Supershear earthquake

During strike-slip, the main component of rupture propagation will be horizontal, in the direction of displacement, as a Mode II (in-plane) shear crack.

Theoretical studies have shown that Mode III cracks are limited to the shear wave velocity but that Mode II cracks can propagate between the S and P wave velocities[9] and this may explain why supershear earthquakes have not been observed on dip-slip faults.

[11] The high rates of strain expected near faults that are affected by supershear propagation are thought to generate what is described as pulverized rocks.

The pulverization involves the development of many small microcracks at a scale smaller than the grain size of the rock, while preserving the earlier fabric, quite distinct from the normal brecciation and cataclasis found in most fault zones.

The link between supershear and the occurrence of pulverized rocks is supported by laboratory experiments that show very high strain rates are necessary to cause such intense fracturing.