Experimental studies on Icelandic rocks demonstrate that due to the high temperature gradient and low lithostatic stress, thermal cracking may be an important process in controlling fracture in the Icelandic crust. This leads to fast increasing permeability. Field observations of mineral-filled veins in exposed deep parts within the TFZ indicate that fluid pressures due to faulting there may be as high as 20 MPa above the least compressive stress. By implication this is thought to be similar in the SISZ. This means that the driving shear stress needed to trigger fault slip is low, only 4-6 MPa. However, for triggering an earthquake the stress conditions along the entire fault plane must be homogenized, for example by fluid flow. This can be of significance for forecasting large earthquakes, if the homogenization process can be monitored. The results are described in Subproject 6.