A High-Resolution Tectonic Stress Map of Iceland

Iceland is one of few locations in the world where oceanic transform faulting processes can be observed on-land. The plate boundary through Iceland consists of oblique rift zones and transform segments with and without well-defined strike-slip faults. Since the installation of the South Iceland Lowland (SIL) seismic network in 1990, approximately half a million earthquakes (M>-2) have been recorded along the Icelandic plate boundary. Here we use the focal mechanisms of more than 200,000 earthquakes to map the state of stress along the plate boundary in detail. In addition, we study temporal variations in the stress field throughout the recent magnitude 6.5 earthquake sequence in the South Iceland Seismic Zone. We demonstrate here how a three-dimensional gridding method ('octree') can be used to examine temporal changes in stress by determining stress parameters at common points at different epochs. Our results provide a high-resolution map of the tectonic stress field in Iceland and enable us to examine how recent large earthquakes have affected adjacent areas.