scholarly journals Joint interpretation of explosive and vibroseismic surveys on cold firn for the investigation of ice properties

2013 ◽  
Vol 54 (64) ◽  
pp. 201-210 ◽  
Author(s):  
Anja Diez ◽  
Olaf Eisen ◽  
Coen Hofstede ◽  
Pascal Bohleber ◽  
Ulrich Polom
Keyword(s):  
Crystal Orientation ◽  
Seismic Waves ◽  
Ice Core ◽  
Radar Data ◽  
Sh Wave ◽  
Seismic Surveys ◽  
Explosive Source ◽  
Strong Surface ◽  
Joint Interpretation ◽  
Monte Rosa

Abstract Two seismic surveys were carried out on the high-altitude glacier saddle, Colle Gnifetti, Monte Rosa, Italy/Switzerland. Explosive and vibroseismic sources were tested to explore the best way to generate seismic waves to deduce shallow and intermediate properties (<100 m) of firn and ice. The explosive source (SISSY) excites strong surface and diving waves, degrading data quality for processing; no englacial reflections besides the noisy bed reflector are visible. However, the strong diving waves are analyzed to derive the density distribution of the firn pack, yielding results similar to a nearby ice core. The vibrator source (ElViS), used in both P- and SH-wave modes, produces detectable laterally coherent reflections within the firn and ice column. We compare these with ice-core and radar data. The SH-wave data are particularly useful in providing detailed, high-resolution information on firn and ice stratigraphy. Our analyses demonstrate the potential of seismic methods to determine physical properties of firn and ice, particularly density and potentially also crystal-orientation fabric.

scholarly journals Seismic wave propagation in anisotropic ice – Part 2: Effects of crystal anisotropy in geophysical data

2015 ◽  
Vol 9 (1) ◽  
pp. 385-398 ◽  
Author(s):  
A. Diez ◽  
O. Eisen ◽  
C. Hofstede ◽  
A. Lambrecht ◽  
C. Mayer ◽  
...  
Keyword(s):  
Seismic Waves ◽  
Ice Core ◽  
Radar Data ◽  
Seismic Wave Propagation ◽  
Elasticity Tensor ◽  
Seismic Velocities ◽  
Data Set ◽  
Ice Dynamics ◽  
Crystal Anisotropy ◽  
Abrupt Changes

Abstract. We investigate the propagation of seismic waves in anisotropic ice. Two effects are important: (i) sudden changes in crystal orientation fabric (COF) lead to englacial reflections; (ii) the anisotropic fabric induces an angle dependency on the seismic velocities and, thus, recorded travel times. Velocities calculated from the polycrystal elasticity tensor derived for the anisotropic fabric from measured COF eigenvalues of the EDML ice core, Antarctica, show good agreement with the velocity trend determined from vertical seismic profiling. The agreement of the absolute velocity values, however, depends on the choice of the monocrystal elasticity tensor used for the calculation of the polycrystal properties. We make use of abrupt changes in COF as a common reflection mechanism for seismic and radar data below the firn–ice transition to determine COF-induced reflections in either data set by joint comparison with ice-core data. Our results highlight the possibility to complement regional radar surveys with local, surface-based seismic experiments to separate isochrones in radar data from other mechanisms. This is important for the reconnaissance of future ice-core drill sites, where accurate isochrone (i.e. non-COF) layer integrity allows for synchronization with other cores, as well as studies of ice dynamics considering non-homogeneous ice viscosity from preferred crystal orientations.

scholarly journals Influence of ice crystal anisotropy on seismic velocity analysis

2014 ◽  
Vol 55 (67) ◽  
pp. 97-106 ◽  
Author(s):  
Anja Diez ◽  
Olaf Eisen ◽  
Ilka Weikusat ◽  
Jan Eichler ◽  
Coen Hofstede ◽  
...  
Keyword(s):  
Seismic Velocity ◽  
Ice Core ◽  
Radar Data ◽  
P Wave ◽  
Seismic Survey ◽  
Sh Wave ◽  
Wave Analysis ◽  
S Wave ◽  
Alpine Glacier ◽  
Reflection Seismic

AbstractIn 2010 a reflection seismic survey was carried out on the Alpine glacier Colle Gnifetti. The processed and depth-converted data could be compared to a nearby ice core, drilled almost to the bed. Comparisons showed that the depth of the P-wave bed reflection was too shallow, while the depth of the SH-wave bed reflection fitted the ice-core length well. We are now able to explain the major part of these differences using the existing crystal orientations of the ice at Colle Gnifetti. We calculate anisotropic velocities for P- and SH-waves that are usually picked for stacking and compare them with zero-offset velocities needed for the depth conversion. Here we take the firn pack at Colle Gnifetti into account for P- and S-wave analysis. To incorporate the S-wave analysis we first derive a new equation for the relationship between density and S-wave velocity from diving waves. We show that anisotropic fabrics observed at Colle Gnifetti introduce a difference of only 1% between stacking and depth-conversion velocities for the SH-wave, but 7% for the P-wave. We suggest that this difference in stacking and depth-conversion velocity for the P-wave can be used to derive information about the existing anisotropy by combining our seismic data with, for example, radar data.

Application of polarimetric radar to infer ice fabric anisotropy

2020 ◽  
Author(s):  
Mohammadreza Ershadi ◽  
Reinhard Drews ◽  
Carlos Martín ◽  
Olaf Eisen
Keyword(s):  
Crystal Orientation ◽  
Ice Core ◽  
Ice Sheets ◽  
Radar Data ◽  
Anisotropic Scattering ◽  
Ice Flow ◽  
Phase Gradient ◽  
Future Evolution ◽  
Model Code ◽  
Wide Range

<p>Understanding ice flow of ice sheets is not only important to predict their future evolution, but is also required for finding future ice-core sites with an intact stratigraphy and a constrained age-depth relationship of the corresponding climate record. Anisotropic ice flow, induced through the formation of aligned Crystal Orientation Fabric (COF), is in this context important as it may cause ice overturning and folding at larger depths. Here, we use a synthetic radar forward model to explore the feasibility of detecting the crystal orientation fabric orientation and strength using coherent, polarimetric ice-penetrating radar data (ApRES). We compare our results, with ApRES data collected in Antarctica. Some of the sites are located near deep drill ice-core sites (e.g., Dome C), and we validate our approach with ice-core data.</p><p>In multilayer models, we distinguish between birefringence (caused by ray propagation through anisotropic COF with unknown strength and orientation) and anisotropic scattering (caused by an unknown depth variability of anisotropic COF). We show analytically that the scattering ratio is determined by the angular dependence of co-polarization extinction nodes. Building on previous work, we infer COF orientation using the depolarization component, and COF strength from the gradient of polarimetric coherence, respectively.</p><p>We apply this approach to polarimetric ApRES datasets. We show COF orientation can often reliably be inferred as long as it does not change significantly with depth. Rotation of principal axis with depth, on the other hand, causes a complicated radar response that is not straightforwardly interpreted. At dome positions, where the ice anisotropy develops more gently compared to flank-flow settings, the degree of anisotropy can be estimated with the phase gradient method. This becomes increasingly more difficult for flank-flow settings where phase unwrapping is required. We delineate a number of anisotropic scattering zones which likely correspond to COF patterns changing abruptly. In some cases, boundaries between anisotropic scattering zones coincide with climate transitions within the ice.</p><p>We provide our model code in the form of a user-friendly GUI, enabling to quickly explore a wide range of possible COF patterns and their corresponding imprint in the radar data. This is useful both for scientific and educational purposes. Our analysis underlines the potential of coherent, polarimetric radars to infer the COF orientation of ice sheets also away from ice core sites. This will provide important data for the inclusion of ice anisotropy in ice-flow models in the future.</p>

scholarly journals Seismic wave propagation in anisotropic ice – Part 2: Effects of crystal anisotropy in geophysical data

2014 ◽  
Vol 8 (4) ◽  
pp. 4397-4430 ◽  
Author(s):  
A. Diez ◽  
O. Eisen ◽  
C. Hofstede ◽  
A. Lambrecht ◽  
C. Mayer ◽  
...  
Keyword(s):  
Seismic Waves ◽  
Ice Core ◽  
Radar Data ◽  
Seismic Wave Propagation ◽  
Elasticity Tensor ◽  
Seismic Velocities ◽  
Ice Dynamics ◽  
Crystal Anisotropy ◽  
Abrupt Changes ◽  
Good Agreement

Abstract. We investigate the propagation of seismic waves in anisotropic ice. Two effects are important: (i) sudden changes in crystal orientation fabric (COF) lead to englacial reflections; (ii) the anisotropic fabric induces an angle dependency on the seismic velocities and, thus, recorded traveltimes. Velocities calculated from the polycrystal elasticity tensor derived for the anisotropic fabric from measured COF eigenvalues of the EDML ice core, Antarctica, show good agreement with the velocity trend determined from a vertical seismic profiling. The agreement of the absolute velocity values, however, depends on the choice of the monocrystal elasticity tensor used for the calculation of the polycrystal properties. With this validation of seismic velocities we make use of abrupt changes in COF as common reflection mechanism for seismic and radar data below the firn–ice transition to investigate their occurrence by comparison with ice-core data. Our results highlight the possibility to complement regional radar surveys with local, surface-based seismic deployment to separate isochrones in radar data from other mechanisms. This is important for the reconnaissance of future ice-core drill sites, where accurate isochrone (i.e. non-COF) layer integrity allows for synchronization with other cores, as well as studies of ice dynamics considering non-homogeneous viscosity from preferred crystal orientations.

scholarly journals Dielectric anisotropy as indicator of crystal orientation fabric in Dome Fuji ice core: method and initial results

2021 ◽  
pp. 1-12
Author(s):  
Tomotaka Saruya ◽  
Shuji Fujita ◽  
Ryo Inoue
Keyword(s):  
Crystal Orientation ◽  
Horizontal Plane ◽  
Ice Core ◽  
Vertical Plane ◽  
Vertical Direction ◽  
Core Sample ◽  
Dielectric Anisotropy ◽  
Principal Axes ◽  
Polycrystalline Ice ◽  
Initial Results

Abstract Polycrystalline ice is known to exhibit macroscopic anisotropy in relative permittivity (ɛ) depending on the crystal orientation fabric (COF). Using a new system designed to measure the tensorial components of ɛ, we investigated the dielectric anisotropy (Δɛ) of a deep ice core sample obtained from Dome Fuji, East Antarctica. This technique permits the continuous nondestructive assessment of the COF in thick ice sections. Measurements of vertical prism sections along the core showed that the Δɛ values in the vertical direction increased with increasing depth, supporting previous findings of c-axis clustering around the vertical direction. Analyses of horizontal disk sections demonstrated that the magnitude of Δɛ in the horizontal plane was 10–15% of that in the vertical plane. In addition, the directions of the principal axes of tensorial ɛ in the horizontal plane corresponded to the long or short axis of the elliptically elongated single-pole maximum COF. The data confirmed that Δɛ in the vertical and horizontal planes adequately indicated the preferred orientations of the c-axes, and that Δɛ can be considered to represent a direct substitute for the normalized COF eigenvalues. This new method could be extremely useful as a means of investigating continuous and depth-dependent variations in COF.

scholarly journals Seismic wave propagation in anisotropic ice – Part 1: Elasticity tensor and derived quantities from ice-core properties

2015 ◽  
Vol 9 (1) ◽  
pp. 367-384 ◽  
Author(s):  
A. Diez ◽  
O. Eisen
Keyword(s):  
Seismic Waves ◽  
Dynamic Behaviour ◽  
Ice Core ◽  
Ice Cores ◽  
Seismic Wave Propagation ◽  
Elasticity Tensor ◽  
Reflection Coefficients ◽  
Seismic Velocities ◽  
Crystal Anisotropy ◽  
Elasticity Tensors

Abstract. A preferred orientation of the anisotropic ice crystals influences the viscosity of the ice bulk and the dynamic behaviour of glaciers and ice sheets. Knowledge about the distribution of crystal anisotropy is mainly provided by crystal orientation fabric (COF) data from ice cores. However, the developed anisotropic fabric influences not only the flow behaviour of ice but also the propagation of seismic waves. Two effects are important: (i) sudden changes in COF lead to englacial reflections, and (ii) the anisotropic fabric induces an angle dependency on the seismic velocities and, thus, recorded travel times. A framework is presented here to connect COF data from ice cores with the elasticity tensor to determine seismic velocities and reflection coefficients for cone and girdle fabrics. We connect the microscopic anisotropy of the crystals with the macroscopic anisotropy of the ice mass, observable with seismic methods. Elasticity tensors for different fabrics are calculated and used to investigate the influence of the anisotropic ice fabric on seismic velocities and reflection coefficients, englacially as well as for the ice–bed contact. Hence, it is possible to remotely determine the bulk ice anisotropy.

scholarly journals Surface accumulation in Northern Central Greenland during the last 300 years

2020 ◽  
Vol 61 (81) ◽  
pp. 214-224 ◽  
Author(s):  
Nanna B. Karlsson ◽  
Sebastian Razik ◽  
Maria Hörhold ◽  
Anna Winter ◽  
Daniel Steinhage ◽  
...  
Keyword(s):  
Large Scale ◽  
Climate Models ◽  
Regional Climate ◽  
Ice Core ◽  
Regional Climate Models ◽  
Radar Data ◽  
Accumulation Rates ◽  
Ground Penetrating ◽  
Core Project ◽  
North Greenland

AbstractThe internal stratigraphy of snow and ice as imaged by ground-penetrating radar may serve as a source of information on past accumulation. This study presents results from two ground-based radar surveys conducted in Greenland in 2007 and 2015, respectively. The first survey was conducted during the traverse from the ice-core station NGRIP (North Greenland Ice Core Project) to the ice-core station NEEM (North Greenland Eemian Ice Drilling). The second survey was carried out during the traverse from NEEM to the ice-core station EGRIP (East Greenland Ice Core Project) and then onwards to Summit Station. The total length of the radar profiles is 1427 km. From the radar data, we retrieve the large-scale spatial variation of the accumulation rates in the interior of the ice sheet. The accumulation rates range from 0.11 to 0.26 m a−1 ice equivalent with the lowest values found in the northeastern sector towards EGRIP. We find no evidence of temporal or spatial changes in accumulation rates when comparing the 150-year average accumulation rates with the 321-year average accumulation rates. Comparisons with regional climate models reveal that the models underestimate accumulation rates by up to 35% in northeastern Greenland. Our results serve as a robust baseline to detect present changes in either surface accumulation rates or patterns.

Detection of tunnels and boulders using shallow SH-SH reflected seismic waves

2019 ◽  
Vol 38 (6) ◽  
pp. 436-441 ◽  
Author(s):  
André J.-M. Pugin ◽  
Kevin Brewer ◽  
Timothy Cartwright ◽  
Steven L. Sargent
Keyword(s):  
Seismic Waves ◽  
Field Experiments ◽  
Sh Waves ◽  
Additional Advantage ◽  
Seismic Surveys ◽  
Shallow Seismic ◽  
Diffracted Waves ◽  
Seismic Sections ◽  
Ground Penetrating ◽  
Abandoned Coal Mine

We present three case studies on detecting buried glacial boulders, a sewage tunnel, and abandoned coal mine tunnels using shear-wave reflection methods. The seismic signature of such subsurface features is in the form of an isolated diffraction, distinctly recognized on seismic sections obtained from shallow seismic surveys using a transverse horizontal (H2) source and a multichannel landstreamer that consists of H2 geophones. We used H2 impulsive and vibrator sources with varying bandwidth. Based on field experiments with multicomponent recordings, we determined that the H2-H2 source-receiver configuration is the most optimal to generate downgoing horizontally polarized shear (SH) waves and upcoming SH reflected and diffracted waves. A shallow SH-SH image using a microvibe high-frequency sweep exhibits a wavelength between 1 and 2 m, which is comparable to that of a ground-penetrating radar image with the additional advantage of deeper penetration.

scholarly journals Modeling and Imaging of Multiscale Geological Media: Exploding Reflection Revisited

Geosciences ◽  
2018 ◽  
Vol 8 (12) ◽  
pp. 476
Author(s):  
Evgeny Landa ◽  
Galina Reshetova ◽  
Vladimir Tcheverda
Keyword(s):  
Seismic Waves ◽  
Fractured Reservoirs ◽  
Single Shot ◽  
Middle Point ◽  
Seismic Surveys ◽  
Geological Interpretation ◽  
Time Migration ◽  
Diffraction Imaging ◽  
Heterogeneous Multiscale ◽  
Seismic Sections

Computation of Common Middle Point seismic sections and their subsequent time migration and diffraction imaging provides very important knowledge about the internal structure of 3D heterogeneous geological media and are key elements for successive geological interpretation. Full-scale numerical simulation, that computes all single shot seismograms, provides a full understanding of how the features of the image reflect the properties of the subsurface prototype. Unfortunately, this kind of simulations of 3D seismic surveys for realistic geological media needs huge computer resources, especially for simulation of seismic waves’ propagation through multiscale media like cavernous fractured reservoirs. Really, we need to combine smooth overburden with microstructure of reservoirs, which forces us to use locally refined grids. However, to resolve realistic statements with huge multi-shot/multi-offset acquisitions it is still not enough to provide reasonable needs of computing resources. Therefore, we propose to model 3D Common Middle Point seismic cubes directly, rather than shot-by-shot simulation with subsequent stacking. To do that we modify the well-known "exploding reflectors principle" for 3D heterogeneous multiscale media by use of the finite-difference technique on the base of grids locally refined in time and space. We develop scalable parallel software, which needs reasonable computational costs to simulate realistic models and acquisition. Numerical results for simulation of Common Middle Points sections and their time migration are presented and discussed.

scholarly journals Characterizing the glaciological conditions at Halvfarryggen ice dome, Dronning Maud Land, Antarctica

2013 ◽  
Vol 59 (213) ◽  
pp. 9-20 ◽  
Author(s):  
Reinhard Drews ◽  
Carlos Martín ◽  
Daniel Steinhage ◽  
Olaf Eisen
Keyword(s):  
Flow Model ◽  
Ice Core ◽  
Ice Cores ◽  
Radar Data ◽  
Ice Thickness ◽  
Atmospheric Conditions ◽  
Ice Flow ◽  
International Partnerships ◽  
Drill Site ◽  
Dronning Maud Land

AbstractWe present a comprehensive approach (including field data, remote sensing and an anisotropic ice-flow model) to characterize Halvfarryggen ice dome in coastal Dronning Maud Land, Antarctica. This is a potential drill site for the International Partnerships in Ice Core Sciences, which has identified the need for ice cores covering atmospheric conditions during the last few millennia. We derive the surface topography, the ice stratigraphy from radar data, and accumulation rates which vary from 400 to 1670 kg m−2 a−1 due to preferred wind directions and changing surface slope. The stratigraphy shows anticlines and synclines beneath the divides. We transfer Dansgaard–Johnsen age–depth scales from the flanks along isochrones to the divide in the upper 20–50% of the ice thickness and show that they compare well with the results of a full-Stokes, anisotropic ice-flow model which predicts (1) 11 ka BP ice at 90% of the ice thickness, (2) a temporally stable divide for at least 2700–4500 years, (3) basal temperatures below the melting point (−12°C to −5°C) and (4) a highly developed crystal orientation fabric (COF). We suggest drilling into the apices of the deep anticlines, providing a good compromise between record length and temporal resolution and also facilitating studies of the interplay of anisotropic COF and ice flow.

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