ALBERT

Notizen: Chains of crystalline-Si nanospheres were studied by means of Raman scattering spectroscopy. We found that the one-phonon Raman scattering peak from the chains was asymmetric and broader than that from bulk Si. This phenomenon can be attributed to a phonon confinement in the silicon nanospheres. The phonon confinement became more obvious by decreasing the size of the silicon nanospheres in the chains. We also found that the Si nanospheres in the chains were under compressive stress by the covering oxide layers through the analysis of the Raman shift. © 2002 American Institute of Physics.

Notizen: Seismic refraction measurements were made in August 1988 to study the crustal structure off Lofoten, Northern Norway. Twenty-four 3-component Ocean Bottom Seismographs (OBS) were used, of which seven were deployed in the area covered by landward-flowing basalt deposited during the early Eocene break-up between Norway and Greenland. The main purpose of the OBS survey was to investigate whether this method can be used to map structures below the basalt, which is not easy to penetrate with conventional seismic reflection techniques. The records obtained showed that the OBS data contain considerable information about structures below the flood-basalt; preopening sediments up to 4.0 km thick is indicated below the 1.0–2.5 km-thick landward-flowing basalt. The success of the OBS survey indicates that such measurements can become an important tool in investigations on passive volcanic margins and, potentially, in other areas where highly reflective boundaries make the reflection technique difficult to apply.

Notizen: In 1988, an extensive geophysical experiment was performed on the Lofoten passive continental margin, which was formed by the continental break-up between Greenland and northern Norway at 58 Ma. The geological units of the outer Lofoten margin are characterized by seaward-dipping reflectors (SDRs) and landward flood basalt, which extends up to 100 km landwards of SDRs. In this study, we obtain the P-wave velocity structure beneath the Lofoten Basin, the SDRs, and the landward flood basalt by use of ocean-bottom seismograph refraction profiling, and we also discuss the formation of the northern Norwegian passive continental margin.In the Lofoten Basin the crust is of oceanic type, consisting of sedimentary layers, oceanic laver 2 (4.9−5.5 km s−1), layer 3A (6.3−6.8 km s−1) and layer 3B (7.0−7.1 km s−1). Beneath the SDRs the crustal layers are identical to those of the Lofoten Basin, but the thickness of the lower crust, which represents the same velocity as layer 3B, increases to 5 km towards the continent side, and a high-velocity lower crustal layer (7.3 km s−1) is formed at the base of the crust. The ocean-continent transition zone is situated between the landward side of the SDRs and the northward continuation of the Vøring Plateau Escarpment. In this region the velocity of the lower crust gradually decreases and approaches the lower crustal velocity beneath the Lofoten Islands (6.8 km s−1). The model also indicates that the high-velocity layer disappears in this region. Comparing our model with the crustal structure on the Vøring margin, it is clear that the lower crustal body (≥7 km s−1) thickens southwards along the northern Norwegian continental margin. Recent results from petrological and geophysical studies of the generation of the oceanic crust have shown that increasing the temperature of the upwelling asthenospheric material increases the thickness of the oceanic crust. We interpret this as that the oceanic crust in the southern area in the Vøring-Lofoten margin was generated by hotter material than that of the northern area.

Notizen: In 1984 an extensive geophysical investigation was conducted in the northernmost part of the Ryukyu Island Arc, south of Kyushu Island. Japan. The aim of this investigation was to obtain new information on the nature of crust and upper mantle at the continental margin through various geophysical measurements (seismic profiling, gravity, magnetism, sea beam and heat flow).This paper presents the crust and upper mantle structure deduced from ocean bottom seismographic profiling conducted along two lines. One line, 190 km long, was taken behind the northernmost part of the Ryukyu Island Arc, parallel to the major tectonic units, i.e. the Okinawa Trough, Ryukyu Arc and Ryukyu Trench. The other, 295 km long, was perpendicular to the tectonic units. Along these profiles, we deployed ocean bottom seismograms spaced 10-20 km apart. As a controlled source, we used both explosives and an airgun array. The experiment was successful and provided quite important information on the tectonics of a trench-island arc-back arc system.The velocity structure obtained for the profile behind the Ryukyu Islands has continental properties. The sediment thickness is 3-4 km. although it shows lateral variations due to basement undulation. The velocities of the upper and lower crust are 5.8-6.2 and 6.6-6.8 km s-1, respectively. The total crustal thickness decreases southwestward, from 27-30 to 23-24 km. This is direct evidence for crustal thinning associated with the process of back-arc spreading.The velocity structure along the profile from the trench to the island arc clearly shows the subduction, accretion and deformation at this margin. The crust beneath the trench has oceanic properties. The sediment thickness is 1.3-3.0 km, beneath which the igneous basement shows severe undulation. The total crustal thickness is 7-8 km. The Pn velocity is slightly less than 8.0 km s-1. Our seismic data revealed a huge sedimentary wedge located 50-150 km landward of the trench. The maximum thickness of this wedge exceeds 12 km. The origin of this wedge may be oceanic because the P-wave velocity in its eastern half is almost comparable to that obtained for the trench area. The velocity structure landward of the wedge is continental and similar to that obtained for the profile behind the island arc.

Notizen: A high-quality multichannel seismic reflection line was acquired in 1987 along a 175 km long profile across the continental shelf off Lofoten, northern Norway. A seismic wide-angle experiment was performed in 1988 along the same profile, using seven three-component Ocean Bottom Seismographs (OBS) with 20-25 km spacing and shotpoint intervals of 240 m.The study of the data has shown that the combination of the multichannel reflection and the wide-angle (OBS) technique provides information about the crustal structure beneath the Lofoten shelf that could not have been achieved using only one of the techniques. the multichannel reflection data provide a detailed image of the shallow (Cretaceous) structures, which represents an important basis for inversion of the OBS data. the lower crust and the Moho are also well mapped in some parts of the area with the multichannel reflection technique.The OBS data reveal that significant amounts of pre-Cretaceous sediments exist along almost the entire profile, with a maximum thickness of about 5 km in the Vestfjorden Basin. From the OBS data the thickness of the lower crust is inferred to decrease from about 11.5 km under the Røst High to about 2 km below the Lofoten Ridge. the OBS data indicate further that the Moho position under the Vestfjorden Basin is considerably deeper than can be inferred from the reflection data.About 10km below Moho a strong dipping event is observed in the OBS data. This upper mantle reflection might be related to a possible seaward dipping master fault, and/or presence of layers of partially hydrated peridotite.