Abstract:The aseismic Iceland-Faeroe-Ridge (IFR) is of central importance in reconstructing the opening of the North Atlantic Ocean. To investigate the crustal structure of the IFR at its southeastern part we conducted a wide aperture seismic survey across the IFR from the Iceland Basin to the Norway Basin. Seismic energy was generated by two 60-litre sleeve guns and recorded by 42 ocean-bottom seismometers (OBS). Kinematic and dynamic forward modeling by two-point ray tracing was applied to develop a 2D velocity-depth… Show more
“…Two lines were completely removed from the Moho dataset. The first line is the IFR profile (Bohnhoff & Makris 2004) across the Iceland -Faroe Ridge, which has a substantially lower Moho depth (23 km) than the FIRE offshore line (Richardson et al 1998) along the ridge (.30 km) (Fig. 4).…”
Seismic refraction data and results from receiver functions were used to compile the depth to the basement and Moho in the NE Atlantic Ocean. For interpolation between the unevenly spaced data points, the kriging technique was used. Free-air gravity data were used as constraints in the kriging process for the basement. That way, structures with little or no seismic coverage are still presented on the basement map, in particular the basins off East Greenland. The rift basins off NW Europe are mapped as a continuous zone with basement depths of between 5 and 15 km. Maximum basement depths off NE Greenland are 8 km, but these are probably underestimated. Plate reconstructions for Chron C24 (c. 54 Ma) suggest that the poorly known Ammassalik Basin off SE Greenland may correlate with the northern termination of the Hatton Basin at the conjugate margin. The most prominent feature on the Moho map is the Greenland-Iceland-Faroe Ridge, with Moho depths .28 km. Crustal thickness is compiled from the Moho and basement depths. The oceanic crust displays an increased thickness close to the volcanic margins affected by the Iceland plume.Gold Open Access: This article is published under the terms of the CC-BY 3.0 license.
“…Two lines were completely removed from the Moho dataset. The first line is the IFR profile (Bohnhoff & Makris 2004) across the Iceland -Faroe Ridge, which has a substantially lower Moho depth (23 km) than the FIRE offshore line (Richardson et al 1998) along the ridge (.30 km) (Fig. 4).…”
Seismic refraction data and results from receiver functions were used to compile the depth to the basement and Moho in the NE Atlantic Ocean. For interpolation between the unevenly spaced data points, the kriging technique was used. Free-air gravity data were used as constraints in the kriging process for the basement. That way, structures with little or no seismic coverage are still presented on the basement map, in particular the basins off East Greenland. The rift basins off NW Europe are mapped as a continuous zone with basement depths of between 5 and 15 km. Maximum basement depths off NE Greenland are 8 km, but these are probably underestimated. Plate reconstructions for Chron C24 (c. 54 Ma) suggest that the poorly known Ammassalik Basin off SE Greenland may correlate with the northern termination of the Hatton Basin at the conjugate margin. The most prominent feature on the Moho map is the Greenland-Iceland-Faroe Ridge, with Moho depths .28 km. Crustal thickness is compiled from the Moho and basement depths. The oceanic crust displays an increased thickness close to the volcanic margins affected by the Iceland plume.Gold Open Access: This article is published under the terms of the CC-BY 3.0 license.
“…However, seismic refraction data provide some indications of the nature and character of the sub-volcanic succession, and information has also been compiled from various studies (e.g. Pálmason 1965;Richardson et al 1998;Smallwood & White 2002;White et al 2003;Bohnhoff & Makris 2004;Raum et al 2005) that intersect the chosen transect of this study (Figs 1-3) where important information such as e.g. the top of the crust has been plotted.…”
Section: Methodsmentioning
confidence: 99%
“…1), whereas the magnetic chrons stop when they reach the ridge. In transect section 1, on the SE part of the IFR, Bohnhoff & Makris (2004) interpreted the crust to be about 15 km thick and of a stretched continental character, with the top at a depth of 3 km (Fig. 4).…”
“…In terms of the pre-volcanic stratigraphy, some information is derived from a NE-SW refraction seismic line orientated approximately perpendicular to the trend of the IFR (Fig. 1b), and which crosses the shallow crustal transect in the southern part of section 2 and at the boundary between sections 3 and 4, where DSDP site 336 is located (Bohnhoff & Makris 2004). At these two intersecting points, a low-velocity layer beneath the volcanic sequence has been proposed, which has been suggested to represent Mesozoic sedimentary rocks, with a thickness of 0.5 and 1.5 km, respectively (Figs 1b & 4).…”
“…Although a number of sub-basins and highs have been interpreted in the western half (Faroese sector) of the FaroeShetland Basin, it is not possible at presentowing to the limited subsurface imaging of the basalt and the lack of well penetrations -to get a clear picture of the underlying pre-volcanic succession. Refraction seismic data have been used to suggest that Mesozoic and Palaeozoic sedimentary rocks might occur between the basement and the volcanic strata (Richardson et al 1998Smallwood & White 2002;White et al 2003White et al , 2008Bohnhoff & Makris 2004;Raum et al 2005), but this remains unsubstantiated as no well in the Faroese sector has penetrated strata older than Paleocene. Thus, the presence of Upper Palaeozoic and Mesozoic rocks in the Faroese sector of the Faroe -Shetland Basin remains largely inferred.…”
This paper presents a summary of the stratigraphy and structure of the Faroese region. As the Faroese area is mostly covered by volcanic material, the nature of the pre-volcanic geology remains largely unproven. Seismic refraction data provide some indications of the distribution of crystalline basement, which probably comprises Archaean rocks, with the overlying cover composed predominantly of Upper Mesozoic (Cretaceous?) and Cenozoic strata. The Cenozoic succession is dominated by the syn-break-up Faroe Islands Basalt Group, which crops out on the Faroe Islands (where it is up to 6.6 km thick) and shelf areas; post-break-up sediments are preserved in the adjacent deep-water basins, including the Faroe-Shetland Basin. Seismic interpretation of the post-volcanic strata shows that almost every sub-basin in the Faroe-Shetland Basin has been affected by structural inversion, particularly during the Miocene. These effects are also observed on the Faroe Platform, the Munkagrunnur Ridge and the Fugloy Ridge, where interpretation of lowgravity anomalies suggests a large-scale fold pattern. The structure of the Iceland-Faroe Ridge, which borders the NW part of the Faroe area, remains ambiguous. The generally thick crust, together with the absence of well-defined seawards-dipping reflectors, may indicate that much of it is underlain by continental material.
The application of multiple waves is an important content of marine exploration, and eliminating or utilizing the multiple waves is one of the significant topics in the processing of seismic data. However, little work is concerned with the multiple waves of Ocean Bottom Seismometer (OBS) wide-angle seismic survey and taking advantage of them to improve the ability of seismic imaging. This study attempts to understand the characteristics of the secondary Pg phases and analyze the applications of seismic imaging in OBS wide angle seismic survey.We firstly identify and know the secondary Pg phases from synthetic seismogram sections and record waveforms then calculate and analyze particle motions of primary Pg and secondary Pg phases through the azimuth angle rotation. After understanding the secondary Pg phases, we get the propagation path by the theoretical model simulation and calculation of measured data with the P wave travel forward modeling method based on the RAYINVR. In addition, improving the seismic imaging is expected, so we used the theoretical model and the actual model of OBS2010 to show the work of the crustal structure imaging.The secondary Pg phases roughly parallel and follow closely the primary Pg phase, and are characterized by continuous, clear phase and strong amplitude. An obvious vibration is observed behind the vibration of the primary Pg with stronger amplitude, which is supposed to be the secondary Pg phase. On the basis of particle motions, the secondary Pg phases belong to the P-wave seismic phase. The travel-time fitting of the possible propagation path based on the test data gave three different results: (a) the χ 2 value is 14.921 when the reflecting layer is water layer and sediment; (b) the χ 2 value is 193.264 when the reflecting layer is the single water layer; and (c) the χ 2 value is 1.786 when the reflecting layer is the single sediment. After theoretical investigation and data tests, we have the following conclusions: (1) the secondary Pg phases are characterized by P-wave; (2) the secondary Pg phases are mainly from the reflection between the sediments, which (3) greatly increase the constraint on the basement, and (4) improve the imaging resolution of the sediments and the upper crust.
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