These swarms can be recorded by seismometers and tiltmeters (a device that measures ground slope) and used as sensors to predict imminent or upcoming eruptions. Rupture dynamics
A tectonic earthquake begins as an area of initial slip on the fault surface that forms the focus. Once the rupture has initiated, it begins to propagate away from the focus, spreading out along the fault surface. Lateral propagation will continue until either the rupture reaches a barrier, such as the end of a fault segment, or a region on the fault where there is insufficient stress to allow continued rupture. For larger earthquakes, the depth extent of rupture will be constrained downwards by the brittle-ductile transition zone and upwards by the ground surface. The mechanics of this process are poorly understood, because it is difficult either to recreate such rapid movements in a laboratory or to record seismic waves close to a nucleation zone due to strong ground motion.In most cases the rupture speed approaches, but does not exceed, the shear wave (S-wave) velocity of the surrounding rock. There are a few exceptions to this:

Supershear earthquakes
Supershear earthquake ruptures are known to have propagated at speeds greater than the S-wave velocity. These have so far all been observed during large strike-slip events. The unusually wide zone of damage caused by the 2001 Kunlun earthquake has been attributed to the effects of the sonic boom developed in such earthquakes. Slow earthquakes
Slow earthquake ruptures travel at unusually low velocities.
Folliculitis nares perforans is characterized by small pustules near the tip of the inside of the nose, lesions that become crusted, and when the crust is removed it is found that the bulbous end of the affected vibrissa is embedded in the inspissated material. : 774

See also
Skin lesion


== References ==