensional velocity model of the shear zone show that velocity variations observed in the field were large enough in magnitude and of sufficient scale to produce reflections observable on the deep seismic reflection profile collected using 6 25 hz frequencies ray trace two dimensional forward modeling of a high density wide angle reflection section demonstrates that deep dipping reflections could result from strain induced acoustic impedance contrasts within the singo or similar nearby shear zones

evidence for early proterozoic plate tectonics from seismic reflection profiles in the baltic shield plate tectonics provides the linking framework for all tectonic and magmatic activity seen today but it is not known when plate tectonics first developed on earth new deep seismic reflection and

impact of flow routing on catchment area calculations slope estimates and numerical simulations of landscape development 1 flow routing across real or modeled topography determines the modeled discharge and wetness index and thus plays a central role in predicting surface lowering rate runoff generation likelihood of slope failure and transition from hillslope to channel forming processes in this contribution we compare commonly used flow routing rules as well as a new routing rule to commonly used benchmarks we also compare results for different routing rules using airborne laser swath mapping alsm topography to explore the impact of different flow routing schemes on inferring the generation of saturation overland flow and the transition between hillslope to channel forming processes as well as on location of saturation overland flow finally we examined the impact of flow routing and slope calculation rules on modeled topography produced by geomorphic transport law gtl based simulations we found that different rules produce substantive differences in the structure of the modeled topography and flow patterns over alsm data our results highlight the impact of flow routing and slope calculation rules on modeled topography as well as on calculated geomorphic metrics across real landscapes as such studies that use a variety of routing rules to analyze and simulate topography are necessary to determine those aspects that most strongly depend on a chosen routing rule

migration of wide angle seismic reflection data from the grenville front in lake huron under the auspices of the great lakes international multidisciplinary program on crustal evolution glimpce coincident steep and wide angle seismic reflection data sets were acquired in lake huron the wide angle data were recorded at stationary onshore receivers during the shooting and recording of the conventional marine steep angle survey to extract information from the wide angle data a variety of processing techniques including automatic trace editing amplitude balancing f k filtering static corrections and predictive deconvolution were applied to the wide aperture common receiver gather before migration the application of a slowness weighted depth migration algorithm which was first tested on synthetic data and which included a slowness filter resulted in an image of the grenville front tectonic zone gftz remarkably similar to that observed in the multichannel steep angle section the migrated wide angle data suggest that prominent bands of east dipping seismic reflections observed across the gftz extend unattenuated to depths of at least 45 km

the use of land recorded long range marine airgun data in crustal reflection refraction investigations summary during the eugeno s field campaign in 1984 a large number of airgun shots were fired at sea in the skagerrak and kattegat and in lake vanern in southwestern sweden the signals were recorded on land by analogue mars and digital sn pcm 80 three channel stations by a digital 48 channel sercel sn348 reflection instrument and by geostore stations the airguns were shot about every 300 m along profiles up to 100 km in length clear reflected and refracted arrivals were observed from 5 km to 250 km shot receiver offset the field and data processing techniques used are briefly described and two examples of data are discussed

deep crustal seismic reflection profiling across two major tectonic zones in southern sweden abstract a seismic reflection profile has been shot in varmland southwestern sweden across two major tectonic zones the protogine zone and the mylonite zone the crustal bedrock units separated by the tectonic zones are clearly distinguished in the seismic profile by changes in the reflection character in the upper 5 6 km the protogine zone is represented by a 15 20 km wide band of dipping structures the mylonite zone dips too steeply to be seen directly and a lack of clear reflectors at depth makes a continuation down through the crust hypothetical in the uppermost 5 6 km between the two tectonic zones stronger and more continuous reflections can be seen and are interpreted as being connected with hyperite intrusions which have been mapped at the surface the lower crust shows generally little reflectivity with only short and weak reflectors an exception occurs at mid crustal depths where a number of clearly recognizable bands of reflected energy are suggested to be major shear zones formed during sveconorwegian grenvillian thrusting towards the east a slight increase in reflectivity in the depth range 42 48 km correlates well with the moho depth determined from refraction seismic studies the possible relationships between data acquisition parameters and the observed scarcity and low strength of reflections from the deeper crust have been considered in some detail it is shown that the use of 28 hz single geophones instead of 10 hz geophone strings along a major part of the profile did not reduce the signal to noise ratio for deep reflections however the varying source characteristics in combination with the different quality of the recordings made computation of the residual static corrections difficult which may have resulted in a partly destructive stacking of seismic traces in this way the low reflectivity of the deeper crust in this area is further brought out in the stacked seismic sections

static corrections on crystalline rocks1 static corrections for reflection seismic data shot on high velocity crystalline rock can be calculated directly from the data using a global iterative stackpower optimization the reflections consist of several peaks creating the possibility of aligning the wrong peak in the signals due to misalignments a large number of local maxima in the stackpower exist in a cyclic manner only slightly smaller than thes stackpower of the best stack therefore the search must be of a global nature a monte carlo search requires long run times a global search method is presented using a varying sequence of parameters within each iteration the ability for a set of static corrections and the associated stackpower to move from a local maximum to a larger maximum is enhanced the performance of the iterative process is improved so a relatively small number about 20 of iterations is needed to obtain the optimum set of corrections the risk of misalignment of traces by using the wrong peak in a signal consisting of several peaks is diminished and it is less important that the initial set of corrections is close to the final set the method is illustrated by a synthetic example and on a data set shot on the granites of dalarna sweden

deep crustal configuration of the valencia trough and its iberian and balearic borders from extensive refraction and wide angle reflection seismic profiling abstract new constraints on the crustal structure of the valencia trough and its iberian and balearic borders have been obtained from a seismic experiment carried out in autumn 1989 a total of 290 sea shots were fired along three refraction wide angle reflection profiles recorded by 10 ocean bottom seismometers obss in the valencia trough and 110 land stations distributed on both flanks the huge amount of recorded data in each profile has been integrated and jointly interpreted to obtain a single 2 d velocity depth model along each line the geometry and deep crustal structure of the basin are fairly well defined in terms of laterally inhomogeneous layered media the sedimentary cover shows a layer of consolidated sediments overlain by neogene and quaternary sediments with a velocity of 5 1 km s interpreted as mesozoic carbonates at the northwestern side of the valencia trough a fairly homogeneous crystalline basement is found on all profiles at a mean depth of 4 km below sea level with a velocity of 6 0 6 1 km s the observed critical distances and arrival times of the moho reflected waves are firm evidence supporting a thinning of the crust towards the centre of the basin the moho rises up to 13 km in the axis of the trough in the nw se and e w profiles and up to 15 km in the ne sw profile moreover the analysis of the well defined pmp phase shows differences between the deep structure of the flanks and the trough respectively a sharp velocity contrast at the moho from a fairly uniform lower crust of 6 4 km s velocity is proposed in both flanks in contrast to a high velocity gradient within the lower crust interpreted near the axis of the trough an anomalous upper mantle velocity of 7 8 km s fits the data throughout the valencia trough and mallorca with slightly higher values of 7 9 km s required towards the continent these velocity values do not favour an interpretation in terms of underplating the geometry of the moho discontinuity shows a gradual deepening towards the iberian peninsula in contrast to a more abrupt slope towards mallorca depth values of 30 32 km typical of a continental crust are inferred about 40 km inland on the iberian peninsula in agreement with the crustal thicknesses already reported for the iberian range and the ebro basin the present crustal thinning resulting from rift episodes in the valencia trough and the iberian border is thus confirmed and constrained from our seismic results of the deep crust and upper mantle

computing spatially distributed sediment delivery ratios inferring functional sediment connectivity from repeat high resolution digital elevation models high resolution digital elevation models dems from repeat lidar or sfm surveys have become an important tool in process geomorphology the spatial pattern of negative and positive changes of surface elevation on raster dems of difference dod can be interpreted in terms of geomorphic processes and has been used for morphological budgeting we show how the application of flow routing algorithms and flow accumulation opens new opportunities for the analysis of dod by accumulating the values of the dod along downslope flowpaths delineated on a dem these algorithms lend themselves to computing the net balance i e sediment yield sy for the contributing area of each cell doing the same for the negative subset of the dod yields a minimum estimate of erosion e within the contributing area the division of sy by e yields a maximum estimate of the sediment delivery ratio sdr that is the proportion of material eroded within the contributing area of each cell that has been exported from that area the resulting sdr is a spatially distributed measure of functional sediment connectivity in this letter we develop the computationally simple approach by means of an example dod from a lateral moraine section in the upper kaunertal valley austrian central alps we also discuss advantages assumptions and limitations and outline potential applications to connectivity research using field laboratory and model based dod

pre critical wide angle reflections from the baltic shield evidence for a 1 8 ga subduction complex abstract during the collaborative babel experiment in 1989 over 30 000 airgun shots were fired along reflection profiles in the gulf of bothnia and baltic sea and recorded at 62 onshore seismic stations giving densely sampled wide angle data of many forms at one such station in line and three dimensional wide angle arrivals from 14 40 km offset were recorded on a linear geophone array placed off end to marine reflection line 2 the multifold data from this station have been cdp sorted and stacked and also displayed as a single fold high resolution time distance record section with an average trace spacing of 4 m prominent wide angle reflections observed on both wide angle stacks and receiver gathers can be correlated with steep northward dipping reflectors observed in the lower crust on coincident near normal incidence reflection marine profiles high resolution ray tracing through a three dimensional model shows that the observed reflections likely occur in a reflective zone 8 km thick composed of individual reflectors 100 300 m thick the necessary impedance contrasts can be produced by alternating high and low velocities or densities these reflectors parallel the trend of the skelleftea mineral district and its associated conductivity anomaly and are here interpreted as metamorphosed remnants of subducted oceanic type crust and its overlying sediments

baroclinic adjustment a comparison between theory observations and models abstract isentropic slopes calculated from northern hemisphere analyses of the zonal mean state of the atmosphere are compared with isentropic slopes calculated from baroclinic adjustment theory in midlatitudes the isentropic slopes are relatively close to the adjusted values in the layer from 2 to 7 km 800 to 400 mb they also have very little variation in latitude and season which implies that baroclinic eddy fluxes supply a strong negative feedback to changes in isentropic slopes the vertical structure of the temperature field in the adjusted layers and the location of the layers suggest that vertical eddy heat fluxes play a significant role in this feedback process isentropic slopes are also calculated from simulations of the current climate by the giss model ii gcm and the ncar ccm2 both models have regions of apparent baroclinic adjustment similar to that in the northern hemisphere atmosphere however compared to the observations the agreement of the simulations with baroclinic adjustmen

determination of poisson s ratio from pre critical wide angle seismic reflection data from the babel project summary the pre critical wide angle seismic reflection data collected during the babel survey using multireceiver spreads contain high amplitude p wave and modeconverted s wave reflected arrivals the two phases can be partially separated and their signal to noise ratio emphasized by exploiting the multifold nature and the increased sensitivity of velocity analysis afforded by these data to produce zero offset corrected stacked sections using these sections a method has been developed to derive estimates of poisson s ratio by optimizing the cross correlation of p wave and s wave arrivals and hence to constrain petrological models of the crust sampled by these data although the apparently high degree of temporal and spatial resolution of reflected arrivals that are visible within the stacked sections must be reduced to achieve a satisfactory degree of correlation robustness the results shed some light on crustal petrology and concur with existing estimates of poisson s ratio for the baltic shield

climatology of summer midtropospheric perturbations in the us northern plains part ii large scale effects of the rocky mountains on genesis propagating convective storms across the us northern plains are often coupled with preexisting midtropospheric perturbations mps initiated over the rocky mountains a companion study part i notes that such mps occur most commonly at 12 utc early morning and 00 utc late afternoon using a regional reanalysis and a general circulation model gcm this study investigates how such a bimodal distribution of the mp frequency is formed the results point to two possible mechanisms working together while each has a different timing in terms of maximum effect the diurnal evolutions between the midtropospheric flows over the rockies and over the great plains are nearly out of phase due to inertial oscillation during the nighttime the westerly flows at 700 500 mb over the rockies intensify while flows at the same level over the great plains turn easterly these two flows converge over the eastern rockies and induce cyclonic vorticity through vortex stretching after sunrise the convergence dissipates and the cyclonic vorticity is redistributed by horizontal vorticity advection moving it downstream this process creates a climatological zonally propagating vorticity signal which in turn facilitates the early morning mp genesis at 12 utc the analysis also reveals marked dynamic instability conducive to subsynoptic scale disturbances in the midtroposphere over the rockies strong meridional temperature gradients appear over the north facing slopes of the rockies due to terrain heating to the south and the presence of cooler air to the north this feature along with persistent vertical shear creates a charney stern type of instability i e sign changes of the meridional potential vorticity gradient meanwhile the development of terrain boundary layer reduces the rossby deformation radius which subsequently enhances the likelihood for baroclinic short waves such effects are most pronounced in the late afternoon and therefore are supportive to the mp genesis around 00 utc examination of gcm experiments with and without orography further supports the critical role of the rocky mountains and its associated boundary layer impacts on the formation of mps

processing of pre critical wide angle seismic reflection data from the babel project summary in addition to using the now widely recognised technique of simultaneously acquiring deep reflection profiles at sea and long range refraction profiles using three component land stations the babel seismic experiment also recorded p and s wave energy from the large airgun array at four linear 38 component land spreads the pioneering nature of this work led in hindsight to several deficiences in design but also pointed the way towards substantial advances in analysis and interpretation of integrated seismic observations the multifold nature of the recordings at offsets providing pre critical reflections from moho depths resulted in interleaved receiver gathers with trace spacings of 4 5 m thus providing some of the most densely spaced deep seismic wide angle sections to date with such a trace density the signal to noise ratio was substantially increased by summation of adjacent traces without degrading spatial resolution stacking the land array data using conventional common midpoint cmp gather techniques over source receiver offsets of 7 78 km doubled the depth range constrained by numerically precise stacking velocity analysis offsets 10 km provide normal moveouts 1 s although the 1 5 km of differential moveout available here limited velocity discrimination and required additional constraints to define zero offset traveltimes for one array stacking velocity errors of 200 m s 1 imposed a resulting error in zero offset time of up to 400 ms without use of any marine data with receiver response functions matched stacked sections using data from geophone arrays exhibit similar features to stacks made using hydrophone arrays at 0 3 km offsets in the same area but also significant differences the differences in reflection amplitudes cannot be simply attributed to theoretical amplitude offset variations and probably represent variation in the reflectivity of the crustal rocks of the baltic shield

velocity analysis for wide aperture seismic data common midpoint data are now being collected with ever increasing source receiver offsets for wide aperture seismic data classical methods of interpretation fail since velocity analyses and signal to noise enhancement methods based on hyperbolic traveltime curves are no longer appropriate therefore the goals of increased velocity resolution and signal enhancement which motivate the increase in offset are not achieved approximate methods involving higher order traveltime curves or extrapolations have been developed for velocity analysis but these are ineffective in the presence of refracted arrivals and lack a physical basis these problems can be minimized by transforming the observational data to the domain of intercept or vertical delay time and horizontal ray parameter p in this domain headwave refractions are collapsed into points and both near vertical and wide angle reflections can be analyzed simultaneously to derive velocity depth information even in the presence of velocity gradients or low velocity zones