Rift-transform junction in North Iceland: rigid blocks and narrow accommodation zones revealed by GPS 1997–1999–2002

International audienceThe current tectonics of North Iceland are characterized by rifting episodes along fissure swarms and by ML 6–7 earthquakes in the transform zone between the northern rift zone and the Kolbeinsey Ridge north of Iceland. The last rifting period (1975–1984) was associated with an average opening of 5 m along the Krafla fissure swarm. Post-rifting deformation has been revealed by GPS investigations in Northern Iceland. A GPS network was occupied in 1997, 1999 and 2002 to quantify present-day displacements and their variation with time, on both sides of the on-land part of the Húsavík–Flatey fault and around the Krafla fissure swarm. The main deformational features observed are: (1) decrease in spreading velocities between the two timespans 1997–1999 and 1999–2002, (2) the existence, south of the transform zone, of a well-defined ∼20–30-km-wide plate boundary where extension dominates, (3) directly adjacent east and west rift shoulders where displacements are close to those observed on the Eurasian and North American plates and (4) a displacement gradient on Tjörnes that could correspond either to elastic deformation related to a currently locked dextral strike-slip fault or to an attenuated post-rifting effect northwest of Krafla