Single-force representation of earthquakes due to landslides or the collapse of caverns

Earthquakes due to landslides and the collapse of caverns are caused by the release of gravitational potential energy rather than elastic strain energy. Landslide (or cavern collapse) is assumed to start with dislocation motion along the lubricated interface of the slide block (or fallen block) that intersects the Earth's free surface. It can be shown that, if each component of the dislocation vector is position-independent and varies only as a function of time, the resultant static displacement is spatially uniform both inside and outside the block, and, therefore, no change occurs in static strain energy. In particular, if the medium is unbounded, the static displacement is zero outside the block. The force system equivalent to this dislocation model is a distribution of single forces equal but opposite to the dislocation acceleration multiplied by the density at each point of the volume constituting the slide block. The physics behind the equivalence is discussed. Single force appears to be a common mechanism for indigeneous earthquakes that do not change the static strain field.