| 1. |
- Berthelsen, A., et al.
(author)
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Recording marine airgun shots at offsets between 300 and 700 km
- 1991
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In: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 18:4, s. 645-648
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Journal article (peer-reviewed)abstract
- This paper demonstrates that - under favorable conditions - by using multichannel recording and subsequent stacking of adjacent records marine airgun shots have been detected at offset distances up to 700 km, the maximum offset at which the authors attempted to record data.^Besides a powerful airgun array, a low noise environment at the recording site and the elimination of static shifts are the prerequisites to obtain refracted and reflected arrivals from the crust and upper mantle at such large offsets.^Primary arrivals detected at offsets between 400 and 700 km image the upper mantle from 70 to about 120 km depth.^Stacking of neighboring shots and/or receivers successfully increases the signal-to-noise ratio, if the traces have been corrected for offset differences, which requires knowledge of the apparent phase velocities.^The data presented here were collected in autumn 1989 during the BABEL Project on the Baltic Shield.
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| 2. |
- Hobbs, R. W., et al.
(author)
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Integrated seismic studies of the Baltic shield using data in the Gulf of Bothnia region
- 1993
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In: Geophysical Journal International. - 0956-540X .- 1365-246X. ; 112:3, s. 305-324
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Journal article (peer-reviewed)abstract
- In the autumn of 1989 a co-operative experiment involving 12 research institutions in northwestern Europe collected 2268 km of deep seismic reflection profiles in the Gulf of Bothnia and the Baltic Sea. the 121 litre airgun array used for this profiling was also recorded by 62 muiticomponent land stations to provide coincident refraction surveys, fan-spreads, and 3-D seismic coverage of much of the Gulf of Bothnia. We thus have potentially both high-resolution impedance contrast images as well as more regional 3-D velocity models in both P- and S-waves. In the Bothnian Bay a south-dipping, non-reflective zone coincides with the conductive Archaean-Proterozoic boundary onshore in Finland. Between the Bothnian Bay and Bothnian Sea observed reflectivity geometries and velocity models at Moho depths suggest structures inherited from a 1.9Ga subduction zone; the upper crust here appears to have anomalously low velocity. Within the Bothnian Sea, reflectivity varies considerably beneath the metasedimentary/granitoid rocks of the Central Svecofennian Province (CSP) and the surrounding metavolcanic-arc rocks. Numerous dipping reflectors appear throughout the metavolcanic crust, whereas the CSP has little reflectivity. Wide-angle reflections indicate that the metasedimentary crust of the Bothnian Basin is 10 km thicker than the neighbouring Svecofennian subprovinces. Near the Åland archipelago Rapakivi granite plutons exhibit bright reflections, a contrast to the usual non-reflective plutons elsewhere in western Europe. Additional dipping reflections deep in the crust of this area may support models of rifting and crustal thinning during emplacement of the 1.70-1.54 Ga Rapakivi granites. Coeval gabbroic/anorthositic magmatism may explain the high reflectivity and high velocity of these plutons. the c. 1.25 Ga mafic sills and feeder dykes of the Central Scandinavian Dolerite Group also produce clear reflections on both near- and far-offset seismic sections. Continued modelling will produce better velocity models of the crust and better constrained contour maps of crustal thickness in this part of the Baltic shield.
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| 3. |
- Serlo, W, et al.
(author)
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Functions and complications of shunts in different etiologies of childhood hydrocephalus.
- 1990
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In: Child's Nervous System. - 0256-7040. ; 6:2, s. 92-94
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Journal article (peer-reviewed)abstract
- Shunt function and complications in different etiologies of childhood hydrocephalus were studied in a series of 306 patients involving 1102 shunt operations. Shunts in patients with hydrocephalus caused by neoplasms proved to be most prone to shunt complications. The patency time for shunts in these patients was significantly shorter than for shunts in other patient categories [Standard number of deviations (SND) 5.9; P less than 0.001, Meyer-Kaplan life table analysis]. When the two main groups of infantile hydrocephalus-congenital obstructive hydrocephalus and hydrocephalus caused by perinatal intracerebral hemorrhage-were compared, the latter group proved to be significantly more prone to shunt infections (P less than 0.01), with an infection rate of 17.8% compared with 8.9% for the former group. The importance of this fact is stressed by the observation that these patients appear to constitute an increasing percentage of hydrocephalic patients. According to the present study, patients with congenital intracranial cysts and hydrocephalus are less prone to shunt complications, i.e., the infection rate is 6.8%, which is significantly less than that of patients with other types of hydrocephalus (P less than 0.01; chi-square test).
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