2D crooked-line seismic reflection surveys in crystalline environments are often considered challenging in their processing and interpretation. These challenges are more evident when complex ...diffraction signals that can originate from out-of-the-plane and a variety of geological features are present. A seismic profile in the Kristineberg mining area in northern Sweden shows an impressive diffraction package, covering an area larger than 25 km
2 in the subsurface at depths greater than 2.5 km. We present here a series of scenarios in which each can, to some extent, explain the nature of this extraordinarily large package of diffractions. Cross-dip analysis, diffraction imaging and modeling, as well as 3D processing of the crooked-line data provided constraints on the interpretation of the diffraction package. Overall, the results indicate that the diffraction package can be associated with at least four main short south-dipping diffractors in a depth range of 2.5–4.5 km. Candidate scenarios for the origin of the diffraction package are: (1) a series of massive sulphide deposits, (2) a series of mafic–ultramafic intrusions, (3) a major shear-zone and (4) multiple contact lithologies. We have also investigated the possible contribution of mode-converted scattered energy in the diffraction package using a modified converted-wave 3D prestack depth migration algorithm with the results indicating that a majority of the diffractions are P-wave diffractions. The 3D prestack migration of the data provided improved images of a series of steeply north-dipping mafic–ultramafic sill intrusions to a depth of about 4 km, where the diffractions appear to focus after the migration. The results and associated interpretations presented in this paper have improved our understanding of this conspicuous package of diffractions and may lead to re-evaluation of the 3D geological model of the Kristineberg mining area.
We reprocessed an ∼35‐km‐long part of the IBESREIS seismic reflection profile which runs over the Iberian Pyrite Belt section of the South Portuguese Zone, SW Iberia, with the goal to image the upper ...crust (<15‐km depth). The applied processing sequence enhanced numerous prominent reflections and diffraction patterns within the uppermost 5‐s travel time relative to high‐amplitude source‐generated noise. A complex subsurface characterized by conflicting dips and a survey following winding roads require a crooked‐line prestack migration scheme for coherent imaging. To interpret sources of diffracted energy, we additionally employed a diffraction imaging scheme which enhances diffractions at the expense of reflections.The final seismic images show south‐vergent imbricate fold‐and‐thrust tectonics, documenting the contractive deformation that the South Portuguese Zone experienced during the Variscan Orogeny. Based on surface geological information, we correlate a low reflective unit with the shallow Upper Carboniferous Flysch Group, a highly reflective unit ranging in depth from 2 to 4 km with the Middle Carboniferous Volcano–Sedimentary Complex Group, which hosts massive sulfide deposits, and a moderately reflective unit with the Upper Devonian Phyllite–Quartzite Group. Below these units, another low‐reflective facies is present, which may represent older Paleozoic metasediments. In addition, the seismic and diffraction images reveal bands of high reflectivity and distinct diffraction patterns that were interpreted as extensive layered mafic intrusions. These proposed mafic bodies may be related to the same event that triggered a huge hydrothermal activity assumed in Early Carbonifereous times.
The sedimentary infill of glacially overdeepened valleys
(i.e., structures eroded below the fluvial base level) is an excellent but
yet underexplored archive with regard to the age, extent, and ...nature of past glaciations. The ICDP project DOVE (Drilling Overdeepened Alpine Valleys) Phase 1 investigates a series of drill cores from glacially overdeepened troughs at several locations along the northern front of the Alps. All sites
will be investigated with regard to several aspects of environmental
dynamics during the Quaternary, with focus on the glaciation, vegetation,
and landscape history. Geophysical methods (e.g., seismic surveys), for
example, will explore the geometry of overdeepened structures to better
understand the process of overdeepening. Sedimentological analyses combined
with downhole logging, analysis of biological remains, and state-of-the-art
geochronological methods, will enable us to reconstruct the erosion and
sedimentation history of the overdeepened troughs. This approach is expected
to yield significant novel data quantifying the extent and timing of Middle
and Late Pleistocene glaciations of the Alps. In a first phase, two sites
were drilled in late 2021 into filled overdeepenings below the
paleolobe of the Rhine Glacier, and both recovered a trough filling composed
of multiphase glacial sequences. Fully cored Hole 5068_1_C reached a depth of 165 m and recovered 10 m molasse bedrock at the base. This hole will be used together with two flush holes (5068_1_A, 5068_1_B) for further geophysical cross-well experiments. Site 5068_2 reached a depth of 255 m
and bottomed out near the soft rock–bedrock contact. These two sites are
complemented by three legacy drill sites that previously recovered filled
overdeepenings below the more eastern Alpine Isar-Loisach, Salzach, and Traun paleoglacier lobes (5068_3, 5068_4, 5068_5). All analysis and
interpretations of this DOVE Phase 1 will eventually lay the ground for an
upcoming Phase 2 that will complete the pan-Alpine approach. This follow-up
phase will investigate overdeepenings formerly occupied by paleoglacier
lobes from the western and southern Alpine margins through drilling sites in France, Italy, and Slovenia. Available geological information and
infrastructure make the Alps an ideal area to study overdeepened structures;
however, the expected results of this study will not be restricted to the
Alps. Such features are also known from other formerly glaciated mountain
ranges, which are less studied than the Alps and more problematic with
regards to drilling logistics. The results of this study will serve as
textbook concepts to understand a full range of geological processes
relevant to formerly glaciated areas all over our planet.
Imaging the architecture of the shallow crust of the South Portuguese Zone fold-and-thrust belt is essential to extend surface mapped geological information to depth and to help in developing models ...of the ore-bearing Iberian Pyrite Belt part of the Variscan orogeny. The recently acquired IBERSEIS seismic-reflection data set provides, for the first time, detailed images of the entire crust, but source-generated noise masks the earliest reflections and limits the shallowest observed signals to depths >500 m. We inverted P- and SV first-arrival traveltimes for the smoothest minimum-structure velocity models, imaging the shallowest few hundreds of metres along four in total ∼60-km-long profiles. A comparison of a 2-D and 2.5-D (3-D forward and 2-D inverse problem) crooked-line inversion scheme revealed that the crooked-line geometry has a negligible effect on the final images. Resolution of the final preferred models was assessed on the basis of an extensive series of checkerboard tests, showing a slightly lower resolution capability of the SV-data due to greater data uncertainty, fewer number of picks and more limited source–receiver offsets compared with the P-data. The preferred final models compare favourably with the mapped surface geology, showing relatively high and uniform velocities (>5.25 km s−1) for the flysch group in the southern part of the investigation area. Low velocities (∼4.5 km s−1) are found for the ‘La Puebla de Guzman antiform’ in the centre of the investigation area, where the phyllite–quartzite group is exposed. Velocities fluctuate the most along the northernmost ∼20 km. Velocity variations reflect more the state of tectonic deformation than being directly correlated with the mapped lithologies. Based on a comparison with coincident seismic-reflection data along the southern half of the area, we suggest that two areas of low to intermediate ratios (∼1.85–1.9) correspond to occurrences of thick and less deformed flysch-group units, whereas high ratios (∼1.95) are interpreted to indicate increased porosity due to intense fracturing.
We reprocessed an ∼35-km-long part of the IBESREIS seismic reflection profile which runs over the Iberian Pyrite Belt section of the South Portuguese Zone, SW Iberia, with the goal to image the upper ...crust (<15-km depth). The applied processing sequence enhanced numerous prominent reflections and diffraction patterns within the uppermost 5-s travel time relative to high-amplitude source-generated noise. A complex subsurface characterized by conflicting dips and a survey following winding roads require a crooked-line prestack migration scheme for coherent imaging. To interpret sources of diffracted energy, we additionally employed a diffraction imaging scheme which enhances diffractions at the expense of reflections.The final seismic images show south-vergent imbricate fold-and-thrust tectonics, documenting the contractive deformation that the South Portuguese Zone experienced during the Variscan Orogeny. Based on surface geological information, we correlate a low reflective unit with the shallow Upper Carboniferous Flysch Group, a highly reflective unit ranging in depth from 2 to 4 km with the Middle Carboniferous Volcano–Sedimentary Complex Group, which hosts massive sulfide deposits, and a moderately reflective unit with the Upper Devonian Phyllite–Quartzite Group. Below these units, another low-reflective facies is present, which may represent older Paleozoic metasediments. In addition, the seismic and diffraction images reveal bands of high reflectivity and distinct diffraction patterns that were interpreted as extensive layered mafic intrusions. These proposed mafic bodies may be related to the same event that triggered a huge hydrothermal activity assumed in Early Carbonifereous times.
2D crooked-line seismic reflection surveys in crystalline environments are often considered challenging in their processing and interpretation. These challenges are more evident when complex ...diffraction signals that can originate from out-of-the-plane and a variety of geological features are present. A seismic profile in the Kristineberg mining area in northern Sweden shows an impressive diffraction package, covering an area larger than 25 km(2) in the subsurface at depths greater than 2.5 km. We present here a series of scenarios in which each can, to some extent, explain the nature of this extraordinarily large package of diffractions. Cross-dip analysis, diffraction imaging and modeling, as well as 3D processing of the crooked-line data provided constraints on the interpretation of the diffraction package. Overall, the results indicate that the diffraction package can be associated with at least four main short south-dipping diffractors in a depth range of 2.5-4.5 km. Candidate scenarios for the origin of the diffraction package are: (1) a series of massive sulphide deposits, (2) a series of mafic-ultramafic intrusions, (3) a major shear-zone and (4) multiple contact lithologies. We have also investigated the possible contribution of mode-converted scattered energy in the diffraction package using a modified converted-wave 3D prestack depth migration algorithm with the results indicating that a majority of the diffractions are P-wave diffractions. The 3D prestack migration of the data provided improved images of a series of steeply north-dipping mafic-ultramafic sill intrusions to a depth of about 4 km, where the diffractions appear to focus after the migration. The results and associated interpretations presented in this paper have improved our understanding of this conspicuous package of diffractions and may lead to re-evaluation of the 3D geological model of the Kristineberg mining area.
The Laser Interferometer Space Antenna (LISA), which is currently under construction, is designed to measure gravitational wave signals in the milli-Hertz frequency band. It is expected that tens of ...millions of Galactic binaries will be the dominant sources of observed gravitational waves. The Galactic binaries producing signals at mHz frequency range emit quasi monochromatic gravitational waves, which will be constantly measured by LISA. To resolve as many Galactic binaries as possible is a central challenge of the upcoming LISA data set analysis. Although it is estimated that tens of thousands of these overlapping gravitational wave signals are resolvable, and the rest blurs into a galactic foreground noise; extracting tens of thousands of signals using Bayesian approaches is still computationally expensive. We developed a new end-to-end pipeline using Gaussian Process Regression to model the log-likelihood function in order to rapidly compute Bayesian posterior distributions. Using the pipeline we are able to solve the Lisa Data Challenge (LDC) 1-3 consisting of noisy data as well as additional challenges with overlapping signals and particularly faint signals.
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