Short Spatial Wavelengths Research Articles

Zircon (U-Th)/He thermochronology reveals pre-Great Unconformity paleotopography in the Grand Canyon region, USA

Abstract The Great Unconformity is an iconic geologic feature that coincides with an enigmatic period of Earth's history that spans the assembly and breakup of the supercontinent Rodinia and the Snowball Earth glaciations. We use zircon (U-Th)/He thermochronology (ZHe) to explore the erosion history below the Great Unconformity at its classic Grand Canyon locality in Arizona, United States. ZHe dates are as old as 809 ± 25 Ma with data patterns that differ across both long (∼100 km) and short (tens of kilometers) spatial wavelengths. The spatially variable thermal histories implied by these data are best explained by Proterozoic syn-depositional normal faulting that induced differences in exhumation and burial across the region. The data, geologic relationships, and thermal history models suggest Neoproterozoic rock exhumation and the presence of a basement paleo high at the present-day Lower Granite Gorge synchronous with Grand Canyon Supergroup deposition at the present-day Upper Granite Gorge. The paleo high created a topographic barrier that may have limited deposition to restricted marine or nonmarine conditions. This paleotopographic evolution reflects protracted, multiphase tectonic activity during Rodinia assembly and breakup that induced multiple events that formed unconformities over hundreds of millions of years, all with claim to the title of a “Great Unconformity.”

Detecting differential ground displacements of civil structures in fast-subsiding metropolises with interferometric SAR and band-pass filtering

Ground displacements due to changes in soil conditions represent a threat to the stability of civil structures in many urban areas, worldwide. In fast-subsiding areas, regional subsidence (wavelength ~ 1,000’s m) can be dominantly high and, consequently, mask other signals at local scales (wavelength ~ 10–100’s m). Still, engineering and construction applications require a comprehensive knowledge of local-scale signals, which can threaten the stability of buildings and infrastructure. Here we present a new technique based on band-pass filters for uncovering local-scale signals hidden by regional subsidence as detected by interferometric SAR measurements. We apply our technique to a velocity field calculated from 21 high-resolution COSMO-SkyMed scenes acquired over Mexico City and obtain components of long (> 478 m), intermediate (42–478 m) and short (< 42 m) spatial wavelengths. Our results reveal that long-wavelength velocities exceed − 400 mm/year, whereas intermediate- and short-wavelength velocities are in the order of ± 15 mm/year. We show that intermediate-wavelength velocities are useful for retrieving signals such as uplift along elevated viaducts of Metro lines 4 and B, as well as differential displacements in Pantitlán station’s pedestrian overpass system and across sharp geotechnical boundaries in the piedmont of Sierra de Santa Catarina—where surface faulting occurs.

Comparison of lidar- and allometry-derived canopy height models in an eastern deciduous forest

Abstract Tree crown geometry and height, especially when coupled with remotely sensed data, can aid in the characterization of tree and forest structure. In this study, we develop mixed-effects model allometric equations for tree height, crown radius, and crown depth using data collected on 374 trees across 14 species within the extent of the joint Center for Tropical Forest Science (CTFS) and Smithsonian Institute’s Forest Global Earth Observatory (ForestGEO) MegaPlot on Prospect Hill at Harvard Forest, Massachusetts. We applied allometry to a census of the 35-ha plot on Prospect Hill to evaluate tree height and crown radius estimates using a lidar canopy height model. We found significant relationships using stem diameter-at-breast-height (DBH) and species to estimate tree height (ρr2 = 0.70, RMSE = 2.96 m), crown depth (ρr2 = 0.35, RMSE = 3.24 m) and crown radius (ρr2 = 0.43, RMSE = 1.22 m). Using Fast Fourier Transforms (FFTs), we compared the power spectra of a lidar canopy height model to five synthetic canopy height models derived from allometric estimates of height and crown radius. The FFTs showed good agreement between lidar and synthetic canopy height models (CHMs) at spatial wavelengths longer than 64 m, or about the distance across 3–4 dominant tree crowns, and poorer agreement at shorter spatial wavelengths, which we attribute to the simple crown shape applied to modeled crowns and a lack of crown overlap in the synthetic CHMs compared to the lidar CHM. At the tree level, some species exhibited tight links between lidar-measured height and estimated tree height (e.g., Quercus rubra, Quercus velutina, Pinus strobus), suggesting height allometry provided reasonable estimates of tree height for some species despite a negative bias in the synthetic canopy height models relative to the lidar canopy height model.

Volcanic deformation of Atosanupuri volcanic complex in the Kussharo caldera, Japan, from 1993 to 2016 revealed by JERS-1, ALOS, and ALOS-2 radar interferometry

A series of uplifts and subsidences of a volcanic complex in the Kussharo caldera in eastern Hokkaido (Japan) has been revealed by interferometric analysis using archived satellite synthetic aperture radar data. A time series of interferograms from 1993 to 1998 showed the temporal evolution of a ground deformation process. The horizontal dimension of the deformation field was about 10 km in diameter, and the maximum amplitude of the deformation was >20 cm. Uplift started in 1994, and concurrent earthquake swarm activity was observed around the uplift area; however, no other phenomena were observed during this period. A subsidence process then followed, with the shape of the deformation forming a mirror image of the uplift. Model simulations suggest deformation was caused by a source at the depth of about 6 km and that the position of the source remained static throughout the episode. Subsidence of the volcanic complex was also observed by another satellite from 2007 to 2010, and likely continued for more than 10 years. In addition to the main uplift–subsidence sequence, small deformation patterns with short spatial wavelengths were observed at the center of the deforming area. Data from three satellites recorded small-scale subsidence of the Atosanupuri and Rishiri lava domes at a constant rate of approx. 1 cm/year from 1993 to 2016.Graphical abstractTemporal evolution of the maximum vertical displacement and average yearly rate of height change

Impact of Lanice conchilega on seafloor microtopography off the island of Sylt (German Bight, SE North Sea)

This study presents a new in situ method to explore the impact of macrofauna on seafloor microtopography and corresponding microroughness based on underwater laser line scanning. The local microtopography was determined with mm-level accuracy at three stations colonised by the tubeworm Lanice conchilega offshore of the island of Sylt in the German Bight (south-eastern North Sea), covering approximately 0.5 m2 each. Ground truthing was done using underwater video data. Two stations were populated by tubeworm colonies of different population densities, and one station had a hydrodynamically rippled seafloor. Tubeworms caused an increased skewness of the microtopography height distribution and an increased root mean square roughness at short spatial wavelengths compared with hydrodynamic bedforms. Spectral analysis of the 2D Fourier transformed microtopography showed that the roughness magnitude increased at spatial wavelengths between 0.020 and 0.003 m independently of the tubeworm density. This effect was not detected by commonly used 1D roughness profiles but required consideration of the complete spectrum. Overall, the results reveal that new indicator variables for benthic organisms may be developed based on microtopographic data. An example demonstrates the use of local slope and skewness to detect tubeworms in the measured digital elevation model.

High-spatial Resolution Figuring by Pulse Width Modulation Controlled Plasma Chemical Vaporization Machining

Numerically controlled plasma chemical vaporization machining (NC-PCVM) is an ultra-precision figuring technique using chemical reactions between radicals generated in atmospheric pressure plasma and surface of the workpiece. Figure error consists of waviness which has long spatial wavelength and roughness which has short spatial wavelength. In the case of NC-PCVM using the cylindrical electrode with a diameter of 3-6mm, it is difficult to remove the small wavelength components (several millimetres in wavelength). Therefore, improvement of spatial resolution in figuring is required for NC-PCVM. To resolve this issue, pulse width modulation (PWM) control unit was developed to control the removal volume distribution instead of scanning speed control of the worktable. Removal error at the position where the set removal depth steeply change drastically decreased to less than 4% by applying PWM controlled figuring, while the maximum removal error of figuring which applied the scanning speed control of the worktable to control the removal depth distribution was 20%. And a new electrode, which limits the irradiation area of plasma by installing of a alumina ceramics cover having a small orifice with a diameter of 1.0mm, was also developed. By applying this electrode, the full width at half maximum (FWHM) of the removal spot was reduced from 4.68mm to 1.10mm. Small spatial wavelength components of 4mm were successfully corrected by NC-PCVM which was combined PWM control and orifice electrode.

Remora fish suction pad attachment is enhanced by spinule friction.

The remora fishes are capable of adhering to a wide variety of natural and artificial marine substrates using a dorsal suction pad. The pad is made of serial parallel pectinated lamellae, which are homologous to the dorsal fin elements of other fishes. Small tooth-like projections of mineralized tissue from the dorsal pad lamella, known as spinules, are thought to increase the remora's resistance to slippage and thereby enhance friction to maintain attachment to a moving host. In this work, the geometry of the spinules and host topology as determined by micro-computed tomography and confocal microscope data, respectively, are combined in a friction model to estimate the spinule contribution to shear resistance. Model results are validated with natural and artificially created spinules and compared with previous remora pull-off experiments. It was found that spinule geometry plays an essential role in friction enhancement, especially at short spatial wavelengths in the host surface, and that spinule tip geometry is not correlated with lamellar position. Furthermore, comparisons with pull-off experiments suggest that spinules are primarily responsible for friction enhancement on rough host topologies such as shark skin.

Surface Roughness and Critical Exponent Analyses of Boron-Doped Diamond Films Using Atomic Force Microscopy Imaging: Application of Autocorrelation and Power Spectral Density Functions

The evolution of the surface roughness of growing metal or semiconductor thin films provides much needed information about their growth kinetics and corresponding mechanism. While some systems show stages of nucleation, coalescence, and growth, others exhibit varying microstructures for different process conditions. In view of these classifications, we report herein detailed analyses based on atomic force microscopy (AFM) characterization to extract the surface roughness and growth kinetics exponents of relatively low boron-doped diamond (BDD) films by utilizing the analytical power spectral density (PSD) and autocorrelation function (ACF) as mathematical tools. The machining industry has applied PSD for a number of years for tool design and analysis of wear and machined surface quality. Herein, we present similar analyses at the mesoscale to study the surface morphology as well as quality of BDD films grown using the microwave plasma-assisted chemical vapor deposition technique. PSD spectra as a function of boron concentration (in gaseous phase) are compared with those for samples grown without boron. We find that relatively higher boron concentration yields higher amplitudes of the longer-wavelength power spectral lines, with amplitudes decreasing in an exponential or power-law fashion towards shorter wavelengths, determining the roughness exponent (α ≈ 0.16 ± 0.03) and growth exponent (β ≈ 0.54), albeit indirectly. A unique application of the ACF, which is widely used in signal processing, was also applied to one-dimensional or line analyses (i.e., along the x- and y-axes) of AFM images, revealing surface topology datasets with varying boron concentration. Here, the ACF was used to cancel random surface “noise” and identify any spatial periodicity via repetitive ACF peaks or spatially correlated noise. Periodicity at shorter spatial wavelengths was observed for no doping and low doping levels, while smaller correlations were observed for relatively higher boron concentration. These semiquantitative spatial analyses may prove useful in comparing synthesis techniques and varying compositional makeups of diamond films and other technologically important electronic materials. These findings in terms of critical exponents are also correlated with traditional Raman spectroscopy and x-ray diffraction structural properties, thus helping to provide insight into the growth kinetics, albeit in reverse manner.

Glacier volume estimation as an ill-posed inversion

AbstractEstimating a glacier’s volume by inferring properties at depth (e.g. bed topography or basal slip) from properties observed at the surface (e.g. area and slope) creates a calculation instability that grows exponentially with the size of the glacier. Random errors from this inversion instability can overwhelm all other sources of error and can corrupt thickness and volume calculations, unless problematic short spatial wavelengths are specifically excluded. Volume/area scaling inherently filters these short wavelengths and automatically eliminates the instability, while numerical inversions can also give stable solutions by filtering the correct wavelengths explicitly, as is frequently done when ‘regularizing’ a model. Each of the scaling and numerical techniques has applications to which it is better suited, and there are trade-offs in resolution and accuracy; but when calculating volume, neither the modeling nor the scaling approach offers a fundamental advantage over the other. Both are significantly limited by the inherently ‘ill-posed’ inversion, and even though both provide stable volume solutions, neither can give unique solutions.

Role of wafer geometry in wafer chucking

Wafer chucks are used in advanced lithography systems to hold and flatten wafers during exposure. To minimize defocus and overlay errors, it is important that the chuck provide sufficient pressure to completely chuck the wafer and remove flatness variations across a broad range of spatial wavelengths. Analytical and finite element models of the clamping process are presented here to understand the range of wafer geometry features that can be fully chucked with different clamping pressures. The analytical model provides a simple relationship to determine the maximum feature amplitude that can be chucked as a function of spatial wavelength and chucking pressure. Three-dimensional finite element simulations are used to examine the chucking of wafers with various geometries, including cases with simulated and measured shapes. The analytical and finite element results both demonstrate that geometry variations with short spatial wavelengths (e.g., high-frequency wafer shape features) present the greatest challenge to achieving complete chucking. The models and results presented here can be used to provide guidance on wafer geometry and chuck designs for advanced exposure tools.

Real Time Surface Measurement Technique in a Wide Range of Wavelengths Spectrum

Real time surface topography measurement in the paper and paperboard industries is a challenging research field. The existing online techniques measure only a small area of paper surface and estimate topographical irregularities in a narrow scale as a single predictor. Considering the limitations and complications in measuring the surface at high speed, a laser line triangulation technique is explored to measure surface topography in a wide scale. The developed technique is new for the paper and paperboard application that scans a line onto the paper-web surface up to 210 mm in length in the cross machine direction. The combination of a narrow laser linewidth imaging, a subpixel resolution, and the selection of a unique measurement location has made it possible to measure roughness and simultaneously characterize paper surface topography from 0.1 to 30 mm spatial wavelength. This spatial range covers wide scale surface properties such as roughness, cockling, and waviness. The technique clearly distinguishes and characterizes the surface of newspaper, and lightweight coated, coated, and uncoated paperboard in real time during the paper manufacturing process. The system temporal noise for the average roughness is estimated as 37 dB. The signal to noise ratio found is from 5.4 to 8.1 in the short spatial wavelength up to 1 mm, whereas it is more than 75 in the long spatial wavelength from 5 to 10 mm.

Assessing the fidelity of surface currents from a coastal ocean model and HF radar using drifting buoys in the Middle Atlantic Bight

The rapid expansion of urbanization along the world’s coastal areas requires a more comprehensive and accurate understanding of the coastal ocean. Over the past several decades, numerical ocean circulation models have tried to provide such insight, based on our developing understanding of physical ocean processes. The systematic establishment of coastal ocean observation systems adopting cutting-edge technology, such as high frequency (HF) radar, satellite sensing, and gliders, has put such ocean model predictions to the test, by providing comprehensive observational datasets for the validation of numerical model forecasts. The New York Harbor Observing and Prediction System (NYHOPS) is a comprehensive system for understanding coastal ocean processes on the continental shelf waters of New York and New Jersey. To increase confidence in the system’s ocean circulation predictions in that area, a detailed validation exercise was carried out using HF radar and Lagrangian drifter-derived surface currents from three drifters obtained between March and October 2010. During that period, the root mean square (RMS) differences of both the east–west and north–south currents between NYHOPS and HF radar were approximately 15 cm s−1. Harmonic analysis of NYHOPS and HF radar surface currents shows similar tidal ellipse parameters for the dominant M2 tide, with a mean difference of 2.4 cm s−1 in the semi-major axis and 1.4 cm s−1 in the semi-minor axis and 3° in orientation and 10° in phase. Surface currents derived independently from drifters along their trajectories showed that NYHOPS and HF radar yielded similarly accurate results. RMS errors when compared to currents derived along the trajectory of the three drifters were approximately 10 cm s−1. Overall, the analysis suggests that NYHOPS and HF radar had similar skill in estimating the currents over the continental shelf waters of the Middle Atlantic Bight during this time period. An ensemble-based set of particle tracking simulations using one drifter which was tracked for 11 days showed that the ensemble mean separation generally increases with time in a linear fashion. The separation distance is not dominated by high frequency or short spatial scale wavelengths suggesting that both the NYHOPS and HF radar currents are representing tidal and inertial time scales correctly and resolving some of the smaller scale eddies. The growing ensemble mean separation distance is dominated by errors in the mean flow causing the drifters to slowly diverge from their observed positions. The separation distance for both HF radar and NYHOPS stays below 30 km after 5 days, and the two technologies have similar tracking skill at the 95 % level. For comparison, the ensemble mean distance of a drifter from its initial release location (persistence assumption) is estimated to be greater than 70 km in 5 days.

Visco‐elastic traffic flow model

SUMMARYTo increase our understanding of the operations of traffic system, a visco‐elastic traffic model was proposed in analogy of non‐Newtonian fluid mechanics. The traffic model is based on mass and momentum conservations, and includes a constitutive relation similar to that of linear visco‐elastic fluids. The further inclusion of the elastic effect allows us to describe a high‐order traffic model more comprehensively because the use of relaxation time indicates that vehicle drivers adjust their time headway in a reasonable and safe range. The self‐organizing behaviour is described by introducing the effects of pressure and visco‐elasticity from the point of view in fluid mechanics. Both the viscosity and elasticity can be determined by using the relaxation time and the traffic sound speed. The sound speed can be approximately represented by the road operational parameters including the free‐flow speed, the jam density, and the density of saturation if the jam pressure in traffic flows is identical to the total pressure at the flow saturation point. A linear stability analysis showed that the traffic flow should be absolutely unstable for disturbances with short spatial wavelengths. There are two critical points of regime transition in traffic flows. The first point happens at the density of saturation, and the second point occurs at a density relating on the sound speed and the fundamental diagram of traffic flows. By using a triangular form flow–density relation, a numerical test based on the new model is carried out for congested traffic flows on a loop road without ramp effect. The numerical results are discussed and compared with the result of theoretical analysis and observation data of traffic flows. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Grazing incidence broad ion beams for reducing line-edge roughness

As semiconductor feature sizes continue to decrease, the phenomena of line-edge roughness (LER) becomes more disruptive in chip manufacturing. While many efforts are underway to decrease LER from the photoresist, post-developed smoothing techniques may be required to continue shrinking chip features economically. This paper reports on one such method employing the use of a broad ion beam at grazing incidence along the features. This method smooths relatively long spatial-length LER, a potential advantage over other smoothing techniques that focus on just molecular-scale LER. LER reduction numbers using Ne and Ar beams are reported at both short and long spatial wavelengths. Variables include beam energy, length of time and angular dependence. LER measurements are taken using the Hitachi image-analysis software on top–down analytical scanning electron microscope (SEM) measurements. Line-profile data are taken from cross-sectional SEM photographs. Tests have achieved a reduction in LER from 9.8 ± 0.67 nm to 5.5 ± 0.86 nm for 45 nm critical dimensions using an Ar beam at 500 eV for 6 s at an 85° angle of incidence. A reduction from 10.1 ± 1.07 nm to 6 ± 1.02 nm was shown using an Ar beam at 1000 eV for 4 s at a 60° angle of incidence.

Reliability of mantle tomography models assessed by spectral element simulation

Global tomographic models collected in the Seismic wave Propagation and Imaging in Complex (SPICE media: a European network) model library (http://www.spice-rtn.org/research/planetaryscale/tomography/) share a similar pattern of long, spatial wavelength heterogeneity, but are not consistent at shorter spatial wavelengths. Here, we assess the performance of global tomographic models by comparing how well they fit seismic waveform observations, in particular Love and Rayleigh wave overtones and fundamental modes. We first used the coupled spectral element method (CSEM) to calculate long-period (>100 s) synthetic seismograms for different global tomography models. The CSEM can incorporate the effect of three-dimensional (3-D) variations in velocity, anisotropy, density and attenuation with very little numerical dispersion. We then compared quantitatively synthetic seismograms and real data. To restrict ourselves to high-quality overtone data, and to minimize the effects of the finite extent of seismic sources and of crustal heterogeneity, we favour deep (>500 km) earthquakes of intermediate magnitude (M w ∼7). Our comparisons reveal that: (1) The 3-D global tomographic models explain the data much better than the one-dimensional (1-D) anisotropic Preliminary Reference Earth Model (PREM). The current 3-D tomographic models have captured the large-scale features of upper-mantle heterogeneities, but there is still some room for the improvement of large-scale features of global tomographic models. (2) The average correlation coefficients for deep events are higher than those for shallow events, because crustal structure is too complex to be completely incorporated into CSEM simulations. (3) The average correlation coefficient (or the time lag) for the major-arc wave trains is lower (or higher) than that for the minor-arc wave trains. Therefore, the current tomographic models could be much improved by including the major-arc wave trains in the inversion. (4) The shallow-layer crustal correction has more effects on the fundamental surface waves than on the overtones.

Uncertainty in determining interval velocities from surface reflection seismic data

The ability of reflection seismic data to uniquely determine the subsurface velocity has been uncertain. This paper uses a tomographic approach to study the resolution of typical seismic survey configurations. The analysis is first carried out in the spatial Fourier domain for the case of a single horizontal reflector. It is found that for a ratio of maximum offset to layer depth of one, the lateral resolution is very low for velocity and interface depth variations of wavelengths of approximately two‐and‐a‐half times the layer thickness. The resolution improves with an increase in the ratio of maximum offset to layer depth. The results of the analysis in the Fourier domain are confirmed by results from a least‐squares tomographic algorithm. It is found that regularization of the tomography by adding damping terms suppresses the spurious oscillations resulting from the areas of low resolution at the expense of loss of resolution at the shorter spatial wavelengths. Analysis of the single layer response for 3‐D survey geometry shows that a 3‐D acquisition with multiazimuthal coverage has the potential to significantly improve velocity determination.

Lateral thinking: 2-D interpretation of thermochronology in convergent orogenic settings

Lateral motion of material relative to the regional thermal and kinematic frameworks is important in the interpretation of thermochronology in convergent orogens. Although cooling ages in denuded settings are commonly linked to exhumation, such data are not related to instantaneous behavior but rather to an integration of the exhumation rates experienced between the thermochronological ‘closure’ at depth and subsequent exposure at the surface. The short spatial wavelength variation of thermal structure and denudation rate typical of orogenic regions thus renders thermochronometers sensitive to lateral motion during exhumation. The significance of this lateral motion varies in proportion with closure temperature, which controls the depth at which isotopic closure occurs, and hence, the range of time and length scales over which such data integrate sample histories. Different chronometers thus vary in the fundamental aspects of the orogenic character to which they are sensitive. Isotopic systems with high closure temperature are more sensitive to exhumation paths and the variation in denudation and thermal structure across a region, while those of lower closure temperature constrain shorter-term behaviour and more local conditions. Discounting lateral motion through an orogenic region and interpreting cooling ages purely in terms of vertical exhumation can produce ambiguous results because variation in the cooling rate can result from either change in kinematics over time or the translation of samples through spatially varying conditions. Resolving this ambiguity requires explicit consideration of the physical and thermal framework experienced by samples during their exhumation. This can be best achieved through numerical simulations coupling kinematic deformation to thermal evolution. Such an approach allows the thermochronological implications of different kinematic scenarios to be tested, and thus provides an important means of assessing the contribution of lateral motion to orogenic evolution.

Characterization of thin film surfaces over an extended spatial wavelength range

The statistical properties of a thin film surface over an extended spatial wavelength have been studied by using the methods of differential scattering and digital analysis of replica micrographs. It can be concluded that, for a given film thickness, the surface features corresponding to long spatial wavelengths greater than several thousand angstroms are dominated mainly by the substrate surface, while the fine details corresponding to short spatial wavelengths are dominated by the thin film material and deposition process. Effects of ion-beam bombardment during deposition on surface roughness are also discussed.

Extreme UV and x-ray scattering measurements from a rough LiF crystal surface characterized by electron micrography

XUV and x-ray scattering by a LiF crystal is measured. The angular distribution of the scattered radiation (ADSR) reveals characteristic features, side peaks or asymmetry. The surface of the sample is statistically characterized by a microdensitometer analysis of electron micrographs resolving the short spatial wavelengths of the surface roughness. This analysis shows that the surface has a large microroughness with an autocovariance function which is Gaussian in its initial portion. The first-order perturbation vector theory of the roughness-induced scattering leads to an interpretation of the ADSR features in terms of the modulation of the surface power spectral density function associated with the microroughness by an optical factor. The possibility of obtaining short scale roughness characterization from XUV or x-ray measurements is discussed.

Elastic Ray-Born L2-Migration/Inversion

Summary The approximate ray Green's tensor in 3-D heterogeneous elastic media combined with the first-order Born approximation lead to new explicit equations for solving, modelling and inverse scattering problems. Individual wave scattering contributions (PP, PS, SP, SS) are represented for four different linear approximations (i.e. parameter linearizations). the first-order Born appoximation yields a scattered wavefield which is linearly related to medium parameter perturbations. the linearized inverse scattering problem is solved in the space-time domain and consists of minimizing a cost function within the l2 norm with a one-step conditioned gradient procedure. From uni- or multicomponent data and a reference heterogeneous background model representing adequately either the long spatial wavelengths of the medium (i.e. the smooth model), and/or its principal features (i.e. the macro-model), this operation reduces to: (1) pre-stack depth-migrating the scattered data yielding three intermediate images; and (2) deconvolving these images by an elastic Hessian correction which produces final high-resolution images representing the medium's short spatial wavelength variations convolved with the source function (e.g. P and S impedances and density maps). If the reference model and data are satisfactory, typical artefacts are due to limited aperture or insufficient coverage. Use of high-frequency and Born approximations require certain constraints. For example, the dominant wavelength must always be smaller than the characteristic length of the reference medium, but larger than the scatterer characteristic length. to increase computational efficiency, the high-frequency approximate Green's tensor is calculated by the paraxial ray method. 2-D elastic synthetic examples for surface reflection and cross-hole experiments show the ability of such a technique to delineate subsurface structure and to recover local changes in elastic properties. However, density variations are more difficult to resolve than P and S impedance or velocity changes.