The earthquake rupture process
An earthquake is a transient process occurring when the stress accumulated
by the tectonic loading is abruptly released on one or several fractures
of the earth crust. Much of the stored elastic strain energy of the
source region is consumed in heating and fracturing of the rocks,
but a portion is converted into seismic waves that propagate outward
from the fault zone.
The rupture originates at the hypocenter (or nucleation point)
and expands over the fault plane as a rupture front, whose shape and
velocity depend on the properties of the rock and on the stress extent.
Each element of the fault plane radiates energy in the form of P and
S waves (body waves) only when reached by the rupture front.
Seismic waves carry on the information about the source process and
their recording at the Earth surface is used to infer the rupture
properties in terms of its space-time evolution.