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

  • Nordic Volcanological Centre, Eimskip Fund of the University of Iceland
  • 978-9979-9914-4-1
  • 22.10.2009

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