Geological studies of exposed parts of the fracture and fault zones in Iceland in conjunction with microearthquakes studies have revealed significant new understanding of the variability of fault zones and faulting in time and space. Established fault zones reveal significant perturbations in stress field.
Both the South Iceland seismic zone (SISZ) and the Tjörnes fracture zone (TFZ) show large variations in mechanical decoupling during short time spans. Comparable variability is also observed on a much shorter time scale. Repeated GPS measurements as well as observations by SAR have during repeated measurements since 1995 revealed variability in time and space as well as the interaction of areas, with different mode of tectonics, in governing the crustal processes. During the 5 years of observations it has been revealed that the dangerous Húsavík-Flatey fault is at present locked above the ductile brittle boundary, below which it has enormously variable creep velocity. It has been modelled how magmatic activity in adjacent volcanic zones can influence the probability of earthquakes in the fault zones. This variability in time highlights the necessity of continuous GPS measurements for risk mitigation in these areas in addition to the seismic methods. The results are described in Subproject 6.
In the SISZ borehole measurements to obtain the horizontal stress directions indicate stability in these since in the 1970s as described under Subproject 4.