Stress-forecasting using small earthquakes as the source of shear-waves is only possible when there is a more-or-less continuous source of small earthquakes. As we have seen, this is extremely rare. To stress-forecast earthquakes without such persistent activity, requires cross-well seismology using a borehole source transmitting orthogonally polarized shear-waves along appropriate ray paths in Band-1 to three-component borehole receivers in further boreholes.
These boreholes exist in northern Iceland near Húsavík close to the Flatey-Húsavík fault of the Tjörnes fracture zone, and an EU project (SMSITES: Developing stress-monitoring sites and infrastructure for forecasting earthquakes, contract no. EVR1-CT1999-4000) developing a Stress-Monitoring Site (SMS) has recently started. The SW of Iceland has proved to be a very active seismic area during the last years. However, shear-wave splitting analysis near the Húsavík transform fault and Grímsey zone has not been very productive up to now, due to lack of continuous swarm activity in the shear-wave windows of the northern stations, GRI, SIG, LEI, and others. The new technique of controlled source measurements are expected to monitor changes in shear-wave splitting near Húsavík more efficiently, as well as reduce the scattering in the time-delays.