Surface Strain Rate Tensor Field for Iceland Based on a GPS Network

Abstract

The theme of this paper is the transformation of velocities from a GPS network into a surface strain rate field that illustrates recent and underlying movements within the tectonic system of Iceland. The surface strain rates presented are derived using GPS measurements at the base stations of the National Land Survey of Iceland reference network. The GPS observations are discussed, and the derived average velocity field for an 11-year period, from 1993 to 2004, is presented. The measurements at the westernmost and the easternmost points, which are located on the oldest parts of the country, i.e., the North America plate and the Eurasia plate, respectively, show the rigid movement of the two crustal plates. The average northwards velocity of the two plates is 25 mm/year, and the differential movement is 22 mm/year in the direction 281° from north. The definitions of strain rate tensor and vorticity tensor are outlined and applied in a numerical analysis to derive tensor strain rates from the GPS data. The strain rate tensor field is displayed on maps showing normal and shear strain rate fields, along with principal and dilatation rate fields, as well as the vorticity field. The derived tensor fields are discussed and interpreted in relation to the present-day view on the tectonism of Iceland and recent tectonic activity. The results indicate that most of the significant strain is concentrated on a tongue zone that goes from the North American plate into a slit in the Eurasian plate. The results clearly show the strained volcanic zone of Iceland and the rigid zones with zero strain on either side of it.