Eijsink, Agathe Maria

Worldwide, subduction zones show very different slip behaviour. Some subduction zones, like the Nankai trough (Japan) and Sumatra (Indonesia), have shown earthquakes of large (Mw>8) magnitudes, whereas others (eg. Hikurangi Margin; Northern New Zealand) have not. In these latter ones, other phenomena like slow slip events (SSE) have been recorded, sometimes associated with very low frequency earthquakes (VLFE) or episodic tremor.  The mechanisms behind these kinds of slip on the subduction interface are not well known and are the focus of this PhD project. The understanding of these events may give insights into the question why subduction zones show only certain kinds of slip and might answer the question if large megathrust events might happen in these otherwise quiet subduction zones. Also, if faults are unstable up to shallow depths, the risk of tsunami's increases substantially.

Since friction is the key word in fault stability research, this project will focus on shear experiments to measure the evolution of sliding friction with velocity along a fault interface. This is combined with microstructural studies to understand the processes going on during shear deformation. Starting point of the project is the Hikurangi margin, where slow slip events occur relatively close to the seafloor and are well documented by geodetic and seismic measurements.

Another outstanding question is how sliding friction is related to surface roughness. Measurements on natural faults have shown that surface roughness can be scaled from the micrometer to the kilometer scale using a self-affine scaling law, with limited variation in the important parameters. This means that it is possible to extrapolate our small-scale lab experiments to real faults, with the advantage that in our lab experiments we control the history of our ‘faults’ and know the friction behaviour.