Updated in situ rock stresses in Norway based on recent estimations and measurements
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This paper presents the current in situ rock stresses in Norway. Information about the stress state was obtained by estimations from focal mechanism, borehole breakout and drilling-induced fractures, and via overcoring and hydraulic fracturing measurements. A N–S and a WNW–ESE major horizontal stress orientations dominated the estimation data from offshore Norway and western, mid and eastern Norway. This is consistent with the ridge push effect from the mid-Atlantic ridge. The measurement data from onshore Norway had scattered orientations, probably caused by local factors like topography. The major horizontal stress generally exceeded the vertical stress in the Norwegian region with an average ratio of 1.2. The stress gradients appeared to decrease with increasing overburden. The influence of topography on the principal stresses seemed to decrease inwards the rock mass. It is intended to update the Fennoscandian in situ rock stress database with the data collected.