| 1. |
- Davis, J.L, et al.
(författare)
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Geodesy by radio interferometry: Effects of atmospheric modeling errors on estimates of baseline length
- 1985
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Ingår i: Radio Science. - 0048-6604 .- 1944-799X. ; 20:6, s. 1593-1607
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Tidskriftsartikel (refereegranskat)abstract
- Analysis of very long baseline interferometry data indicates that systematic errors in prior estimatesof baseline length, of order 5 cm for ~8000-km baselines, were due primarily to mismodeling of theelectrical path length of the troposphere and mesosphere ("atmospheric delay"). Here we discussobservational evidence for the existence of such errors in the previously used models for the atmosphericdelay and develop a new "mapping" function for the elevation angle dependence of this delay. Thedelay predicted by this new mapping function differs from ray trace results by less than ~5 mm, at allelevations down to 5° elevation, and introduces errors into the estimates of baseline length of •
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| 2. |
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| 3. |
- Widenfalk, Lennart, et al.
(författare)
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A multidisciplinary investigation of the Notträsk Gabbro, northern Sweden
- 1985
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Ingår i: Geologiska föreningens i Stockholm förhandlingar. - : Informa UK Limited. - 0016-786X. ; 107:2, s. 109-126
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Tidskriftsartikel (refereegranskat)abstract
- The differentiated, sulfide-bearing gabbro near the city of Boden in northern Sweden has been investigated in order to get a plausible model for its formation, shape and age. The gabbro is associated with a major fault system along which several intrusive bodies occur. The largest of these has been traversed by a gravimetric, magnetometric and geological profile. The investigated intrusion is undeformed and oval-shaped and covers some 20 km2. The outer parts of the body consist of a norite in contact with older meatasediments and granites of varying age. Inside the norite occurs a magnetite-rich gabbro, which forms a ring around the centre of the massif, which in turn consists of leucogabbro-olivine gabbro. Fe, Ti and K are low in the centre where Mg and Cr have their highest contents. Impregnations of sulfides and a massive pyrrhotite vein with some 1 % Ni are located in the norite. A number of intrusion models have been tested by computer modelling combining gravimetric and magnetic field data. The most probable model seems to be a funnel-shaped body pointing downwards. The different gabbro types dip steeply inwards indicating vertical zones rather than horizontal. Palaeomagnetic measurements show that the intrusion has a similar orientation of magnetization as other gabbros of the Haparanda series in northern Sweden (1800-1900 Ga, Rb-Sr). Furthermore, the pole distributions show that the rock cooled slowly, which may indicate that the present outcrop is a deep part of an eroded intrusion. The massif is supposed to have been formed by a diapiric re-emplacement of primary horizontal cumulates formed in the sequence olivine gabbro-leucogabbro-magnetite-bearing gabbro-norite.
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| 4. |
- Alfsen, K. H., et al.
(författare)
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Electric field and plasma observations near the magnetopause and bow shock during a rapid compression.
- 1984
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Ingår i: Achievements of the International Magnetospheric Study (IMS). ; , s. 99-104
-
Tidskriftsartikel (refereegranskat)abstract
- A fast compressional motion of the magnetopause resulting from the interaction of an interplanetary shock and the Earth's magnetosphere is discussed. The ISEE-1 and 2 satellites were in the frontside magnetosphere before the shock. A magnetosonic wave front, the magnetopause, and the bow shock passed them in a very short time. By a combination of electric and magnetic field data it is possible to determine the magnetosonic and the magnetopause velocity. -from STAR, 23(14), 1985
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| 5. |
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| 6. |
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| 7. |
- Boldreel, Lars Ole
(författare)
-
An attempt based on an interpretation of multichannel reflection seismic data to delineate sedimentary sequences, structures and evolution in the part of the Western Barents Sea 72° - 74°N and 10° - 17°E
- 1988
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is an attempt to throw further light on the structural development of the passive continental margin of the Western Barents Sea in the area from 72000'N to 74000'N and from 17000'E to 10000'E. It is based mainly on multichannel reflection seismics but available aeromagnetic, shipborne magnetic and free-air gravimetric data have also been analyzed. It seems from the results that the area between what is generally called the Senja fracture zone and the possible southernmost part of the Hornsund fault zone consists of a nonoceanic basement. The transition between the oceanic and the continental basement is placed adjacent to the Senja fracture zone and its northern continuation up to 740 N. The transition zone to the east of the Senja Fracture Zone in the area 720 50'N to 74000'N suggested in earlier works is here correlated with the development of a listric fault complex rooted in a detachment zone. The non-oceanic basement to the east of the Senja Fracture Zone is also examined and it is suggested that this basement is a stretched continental crust. A chronology for the sequences chosen has been established using the wells 711719-1 and 711719-2 located to the south of the area studied. The structural development of the margin has been dated on the basis of seven depth maps and four isopach maps of the sequences representing the time from the onset of the Tertiary to the end of the Oligocene. The main result is that the end of a major rifting phase corresponds to the beginning of the Paleocene while the onset of the sea floor spreading corresponds to the time interval from Early Eocene to Late Eocene. It appears from backstripping studies that the free-air gravity anomaly associated with the Senja Fracture Zone is probably due to the sediments loading an oceanic plate. This would mean that the Senja "Fracture Zone" is not really a fracture zone. It also seems that the seafloor spreading took place in an oblique northwards manner and that the oceanic basement closest to the Senja "Fracture Zone" and its northern continuation up to 740N is of Eocene age. If this interpretation is correct it would call for a modification of the 2-stage opening model of this area proposed in earlier works.
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| 8. |
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| 9. |
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| 10. |
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| 11. |
- Chouliaras, Gerassimos, et al.
(författare)
-
The application of the magnetotelluric impedance tensor to earthquake prediction research in Greece
- 1988
-
Ingår i: Tectonophysics. - : Elsevier BV. - 0040-1951 .- 1879-3266. ; 152:1-2, s. 119-135
-
Tidskriftsartikel (refereegranskat)abstract
- Continuous short period (0.1-3600 s) measurements of the magnetotelluric field components were conducted simultaneously at two sites in Greece for a period of 5 weeks. The estimation of the impedance tensor elements from 8-hr windows of recorded data, at each station, is found to describe the local electromagnetic induction with great accuracy. The computation of the residual electric field, obtained as the difference between the observed and estimated inductive part of the electric fields, clearly improves the detection of any local electric field anomaly. This method was used in an attempt to detect precursory Sci smic electrical signals (SES) that have been reported to precede earthquakes in Greece. The results indicate the success of this method in resolving ambiguities about the nature of the reported SES, i.e. whether it has an external or internal source. Although during the recording period no large earthquake occurred, five with a magnitude of between ML = 4.0 and ML = 4.3 occurred within a radius of 150 km from one of the stations. The magnetotelluric recordings and the computed residual electric fields for the time intervals reported to contain the SES precursors to these events were analysed in some detail. In two of the cases it was found that the sources could not be related to earthquake processes. In the other three cases the nature of the source of the suspected SES, although electric, could not be established with certainty. These results indicate that for earthquakes of small magnitude (ML ≤ 4.3) or of large epicentral distance (r ≥ 100 km), the detection of a SES is extremely difficult.
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| 12. |
- Das, U.C., et al.
(författare)
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Resistivity and induced polarization responses of arbitarily shaped 3-D bodies in a two-layered Earth
- 1987
-
Ingår i: Geophysical Prospecting. - : Wiley. - 0016-8025 .- 1365-2478. ; 35:1, s. 98-109
-
Tidskriftsartikel (refereegranskat)abstract
- Numerical computations using the integral equation method are presented for resistivity and IP responses due to arbitrarily shaped 3‐dimensional bodies in a layered earth. The unknown surface charge density distribution is expressed as the solution of Fredholm's integral equation of the second kind. Use of moment method (with pulse basis function and point‐collocation) yields the matrix equations for the unknowns. The contributions to Green's function are solved (a) analytically for the primary and (b) by convolution for the secondary contributions resulting in a fast algorithm. The further step of computing potential, apparent resistivity, chargeability etc., for any electrode system, is straightforward. Our results show a good agreement with those from finite difference methods and physical tank experiments. The CPU time is only 138 s on a super‐minicomputer for an apparent resistivity pseudo‐section, even with 96 elementary cells as used for discretization. A large number of models for different geological situations were studied; some are presented here.
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| 13. |
- Dyrelius, D., et al.
(författare)
-
Bergarters fysik
- 1985
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Ingår i: Geofysik. - Uppsala : Svenska fysikersamfundet. - 9186344285
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Bokkapitel (populärvet., debatt m.m.)
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| 14. |
- Elming, Sten-åke
(författare)
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A palaeomagnetic study of Svecokarelian basic rocks from northern Sweden
- 1985
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Ingår i: Geologiska föreningens i Stockholm förhandlingar. - : Informa UK Limited. - 0016-786X. ; 107:1, s. 17-35
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Tidskriftsartikel (refereegranskat)abstract
- This palaeomagnetic investigation comprises basic rocks from six localities from the Svecokarelian zone in northern Sweden. Most of the pole positions in this study and other reported poles of Svecokarelian and post-Svecokarelian rocks fall within an approximately 12 degrees wide band running from east to west representing ages of magnetizations from 1880-1700 to ∼ 1530 Ma. Thermal demagnetizations of specimens of the probably oldest massifs indicate a possible backward continuation of the polar wandering path. Mineralogical studies of thin sections of the rocks show ore symplectites and myrmekitic textures indicating a slow rate of cooling at least at the end of the rock formation. Signs of metamorphism are demonstrated by the existence of secondary minerals, including magnetite, not related to late magmatic alterations. The distribution of site means as well as the change of directions of the remanence vectors during thermal demagnetization can be explained by a slow rate of cooling and where signs of metamorphism exist by partial remagnetization of the rock. This study has, apart from the palaeomagnetic results, demonstrated the difficulty of correlating radiometric ages with ages of magnetization
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| 15. |
- Elming, Sten-Åke
(författare)
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Density and magnetic properties of rocks in the Caledonides of Jämtland, Sweden
- 1980
-
Ingår i: Geologiska föreningens i Stockholm förhandlingar. - : Informa UK Limited. - 0016-786X. ; 102:4, s. 439-453
-
Tidskriftsartikel (refereegranskat)abstract
- Density and magnetic properties were determined on some 1350 rock samples, taken from the different lithologies in the Caledonides of Jmtland, Sweden. The density determinations showed a strong trend of increasing density when moving from east to west in the investigated area. There was also a general increase in density upwards in the tectono-stratigraphy from the autochthon to the Seve of the Seve-Kli Nappe Complex. The determination of magnetic properties showed that east of the Caledonian Front the dominating high-susceptibility rock was the Rtan granite. In the Eastern Complex, west of the Caledonian Front, high-susceptibility rocks were found in the parautochthonous and allochthonous crystalline basement, whereas in the Western Complex the Ottfjllet dolerite in the Srv Nappe was the dominating high-susceptibility rock.
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| 16. |
- Elming, Sten-Åke
(författare)
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Geological modelling based on gravity data from the central part of the Swedish caledonides
- 1988
-
Ingår i: Geologiska föreningens i Stockholm förhandlingar. - : Informa UK Limited. - 0016-786X. ; 110:4, s. 317-327
-
Tidskriftsartikel (refereegranskat)abstract
- Gravimetric measurements have been carried out within a c. 500 km2 area of western Jämtland in the Swedish Caledonides. Using different types of regional-residual gravity field separations, various geological models have been tested to fit the measured gravity data. Information on the geology and density of the rocks have reduced the number of possible models which are presented along two profiles. These models confirm the existence of antiforms and synforms running approximately parallel to the mountain range. The main profile crosses the two synforms over which positive anomalies are identified. Both in the western Tnnfors Synform and the eastern re Synform this is explained by the presence of high density Seve rocks, in the former case occurring beneath a cover of Kli Nappes. The depth to the base of the Seve Nappe units in the Tnnfors Synform is calculated at 4.5 km and in the re Synform at 3 km. The maximum depth to the interface between Kli and Seve rocks in the Tnnfors district is 3.2 km. Gravimetric models of the basement rocks in the windows, and difference in physical properties between the crystalline rocks of the windows and those of the autochthonous basement east of the Caledonian thrust front, imply that the basement exposed in the antiforms is allochthonous. A gravity minimum east of the re Synform is interpreted as a southern continuation of low density granites related to the Olden Complex. The inferred thickness of these low density rocks suggests that it may be a part of the autochthonous basement.
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| 17. |
- Elming, Sten-åke
(författare)
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Magnetic properties of pyrrhotite
- 1981
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Ingår i: Geoexploration. - : Elsevier BV. - 0016-7142. ; 19:2, s. 144-
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 18. |
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| 19. |
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| 20. |
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| 21. |
- Flensburg, M., et al.
(författare)
-
The effective string and SU(2) lattice MC data
- 1987
-
Ingår i: Zeitschrift für Physik C Particles and Fields. - 0170-9739. ; 36:4, s. 629-637
-
Tidskriftsartikel (refereegranskat)abstract
- We present high statistics MC calculations of the static potential in three-dimensional SU(2) for a wide range of β values on a 243 lattice. The deviations from area law are unambiguously demonstrated by use of 2nd lattice R derivative. After a clear crossover at β=4.5 the data show signs of an effective string roughening up to β=6.5, while scaling is not strictly obeyed in this interval. Pure fermionic strings do not provide better fits. The effect of regularization prescription on the effective string model up to two-loop correction is discussed and is found to be small. We also make a comparative study of existing data on Z(2) and SU(3) together with new data on fourdimensional SU(2) presented here. It is pointed out that standard variance reduction methods as applied especially to Wilson lines are plagued by severe long range auto-correlations, whereas larger Wilson loops are less affected.
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| 22. |
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| 23. |
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| 24. |
- Korja, Toivo, et al.
(författare)
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The geoelectric model of the POLAR Profile, Northern Finland
- 1989
-
Ingår i: Tectonophysics. - : Elsevier BV. - 0040-1951 .- 1879-3266. ; 162:1-2, s. 113-133
-
Tidskriftsartikel (refereegranskat)abstract
- Electromagnetic soundings have been made in order to construct a geoelectrical (conductivity) model of the crust along the European Geotraverse (EGT) POLAR Profile. Forty magnetotelluric (MT) soundings, eighteen audiomagnetotelluric (AMT) soundings and ten magnetohydrodynamic (MHD) soundings were made on the main POLAR Profile (POLAR I) and ten more MT soundings on a parallel profile (POLAR II), 40 km to the southeast of the main profile. Analysis of simultaneous recordings by the EISCAT magnetometer chain, and thin-sheet modelling of the effect of the Barents Sea, indicate that neither the source field effects nor the presence of the ocean are significant at periods below 200 s in the measurement area. The magnetotelluric data have been modelled with two-dimensional models representing the regional structure along the profiles. In addition to the regional structure, a thin inhomogeneous surface layer is included in the models in order to explain some local features of the measured response functions. Although details of the surface electrical structures are poorly resolved, the gross features of the geoelectrical cross section are considered to be reliable. The results divide the POLAR Profile into three different blocks. The better conducting Karasjok-Kittilä Greenstone Belt in the south has an average resistivity of less than 10 Ωm. The more resistant Lapland Granulite Belt, with a resistivity between 100 and 200 Ωm, is underlain by conductive (< 5 Ωm), N-dipping layers. The depth for the uppermost conductive layer varies from a few kilometres in the southwestern part of the granulite belt to 13 km in the northeastern part, from where it rises steeply towards the surface close to the boundary between the Lapland Granulite Belt and the Inari Terrain. These features appear to be continuous between the two parallel MT profiles. Within the Inari Terrain a conductive zone at an approximate depth of 10 km and with a resistivity of about 20 Ωm was identified in a resistive upper crust. The geoelectric cross section agrees, in gross detail, with the corresponding gravity, refraction seismic and reflection seismic cross sections of the POLAR Profile. All methods indicated a similar shape for the southwestern part of the Lapland Granulite Belt i.e., granulites have a gently NE-dipping boundary against the underlying Karelian Province. In the northeastern part of the granulite belt the geoelectric model and the gravimetric model show a rather steep S-dipping boundary against the Inari Terrain northeast of the granulite belt.
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| 25. |
- Lindqvist, Gustaf
(författare)
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Applied Geophysics in Norden
- 1985
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Ingår i: The Leading Edge. - : Society of Exploration Geophysicists. - 1070-485X .- 1938-3789. ; :4, s. 68-69
-
Tidskriftsartikel (refereegranskat)abstract
- The five countries comprising the area now known as Norden are Denmark, Finland, Iceland, Norway, and Sweden. Scandinavia is a part of Norden and it includes Norway, Sweden and Denmark. Associated with Denmark are the Faroe Islands and Greenland. The population of Denmark and Finland is around 5 million each, Norway is 4 million, and Sweden 8 million. The outlying islands have small populations: Iceland 200,000, Greenland 50,000, and the Faroe Islands, 10,000. The use of geophysics in Scandinavia and Greenland is associated with ore prospecting, engineering activities, and oil exploration. Geophysical work in Iceland is dominated by geothermal and volcanological investigations
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| 26. |
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| 27. |
- Lindqvist, Per-Arne, 1954-
(författare)
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POTENTIAL OF ISEE IN DIFFERENT PLASMA ENVIRONMENTS.
- 1983
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Ingår i: European Space Agency, (Special Publication) ESA SP. ; , s. 25-33
-
Konferensbidrag (refereegranskat)abstract
- The quasistatic electric field experiment on the ISEE-1 satellite uses spherical double probes to measure the electric field. The potential of each probe relative to the plasma potential can be controlled with a bias current, which compensates for the loss of photoelectrons from the probe. Thus, keeping a probe at plasma potential, the satellite potential is measured with reference to the probe. The dependence of the satellite potential on the ambient plasma electron flux is discussed. It is shown theoretically and found experimentally that the satellite potential is proportional to log(n//eT//e** one-half ). Examples are given of how the satellite potential varies in different regions of space penetrated by ISEE.
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| 28. |
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| 29. |
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| 30. |
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| 31. |
- Orsini, S., et al.
(författare)
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DC ELECTRIC FIELD IN SPACE : DIRECT MEASUREMENTS AND INFERENCES FROM COLD PLASMA DRIFTS.
- 1983
-
Ingår i: Proceedings of the 17th ESLAB Symposium. ; , s. 69-72
-
Konferensbidrag (refereegranskat)abstract
- Data from the satellites GEOS-2 and ISEE are used for a comparison between electric fields directly measured on board satellites and inferred from drift properties of ambient plasma. It is found that, within the errors, a satisfactory agreement exists.
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| 32. |
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| 33. |
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| 34. |
- Parasnis, Dattatray
(författare)
-
Principles of applied geophysics
- 1986. - 4
-
Bok (övrigt vetenskapligt/konstnärligt)abstract
- Anyone who compares the present thoroughly revised and enlarged edition of this book with the three previous ones, the first of which was published in 1962, may well ask whether the principles of applied geophysics have become more numerous during the last 25 years or so. Such is not the case and the much larger size of the present edition is due to the principles' having been explained in greater detail than heretofore. There are major and minor alterations, additions and emendations, too numerous to be listed here, throughout the book but I would like to draw attention specifically to some of them. The chapter on seismic methods is now far more extensive than before and so are also the chapters on electric and electromagnetic methods. There is also a separate chapter on well logging in oil fields giving the essential ideas. Considering the virtual plethora of available books on seismic methods and on well logging I have not thought it necessary to extend these chapters further. This has enabled me to keep the book to a reasonable length and at the same time retain its fairly comprehensive character. Other features of the present edition are solved examples in the text and the problems at the end of all principal chapters. Answers and hints to the latter are given at the end of the book.
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| 35. |
- Parasnis, Dattatray
(författare)
-
Reciprocity theorems in geoelectric and geoelectromagnetic work
- 1988
-
Ingår i: Geoexploration. - : Elsevier BV. - 0016-7142. ; 25:3, s. 177-198
-
Tidskriftsartikel (refereegranskat)abstract
- The following two theorems are proved and discussed: 1. (1) the open-circuit potential difference between two electrodes M,N when steady current is passing through electrodes A,B is equal to that between A and B if the same current is passed through M,N for any arbitrary conductivity distribution in the ground provided only the ground is a linear medium;2. (2) the complex electromotive force developed in a receiver circuit R of small dimensions, due to alternating current flowing in a transmitter circuit T of small dimensions is exactly equal to the complex e.m.f. in T if the same current is flowing in circuit R, no matter how arbitrary the distribution of conductivity, magnetic permeability and dielectric permittivity in the ground, provided only the ground is a linear medium.A linear medium is one in which the current density, magnetic flux density and electric displacement are linear functions of electric and magnetic field intensities. The more general form of the second theorem when the dimensions of the circuits are not small is proved first and the special case of (2) derived from it.
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| 36. |
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| 37. |
- Parasnis, Dattatray S.
(författare)
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Geothermal flow and phenomena in two Swedish localities north of the Arctic circle
- 1982
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Ingår i: Geophysical Journal International. - 0956-540X .- 1365-246X. ; 71:3, s. 545-554
-
Tidskriftsartikel (refereegranskat)abstract
- Temperature measurements in eight holes reaching vertical depths between 287 and 1100m below ground surface in the Malmberget area (lat. 67° 10' N, long. 20° 40' E Gr.) and the Kiruna area (lat. 67° 52' N, long. 20° 9' E Gr.) in the Swedish Precambrian are reported. The mean equilibrium heat flow in this part of the Swedish shield after climatic correction is 52.6 ± 1.7mWm-2. The mean uncorrected heat flow is 46.6 mWm-2. Comparison with other shield areas shows that in common with the S. African and Indian shields, the north Swedish shield has a greater heat flow than the remaining shield areas of the world.
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| 38. |
- Parasnis, Dattatray S., et al.
(författare)
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The non-magnetic house of the University of Luleå, Sweden
- 1982
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Ingår i: Geologiska Föreningen i Stockholm Förhandlingar. - : Informa UK Limited. - 0016-786X. ; 104:2, s. 186-188
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Tidskriftsartikel (refereegranskat)abstract
- The building of a very quiet non-magnetic house can raise special problems in Precambrian areas and in the cold climate of northern Sweden. The special precautions taken in the construction of a non-magnetic house belonging to the University of Lule have resulted in a laboratory for high-precision rock magnetic and palaeomagnetic work. The mean total field in the house one metre above the floor is 52011 ±3 nT and the maximum variation inside is 12 nT. The geographical, position is the mountain Rånekölen, latitude 65.8°N, longitude 22.3°EGr, about 30 km north of Luleå.
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| 39. |
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| 40. |
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| 41. |
- Pedersen, Laust Börsting, et al.
(författare)
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Inversion Of Magnetotelluric Data: A Non‐Linear Least‐Squares Approach
- 1989
-
Ingår i: Geophysical Prospecting. - : Wiley-Blackwell. - 0016-8025 .- 1365-2478. ; 37:6, s. 669-695
-
Tidskriftsartikel (refereegranskat)abstract
- The inverse problem of magnetotellurics over a horizontally stratified earth is described, with emphasis on practical application. The inversion is divided into basically two steps. The construction of some best solution, and the analysis of that solution with regard to uncertainty and complexity. For the construction of best solutions a robust non‐linear solver was developed, and for the estimation of parameter errors a modified eigenvalue‐eigenvector analysis is performed to better describe non‐linear effects. The choice of the number of layers is shown to be intimately connected with the structure of data errors and the misfit between model and data. An example from the Siljan impact structure in Sweden illustrates the power of the technique.
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| 42. |
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| 43. |
- Pesonen, L. J., et al.
(författare)
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Crustal evolution of Fennoscandia : palaeomagnetic constraints
- 1989
-
Ingår i: Tectonophysics. - : Elsevier BV. - 0040-1951 .- 1879-3266. ; 162:1-2, s. 27-49
-
Tidskriftsartikel (refereegranskat)abstract
- Palaeomagnetic poles from Fennoscandia, ranging in age from Archaean to Tertiary, are compiled and graded using a modified Briden-Duff classification scale. An new "filtering" technique is applied to select only the most reliable poles for analysis. The filtering takes into account the following information: 1. (1) source block of rock unit,2. (2) age of rock,3. (3) age of magnetization component,4. (4) scatter of palaeomagnetic directions,5. (5) information from multicomponent analysis of natural remanent magnetization (NRM),6. (6) whether the pole considered belongs to a cluster or subcluster of poles,7. (7) magnetic polarity and8. (8) the author's original assignment of results.Data are still insufficient for the drawing of separate Apparent Polar Wander Paths (APWP) for different blocks or cratons of Fennoscandia. Treating Fennoscandia as a single plate, a new APWP from Archaean to Permian is constructed. From the five previously drawn APWP loops (or "hairpins"), only one, the Jatulian loop (2200-2000 Ma), disappears in filtering. The loops during 1925-1700 Ma and during 1100-800 Ma ago are linked to Svecofennian and Sveconorwegian orogenies, respectively. Palaeomagnetic data support the concept that these orogenies took place episodically; three distinct orogenic pulses (early, middle and late) can be distinguished in the cluster plots of palaeopoles. The drift history of Fennoscandia from Archaean to Permian is presented. During most of geological history, Fennoscandia has occupied low to moderate latitudes and undergone considerable latitudinal shifts and rotations. The Svecofennian and Sveconorwegian orogenies have different kinematic characteristics. During the Svecofennian orogeny, Fennoscandia drifted slowly while rotating a large amount in an anticlockwise sense. During the Sveconorwegian orogeny, it drifted rapidly and rotated first clockwise and then anticlockwise. The most striking feature in the drift velocity curves is, however, the pronounced maxima in the latitudinal drift and rotation rates (˜ 9 cm/yr and ˜ 0.8°/Ma, respectively) during the late Subjotnian-Jotnian anorogenic magmatism and rifting phase (˜1450-1250 Ma ago), possibly reflecting the passage of Fennoscandia across a thermal upwelling (hotspot) at equatorial latitudes. The use of palaeomagnetism in delineating and dating movements between blocks is demonstrated with three examples from the POLAR Profile area, the northernmost section of the European Geotraverse.
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| 44. |
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| 45. |
- Rasmussen, Thorkild Maack
(författare)
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Magnetotellurics in southwestern Sweden: Evidence for electrical anisotropy in the lower crust?
- 1988
-
Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 93:B7, s. 7897-7907
-
Tidskriftsartikel (refereegranskat)abstract
- Magnetotelluric data from measurements conducted on the SW part of the Baltic Shield are analyzed with respect to crustal and upper mantle structures. The interpretations have been done using ordinary 2-D and transverse anisotropic layered models in which distortions of the impedance tensors due to near-surface electrical structures are included in the interpretation procedures. The anisotropic model is able to explain the gross features of the data, whereas the 2-D model only displays features observed at long periods. The 2 main results from the study with anisotropic models are the interpretation of a possible transverse anisotropic lower crust and a depth to the uppermost conductive layer within the mantle of more than 200 km. The minimum depth to the conductive mantle layer is found from a most squares analysis.
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| 46. |
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| 47. |
- Zhang, Ping, et al.
(författare)
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Electric resistivity structure of the Siljan impact region ( Sweden)
- 1988
-
Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 93:B6, s. 6485-6501
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Tidskriftsartikel (refereegranskat)abstract
- Based on 65 magnetotelluric (MT) measuring stations, a cross section of the electric conductivity structure in the Siljan impact area, located in the central part of Sweden, is presented. Static shift effects due to local near-surface inhomogeneities are present in nearly all of the MT soundings.In an attempt to correct for near-surface distortions, average impedance data and distortion parameters were interpreted. Derived 2-D models show some coincidence with seismic reflection results and support an impact origin of the Siljan area. Fluid migration through the fractures generated by the impact is one possible explanation for the anomalously high conductivity within the upper crust
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| 48. |
- Zoback, Mary Lou, et al.
(författare)
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Global patterns of tectonic stress
- 1989
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 341:6240, s. 291-298
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Forskningsöversikt (refereegranskat)abstract
- Regional patterns of present-day tectonic stress can be used to evaluate the forces acting on the lithosphere and to investigate intraplate seismicity. Most intraplate regions are characterized by a compressional stress regime; extension is limited almost entirely to thermally uplifted regions. In several plates the maximum horizontal stress is subparallel to the direction of absolute plate motion, suggesting that the forces driving the plates also dominate the stress distribution in the plate interior.
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