Large-magnitude earthquakes remain one of the most pressing issues in Earth science, especially those which also generate large tsunamis and landslides. Despite many advances in earthquake science, we are still only scratching the surface on understanding how and why fault zones move. Recent large magnitude earthquakes have shown that coseismic slip can propagate all the way to the Earth’s surface, with devasting consequences. Furthermore, within the last few decades, it has also become known that faults can also move in slower episodes, as a family of “slow slip” or “slow earthquakes” which undoubtedly can also affect the occurrence of ordinary earthquakes.
To study the motion of faults, laboratory studies play an essential role, by allowing simulating such movement in the laboratory under controlled conditions, including the generation of laboratory earthquakes, or “stick-slip”. Importantly, in order for laboratory studies to be as representative of real fault zones as possible, real material from fault zones should be tested. Fortunately, these are available via scientific drilling, which can core and recover material from within fault zones and also wall rocks from km-scale depths. These samples are important because they preserve the mineralogic composition, induration state, and structural fabric of the fault.
I discuss here the results of laboratory friction experiments conducted in the Marum laboratory, focusing on natural fault zone materials obtained by scientific drilling projects around the world. Some important aspects of the experiments include the importance of preserved, intact fault zone samples, testing at realistically slow cm/yr driving rates, and the roles of microstructure and surface roughness. Some intriguing results include an explanation for the appearance of slow slip events, a possible connection between low healing and shallow earthquake slip, and the appearance of slip instabilities in clayey material previously assumed to be stable.
