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Stress and strain of a plate boundary - the Reykjanes Peninsula, SW Iceland


The Reykjanes Peninsula in southwest Iceland offers excellent opportunities to
study the dynamics of an obliquely divergent plate boundary zone. Both leftlateral
shear and extension are accommodated on the peninsula, resulting in a
plate boundary zone characterised by high earthquake activity as well as recent
volcanism. This thesis investigates crustal deformation and earthquakes along
the plate boundary on the Reykjanes Peninsula, using a variety of geophysical
In the first paper, we use GPS velocities from 2000–2006 to derive a kinematic
elastic half-space model of the plate boundary deformation on the Reykjanes
Peninsula. The model predicts left-lateral motion of 18+4
−3 mm/yr and opening
of 7+3
−2 mm/yr below a locking depth of 7+1
−2 km (95% confidence levels). The
resulting deep motion, of 20+4
−3 mm/yr in the direction of N(100+8
−6)"E, agrees
well with the predicted relative North America - Eurasia rate, showing that the
observed surface deformation is consistent with the plate motion models. The
GPS strain rate fields, however, reveal temporal and spatial variations within the
plate boundary zone due to shallow sources related to earthquakes or geothermal
The second paper presents the first comprehensive analysis of the seismicity
on the Reykjanes Peninsula, since early instrumental earthquake recordings in
1926. The seismicity on the peninsula shows a systematic change from primarily
earthquake swarms in the west to mainshock-aftershock sequences in the east,
reflecting the transition from seafloor spreading along the Reykjanes Ridge to
transform motion in the South Iceland Seismic Zone. The state of stress during
1997–2006, as estimated from inversion of micro-earthquake focal mechanisms,
is mainly strike-slip with a tendency toward a normal stress state. We find an excellent agreement between the directions of least compressive stress from
inversion of earthquake data and the directions of greatest extensional strain rate
derived from GPS data, indicating that the earthquakes are primarily driven by
plate motion.
Finally, the third paper presents a geodetic study of the crustal deformation
on the Reykjanes Peninsula, using Interferometric Synthetic Aperture Radar (In-
SAR) data from 1992–1999 and 2003–2008, as well as GPS data from 2000–2009.
The geodetic data reveal deformation due to the plate spreading, anthropogenic
subsidence due to geothermal fluid extraction in the Reykjanes, Svartsengi and
Hellisheidi fields and, possibly, increasing pressure in the Krísuvík geothermal system.
The installation of the Reykjanes geothermal power plant in 2006 results in
subsidence of around 10 cm during the first two years of production. Short-lived
swarms of micro-earthquakes as well as aseismic fault movement appear to be
triggered by the stresses due to geothermal fluid extraction.




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