Strain accumulation along an oblique plate boundary: The Reykjanes Peninsula, southwest Iceland

We use annual GPS observations on the Reykjanes Peninsula (RP) from 2000 to 2006 to generate maps of surface velocities and strain rates across the active plate boundary. We find that the surface deformation on the RP is consistent with oblique plate boundary motion on a regional scale, although considerable temporal and spatial strain rate variations are observed within the plate boundary zone. A small, but consistent increase in eastward velocity is observed at several stations on the southern part of the peninsula, compared to the 1993-1998 time period. The 2000-2006 velocities can be modelled by approximating the plate boundary as a series of vertical dislocations with left-lateral motion and opening. For the RP plate boundary we estimate left-lateral motion 18_-3⁺⁴ mm yr^-1 and opening of 7_-2⁺³ mm yr^-1 below a locking depth of 7_-2⁺¹ km. The resulting deep motion of 20_-3⁺⁴ mm yr^-1 in the direction of N(100_-6⁺⁸)°E agrees well with the predicted relative North America-Eurasia rate. We calculate the areal and shear strain rates using velocities from two periods: 1993-1998 and 2000-2006. The deep motion along the plate boundary results in left-lateral shear strain rates, which are perturbed by shallow deformation due to the 1994-1998 inflation and elevated seismicity in the Hengill-Hrómundartindur volcanic system, geothermal fluid extraction at the Svartsengi power plant, and possibly earthquake activity on the central part of the peninsula.