Definition and classification of fault damage zones: A review and a new methodological approach

Although the widths of fault damage zones commonly show a positive correlation with displacements, these relationships also show a somewhat scattered distribution. We believe that one of the fundamental reasons for this problem is strongly related to subjective definitions and inconsistent uses of the term ‘damage zone’. Thus, firstly we classify damage zones into along-fault, around-tip and cross-fault damage zones based on descriptive views of an arbitrary fault exposure as well as their tridimensional locations around a segmented fault system. Secondly, we propose an advanced field technique and data acquisition method to more accurately define a damage zone using the distribution of cumulative fracture frequency. We tested this method on new field and borehole observations as well as previously published data to identify damage zone boundaries, and express them as a change in slope gradients of the cumulative distribution of deformation structures. The results show how this slope change can be a useful criterion in accurately defining the width of damage zones and some internal properties of fault zones. We argue that this damage zone classification and definition method should be adopted and used to prevent discrepancies in field data. This will help us to gain a better understanding of fault damage zone properties and their scaling with fault displacement.