Geophys. Res. Lett. http://dx.doi.org/10.1029/2011GL048552 (2011)

Credit: © NASA/GSFC/LARC/JPL

Earthquakes at subduction zones can sometimes generate large tsunamis, but only when the rupture propagates towards the surface through thick accumulations of clay-rich sediments. Experimental analyses show that fault slip penetrates through clay only when the fault ruptures at a high velocity.

Daniel Faulkner of the University of Liverpool and colleagues used analogue models to simulate fault slips in clay materials in the laboratory. They found that if the initial fault slip during the nucleation of an earthquake was slow, the clays would become stronger and resist further breakage. This explains why earthquakes generally do not occur within the clay-rich sediments found at the surface in subduction zones. However, if the initial slip on the fault was very fast, fluids within the fault heated up and became pressurized. As a result, the clay-rich rocks weakened, allowing earthquake rupture to propagate through the material.

The researchers suggest that rapid fault slip is required for earthquake ruptures to propagate through clay-rich rocks at subduction zones and to generate a tsunami.