High resolution shallow reflection seismic profiles, Val Gagne, Ontario Test Site

Lift-off moraines: markers of last ice-flow directions on the Scotian Shelf

Canadian Journal of Earth Sciences ◽

10.1139/e00-066 ◽

2000 ◽

Vol 37 (12) ◽

pp. 1723-1734 ◽

Cited By ~ 9

Author(s):

Michael R Gipp

Keyword(s):

High Resolution ◽

Continental Margin ◽

Flow Direction ◽

Seismic Profiles ◽

Scotian Shelf ◽

Ice Flow ◽

Reflection Seismic ◽

Flow Directions ◽

Lift Off ◽

Seismic Lines

Lift-off moraines are acoustically incoherent, subparallel ridges observed on sidescan sonograms and high-resolution reflection seismic profiles on the southeastern continental margin of Canada. They are up to 3 m high, 2080 m wide, and are commonly overlain by stratified proglacial sediments. Although little is known about them, detailed study of high-resolution seismic profiles from the Emerald Basin and the LaHave Basin, on the Scotian Shelf, show that their height:width ratio varies with the sounderseabed separation, suggesting that the ridges may be narrower than they appear. Their morphology is similar to DeGeer moraines or cross-valley moraines, which form perpendicular to ice-flow direction. As their orientations can be estimated at the intersection of seismic lines, they can be used to estimate ice-flow directions. Since proglacial sediments are draped directly over top of them, they are assumed to record the direction of last ice flow. This directional data suggests that ice retreated not only northward (to Nova Scotia), but also toward local topographic highs on the continental shelf, which acted as anchoring points for ice rises around both the Emerald and LaHave Basins. This pattern of ice-flow directions suggests that ice flowed from the high ground of banks, converging into basin deeps, suggesting that small moraines within the basins are probably of interlobate origin.

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Using GEDI Waveforms for Improved TanDEM-X Forest Height Mapping: A Combined SINC + Legendre Approach

Remote Sensing ◽

10.3390/rs13152882 ◽

2021 ◽

Vol 13 (15) ◽

pp. 2882

Author(s):

Hao Chen ◽

Shane R. Cloude ◽

Joanne C. White

Keyword(s):

High Resolution ◽

Forest Canopy ◽

Test Site ◽

Convergent Series ◽

Canopy Height ◽

Ecosystem Dynamics ◽

Sinc Function ◽

Vertical Profiles ◽

Legendre Series ◽

Vertical Profiling

In this paper, we consider a new method for forest canopy height estimation using TanDEM-X single-pass radar interferometry. We exploit available information from sample-based, space-borne LiDAR systems, such as the Global Ecosystem Dynamics Investigation (GEDI) sensor, which offers high-resolution vertical profiling of forest canopies. To respond to this, we have developed a new extended Fourier-Legendre series approach for fusing high-resolution (but sparsely spatially sampled) GEDI LiDAR waveforms with TanDEM-X radar interferometric data to improve wide-area and wall-to-wall estimation of forest canopy height. Our key methodological development is a fusion of the standard uniform assumption for the vertical structure function (the SINC function) with LiDAR vertical profiles using a Fourier-Legendre approach, which produces a convergent series of approximations of the LiDAR profiles matched to the interferometric baseline. Our results showed that in our test site, the Petawawa Research Forest, the SINC function is more accurate in areas with shorter canopy heights (<~27 m). In taller forests, the SINC approach underestimates forest canopy height, whereas the Legendre approach avails upon simulated GEDI forest structural vertical profiles to overcome SINC underestimation issues. Overall, the SINC + Legendre approach improved canopy height estimates (RMSE = 1.29 m) compared to the SINC approach (RMSE = 4.1 m).

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The use of geophysical prospecting for imaging active faults in the Roer Graben, Belgium

Geophysics ◽

10.1190/1.1444925 ◽

2001 ◽

Vol 66 (1) ◽

pp. 78-89 ◽

Cited By ~ 62

Author(s):

Donat Demanet ◽

François Renardy ◽

Kris Vanneste ◽

Denis Jongmans ◽

Thierry Camelbeeck ◽

...

Keyword(s):

High Resolution ◽

Physical Properties ◽

Fault Zone ◽

Geophysical Methods ◽

Depth Range ◽

Electrical Tomography ◽

Reflection Seismic ◽

Refraction Seismic ◽

Geophysical Surveys ◽

Geophysical Techniques

As part of a paleoseismological investigation along the Bree fault scarp (western border of the Roer Graben), various geophysical methods [electrical profiling, electromagnetic (EM) profiling, refraction seismic tests, electrical tomography, ground‐penetrating radar (GPR), and high‐resolution reflection seismic profiles] were used to locate and image an active fault zone in a depth range between a few decimeters to a few tens of meters. These geophysical investigations, in parallel with geomorphological and geological analyses, helped in the decision to locate trench excavations exposing the fault surfaces. The results could then be checked with the observations in four trenches excavated across the scarp. Geophysical methods pointed out anomalies at all sites of the fault position. The contrast of physical properties (electrical resistivity and permittivity, seismic velocity) observed between the two fault blocks is a result of a differences in the lithology of the juxtaposed soil layers and of a change in the water table depth across the fault. Extremely fast techniques like electrical and EM profiling or seismic refraction profiles localized the fault position within an accuracy of a few meters. In a second step, more detailed methods (electrical tomography and GPR) more precisely imaged the fault zone and revealed some structures that were observed in the trenches. Finally, one high‐resolution reflection seismic profile imaged the displacement of the fault at depths as large as 120 m and filled the gap between classical seismic reflection profiles and the shallow geophysical techniques. Like all geophysical surveys, the quality of the data is strongly dependent on the geologic environment and on the contrast of the physical properties between the juxtaposed formations. The combined use of various geophysical techniques is thus recommended for fault mapping, particularly for a preliminary investigation when the geological context is poorly defined.

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Geophysical imaging of permafrost in the SW Svalbard – the result of two high arctic expeditions to Spitsbergen

10.5194/egusphere-egu2020-8136 ◽

2020 ◽

Author(s):

Mariusz Majdanski ◽

Artur Marciniak ◽

Bartosz Owoc ◽

Wojciech Dobiński ◽

Tomasz Wawrzyniak ◽

...

Keyword(s):

Surface Waves ◽

Active Layer ◽

High Arctic ◽

The Arctic ◽

Seismic Profiles ◽

Frozen Ground ◽

Near Surface ◽

Seismic Processing ◽

Reflection Seismic ◽

Sea Coast

The Arctic regions are the place of the fastest observed climate change. One of the indicators of such evolution are changes occurring in the glaciers and the subsurface in the permafrost. The active layer of the permafrost as the shallowest one is well measured by multiple geophysical techniques and in-situ measurements.Two high arctic expeditions have been organized to use seismic methods to recognize the shape of the permafrost in two seasons: with the unfrozen ground (October 2017) and frozen ground (April 2018). Two seismic profiles have been designed to visualize the shape of permafrost between the sea coast and the slope of the mountain, and at the front of a retreating glacier. For measurements, a stand-alone seismic stations has been used with accelerated weight drop with in-house modifications and timing system. Seismic profiles were acquired in a time-lapse manner and were supported with GPR and ERT measurements, and continuous temperature monitoring in shallow boreholes.Joint interpretation of seismic and auxiliary data using Multichannel analysis of surface waves, First arrival travel-time tomography and Reflection imaging show clear seasonal changes affecting the active layer where P-wave velocities are changing from 3500 to 5200 m/s. This confirms the laboratory measurements showing doubling the seismic velocity of water-filled high-porosity rocks when frozen. The same laboratory study shows significant (>10%) increase of velocity in frozen low porosity rocks, that should be easily visible in seismic.In the reflection seismic processing, the most critical part was a detailed front mute to eliminate refracted arrivals spoiling wide-angle near-surface reflections. Those long offset refractions were however used to estimate near-surface velocities further used in reflection processing. In the reflection seismic image, a horizontal reflection was traced at the depth of 120 m at the sea coast deepening to the depth of 300 m near the mountain.Additionally, an optimal set of seismic parameters has been established, clearly showing a significantly higher signal to noise ratio in case of frozen ground conditions even with the snow cover. Moreover, logistics in the frozen conditions are much easier and a lack of surface waves recorded in the snow buried geophones makes the seismic processing simpler.Acknowledgements&#160; &#160; &#160; &#160; &#160; &#160; &#160; &#160;This research was funded by the National Science Centre, Poland (NCN) Grant UMO-2015/21/B/ST10/02509.

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Lithoprobe-Phase 1: southern Vancouver Island: preliminary analyses of reflection seismic profiles and surface geological studies

10.4095/120150 ◽

1985 ◽

Cited By ~ 2

Author(s):

C J Yorath ◽

R M Clowes ◽

A G Green ◽

A Sutherland-Brown ◽

M T Brandon ◽

...

Keyword(s):

Phase 1 ◽

Vancouver Island ◽

Seismic Profiles ◽

Reflection Seismic

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Structural analysis of S-wave seismics around an urban sinkhole; evidence of enhanced subrosion in a strike-slip fault zone

10.5194/nhess-2017-315 ◽

2017 ◽

Author(s):

Sonja H. Wadas ◽

David C. Tanner ◽

Ulrich Polom ◽

Charlotte M. Krawczyk

Keyword(s):

Strike Slip ◽

Strike Slip Fault ◽

Key Factors ◽

S Wave ◽

Seismic Profiles ◽

Reflection Seismic ◽

Dextral Strike Slip Fault ◽

Seismic Sections ◽

The Town ◽

Dextral Strike Slip

Abstract. In November 2010, a large sinkhole opened up in the urban area of Schmalkalden, Germany. To determine the key factors which benefited the development of this collapse structure and therefore the subrosion, we carried out several shear wave reflection seismic profiles around the sinkhole. In the seismic sections we see evidence of the Mesozoic tectonic movement, in the form of a NW–SE striking, dextral strike-slip fault, known as the Heßleser Fault, which faulted and fractured the subsurface below the town. The strike-slip faulting created a zone of small blocks (

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Reflection seismic imaging of buried shallow salt structures – examples from ongoing case studies in Northern Germany

10.5194/egusphere-egu21-11685 ◽

2021 ◽

Author(s):

Ulrich Polom ◽

Rebekka Mecking ◽

Phillip Leineweber ◽

Andreas Omlin

Keyword(s):

High Resolution ◽

Water Resources ◽

Industrial Development ◽

Geophysical Methods ◽

Hydrocarbon Exploration ◽

P Wave ◽

Depth Range ◽

Reflection Seismic ◽

Wide Range ◽

Cap Rock

In the North German Basin salt tectonics generated a wide range of evaporite structures since the Upper Triassic, resulting in e.g. extended salt walls, salt diapirs, and salt pillows in the depth range up to 8 km. Due to their trap and seal properties these structures were in the focus of hydrocarbon exploration over many decades, leading to an excellent mapping of their geometries below 300 m in depth. During salt rise Rotliegend formations were partly involved as a constituent. Some structures penetrated the salt table, some also the former surface. Dissolution (subrosion) and erosion of the salt cap rock by meteoric water took place, combined with several glacial and intraglacial overprints. Finally the salt structures were covered by pleistocene and holocene sediments. This situation partly resulted in proneness for ongoing karstification of the salt cap rock, leading to e.g. local subsidence and sinkhole occurrence at the surface. The geometry, structure and internal lithology of these shallow salt cap rocks are widely unknown. Expanding urban and industrial development, water resources management and increasing climate change effects enhance the demands for shallow mapping and characterization of these structures regarding save building grounds and sustainable water resources.Results of shallow drilling investigations of the salt cap rock and the overburden show unexpectedly heterogenous subsurface conditions, yielding to limited success towards mapping and characterization. Thus, shallow high-resolution geophysical methods are in demand to close the gaps with preferred focus of applicability in urban and industrial environments. Method evaluations starting in 2010 geared towards shallow high-resolution reflection seismic to meet the requirements of both depth penetration and structure resolution. Since 2017 a combination of S-wave and P-wave seismic methods including depth calibrations by Vertical Seismic Profiling (VSP) enabled 2.5D subsurface imaging starting few meters below the surface up to several hundred meters depth in 0.5-5 m resolution range, respectively. The resulting profiles image strong variations along the boundaries and on top of the salt cap rock. Beside improved mapping capabilities, aim of research is the development of characteristic data features to differentiate save and non-save areas.

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