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Crustal stress in and around Norway: a compliation of in situ stress observations

2000; Geological Society of London; Volume: 167; Issue: 1 Linguagem: Inglês

10.1144/gsl.sp.2000.167.01.18

2041-4927

Morten Fejerskov, Conrad Lindholm, A Myrvang, H. Bungum,

Geological and Geochemical Analysis

Abstract In-situ rock stresses yield information about geodynamic processes in the crust, and are important input data for almost all kinds of geomechanics work. Compilations of rock stress measurements, such as the World Stress Map, have been used to characterize the regional stress field. On the basis of new data from the Norwegian region, a map of the maximum horizontal stress ( σ H ) direction, for both on- and offshore Norway, has been established. Four main stress provinces with different regional stress trends are identified. The Barents Sea and northern Norway province exhibits a very consistent N-S σ H direction, with high horizontal stresses. In the Norwegian Sea and mid-Norway province the σ H direction has rotated towards NW-SE. Also here, high horizontal stresses are measured and a compressional regime appears. In the northern North Sea and western Norway province the σ H direction is more scattered. A WNW-ESE direction dominates, but a NNE-SSW trend, parallel to the major structures in the area, also appears. The stress regime is primarily compressional, but in the Stord area normal faulting earthquakes are observed. The southern North Sea province yields a very scattered σ H direction. However, a NW-SE trend, which aligns with the stress system in western Europe, is identified. The high variation, both laterally and with depth, indicates near-isotropic horizontal stresses and influence by local features. The different stress determination techniques applied (overcoring, borehole breakouts and earthquake focal mechanisms) yield approximately the same stress orientation, and regional and internal variation, although they cover different depth intervals. They further manifest high horizontal stresses in the Norwegian area, generally exceeding the vertical stress. This indicates the presence of compressional tectonic stresses penetrating deep into the crust. The first-order stress pattern in Norway and adjacent offshore regions show a rotation in σ H direction from N-S in the Barents Sea to WNW-ESE in the North Sea. This rotation can be explained by the ridge push effect alone, but other effects may also be contributing factors. The increased scatter in σ H direction in the south is believed to be due to changes in the tectonic stress magnitudes, or related to relative changes in angle between the continental margin and the ridge push force.