Plate Boundary Deformation in North Iceland during 1992-2009 observed by GPS and InSAR Time-Series Analysis
Metzger, Sabrina¹; Jonsson, Sigurjon^2
1Helmholtz Centre, GFZ Potsdam, GERMANY; ²King Abdullah University of Science and Technology, SAUDI ARABIA

In North Iceland, the plate boundary between Eurasia and North America is represented by the on-land Northern Volcanic Zone, consisting of a set of central volcanos and fissure swarms, and the mostly offshore Tjoernes Fracture Zone, a NW-SE oriented, complex transform zone comprised of two main lineaments. One of the transform lineaments, the right-lateral strike-slip Husavik-Flatey fault (HFF), links the Northern Volcanic Zone to the offshore mid-Atlantic Ridge. This fault has not ruptured for 140 years and poses a significant hazard to Husavik, a town located on top of the fault, with historical earthquakes estimated to be as large as magnitude 6.5 to 7.

We present the final results of a 6-year project, whose aim was to improve the understanding of the complicated tectonics of this plate boundary zone and to estimate the seismic potential of the HFF using GPS and InSAR time-series analysis. We used observations from continuous GPS stations, most of which were installed in 2006, along with 13 years of campaign GPS data and 17 years of InSAR data of the ERS satellites. We first characterized and removed transient volcanic deformation signals of nearby volcanoes to isolate the interseismic deformation field of the plate boundary zone. Using a kinematic, interseismic plate-boundary model we estimated the key parameters of the system such as the partition of motion between the two lineaments in the Tjoernes Fracture Zone, as well as slip-rate and locking depth of the HFF.

We find that the transform motion in the Tjoernes Fracture Zone is divided among the two main lineaments, with one third (~6.8 mm/yr) on the HFF and two thirds on the second lineament, the Grimsey Oblique Rift, and that the locking depth of the HFF is at shallow 6.2 km. We also suggest that the locking depth may be varying along the fault, with higher values for the offshore part of the fault. Given complete stress release of the fault after the last earthquakes in 1872 and steady stress accumulation since then the current seismic potential of the HFF is found to be equivalent to a Mw6.8 earthquake. However, this estimate does not include the uncertain influence of the last rifting episode in the Northern Volcanic Zone (Krafla Rifting Episode 1975-1984) on the accumulated stress on the fault.

The results of the InSAR time-series analysis exhibit many different deformation signals in the region, e.g. inflation and deflation of the Theistareykir and Krafla volcanoes, respectively. When the volcanic signals are removed, localized inter-rifting deformation along the western edge of the Theistareykir fissure swarm and the eastern border of the Krafla fissure swarm becomes apparent.

References:

S. Metzger et al. (2012), Present kinematics of the Tjornes Fracture Zone, North Iceland from campaign and continuous GPS measurements, Geophys. J. Int., 192:441-455

S. Metzger et al. (2011), Locking depth and slip-rate of the Husavik Flatey fault, North Iceland,derived from continuous GPS data 2006-2010, Geophys. J. Int., 187:564-567