This work has been carried out in relation to providing information and warnings about ongoing activity. It has been linked with increased probability of the occurrence of large earthquakes, on one hand in SW Iceland and on the other hand near the Húsavík earthquake fault in North Iceland.
Very much work which concerns all aspects of Task 2 has been devoted to the Hengill-Ölfus area in SW Iceland. An earthquake sequence has been ongoing in this region since 1994, related on one hand to E-W transversal motion across the plate boundary, and on the other to an expansion source at 8-10 km depth below the Hengill area. The largest earthquakes of this sequence took place on June 4, 1998, magnitude 5.1, and on November 13, 1998, magnitude 5. The sequence of events, as observed seismologically and geodetically related to the time period of these events is of enormous significance for understanding, build-up of stress before earthquakes and for understanding the nucleating process or the short-term precursor activity before earthquakes (Figure 3) [3,44,54].
After the earthquake of June 4, 1998, and the following earthquake sequence and deformation, stress was modified up to 50 km distance to east and west from the epicenter, along the E-W plate boundary. This appeared in widespread seismic activity, but also in increases in shear-wave splitting delay time, which lead to earthquake forecast [16].
Work which is concerned with the possibility of an impending large earthquake, i.e. earthquake of magnitude 7, near the town Húsavík in North Iceland, was discussed at a special PRENLAB-2 workshop in Húsavík, July 30, 1998. Work is going on under several subprojects with risk related research in this region. Subproject 1 has besides providing seismological data, taken initiative in planning new observations to be made in the area, on basis of the results of ongoing work. The objective is to provide observations which can create a better basis for modelling of the Húsavík earthquake, for an improved hazard assesssment and for better real-time monitoring possibly involving short-term warnings [53].
Work is ongoing within Subproject 1 regarding the Tjörnes fracture zone in general [44].