ABSTRACT
A deformation cycle in a region may be divided into 4 stages, corresponding to long-term, medium-term, short-term to imminent stages before earthquake and instability, respectively. Anomalies appearing in stages I and II may be caused by changes in driving force and anomalies in stage III may be caused by fault propagating or fault weakening. In order to reveal distribution of anomalies in different stages, increments of mean stress and maximum shear stress for models with en-echelon faults and other fault patterns are studied numerically. It is shown that distribution of increment of maximum shear stress in stages I and II are similar to the background stress field while variation of incremental mean stress in stage II is outstanding at en-echelon jogs. Distribution of incremental maximum shear stress and incremental mean stress display an eight-petaline pattern and a four-quadrant pattern, respectively, surrounding the propagation area in stage III. The eight-petaline pattern, four-quadrant pattern and strong undulating of dynamic characteristics in mean stress may help to distinguish possible upcoming unstable fault
