3D reflection seismic imaging at the 2.5km deep COSC-1 scientific borehole, central Scandinavian Caledonides

Hedin, Peter; Almqvist, Bjarne; Berthet, Théo; Juhlin, Christopher; Buske, Stefan; Simon, Helge; Giese, Rüdiger; Krauß, Felix; Rosberg, Jan-Erik; Alm, Per Gunnar

doi:10.1016/j.tecto.2015.12.013

Cited by 36 publications

(85 citation statements)

References 37 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The seismic velocities measured on the samples, especially the sample perpendicular to foliation, are in agreement with sonic logs and the seismic velocity model used in the reflection seismic profiles [cf. Hedin et al , ; Hedin et al , ; Wenning et al , ]. A range of moduli magnitude is reported where the 40 MPa confining pressure measurement represents the middle of the borehole and the base of the borehole is given by the 70 MPa confining pressure measurement.…”

Section: Resultsmentioning

confidence: 99%

“…Borehole logs, stereographic projections, and rose diagrams of breakouts, A‐DITF, foliation, and fractures. (a) Lithology log (after Hedin et al []). (b) Breakout (red with black bars indicating breakout width) and A‐DITF (green) occurrence along the borehole.…”

Section: Stress Orientation Analysis Methodsmentioning

confidence: 99%

“…The proximal topography reaches a low of ~370 m in the nearby Indalsälven river valley. The borehole location was placed along the site investigation 2‐D reflection seismic profile [ Hedin et al , ], and subsequent 3‐D seismic investigations (see 2‐D subsection in Figure c) around the borehole have produced detailed subsurface reflectivity images [ Hedin et al , ].…”

Section: Geologic Settingmentioning

confidence: 99%

See 2 more Smart Citations

Image log analysis of in situ stress orientation, breakout growth, and natural geologic structures to 2.5 km depth in central Scandinavian Caledonides: Results from the COSC‐1 borehole

et al. 2017

Self Cite

View full text Add to dashboard Cite

Stress‐induced borehole deformation analysis in the Collisional Orogeny in the Scandinavian Caledonide deep scientific borehole establishes in situ stress orientation in a poorly characterized region in central Sweden. Two acoustic televiewer logging campaigns, with more than 1 year between campaigns, provide detailed images along the full length of the 2.5 km deep borehole for breakout, drilling‐induced tensile fracture (DITF), and natural occurring structural analysis. Borehole breakouts occur in 13 distinct zones along total length of 22 m, indicating an average maximum horizontal stress, SHmax, orientation of 127° ± 12°. Infrequent DITFs are constrained within one zone from 786 to 787 m depth (SHmax orientation: 121° ± 07°). These SHmax orientations are in agreement with the general trend in Scandinavia and are in accordance with many mechanisms that generate crustal stress (e.g., ridge push, topographic loading, and mantel driven stresses). The unique acquisition of image logs in two successions allows for analysis of time‐dependent borehole deformation, indicating that six breakout zones have crept, both along the borehole axis and radially around the borehole. Strong dynamic moduli measured on core samples and an inferred weak in situ stress anisotropy inhibit the formation of breakouts and DITFs. Natural fracture orientation below 800 m is congruent to extensional or hybrid brittle shear failure along the same trend as the current SHmax. Analysis of foliation in the image logs reinforces the interpretation that the discontinuous seismic reflectors with fluctuating dip observed in seismic profiles are due to recumbent folding and boudinage.

show abstract

Section: Resultsmentioning

confidence: 99%

Section: Stress Orientation Analysis Methodsmentioning

confidence: 99%

Section: Geologic Settingmentioning

confidence: 99%

See 1 more Smart Citation

Image log analysis of in situ stress orientation, breakout growth, and natural geologic structures to 2.5 km depth in central Scandinavian Caledonides: Results from the COSC‐1 borehole

et al. 2017

Self Cite

View full text Add to dashboard Cite

show abstract

“…Along the thrust contact between the Seve Nappe Complex and the underlying strongly folded and intensely foliated turbidites of the Lower Allochthon, there occurs a sheet of felsic gneisses, locally underlain by a few tens of meters of ductilely deformed Särv Nappe metasandstones and concordant greenstones. Based on the seismic data acquired over the Åre Synform to date (Palm et al, 1991;Hedin et al, 2012Hedin et al, , 2016, prominent reflective units that do not crop out in the eastern limb of the synform are expected to be present at depth further west, beneath its central and western parts. Results from the 2.5 km deep COSC-1 borehole show that the reflectivity of the Seve Nappe Complex is due to the contrast between the high metamorphicgrade gneisses and amphibolites .…”

Section: From Liten To Byxtjärnmentioning

confidence: 99%

Seismic imaging in the eastern Scandinavian Caledonides: siting the 2.5 km deep COSC-2 borehole, central Sweden

et al. 2016

Self Cite

View full text Add to dashboard Cite

Abstract. The Collisional Orogeny in the ScandinavianCaledonides (COSC) project, a contribution to the International Continental Scientific Drilling Program (ICDP), aims to provide a deeper understanding of mountain belt dynamics. Scientific investigations include a range of topics, from subduction-related tectonics to the present-day hydrological cycle. COSC investigations and drilling activities are focused in central Scandinavia, where rocks from the middle to lower crust of the orogen are exposed near the SwedishNorwegian border. Here, rock units of particular interest occur in the Seve Nappe Complex (SNC) of the so-called Middle Allochthon and include granulite facies migmatites (locally with evidence of ultra-high pressures) and amphibolite facies gneisses and mafic rocks. This complex overlies greenschist facies metasedimentary rocks of the doleriteintruded Särv Nappes and underlying, lower grade Jämt-landian Nappes (Lower Allochthon). Reflection seismic profiles have been an important component in the activities to image the subsurface structure in the area. Subhorizontal reflections in the upper 1-2 km are underlain and interlayered with strong west-to northwest-dipping reflections, suggesting significant east-vergent thrusting. Two 2.5 km deep fully cored boreholes are a major component of the project, which will improve our understanding of the subsurface structure and tectonic history of the area. Borehole COSC-1 (IGSN: http://hdl.handle.net/10273/ICDP5054EEW1001), drilled in the summer of 2014, targeted the subduction-related Seve Nappe Complex and the contact with the underlying allochthon. The COSC-2 borehole will be located further east and will investigate the lower grade, mainly Cambro-Silurian rocks of the Lower Allochthon, the Jämtlandian décollement, and penetrate into the crystalline basement rocks to identify the source of some of the northwest-dipping reflections.A series of high-resolution seismic profiles have been acquired along a composite ca. 55 km long profile to help locate the COSC drill holes. We present here the results from this COSC-related composite seismic profile (CSP), including new interpretations based on previously unpublished data acquired between 2011 and 2014. These seismic data, along with shallow drill holes in the Caledonian thrust front and previously acquired seismic, magnetotelluric, and magnetic data, are used to identify two potential drill sites for the COSC-2 borehole.

show abstract

“…According to Hedin et al (2016), the in situ downhole density and P-wave velocity logs reveal a higher average density (3000 kg m −3 ) and P-wave velocity (6000 m s −1 ) for the mafic rocks compared to the dominant felsic gneisses (2800 kg m −3 , 5700 m s −1 ). Also, the occurrence of anisotropy might influence the velocity gradient, at least to a small amount.…”

Section: Vertical Velocity Gradientmentioning

confidence: 99%

The derivation of an anisotropic velocity model from a combined surface and borehole seismic survey in crystalline environment at the COSC-1 borehole, central Sweden

Simon

Buske

Krauß

et al. 2017

Geophysical Journal International

View full text Add to dashboard Cite

. (2017): The derivation of an anisotropic velocity model from a combined surface and borehole seismic survey in crystalline environment at the COSC-1 borehole, central Sweden. -Geophysical Journal International, 210, 3, pp. 1332-1346 S U M M A R YThe Scandinavian Caledonides provide a well-preserved example of a Palaeozoic continentcontinent collision, where surface geology in combination with geophysical data provides information about the geometry of parts of the Caledonian structure. The project COSC (Collisional Orogeny in the Scandinavian Caledonides) investigates the structure and physical conditions of the orogen units and the underlying basement with two approximately 2.5 km deep cored boreholes in western Jämtland, central Sweden. In 2014, the COSC-1 borehole was successfully drilled through a thick section of the Seve Nappe Complex. This tectonostratigraphic unit, mainly consisting of gneisses, belongs to the so-called Middle Allochthons and has been ductilely deformed and transported during the collisional orogeny. After the drilling, a major seismic survey was conducted in and around the COSC-1 borehole with the aim to recover findings on the structure around the borehole from core analysis and downhole logging. The survey comprised both seismic reflection and transmission experiments, and included zero-offset and multiazimuthal walkaway Vertical Seismic Profile (VSP) measurements, three long offset surface lines centred on the borehole, and a limited 3-D seismic survey. In this study, the data from the multiazimuthal walkaway VSP and the surface lines were used to derive detailed velocity models around the COSC-1 borehole by inverting the first-arrival traveltimes. The comparison of velocities from these tomography results with a velocity function calculated directly from the zero-offset VSP revealed clear differences in velocities for horizontally and vertically travelling waves. Therefore, an anisotropic VTI (transversely isotropic with vertical axis of symmetry) model was found that explains first-arrival traveltimes from both the surface and borehole seismic data. The model is described by a vertical P-wave velocity function derived from zero-offset VSP and the Thomsen parameters = 0.03 and δ = 0.3, estimated by laboratory studies and the analysis of the surface seismic and walkaway VSP data. This resulting anisotropic model provides the basis for further detailed geological and geophysical investigations in the direct vicinity of the borehole.

show abstract

3D reflection seismic imaging at the 2.5km deep COSC-1 scientific borehole, central Scandinavian Caledonides

Cited by 36 publications

References 37 publications

Image log analysis of in situ stress orientation, breakout growth, and natural geologic structures to 2.5 km depth in central Scandinavian Caledonides: Results from the COSC‐1 borehole

Image log analysis of in situ stress orientation, breakout growth, and natural geologic structures to 2.5 km depth in central Scandinavian Caledonides: Results from the COSC‐1 borehole

Seismic imaging in the eastern Scandinavian Caledonides: siting the 2.5 km deep COSC-2 borehole, central Sweden

The derivation of an anisotropic velocity model from a combined surface and borehole seismic survey in crystalline environment at the COSC-1 borehole, central Sweden

Contact Info

Product

Resources

About

3D reflection seismic imaging at the 2.5km deep COSC-1 scientific borehole, central Scandinavian Caledonides

Cited by 36 publications

References 37 publications

Image log analysis of in situ stress orientation, breakout growth, and natural geologic structures to 2.5 km depth in central Scandinavian Caledonides: Results from the COSC‐1 borehole

Image log analysis of in situ stress orientation, breakout growth, and natural geologic structures to 2.5 km depth in central Scandinavian Caledonides: Results from the COSC‐1 borehole

Seismic imaging in the eastern Scandinavian Caledonides: siting the 2.5 km deep COSC-2 borehole, central Sweden

The derivation of an anisotropic velocity model from a combined surface and borehole seismic survey in crystalline environment at the COSC-1 borehole, central Sweden

Contact Info

Product

Resources

About

Seismic imaging in the eastern Scandinavian Caledonides: siting the 2.5 km deep COSC-2 borehole, central Sweden