Crustal stress in Iceland |
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Authors: | Bezalel C Haimson Barry Voight |
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Institution: | (1) Dept. of Mineral Engineering, University of Wisconsin, 53706 Madison, Wisconsin, USA;(2) Dept. of Geology & Geophysics, Penn. State University, 16802 University Park, Pennsylvania, USA |
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Abstract: | Hydrofracturing stress measurements have been carried out to about 0.4 km in two boreholes in Quaternary volcanic rocks in Reykjavik, Iceland, on the flank of the Reykjanes-Langjökull continuation of the Mid-Atlantic Ridge. The measurements indicate a dominant orientation of H max approximately perpendicular to the axial rift zone, in contrast to earthquake focal mechanism solutions from within the axial rift zone of the Reykjanes Peninsula. In one hole (H32) a depth-dependent change in stress orientation is indicated, with 1 horizontal above a depth of about 0.25 km, and vertical below it; however the orientation of H max remains unchanged. The data thus suggest reconciliation of an apparent conflict between the dominantly compressive indications of shallow overcoring stress measurements and dominant extension as required by focal mechanism solutions. The measured stresses are supported by the more reliable of overcoring measurements from southeast Iceland, and by recent focal mechanism solutions for the intraplate Borgarfjördur area. A fundamental change in crustal stresses appears therefore to occur as a function of distance from the axis of the axial rift zone. The data seem reasonably explicable in terms of a combination of thermoelastic mechanisms associated with accretion and cooling of spreading lithosphere plates. Stresses directly associated with the driving mechanisms of plate tectonics apparently do not dominate the observed stress pattern. |
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Keywords: | Stress hydrofracture Stress at plate boundaries State of stress Tectonics of Iceland |
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