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Christophe Pascal, NGU, Geological Survey of Norway (Norway)
David Roberts, NGU, Geological Survey of Norway (Norway)
Roy H. Gabrielsen, Department of Geosciences, University of Oslo (Norway)
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Investigations were conducted in different regions of Norway with the purpose of detecting and measuring stress-relief features (i.e., drillhole offsets and axial fractures) and to derive from them valuable in-formation on the shallow-crustal stress state. Stress-release features of this kind are induced by blasting and sudden rock unloading in road construction and quarrying operations. Reverse-slip offsets and axial fractures are less common in the Oslo Region than in Finnmark or in Trøndelag, suggesting that stress magnitudes at shallow depths in the Oslo Region are lower than in northern and central Norway. In Finnmark, mechanical considerations lead to the conclusion that the magnitude of the maximum horizontal stress at the surface is in the range ∼0.1 to ∼1 MPa. In Trøndelag, the Møre-Trøndelag Fault Complex appears to separate two distinct stress provinces. In the three studied areas, the mean orientation of the maximum horizontal compressive stress axis is NW-SE, in agreement with the notion that compression is induced by North Atlantic ridge-push forces.
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