The purpose of the lecture is to quantify and introduce the theoretical concepts on the stability and strength of rock, the growth and interaction of cracks and faults, and the effects of fault rupture and dislocation sources on the field variables of the continuum. The theoretical basis is important to understand when and how earthquakes rupture, how seismicity is described, how fluid and magma-filled cracks form and how we can use the field data measured at the surface and in the Earth to infer parameters of the source and of the strength and stress state in the Earth.

The content is focused on dislocation sources with relevance in seismology, volcanology and geology. We start with a general introduction to the elastic and brittle behavior of fractured and poroelastic rocks. The following chapters concentrate on the theoretical description of point and dislocation sources and the deformation and stress they generate including the radiation of elastic waves.  The source spectra, the effects of the kinematic rupture and the radiation directivity are considered, and how these effects can be studied by seismic body and surface waves. One chapter is dedicated to the dynamic source parameter and the scaling relations of earthquakes. The last chapter refers to basic aspects of dynamic rupture propagation.