Seismic crustal study of the Oslo Rift |
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Authors: | Johannes Tryti Markvard A Sellevoll |
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Institution: | (1) Statoil, Lagårdsvei 78, 4000 Stavanger, Norway;(2) Seismological Observatory, University of Bergen, Villavei 9, 5014 Bergen-U, Norway |
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Abstract: | A seismic refraction investigation across the southern part of the Oslo Rift has been made, based on quarry blasts at three localities. The study shows a three-layered crust with the followingP-wave velocities:
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the upper mantleP-wave celocity, is 8.07 km/s. The velocity-depth relationship for the uppermost crust, obtained by solving the Wiechert-Herglotz integral equation numerically, shows a continuously decreasing velocity gradient in the region of the Oslo Rift which approaches zero at a depth of 9 km, the corresponding increase in theP-wave velocity being from 5.55 km/s to 6.34 km/s. The interface separating the subsurface layer (
=6.60 km/s) from the uppermost layer
, interpreted as the Conrad discontinuity, is essentially horizontal in the investigated part of the Oslo Rift at a depth of approximately 15 km. A deep crustal layer with aP-wave velocity of 7.10 km/s appears to be related to the rift, though the top of this layer extends somewhat eastwards beneath the Precambrian rocks from the southern part of the rift at a depth of approximately 20 km. The Moho discontinuity is elevated beneath the Oslo Region compared with the surrounding area. A broad regional gravity high of about 45 mgal is observed along the entire rift zone. It is suggested that this anomaly is caused by the elevation of the sub-Conrad and Moho discontinuities during the rifting processes. |
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Keywords: | Crustal structure of the Oslo rift Oslo rift crustal structure Seismic study of the Oslo rift |
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