THE VELOCITY DESCRIPTION OF DEFORMATION .1. THEORY

There are several advantages in using velocities to describe the deformation of the crust and lithosphere induced by extension, compression, isostasy and other processes. (1) The method is very general. Any deformation style can be described in this way. Simple examples are: pure shear, inclined or vertical simple shear, bulk rotation; Airy or flexural isostasy and compaction. (2) Velocity fields can be combined to model more complex deformation. (3) The syn-tectonic evolution of parameters such as temperature, pressure, hydrocarbon maturity and porosity are easily modelled once the deformation velocities are specified. (4) The syn-tectonic evolution of sedimentary architectures can be modelled using a general tectono-sedimentary forward modelling equation which incorporates the deformation velocities. These advantages are illustrated by a computer model which simulates elastic sediments prograding into an active half-graben formed by extension above a listric fault. Processes included in this model are compaction of the sediments, hanging wall deformation by inclined simple shear and simultaneous footwall deformation. To avoid space problems, the velocity field for the hanging wall block above the non-rigid footwall must obey a simple contact condition.