They calculate stress history with a fault model of plastic clay fault gouge between two elastic rock blocks. A fault with a moving edge dislocation may undergo horizontal displacement. Screw dislocations may propogate vertically, arising from depth perhaps. Fault gouge plays a significant role in creep processes but derived models do not assign a unique constitutive equation to the material. Fault gouge may be regarded as self-healing in the respect that after a creep event the upper yield strength along the fault recurs.
Creep events begin again once stresses reach the yield point.
Movement then extends from a structurally weak point, therafter propogating toward the surface and along the fault. Yet, creep releases sizeable amounts of tectonic strain . The slowness of particle motion accounts for the inability of creep to induce seismic activity. Creep events tend to be separated by quiet periods of several months. Event offset increases to a steady state with time and slows when velocity lowers at the end of an event.