Stress measurements in Iceland

Conference · Wed Dec 01 04:00:00 EST 1976 · EOS, Trans., Am. Geophys. Union; (United States)

OSTI ID:5275159

Haimson, B C ^[1]; Voight, B

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1. Univ. of Wisconsin, Madison

Hydrofracturing stress measurements were conducted in two boreholes in Quaternary volcanics in Reykjavik, Iceland, on the flank of the Reykjanes-Langjokull continuation of the Mid-Atlantic Ridge. Four tests were conducted in hole H32 in jointed basalt between 200 and 375m depth. The least compressive stress was horizontal (sigma/sub Hmin/) and varied between 40 to 60 bars. The largest horizontal stress (sigma/sub Hmax/) was approximated at 50 to 100 bars. The direction of sigma/sub Hmax/ based on three fracture impressions was N25/sup 0/W +- 5/sup 0/. The vertical stress (sigma/sub V/) was calculated based on a gradient of 0.27 bars/m. In borehole H18 extensive jointing limited us to only three successful tests. The test at 180m was in basalt; the lower tests at 290 and 324m were in an intrusive dolerite. sigma/sub Hmin/ increased with depth from 40 to 80 bars, sigma/sub Hmax/ varied from 120 to 160 bars, and sigma/sub V/ from 50 to 90 bars. Two contradictory hydrofracture directions were obtained: N20/sup 0/E for the 180m test, and N45/sup 0/W for the 290m test. The ratio of the average horizontal stress to vertical stress was 1.25, as compared to 1.0 for H32. Linear approximations of the data for both holes between 200m and 350m depth give sigma/sub Hmin/ = 0.21 bars/m, sigma/sub Hmax/ = 30 bars + 0.30 bars/m, and sigma/sub V/ = 0.27 bars/m. Measured stress orientation (H32) bears no obvious relationship to the NE strike of individual rift zone fissures and faults, inferred WNW direction of lithospheric plate motion, or axial rift zone earthquake focal solutions which indicate NW-trending sigma/sub Hmin/. The measured stresses could be related to a hot spot, or could reflect local phenomena involving the extinct NNW-trending Kjalarnes central volcano or ground distortion due to fluid withdrawal from Laugarness hydrothermal system.

• OSTI ID: 5275159
• Conference Information: Journal Name: EOS, Trans., Am. Geophys. Union; (United States) Journal Volume: 57:12
• Country of Publication: United States
• Language: English

Related Subjects

15 GEOTHERMAL ENERGY
150202* -- Geology & Hydrology of Geothermal Systems-- Non-USA-- (-1989)
BOREHOLES
CAVITIES
EARTHQUAKES
EUROPE
FLUID WITHDRAWAL
FRACTURING
GEOLOGIC FAULTS
GEOLOGIC STRUCTURES
GEOLOGY
GEOTHERMAL SYSTEMS
HYDRAULIC FRACTURING
HYDROTHERMAL SYSTEMS
ICELAND
ORIENTATION
PLATE TECTONICS
RIFT ZONES
SEISMIC EVENTS
STRESSES
TECTONICS
VOLCANIC REGIONS