remote trigger of deep convection by cold outflow over the taiwan strait in the mei yu season a modeling study of the 8 june 2007 case abstractin this study the heavy rainfall event over central taiwan during the mei yu season on 8 june 2007 is investigated with an emphasis on the triggering mechanism for the deep convection that produced the rain observations indicate that there existed two lines of forcing with convection prior to the rain one over the northern taiwan strait along the mei yu front and the other over the southern taiwan strait yet the convection in question developed over the central strait between these two lines in an unstable environment with strong westerly vertical wind shear this motivated the authors to carry out the present study the cloud resolving storm simulation cress of nagoya university was used and the event was reproduced at a horizontal grid size of 2 km including the initiation of new convection over the central strait at the correct location and time the model results suggest a crucial role played by the series of active persistent and propagating storms in the southern strait along the

the tectonic evolution of the zoumi sandstone western moroccan rif the zoumi sandstone is an oligo miocene syn tectonic flysch sequence deposited on the back of the mesorif thrust sheet whose sediment source was from the foreland to the south variations within the zoumi sandstone from thick to thin bedded turbidite lobes are explained as the result of deposition in small confined basins or larger more extensive basins respectively formation of small basins is related to contractional deformation in the underlying mesorif thrust sheet propagation of the zoumi thrust through the developed basin with areas of relative uplift and subsidence produced complex hanging wall cutoff geometry a complicated footwall geometry exists because deformation in the more external mesorif thrust sheet preceded the final displacement of the more internal intrarif thrust sheet the latter incorporated the zoumi sandstone into its leading edge and thrust it over the mesorif during the miocene this deformation sequence of two or more simultaneously active thrust sheets is described as synchronous thrusting

ground penetrating radar and its use in sedimentology principles problems and progress abstract ground penetrating radar gpr also referred to as ground probing radar surface penetrating radar subsurface radar georadar or impulse radar is a noninvasive geophysical technique that detects electrical discontinuities in the shallow subsurface

a classification of thrust fronts reply unlike root 1987 i do not have first hand experience of the appalachians hence my use of the appalachians as an example of a type 1 buried thrust front was entirely based upon interpretations from publications i hope that the lit erature is not misrepresented in this discussion the main point of root s 1987 criticism centers on the burning springs anticline and cambridge arch these structures are however anomalous rodgers 1 3 the trends of the burning springs anticlme and cambridge arch approximately north south to north northwe st southsoutheast are divergent from the general appalachian structural trend northeast southwest rodgers 1963 his figure 1 and they do not follow or represent the regional trend of the appalachian thrust front the oblique trend closely follows the lateral termination of salt in the upper salina group rodgers 1963 the same cannot be said for the main area of plateau deformation where folding albeit weaker continues beyond the salt termination in the appa lachian plateau area northeast of the burning springs anti cline davis and engelder 1985 their figure 6 as root suggests the burning springs anticline cambridge arch trend may be an example of a type 2 buried thrust front it is also more akin to the termination of a blind oblique ramp than a frontal thrust

ground penetrating radar signal processing improves mapping accuracy of underground voids and seawater table an application in deteriorating coastal structure nanfangao port taiwan efficient restoration of deteriorating coastal structures requires an accurate picture of both above ground and underground features although ground penetrating radar gpr can map underground features it creates reflection artifacts here a model for deconvolution calibration was developed in an outdoor small scale experiment gpr parameters were established then applied at a deteriorating fishing port in northeast taiwan the deconvolution filter removed repetitive reflection patterns under the lowest part of the void creating a more accurate map a 3d map was created from interpolated sketched void boundaries due to its high lossy nature at radar frequencies and large contrasting relative dielectric permittivity rdp to the upper medium the seawater table swt is easily identified the upper boundary of reflection free area in the deconvoluted radargram therefore indicates the swt the methods developed here are easily modified to fit a wide range of situations

the internal structure of scrolled floodplain deposits based on ground penetrating radar north thompson river british columbia abstract a study of floodplain deposits using ground penetrating radar gpr was conducted on a confined meander of the north thompson river near kamloops british columbia a survey grid consisting of 20 individual gpr profiles from 200 m to 900 m in length was constructed on a 0 9 km2 section of the floodplain all gpr profiles were collected using a pulse ekkotm iv gpr system with 100 or 200 mhz antennae dependent on the thickness of floodplain sediments floodplain sediments consist of sand and gravel deposits approximately 7 to 14 m thick that overlie silts and clays interpreted to be glaciolacustrine in origin vibracore and auger data obtained at nine locations in the gpr survey grid show that changes from medium sand to gravel do not produce distinct radar reflections in gpr profiles but that the water table may locally produce a distinct high amplitude radar reflection area well log data show that rapid signal attenuation at depth in all gpr profiles coincides with underlying silt and clay sediments gpr profiles were therefore useful in mapping 3 d variability in the thickness of floodplain deposits all gpr profiles were divided into macroscale 150 m2 in 2 d cross section radar facies delineated on the basis of the nature and orientation of reflections relative to surface scroll topography radar stratigraphy suggests that the floodplain is composed of a single complex lateral accretion deposit with periodic channel fills located between surface scroll ridges dip direction profiles normal to surface scroll ridges exhibit mainly inclined stratification is and or preserved ridge and swale ras deposits dipping in the direction of floodplain accretion well developed ras architecture in 200 mhz gpr profiles displays mainly wavy reflections conforming with surface topography and little inclined stratification these reflectors are interpreted to be the result of processes of vertical accretion associated with floodplain formation preserved scroll ridge deposits exhibit asymmetry at depth dipping more steeply in the direction of floodplain accretion profiles of strike direction parallel to surface scroll ridges show either parallel or slightly inclined 1 2 reflections dipping in the downstream direction

gpr in sediments advice on data collection basic processing and interpretation a good practice guide within sedimentological studies ground penetrating radar gpr is being used with increasing frequency because it yields images of the shallow subsurface that cannot be achieved by any other non destructive method the purpose of this paper is to provide an introduction to the collection processing and interpretation of gpr data so that future sedimentary studies can be improved with gpr equipment now being lightweight robust and portable proper data collection and survey design methods need to be followed in order to acquire high resolution subsurface digital data various factors are discussed including reflection profiling velocity soundings test surveys topography logistics data quality and extreme environments basic data processing and visualization are then reviewed followed by a discussion on gpr interpretation strategies including a background to radar stratigraphy for the sedimentary geologist or geomorphologist gpr offers unique data of the shallow subsurface including stratigraphy geometry architecture and structure

ground penetrating radar antennae frequencies and transmitter powers compared for penetration depth resolution and reflection continuity1 twelve ground penetrating radar gpr experiments were conducted on the modern wave influenced william river delta on the southern shore of lake athabasca in northern saskatchewan canada the delta is a well sorted quartzoserich clean sand dominated water saturated geomorphic feature which provided an ideal site to test gpr penetration depths resolution and continuity of reflections were compared for different antennae frequencies 25 50 100 200 mhz and transmitter powers pulser voltage 400 v 1000 v the data show significant variations in vertical resolution from 0 15 m to 0 76 m 200 25 mhz depth of penetration from 14 m 28 m 200 25 mhz and continuity of reflections increasing the transmitter power from 400 v to 1000 v increases the depth of penetration by 5 to 14 and improves the continuity of reflections with little effect on the resolution

landform development in a zone of active gedi fault eastern kachchh rift basin india abstract an earthquake of 2006 mw 5 7 occurred along east west trending gedi fault gf to the north of the kachchh rift basin in western india which had the epicenter in the wagad upland which is approximately 60 km northeast of the 2001 mw 7 7 earthquake site or epicenter development of an active fault scarp shifting of a river channel offsetting of streams and uplift of the ground indicate that the terrain is undergoing active deformation based on detailed field investigations three major faults that control uplifts have been identified in the gf zone these uplifts were developed in a step over zone of the gf and formed due to compressive force generated by left lateral motion within the segmented blocks in the present research a terrace sequence along the north flowing karaswali river in a tectonically active gf zone has been investigated reconstructions based on geomorphology and terrace stratigraphy supported by optical chronology suggest that the fluvial aggradation in the wagad area was initiated during the strengthening at 8 ka and declining 4 ka of the indian summer monsoon ism the presence of younger valley fill sediments which are dated 1 ka is ascribed to a short lived phase of renewed strengthening of ism before present day aridity based on terrace morphology two major phases of enhanced uplift have been estimated the older uplift event dated to 8 ka is represented by the tertiary bedrock surfaces which accommodated the onset of valley fill aggradation the younger event of enhanced uplift dated to 4 ka was responsible for the incision of the older valley fill sediments and the tertiary bedrock these ages suggest that the average rate of uplift ranges from 0 3 to 1 1 mm yr during the last 9 ka implying active nature of the area

ground penetrating radar derived measurements of active layer thickness on the landscape scale with sparse calibration at toolik and happy valley alaska active layer thickness alt is an important parameter for studying surface energy balance ecosystems and hydrologic processes in cold regions we measured alt along 10 routes with lengths ranging from 0 7 to 6 9 km located on the alaska north slope near toolik lake and the happy valley airstrip between 68 475 and 69 150 n and 149 512 and 148 769 e using a ground penetrating radar gpr system in a common offset configuration we measured the two way traveltimes from the surface to the bottom of the active layer at the end of summer when the thaw depth was greatest we used 500 and 800 mhz antennas the 500 mhz antenna provided suitable vertical resolution while producing more unambiguous active layer reflections in the presence of nonideal antenna coupling and active layer inhomogeneity we derived alt measurements and their uncertainties from gpr two way traveltimes with mechanical probing for velocity calibration using an empirical relationship between the wave velocity and soil volumetric water content vwc we found that the velocities were consistent with soil vwcs ranging from 0 46 to 0 63 in 31 of traces the permafrost table horizon was identifiable resulting in alt measurements with uncertainties of generally less than 25 the average alt was 48 1 cm with a standard deviation of 16 1 cm we found distinct patterns of alt spatial variability at different sites and different length scales at some sites the alt at one point was effectively uncorrelated with alt at other points separated by lag distances as small as tens of meters for other sites there was correlation at lag distances up to approximately 400 m the alt statistics were similar to nearby long term in situ alt measurements from the circumpolar active layer monitoring network through which yearly alt measurements have been made since 1990

late cenozoic geomorphic evolution in response to inversion evidence from field and gpr studies in kim drainage basin western india abstract this study presents field and ground penetrating radar gpr data for understanding geomorphic evolution of the kim drainage basin in response to tectonic inversion of the narmada ankleshwar block of the cambay rift basin located on the western continental margin of india the narmada ankleshwar block underwent continuous sedimentation up to mio pliocene and subsequently was subjected to compressional inversion four geomorphic surfaces are recognised that formed in response to the varying degrees of tectonic activity related to phases of inversion these are the early pleistocene erosional surface epes late pleistocene depositional surface lpds early holocene erosional surface ehes and the late holocene depositional surface lhds the phases of increased tectonic activity relate to two erosional episodes while two depositional periods relate to waning tectonic activity or quiescent periods we show that the narmada ankleshwar block suffered inversion earlier than other parts of the cambay basin to the north of the nsf localisation of early inversion movements occurred in an area characterised by thinner crust and involved the development of new reverse faults and transformation of the nsf from a normal to a reverse fault gpr studies indicate the reverse nature of the various faults in the kim drainage basin and provide evidence of their late reactivation under compression the study demonstrates that the parts of a large sedimentary basin can undergo inversion at different times depending on the orientation of pre existing crustal discontinuities with respect to the controlling stress trajectories

a quantitative three dimensional depositional model of gravelly braided rivers a quantitative three dimensional depositional model of gravelly braided rivers has been developed based largely on the deposits of the sagavanirktok river in northern alaska these deposits were described using cores wireline logs trenches and ground penetrating radar profiles the origin of the deposits was inferred from observations of 1 channel and bar formation and migration and channel filling interpreted from aerial photographs 2 water flow during floods and 3 the topography and texture of the river bed at low flow stage this depositional model quantitatively represents the geometry of the different scales of strataset the spatial relationships among them and their sediment texture distribution porosity and permeability in the model are related to sediment texture the geometry of a particular type and scale of strataset is related to the geometry and migration of the bedform type e g ripples dunes bedload sheets bars associated with deposition of the strataset in particular the length to thickness ratio of stratasets is similar to the wavelength to height ratio of associated bedforms furthermore the wavelength and height of bedforms such as dunes and bars are related to channel depth and width therefore the thickness of a particular scale of strataset i e medium scale cross sets and large scale sets of inclined strata will vary with river dimensions these relationships between the dimensions of stratasets bedforms and channels mean that this depositional model can be applied to other gravelly fluvial deposits the depositional model can be used to interpret the origin of ancient gravelly fluvial deposits and to aid in the characterization of gravelly fluvial aquifers and hydrocarbon reservoirs

the role of unbalanced mesoscale circulations in dust storms 1 in this study two dust storms in northwestern nevada february 2002 and april 2004 are investigated through the use of weather research and forecasting wrf model simulations the focus of the study is twofold 1 examination of dynamic processes on the meso scale for both cases and 2 analysis of extreme upper air cooling prior to storm formation and the development of a nearly discontinuous gust front in the 2002 case that could not be validated in an earlier synoptic scale study results of the simulations suggest that the driving mechanism for dust storm dynamics derives from the breakdown and subsequent balance between the advection of geostrophic wind and total wind in the exit region of the polar jet in this process the deviation from quasi geostrophic q g balance creates a plume of ascent along and to the right of the jet s exit region the cold pool generation in the mid lower troposphere in consequence of this adjustment sets up the kinetic energy in the planetary boundary layer and creates a forward leaning slope from north to south cold front under the jet exit region surface heating is coupled with this frontal structure and rapid surface pressure falls rises occur initially later in response to diabatic adiabatic processes the adjustments occur at fast time scales scales that are radically different from those in studies that followed the q g tenets of the danielsen paradigm the results of this study indicate that meso scale features associated with subgeostrophy in the exit region of the curved jet aloft and associated thermal wind imbalance 700 500 hpa lead to significant velocity divergence aloft mass momentum adjustments and the associated cooling strengthen the baroclinic zone aloft the restoration to thermal wind balance accompanying this cooling resulted in a narrow zone of surface pressure rise and strong low level isallobaric winds the turbulent momentum for dust ablation comes from this sequence of processes

the use and application of gpr in sandy fluvial environments methodological considerations ground penetrating radar gpr is a popular technique for imaging and interpreting sedimentary architecture however current literature shows a wide range in the quality of information provided on the gpr methodology and processing technique it is therefore difficult to judge the validity of the gpr interpretations and this produces inherent difficulties for comparison between surveys this paper describes the key steps required to collect process and interpret gpr surveys in sandy fluvial sediments gpr data from the south saskatchewan river canada are used to illustrate each stage of data collection and processing particular attention is given to the appropriate set up conditions for the gpr software and hardware the selection of data processing techniques and velocity analysis methods for the interpretation of gpr reflectors are also investigated using ground truth control provided by a cut face exposure this paper presents recommendations for a systematic and rigorous methodology for the collection processing and interpretation of gpr data in sandy fluvial environments the paper suggests that all data collection parameters and processing steps should be recorded or tabulated in any gpr publication to facilitate comparisons between surveys

turbulent mixing processes in atmospheric bores and solitary waves deduced from profiling systems and numerical simulation abstract families of solitary waves solitons associated with two atmospheric bores on the same day were observed by an unprecedented number of ground based and airborne profiling systems during the international h2o project ihop in addition a very high resolution numerical weather prediction model initialized with real data was used with success to simulate one of the bores and the evolving soliton the predicted wave amplitude phase speed wavelength and structure compared well to these extraordinarily detailed observations the observations suggest that during the active phase when turbulent mixing was active which was prior to bore collapse the bores and waves vigorously mixed dry air from above a nocturnal boundary layer down to the surface refractivity computed from near surface radar observations showed pronounced decreases due to sudden drying during the passage of the bores in this phase but refractivity increases appeared during the period of bore collapse during both phases the

simulations of convectively driven density currents in the atlas region using a regional model impacts on dust emission and sensitivity to horizontal resolution and convection schemes 1 during the samum field campaign in southern morocco in may and june 2006 density currents generated by evaporative cooling after convective precipitation were frequently observed at the sahara side of the atlas mountain chain the associated strong surface cold air outflow during such events has been observed to lead to dust mobilization in the foothills here a regional model system is used to simulate a density current case on 3 june 2006 and the subsequent dust emission the model studies are performed with different parameterization schemes for convection and with different horizontal model grid resolutions to examine to which extent the model system can be used for reproducing dust emissions in this region the effect of increasing the horizontal model grid resolution from 14 km to 2 8 km on the strength on the density currents and thus on dust emission is smaller than the differences due to different convection parameterization schemes in this case study while the results in reproducing the observed density current at the atlas mountain varied with different convection parameterizations the most realistic representation of the density current is obtained at 2 8 km grid resolution at which no parameterization of deep convection is needed

sea level markers identified in ground penetrating radar data collected across a modern beach ridge system in a microtidal regime sea level rise has been related to global warming the modern system on the northern coast of anholt denmark may well be analogous to other beach ridge systems formed in microtidal regimes and our results should have impact on estimation of past sea level variation ground penetrating radar data collected across the modern 30 years old berm beach ridge and swale deposits resolve downlapping reflections interpreted to mark sea level at the time of deposition existing time series of sea level data constrain actual sea level variation nineteen readings of sea level markers made along our profile fluctuate within 0 42 and 0 57 m above present mean sea level consistent with 95 of the sea level data these fluctuations reflect tidal effects and meteorological conditions main data uncertainties are well known and the sea level markers may be identified with a high degree of confidence

estimating stone and boulder content in forest soils evaluating the potential of surface penetration methods abstract given the amount and variation of stones and boulders in forest soils it is remarkable that little attention has been paid to this property in the analysis and modelling of soil processes this study aims a to investigate the stoniness relative volume of stones and boulders of representative forest soils in central sweden b to evaluate the possibilities to predict soil stoniness with non destructive surface penetration methods particularly the rod penetration method suggested by viro in 1952 the content of stones and boulders down to 0 4 m depth in forest till were quantified in 200 systematically distributed pits the mean content of stones and boulders was 0 50 with a range of 0 14 0 78 penetration depths were useful as predictors only for cases of stoniness below 0 50 where 75 of the variation could be explained the general evaluation of surface penetration methods revealed that large errors in very stony soils cannot be avoided the major source of error is inherent in the method and not caused by sampling this conclusion may lower expectations that ground penetrating radar systems will become useful for predicting stoniness

on double rossby wave breaking in the north atlantic we discuss the dynamical features associated with double rossby wave breaking dwb concurrent cyclonic and anticyclonic breakings over the north atlantic with a focus on the north atlantic oscil

gpr and high resolution seismic integrated methods to understand the liquefaction phenomena in the mirabello village earthquake ml 5 9 2012 abstract we performed a geophysical survey in mirabello a village of emilia romagna region of northern italy to study the soil affected by the ml 5 9 earthquake of 2012 specifically the formation of surface ruptures by sand ejection due to the liquefaction of shallow subsurface layers the investigation was carried out using ground penetrating radar and seismic reflection refraction techniques this work confirms the importance of electromagnetic waves to map the shallow subsurface extent of fractures and liquefied sand bodies while the high resolution seismic reflection profile allowed us to map the fractures at depth the result obtained by tomographic inversion of first arrivals of seismic data has been compared with a ground penetrating radar section acquired in the same place furnishing complementary information for the interpretation of the section

cave detection in limestone using ground penetrating radar ground penetrating radar gpr is becoming a more common component of the standard array of geophysical techniques that are used by archaeologists in this paper we report on the use of gpr to survey an area of archaeologically important karst topography at kitley caves in devon u k we describe the use of gpr to detect voids within a limestone outcrop as an aid to locating cave systems which might contain sediments suitable for excavation the performance of the gpr equipment is analysed and the results compared to those obtained with an electrical resistance survey carried out at the same location in particular the depth of penetration of the gpr is estimated and we report discernible echo signals from a much greater depth than is usually reported in archaeological applications of gpr

the role of salt in fold and thrust belts davis d m and engelder t 1985 the role of salt in fold and thrust belts in n l carter and s uycda editors collision tectonics deformation of continental lithosphere tectonophysics 119 67 88 the style of deformation in thin skinned fold and thrust belts is critically dependent upon the resistance to sliding along the detachment between the mass of deforming sediments and the underlying rocks evaporites can provide an extremely weak horizon within which a basal detachment can form and along which only a relatively small shear traction can be supported fold and thrust belts that form atop a salt layer such as the appalachian plateau the franklin mountains in northwestern canada and the jura of the alps among others share several readily observable characteristics as predicted by a simple mechanical model for fold and thrust belts a detachment in salt permits a thrust belt to have an extremely narrow cross sectional taper in addition predicted orientations of the principal stress axes over a salt dtcollement are consistent with the commonly observed lack of a consistently dominant vergence direction of structures within the thrust belt other common attributes of salt basal thin skinned deformation include the presence of several widely but regularly spaced folds and abrupt changes in deformational style at the edge of the salt basin

significance of shallow seismic reflection ssr and ground penetrating radar gpr profiling on the modern coast line history of the bedre area egirdir lake isparta turkey abstract lake level changes and settlement places constitute the main problems in controlling the coastal environment along the egirdir lake sw turkey the quaternary geology in the bedre coast was studied based on shallow seismic reflection ssr survey ground penetrating radar gpr profiles and the data derived from boreholes and investigations in the field thus six seismic and five radar facies were determined respectively the geological units from the basement rock to the holocene deposits were imaged by the ssr technique gpr technique is used for the shallower part ranging from the ancient to the modern lacustrin sediments the quaternary lake level changes borehole seismic and radar data indicate that a pond with a connected to the lake around the bedre area existed in the last century sand barriers climate topographical elevation and erosions of the basement rocks control the sedimentation of the back barrier of the coastal line marsh muddies and ancient beach sands are the main sediments of the pond area from the profiles ancient buried sand barriers were also seen in the lake side in our view as the previous lake level dropped from the highstand the ancient sand barrier was formed which divided the lake and the pond and isolated a small inland lake which lies 4 m below the level of the coastal barrier for agricultural purposes artificial man made constructions were done on the barrier and channels thus dry agricultural land appeared in the last 50 years on the pond side

the terminology of structures in thrust belts abstract a review of structures and geometric relationships recognized in thrust belts is presented a thrust is defined as any contractional fault a corollary being that thrusts must cut up section in their transport direction flats are those portions of a thrust surface which were parallel to an arbitrary datum surface at the time of displacement and ramps are those portions of thrusts which cut across datum surfaces ramps are classified on the basis of their orientation relative to the thrust transport direction and whether they are cut offs in the hangingwall or footwall of the thrust lateral variations in the form of staircase trajectories are joined by oblique or lateral ramps which have a component of strike slip movement an array of thrusts which diverge in their transport direction may form by either of two propagation models these are termed piggy back propagation which is foreland directed and overstep propagation which is opposed to the thrust transport direction an array of thrust surfaces is termed an imbricate stack and should these surfaces anastamose upwards a duplex will result the fault bounded blocks are termed horses a duplex is bounded by a higher roof thrust and a lower floor thrust the intersection of any two thrust planes is termed a branch line thrusts can be classified on the basis of their relationship to asymmetric fold limbs which they cut a further classification arises from whether a particular thrust lies in the hangingwall or footwall of another one the movement of thrust sheets over corrugated surfaces or the local development of thrust structures beneath will fold higher thrust sheets these folds are termed culminations and their limbs are termed culmination walls accommodation of this folding may require movement on surfaces within the hangingwall of the active thrust these accommodation surfaces are termed hangingwall detachments and they need not root down into the active thrust this category of detachment includes dip slip hangingwall drop faults which are developed by differential uplift of duplex roofs and out of the syncline thrusts which develop from overtightened fold hinges back thrusts as well as forming as hangingwall detachments may also form due to layer parallel shortening above a sticking thrust or by rotation of the hangingwall above a ramp

changes in holocene relative sea level and coastal morphology a study of a raised beach ridge system on samso southwest scandinavia changes in relative sea level rsl during the holocene are reconstructed based on ground penetrating radar gpr data collected across a raised beach ridge system on the island of samso denmark the internal architecture of the beach ridge and swale deposits is divided into characteristic radar facies we identify downlap points interpreted to mark the transition from the beachface to the upper shoreface and thus sea level at the time of deposition this new data set shows that beach steps can be preserved and resolved in gpr reflection data this is important as downlap points identified at the base of the beach steps should be corrected for beach step height in order to be used as a marker of sea level identification of beach steps in combination with observed changes in dips of the interpreted beachface reflections can give information about changes in the morphodynamic conditions of beach ridge progradation through time the vertical levels of identified downlap points are combined with an age m

dating of late holocene beach shoreline positions by regional correlation of coseismic retreat events in the columbia river littoral cell usa abstract beaches and barrier spits of the columbia river littoral cell crlc 160 km in length experienced substantial progradation 0 5 2 5 km in width during the late holocene the accreted beach plains and barriers preserved evidence of episodic catastrophic retreat that was forced by coseismic subsidence the abrupt subsidence events 0 5 1 5 m submergence are associated with slip on the underlying cascadia megathrust with a mean recurrence interval of 500 yr ground penetrating radar gpr profiles taken across the barriers and beach plains show high angle beach retreat scarps 3 15 m vertical relief and foredune ridge slump scarps 5 15 m vertical relief the upper shoreface retreat features are correlated throughout the littoral cell by radiocarbon age position relative to abandoned foredune ridges and distinct sequences of large and small scarps particularly large retreat scarps 10 15 m in height are associated with the first oldest and fourth oldest prehistoric scarps a and d respectively a maximum of 10 retreat scarps in the long beach subcell date from 216 211 calrcybp to 4756 114 calrcybp the youngest seven scarps a g are correlated between all four subcells showing a regional response to the coseismic strain cycles backshore disturbance features 1 3 m vertical relief are observed in the gpr profiles but they are not identified here due to their discontinuities between adjacent profiles at 5 km longshore spacing the seven regional scarps a g are directly correlated to seven coseismic subsidence events reported to date between 0 3 and 3 2 ka the correlation of scarps to earthquake events provides high resolution proxy ages for shoreline positions in late holocene time the proxy shoreline positions are dated at 0 3 1 1 1 3 1 7 2 5 2 8 and 3 2 ka based on buried wetland sequences from adjacent tidal basins the paleoshoreline dating demonstrates that the onset of net shoreface progradation between 4 7 and 0 3 ka was delayed with increasing distance 0 100 km from the columbia river sand source the history of beach progradation reflects the sequential filling of bay and shoreface accommodation spaces located down drift of the columbia river mouth these late holocene shoreline changes portend future redistributions of existing sand within the littoral system as the limited sand reserves continue to migrate away from the columbia river mouth source

a comparison of the correlation structure in gpr images of deltaic and barrier spit depositional environments we have used geostatistical analysis of radar reflections to quantify the correlation structures found in 2 d ground penetrating radar gpr images we find that the experimental semivariogram the product of the geostatistical analysis of the gpr data is well defined and can be modeled using standard geostatistical models to obtain an estimate of the range or correlation length and the maximum correlation direction in the 2 d gpr image when we compare the results from geostatistical analysis of gpr data from selected deltaic and barrier spit depositional environments we find different correlation structures in gpr images from different depositional environments gpr images from braid deltas have near horizontal correlation directions and correlation lengths on the order of a few meters in contrast the gpr image of a fan foreset delta has a very long 24 m correlation length and a maximum correlation direction plunging 20 in the gpr images from barrier spits we find maximum correlation directio

a composite perspective on bore passages during the pecan campaign abstractatmospheric bores have been shown to have a role in the initiation and maintenance of elevated convection previous observational studies of bores have been case studies of more notable eve

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

autogenic incision and terrace formation resulting from abrupt late glacial base level fall lower chippewa river wisconsin usa abstract a paucity of research exists regarding the millennial scale response of inland alluvial streams to abrupt base level fall studies of modern systems indicate that over short time scales the response is a diffusion like process of upstream propagating incision in contrast evidence from the lower chippewa river lcr located in the upper midwest of the usa suggests that autogenic controls operating over time scales of several millennia can overwhelm diffusion resulting in incision that is prolonged and episodic during the last glacial maximum the lcr drained the chippewa lobe of the laurentide ice sheet to the glacial upper mississippi river umr as a meltwater stream it aggraded and filled its valley with glacial outwash as did its largest tributaries which were also meltwater streams its nonglacial tributaries aggraded too filling their valleys with locally derived sediment during deglaciation the umr incised at least twice abruptly lowering the lcr s base level 15 m at 16 ka or earlier and an additional 40 m at ca 13 4 ka each of these base level falls initiated incision of the lcr led by upstream migrating knickpoints the propagation of incision has however been a lengthy process the optically stimulated luminescence osl ages of terrace alluvium indicate that by 13 5 ka incision had advanced up the lcr only 15 km and by 9 ka only 55 km the process has also been episodic resulting in the formation of fill cut terraces inferred from gpr surveys and exposures of terrace alluvium that are younger and more numerous in the upstream direction autogenic increases in sediment load and autogenic bed armoring the result of periodic tributary stream rejuvenation and preferential winnowing of fines by the incising river may have periodically caused knickpoint migration and incision to slow and possibly stop allowing lateral erosion and floodplain formation to dominate a decline in sediment flux from stabilizing incised tributary stream systems would have led to renewed knickpoint migration and incision when floods of sufficient magnitude to breach the channel armor occurred minimal floodplain development along the upper section of the present day lcr along with the channel morphology of an unstable wandering gravel bed river immediately downstream from it suggest that the river is still responding to the base level falls that happened many millennia ago the autogenic controls on the lcr s response to umr incision are a direct consequence of the thick fills of noncohesive sediment that accumulated in its valley and the valleys of its tributary streams during the late wisconsinan making the lcr a prime example of a former proglacial river that remains a paraglacial fluvial system

ground penetrating radar of northern lacustrine deltas ground penetrating radar gpr was used in several selected deltaic sedimentary environments to better understand subsurface stratigraphy and reconstruct former depositional environments the profiles provide high resolution continuous subsurface data on facies thickness and depths orientation of major sedimentary structures postdepositional failure planes and depth of peat deposits field experiments were carried out on six river deltas records from four of the deltas exhibit sedimentary facies a record from one delta shows a possible slump and records from another delta reveal the thickness and stratigraphic relationships of peat deposits the delta types are i sandy wave influenced ii sandy immature wave influenced steeper middle and lower shoreface iii sandy braided and iv gravelly fan foreset in areas of limited subsurface control stratigraphic logs from drill core cutbank exposure or geophysical logs radar profiles can provide big picture perspectives of the subsurface

a climatology of rossby wave breaking along the subtropical tropopause ten years 1986 95 of global analyses from the european centre for medium range weather forecasts are used to investigate the temporal and spatial distributions of rossby wave breaking rwb at 350 k along the tropopause herein defined by the 61 5 potential vorticity pv unit 10 26 km 2 s21 kg21 contours though many studies acknowledge rwb as an important contributor to the complex of mixing processes in the atmosphere there exists no prior climatological study of its distribution near the tropopause as in previous studies rwb is identified in the global analyses by southward directed pv gradients at 350 k rwb along the tropopause occurs preferentially during summer over the midoceans in relative proximity to the planetary scale high pressure systems in the subtropics isentropic trajectories at 350 k show that outflow from the tops of these subtropical highs directly participates in rwb over the adjacent downstream oceanic regions two regions are highlighted in this study the north pacific during boreal summer and the south atlantic during austral summer synoptic maps of breaking rossby waves in these regions are provided to reveal the acute tropopause folding in the meridional plane which characteristically accompanies rwb the rich interaction between the tropical flow and the extratropical westerly current exhibited by these cases suggests that the subtropical highs serve as important agents in the coupling between the tropical troposphere and the extratropical stratosphere as expected from theoretical considerations the locations where rwb occurs most frequently known as surf zones are shown to coexist with regionally weak time mean wind speeds and horizontal gradients of pv at 350 k

towards a morphogenetic classification of eskers implications for modelling ice sheet hydrology abstract validations of paleo ice sheet hydrological models have used esker spacing as a proxy for ice tunnel density changes in crest type cross sectional shape along esker ridges have typically been attributed to the effect of changing subglacial topography on hydro and ice dynamics and hence subglacial ice tunnel shape these claims assume that all eskers formed in subglacial ice tunnels and that all major subglacial ice tunnels produced a remnant esker we identify differences in geomorphic context sinuosity cross sectional shape and sedimentary architecture by analysing eskers formed at or near the margins of the last cordilleran ice sheet on british columbia s southern fraser plateau and propose a morphogenetic esker classification three morphogenetic types and 2 subtypes of eskers are classified based on differences in geomorphic context ridge length sinuosity cross sectional shape and sedimentary architecture using geophysical techniques and sedimentary exposures they largely record seasonal meltwater flows and glacial lake outburst floods glofs through sub en and supraglacial meltwater channels and ice walled canyons general principles extracted from these interpretations are 1 esker ridge crest type and sinuosity strongly reflect meltwater channel type eskers formed in subglacial conduits are likely to be round crested with low sinuosity except where controlled by ice structure or modified by surging and contain faults associated with flank collapse eskers formed near or at the ice surface are more likely to be sharp crested highly sinuous and contain numerous faults both under ridge crest lines and in areas of flank collapse 2 esker ridges containing numerous flat crested reaches formed directly on the land surface in ice walled canyons unroofed ice tunnels or in ice tunnels at atmospheric pressure and therefore likely record thin or dead ice 3 eskers containing macroforms exhibiting headward and downflow growth likely record flood scale flows possibly glofs where a lake can be inferred these conclusions suggest that esker crest type sinuosity and geomorphic context when understood along with sedimentary architecture largely reflect formational position with respect to the ice surface reconstructions of ice sheet hydrology need to account for variation in esker morphology because basing hydrodynamic inferences on the presence or absence of an esker alone ignores encoded differences in water source supply flow magnitude and frequency and conduit position

ground penetrating radar tomography for soil moisture heterogeneity many ground penetrating radar gpr studies incorporate tomographic methods that use straight raypaths for direct model reconstruction which is unrealistic for media with gradually changing petrophysics ray bending algorithms can sometimes lead to unreliable resolution especially at interfaces of abrupt dielectric changes we present an improved gpr tomography technique based on a combination of seismic tomographic methods and a finite difference solution of the eikonal equation our inversion algorithm uses velocity gradient zones and bending rays that represent realistic geology in the subsurface we tested the technique on theoretical and experimental models with anomalous bodies of varying saturations and velocity and applied it to data from a gpr field experiment that analyzed the root zones of trees synthetic results showed that the resolution of our technique is better than that of published methods especially for local anomalies with sharp velocity contacts our laboratory experiments consisted of four objects buried in sand with various water saturations the gpr tomogram could map the objects and determine their degree of saturation the velocities are compatible with those of the complex refraction index method their relationship to the water content fits a previously published empirical equation our original field experiment around a poplar tree could map the heterogeneous subsurface and distinguish a central low velocity beneath the tree from the peripheral negative anomaly of a refill this zone reflects the whole root zone and is caused by its bulk water content of both the organic root network and its surrounding soils

radar facies of paraglacial barrier systems coastal new england usa analysis of a large data base of ground penetrating radar gpr profiles from both natural and developed paraglacial barriers along the coast of new england has allowed identification of eight reflection configurations that characterize this type of mid to high latitude coastal environment bedrock anchor points yield primarily hyperbolic configurations whereas glacial anchor points and sediment source areas are characterized by chaotic parallel and tangential oblique configurations beaches and dunes produce predominantly sigmoidal oblique hummocky reflection free and bounding surface configurations back barrier sediments may yield basin fill configurations but generally include abundant signal attenuating units the gpr data calibrated with information from cores were collected across swash aligned and drift aligned barriers in a variety of wave and tidal energy settings application of a 120 mhz antenna as used in this study enables portrayal of a range of sedimentary units from individual bedforms on single records to entire barrier elements using large numbers of intersecting gpr sections at maximum vertical resolutions that vary between 0 2 m and 0 7 m the most important drawback of gpr in the coastal environment is attenuation of the electromagnetic em signal by layers of salt marsh peat or by brackish or salty groundwater primarily along barrier edges this disadvantage is offset by many benefits data can be collected at rates of several km per day making gpr an excellent reconnaissance tool a core that is used in the calibration of gpr data can be matched with great accuracy to its position on the complementary gpr record allowing detailed correlation between lithostratigraphy and reflection configuration

slave river delta geomorphology sedimentology and holocene reconstruction the holocene slave river delta 8300 km2 is a long 170 km narrow 42 km average width alluvial sand body which extends north from the slave river rapids at fort smith to great slave lake northwest territories the delta is flanked by the talston and tethul rivers and canadian shield to the east and by the little buffalo river to the west wave associated sedimentary structures in lithostratigraphic logs from river cutbanks indicate that the sandy delta was wave influenced most of the logs 34 consist of three facies basal laminated mud unknown thickness interbedded mud and sand 2 5 m and planar tabular ripple sets interbedded with cross laminated to flat bedded sand 3 0 14 5 m eleven radiocarbon dated wood samples from river cutbanks were used to reconstruct the delta paleoshoreface and to calculate the rate of progradation which averaged 20 7 m year from 8070 bp to the present in the same period isostatic rebound of the delta region relative to the liard river delta averaged 12 cm km

challenges in geophysical mapping of glaciotectonic structures abstractglaciotectonic complexes have been recognized worldwide traditionally described on the basis of outcrops or geomorphological observations in the past few decades geophysics has become an integral part of geologic mapping which enables the mapping of buried glaciotectonic complexes the geophysical methods provide different types of information and degrees of resolution and thus a different ability to resolve the glaciotectonic structures we evaluated these abilities on the basis of an integrated application of four commonly used geophysical methods airborne transient electromagnetics high resolution reflection seismic geoelectrical and ground penetrating radar gpr we covered an area of 100 km2 in a formerly glaciated region in the western part of denmark the geologic setting was highly heterogeneous with glaciotectonic deformation observed in the form of large scale structures in the seismic and airborne transient electromagnetic data to small scale structures seen in the gpr and g

ground penetrating radar investigations at marj rabba a chalcolithic site in the lower galilee of israel the chalcolithic site of marj rabba in the lower galilee of israel features shallow limestone structures situated in a terra rossa matrix calcareous substrates such as terra rossa common throughout the region are often not considered amenable to ground penetrating radar gpr studies due to strong attenuation particularly within the relatively high frequency range most often used in archaeological gpr surveys energy loss due to scattering from small embedded stones also exacerbates attenuation at this particular site in addition to obscuring detected archaeological features thereby complicating interpretation because features are fairly shallow upper 1 5 m and contrast well with the soil however gpr was successful in spite of poor substrate quality the selection of a somewhat lower antenna frequency 250 mhz than is often recommended for archaeology played a role in the success of the work the end result expands the known spatial extent of the site by five fold increasing our knowledge of architectural and village plans for a time period which is poorly understood in this region the settlement scale and complexity shown by these new results indicates that chalcolithic villages are not only present in the galilee but are as extensive and architecturally sophisticated as contemporaneous settlements in other regions in combination with excavation results the structures detected with gpr at marj rabba provide the largest plan of an early chalcolithic settlement in the galilee

the influence of the rocky mountains on the 13 14 april 1986 severe weather outbreak part ii evolution of a prefrontal bore and its role in triggering a squall line abstract in this paper part ii of a series the evolution of a prefrontal bore on the leeside of the rockies and its subsequent propagation and initiation of convection farther downstream over eastern colorado and western nebraska are investigated the observational evidence for this sequence of events was obtained from combined analyses of high resolution goes satellite imagery and program for regional observing and forecasting services mesonetwork data over the colorado region for the severe weather event that occurred during 13 14 april 1986 a 2d nonhydrostatic numerical model is used to further understand the initiation of the bore and its ability to propagate farther downstream and trigger convection analysis of satellite imagery and mesonet data indicated that an internal bore ahead of a cold front a moderate downslope windstorm and a quasi stationary hydraulic jump were generated within a few hours along the iceslope as a pacific cold front and its attendant upper level jet streak advanced o

new temple discovery at the archaeological site of nysa western turkey using gpr method abstract we carried out a ground penetrating radar gpr study at specific sites around the nysa city western turkey to assess the potential of detection method and imaging of buried archaeological features as a major educational and cultural aegean city during the hellenistic and roman times nysa has been the focus of archaeological investigations for the last 100 yrs past and ongoing excavations have revealed major ancient buildings such as theatres amphitheatres a library and shops however it is suspected that the original city may have extended further and reached a larger size we collected 22 profiles using a gpr system equipped with two shielded antennas of 250 and 500 mhz central frequencies after processing steps gpr results revealed the existence of buried walls located at 50 m west of the library they systematically display a characteristic signature hyperbolic shaped point source reflections in gpr profiles and may be described in terms of location geometry and dimension to a certain extent of construction style excavations made after our study confirmed our results and unearthed a previously unknown temple hence shallow geophysical investigations helped in gathering crucial archaeological information to better characterize the extent and richness of the city of nysa

influence of grain size shape and compaction on georadar waves examples of aeolian dunes summary many ground penetrating radar gpr profiles acquired in dry aeolian environment have shown good reflectivity inside present day dunes we show that the origin of this reflectivity is related to changes in grain size distribution packing and or grain shape in a sandy material we integrate these three parameters into analytical models for bulk permittivity in order to predict the reflections and the velocity of gpr waves we consider two gpr cross sections acquired over aeolian dunes in the chadian desert the 2d migration of gpr data suggests that dunes contain different kinds of bounding surfaces we discuss and model three kinds of reflections using reasonable geological hypothesis about aeolian sedimentation processes the propagation and the reflection of radar waves are calculated using the 1d wavelet modelling method in spectral domain the results of the forward modelling are in good accordance with real observed data

the life cycle of an undular bore and its interaction with a shallow intense cold front abstract the evolution of an undular bore and its associated wind shift spawned by the passage of a shallow surface cold front over the southern great plains of the united states is examined using surface and remote sensing observations along with output from a high resolution numerical model simulation observations show that a separation between the wind shift and thermodynamic properties of the front was induced by the formation of a bore over south central kansas around 0200 utc 29 november 2006 by the time the front bore complex passed through lamont oklahoma approximately 4 h later the bore had reached its maximum intensity and its associated wind shift preceded the trailing baroclinic zone by 20 min within several hours the bore decayed and a cold frontal passage characterized by a wind shift coincident with thermodynamic properties was observed at okmulgee oklahoma thus a substantial transformation in both the structural and dynamical characteristics of the bore as well as its relations

the potential role of atmospheric bores and gravity waves in the initiation and maintenance of nocturnal convection over the southern great plains abstractthis investigation explores the relationship among bores gravity waves and convection within the nocturnal environment through the utilization of measurements taken during the internation

fluvial geomorphology and neotectonic activity based on field and gpr data katrol hill range kachchh western india abstract the largely rocky and rugged landscape of the katrol hill range composed of mesozoic rocks and structurally controlled occurrences of quaternary sediments is delimited to the north by north facing range front scarps of the seismically active e w trending katrol hill fault khf the landscape and drainage characteristics of the katrol hill range are documented together with ground penetrating radar gpr investigations along the khf to delineate its nature for understanding neotectonic activity in the contemporary tectonic setting the overall geomorphology is controlled by the south oriented tilt block structure of the range indicated by its pronounced influence on the morphology and drainage network the drainage comprises north flowing and south flowing rivers with the drainage divide located close to the northern edge of the range which also marks the highest topographic elevations the narrow zone between the crest line and the drainage divide has been identified as the zone of gorges where gorges and deeply incised fluvial valleys have been formed within quaternary sediments by the various north flowing streams the quaternary sediments consist of bouldery colluvial deposits in front of the range front scarps valley fill miliolites and alluvial deposits of late pleistocene age within the back valleys and scarp derived colluvium forming the youngest deposit based on the geomorphic and stratigraphic evidence three major phases of quaternary tectonic uplift in the katrol hill range are inferred the oldest pre miliolite phase middle pleistocene was followed by a prominent phase of fluvial incision with formation of gorges during early holocene and then by the last one during late holocene continuing at present uplift of the range occurred in well marked phases during the quaternary in response to differential uplift along the khf under an overall compressive stress regime gpr investigations at selected sites show that the khf is a steep south dipping reverse fault near the surface which becomes vertical at depth this suggests neotectonic reactivation of the khf under a compressive stress regime responsible for active southward tilting of the katrol hill range

radiometer and profiler analysis of the effects of a bore and a solitary wave on the stability of the nocturnal boundary layer abstract this study uses data from a microwave profiling radiometer mpr along with 915 mhz wind profiler doppler radar and surface data to quantify the kinematic and thermodynamic effects of two wave features an undular bore and a soliton on the nocturnal boundary layer nbl at high temporal resolution both wave features passed directly over the mpr and the wind profiler allowing for detailed analyses the effects of the wave features on the convective environment are examined and convective initiation ci associated with the wave features is discussed the undular bore was illustrated well in doppler velocity data and profiler measurements indicated that it produced four wavelengths of upward and downward motion mpr derived time height sections of potential temperature and mixing ratio showed an increase in the depth of the stable boundary layer along with a decrease in stability partially associated with mixing of the nbl the soliton produced a temporary decrease in the depth of the nbl

atmospheric dynamics of a saharan dust outbreak over mindelo cape verde islands preceded by rossby wave breaking multiscale observational analyses and simulations

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

the harmattan over west africa nocturnal structure and frontogenesis this article presents observations and model simulations of the low level nocturnal structure of the atmosphere over west africa the measurements are taken from the dry season special observing period sop 0 of the african monsoon multidisciplinary analysis amma at niamey niger on 23 and 24 january 2006 during this time mesoscale structures in the atmospheric aerosol loadings were observed the available observations indicate that these mesoscale features at niamey are consistent with the passage of gravity currents or bores in the northerly harmattan winds model simulations at resolutions down to 1 km indicate that the mesoscale structures are caused by nocturnal frontogenesis in the baroclinic zone to the south of the sahara in the winter months this frontogenesis is a continental scale phenomenon which has significant implications for the uplift and transport of dust and biomass burning aerosols in the region an accompanying frontogenetic feature appears further south in the model simulations associated with the winter intertropical front the frontogenesis is possibly linked with the development of structures showing characteristics of canonical mesoscale phenomena including internal bores and gravity currents representation of these features in the uk met office unified model at different resolutions from 12 km to 1 km is discussed

ground penetrating radar for high resolution mapping of soil and rock stratigraphy ground penetrating radar is a technique which offers a new way of viewing shallow soil and rock conditions the need to better understanding overburden conditions for activities such as geochemical sampling geotechnical investigations and placer exploration as well as the factors controlling groundwater flow has generated an increasing demand for techniques which can image the subsurface with higher resolution than previously possible the areas of application for ground penetrating radar are diverse the method has been used successfully to map ice thickness water depth in lakes bedrock depth soil stratigraphy and water table depth it is also used to delineate rock fabric detect voids and identify karst features the effective application of the radar for the high resolution definition of soil stratigraphy and fractures in bedrock is highlighted the basic principles and practices involved in acquiring high quality radar data in the field are illustrated by selected case histories one example demonstrates how radar has been used to map the bedrock and delineate soil horizons to a depth of more than 20 m two case histories show how radar has been used to map fractures and changes of rock type to 40 m range from inside a mine another case history demonstrates how radar has also been used to detect and map the extent of groundwater contamination the corroboration of the radar results by borehole investigations demonstrates the power and utility of the high resolution radar method as an aid for interpolation and extrapolation of the information obtained with conventional coring programmes with the advent of new instrumentation and field procedures the routine application of the radar method is becoming economically viable and the method will see expanded use in the future

a nonclassical cold front observed during cops 91 frontal structure and the process of severe storm initiation abstract this case study addresses the issue of gravity current and bore development at surface cold fronts and the role of these phenomena in the generation of severe frontal convection the event investigated occurred on 27 april 1991 during the cooperative oklahoma profiler studies 1991 field project the development of a bore from a gravity current like structure along a cold front the subsequent propagation of the bore ahead of the front on a low level inversion and the process of severe thunderstorm development along the front are revealed by a dense network of remote sensing and other special observations evidence for the gravity current and bore is strengthened by comparisons made between the synthesized observations and theory the bore developed after a nocturnal inversion which acted as a waveguide had become established the bore and gravity current were both evident as fine lines in the radar reflectivity displays a microscale envelope of enhanced water vapor with an embedded roll cl

out of sequence thrusts out of sequence thrusts oost are those thrusts which do not obey the foreland propagating or in sequence deformation style they include both isolated thrusts which develop hindward of the thrust front and sequences of break back thrusts which propagate from the foreland to the hinterland two end members of a series of oost types are recognized 1 older in sequence thrusts which are reactivated along their entire length and 2 completely new thrusts which propagate through already deformed thrust sheets between the two end members are thrusts composed partially of reactivated in sequence thrust sequences and partially of new entirely out of sequence segments oosts can be initiated for a variety of reasons including 1 keeping the orogenic wedge at critical taper 2 break back sequences from the suture zone in the overriding plate 3 ramping to overcome a sticking point which inhibits in sequence thrust propagation and 4 during simultaneous displacement along two stacked thrusts culminations which bow up segment of the upper thrust may be chopped through to permit continued displacement on the upper thrust many different types of thrust behavior including gravity sliding plucking and derivation of isolated horses from ramps may mimic some of the characteristics of oosts consequently it may be difficult to conclusively prove an oost origin for a complex thrust geometry

gpr measurements to assess the emeelt active fault s characteristics in a highly smooth topographic context mongolia to estimate the seismic hazard the geometry dip length and orientation and the dynamics type of displacements and amplitude of the faults in the area of interest need to be understood in this paper in addition to geomorphologic observations we present the results of two ground penetrating radar gpr campaigns conducted in 2010 and 2011 along the emeelt fault in the vicinity of ulaanbaatar capital of mongolia located in an intracontinental region with low deformation rate that induces long recurrence time between large earthquakes as the geomorphology induced by the fault activity has been highly smoothed by erosion processes since the last event the fault location and geometry is difficult to determine precisely however by using gpr first a non destructive and fast investigation the fault and the sedimentary deposits near the surface can be characterized and the results can be used for the choice of trench location gpr was performed with a 50 mhz antenna over 2 d lines and with a 500 mhz antenna for pseudo 3 d surveys the 500 mhz gpr profiles show a good consistency with the trench observations dug next to the pseudo 3 d surveys the 3 d 500 mhz gpr imaging of a palaeochannel crossed by the fault allowed us to estimate its lateral displacement to be about 2 m this is consistent with a right lateral strike slip displacement induced by an earthquake around magnitude 7 or several around magnitude 6 the 2 d 50 mhz profiles recorded perpendicular to the fault show a strong reflection dipping to the ne which corresponds to the fault plane those profiles provided complementary information on the fault such as its location at shallow depth its dip angle from 23 to 35 and define its lateral extension central asia is known for its high level of seismic hazards especially mongolia which has been one of the most seismically active intracontinental regions in the world with four large earthquakes magnitude around 8 along its active faults in the western part of the country during the last century khilko et al 1985 the deformation in mongolia is located between compressive structures related to the collision and penetration of the indian plate into the eurasian plate and extensive structures in the north of the country related with the baykal rift tapponnier molnar 1979 baljinnyam et al 1993 schlupp 1996 bayasgalan jackson 1999 the seismic activity observed in the vicinity of ulaanbaatar ub capital of mongolia is relatively low compared to the activity observed in western mongolia nevertheless since 2005 the seismic activity around ub not only has increased but is also organized see fig 1 at the west of ub along two perpendicular directions which determine two active faults emeelt fault discovered in 2008 nnw sse direction 25 km long minimum and situated about 10 km w of ub and hustai fault wsw ene direction 80 km long with its ne tip at less than 20 km west of ub their length and morphology indicate that they can produce earthquakes of magnitude 6 5 7 5 schlupp et al 2012 most of the mongolian population 1 2 million over 3 million is concentrated at ub which is the main political and economical centre of the country hence the study of seismic hazard and the estimation of the probability of future destructive earthquakes are of primary importance for the country dugarmaa et al 2006 since the last large earthquake the faults geomorphology has been highly smoothed by erosional processes and the exact location of the fault plane surface rupture is thus hidden within a several metre wide strip the gpr method has been proven to give good and useful results to characterize faults by identifying offsets of radar reflections malik et al 2007 christie et al 2009 yalciner et al 2013 and

stratal extension in thrust footwalls makran accretionary prism implications for thrust tectonics small scale stratal extension is commonly associated with thrust faults in the makran accretionary prism of southwest pakistan low angle normal faults dipping in the direction of transport relative to the thrust are common in gouge zones and duplexes and may also cut the footwall and hanging wall where they cause stratal extension these faults are probably riedel shears we have studied a broad zone of more complex extensional deformation beneath one bedding parallel thrust the zone disrupts earlier compressional structures and affects a significant volume of the footwall normal faults initiating in a rearward sequence branch off the thrust and cut down into the footwall merging at a lower stratigraphic level part of the thrust displacement was thereby transfe red to that level and fragments of the footwall were detached and transferred southward beneath the hanging wall the latter remained undeformed and accommodation structures are confined to the footwall these effects may have been caused by variations in sliding resistance along the fault if a thrust transfers part or all of its displacement down section along normal faults in this way before eventually cutting back up toward the surface it will detach a rootless fragment of footwall rocks from a position forward of the initial ramp through that horizon this process can be referred to as footwall plucking it can explain rootless basement slices along thrusts for example and it has important implications for section restoration techniques and the interpretation of thrust belts

high resolution subsurface gpr imaging and sedimentology of coastal ponds maine u s a implications for holocene back barrier evolution ground penetrating radar gpr transects and sediment cores have been used to examine the basement morphology stratig raphy and environmental history of maritime ponds along the pen insular coast of maine silver lake lily pond and north pond are shallow 3 m water bodies bordered by steep bedrock ridges in the north east and west and sandy barriers to the south the bedrock basins of the ponds are formed in metasedimentary rocks surrounded by resistant pegmatitic intrusions a dense network of gpr traverses obtained over the ice covered silver lake reveals a series of prominent wavy parallel and basin fill reflector geometries terminating against the bedrock or grading into the barrier sediments and interpreted as organic lake bottom facies the transparent units represent sand rich horizons mostly eolian in origin convex up structures found both on the surface and within the basin fill sequence are interpreted as pre served parts of coastal dunes the present study indicates that fresh water conditions prevailed since at least 4 6 ka with an initial sedi mentation rate of 1 7 mm yr the position of this unit below the con temporary sea level suggests presence of a welded barrier by that time radar profiles taken along the shores of lily pond a small water body behind the sand dune barrier indicate a significantly larger areal extent of the pond in the past a succession of organic deposits over lying a pleistocene glaciomarine unit indicates progressive inundation of the paleo lagoon by rising sea level saltwater peat seaward of lily pond was buried by washover sands about 1 2 ka and a narrow pond existed here prior to dredging and artificial infilling of its eastern part in the 1950s 60s the organic and eolian units are absent in the north pond where sedimentary fill consists of glaciomarine clay overlain by marine sands a proposed three stage model of pond evolution along an embayed coastline consists of 1 organic accumulation in an up land depression during lower sea level 2 predominantly washover or tidal deposition in a lagoon stage 2a or blocked coastal pond stage 2b during initial transgression and 3 mainly eolian and organic de position behind a prograded or aggraded barrier future accelerated rise in relative sea level and inadequate sediment supply will cause many back barrier ponds to reenter stage 2 of the proposed model

internal architecture of a raised beach ridge system anholt denmark resolved by ground penetrating radar investigations abstract the internal architecture of raised beach ridge and associated swale deposits on anholt records an ancient sea level the holocene beach ridges form part of a progradational beach ridge plain which has been interpreted to have formed during an isostatic uplift and a relative fall in the sea level over the past 7700 years the ridges are covered by pebbles and cobbles and commonly show evidence of deflation material presumably removed from the beach ridges and adjacent swales form the present dune forms on anholt ground penetrating radar gpr reflection lines have been collected with 250 mhz shielded antennae across the fossil ridge and swale structures the signals penetrate the subsurface to a maximum depth of 10 m below the fossil features the gpr data resolve the internal architecture of the beach ridges and swales with a vertical resolution of about 0 1 m gpr mapping indicates that the holocene beach ridges are composed of seaward dipping beachface deposits as well as minor amounts of inland dipping deposits of wash over origin the beachface deposits downlap on underlying shoreface deposits and we use these surfaces as markers of a relative palaeo sea level the new data indicate that the highest relative sea level at about 8 5 m was reached 6500 years ago 700 years later the relative sea level had dropped 0 7 m indicating a change in the relative sea level around 1 mm year this fall in the relative sea level most likely records the influence of an isostatic rebound causing younger beach ridge deposits to indicate lower sea levels

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

numerical study of convection observed during the winter monsoon experiment using a mesoscale two dimensional model abstract a two dimensional version of the pennsylvania state university mesoscale model has been applied to winter monsoon experiment data in order to simulate the diurnally occurring convection observed over the south china sea the domain includes a representation of part of borneo as well as the sea so that the model can simulate the initiation of convection also included in the model are parameterizations of mesoscale ice phase and moisture processes and longwave and shortwave radiation with a diurnal cycle this allows use of the model to test the relative importance of various heating mechanisms to the stratiform cloud deck which typically occupies several hundred kilometers of the domain frank and cohen s cumulus parameterization scheme is employed to represent vital unresolved vertical transports in the convective area the major conclusions are ice phase processes are important in determining the level of maximum large scale heating and vertical motion because there is a strong anvil componen

the formation of a large summertime saharan dust plume convective and synoptic scale analysis haboobs are dust storms produced by the spreading of evaporatively cooled air from thunderstorms over dusty surfaces and are a major dust uplift process in the sahara in this study observations reanalysis and a high resolution simulation using the weather research and forecasting model are used to analyze the multiscale dynamics which produced a long lived over 2 days saharan mesoscale convective system mcs and an unusually large haboob in june 2010 an upper level trough and wave on the subtropical jet 5 days prior to mcs initiation produce a precipitating tropical cloud plume associated with a disruption of the saharan heat low and moistening of the central sahara the restrengthening saharan heat low and a mediterranean cold surge produce a convergent region over the hoggar and air mountains where small convective systems help further increase boundary layer moisture emerging from this region the mcs has intermittent triggering of new cells but later favorable deep layer shear produces a mesoscale convective complex the unusually large size of the resulting dust plume over 1000 km long is linked to the longevity and vigor of the mcs an enhanced pressure gradient due to lee cyclogenesis near the atlas mountains and shallow precipitating clouds along the northern edge of the cold pool dust uplift processes identified are 1 strong winds near the cold pool front 2 enhanced nocturnal low level jet within the aged cold pool and 3 a bore formed by the cold pool front on the nocturnal boundary layer

mesoscale ascent in nocturnal low level jets abstracta theory for gentle but persistent mesoscale ascent in the lower troposphere is developed in which the vertical motion arises as an inertia gravity wave response to the sudden decrease of t

ground penetrating radar 2 d and 3 d subsurface imaging of a coastal barrier spit long beach wa usa abstract the ability to effectively interpret and reconstruct geomorphic environments has been significantly aided by the subsurface imaging capabilities of ground penetrating radar gpr the gpr method which is based on the propagation and reflection of pulsed high frequency electromagnetic energy provides high resolution cm to m scale and shallow subsurface 0 60 m near continuous profiles of many coarser grained deposits sediments of low electrical conductivity this paper presents 2 d and 3 d gpr results from an experiment on a regressive modern barrier spit at willapa bay wa usa the medium grained sand spit is 38 km long up to 2 3 5 km wide and is influenced by a 3 7 m tidal range spring as well as high energy longshore transport and high wave energy depositional processes the spit has a freshwater aquifer recharged by rainfall the gpr acquisition system used for the test was a portable digital pulseekko system with antennae frequency ranging from 25 to 200 mhz and transmitter voltages ranging from 400 to 1000 v step sizes and antennae separation varied depending on the test requirements in addition 100 mhz antennae were used for conducting antennae orientation tests and collecting a detailed grid of data 50 50 m sampled every meter the 2 d digital profiles were processed and plotted using pulseekko software the 3 d datasets after initial processing were entered into a landmark workstation that allowed for unique 3 d perspectives of the subsurface to provide depth near surface velocity measurements were calculated from common midpoint cmp surveys results from the present study demonstrate higher resolution from the 200 mhz antennae for the top 5 6 m whereas the 25 and 50 mhz antennae show deeper penetration to 10 m for the study site 100 mhz antennae provided acceptable resolution continuity of reflections and penetration the dip profiles show a shingle like accretionary depositional pattern whereas strike profiles show a horizontal and subhorizontal nearly continuous reflection pattern results from the gpr experiment reveal upper shoreface reflections with dip towards the ocean at about 1 2 the loss of signal from below a depth of 6 8 m indicates a lithofacies change because of the storm wave base the parallel broadside and perpendicular broadside antennae orientation tests show detailed stratigraphy continuity and depth of penetration the cross polarization test exhibits reduced continuity of reflections and less depth of penetration but dipping reflections are apparent the grid pattern data provided a detailed view of 3 d geometry of individual reflections high quality data were obtained processed and directly exported into a landmark workstation for interpretation the resulting interpretations of the upper shoreface beds from the test cube 50 50 m total 2600 traces are shown as vertical sections slices horizontal sections time slices contour maps 3 d representations of individual beds and an isopach map the 3 d depositional framework allows a more detailed interpretation than widely spaced 2 d profiles

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

passive roof duplex geometry in the frontal structures of the kirthar and sulaiman mountain belts pakistan abstract exploration for hydrocarbons over the past few years has greatly improved our understanding of the geometry of frontal mountain belt structures in this study we introduce and discuss the concept of the passive roof duplex using as the main example the kirthar and sulaiman ranges in the baluchistan province of pakistan structures similar to those described here have been recognized previously in other mountain belts and they appear to exist as a common feature in many more frontal regions of mountain belts our example of a passive roof duplex which we describe from pakistan is compared briefly with similar structures reported by others the passive roof duplex is here defined as a duplex whose roof thrust has backthrust sense passive roof thrust and whose roof sequence those rocks lying above the roof thrust remains relatively stationary during foreland directed piggy back style propagation of horses within the duplex