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Seismic crustal study of the Oslo Rift

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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:\(V_{P_{g(av)} } = 6.20 km/s, V_{P_b } = 6.60 km/s, V_{P^x } = 7.10 km/s\).\(V_{P_n } \) 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 (\(V_{P_b } \)=6.60 km/s) from the uppermost layer\((V_{P_{g(av)} } = 6.20 km/s)\), 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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Tryti, J., Sellevoll, M.A. Seismic crustal study of the Oslo Rift. PAGEOPH 115, 1061–1085 (1977). https://doi.org/10.1007/BF00881227

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key words

  • Crustal structure of the Oslo rift
  • Oslo rift, crustal structure
  • Seismic study of the Oslo rift