The aim of my research is to study the temperature and stress conditions whereby faults can nucleate tectonic and fluid-induced seismicity, as well as relevant changes in fault strength. This objective will be realized through a series of hydrothermal ring shear experiments using different metamorphic rock samples from active rift zones, with the view of developing a clear understanding of the transition from seismic to aseismic sliding in these rock types. The findings should provide critical data for seismic hazard assessment, the improvement of numerical models of the seismic cycle, and large-scale geodynamic models.