2 A Simple Way of Defining and Recognizing Common Fracture Types‌

A simplified representation of the kinematics of fracture types is illustrated in Figure 6. This follows more or less the displacement discontinuity concept of S.L. Crouch (1976) of the University of Minnesota.

Figure 6 – Left: Schematic diagram showing basic kinematics of fractures. Full arrows indicate dilation/opening and compaction/closure, and half arrows indicate shear. Right: The displacement discontinuity concept of S.L. Crouch (1976) is based on displacements of adjacent points on the two faces of a fracture, the difference of which defines the displacement discontinuity. Displacements along each face may be assumed to be positive in the positive coordinate directions. Then, displacement discontinuity normal to the fracture Dn = 𝑈_y+− 𝑈_y− defines opening if positive and closing if negative. Displacement discontinuity parallel to the fracture Ds = 𝑈_x+− 𝑈_x− denotes shear displacement discontinuity. Modified from Crouch (1976).

The three major fracture kinematics are defined as opening mode fractures (joints), closing mode fractures (pressure solution seams and compaction structures) and shearing mode fractures (shear fractures or faults). What is listed as deformation bands in Figure 2 and Figure 4 is a particular structure type formed by a unique mechanism of localization of deformation into narrow bands in the three kinematics mentioned earlier: dilation bands (opening), compaction bands (closing) and shear bands.