GEOLOGI SLANG FRACTURE , JOINT AND FAULTS Fractures and faults are prominent in the upper part of the continental and oceanic lithosphere, where they are often associated with earthquake activity. Joints and fractures are the most abundant signs of strain and deformation in rocks. They are ubiquitous and may part rocks in various regular or irregular sizes as small as a fraction of an inch. The term fracture is general and includes any break in rocks. Some fractures that look like joints are actually shear fractures, which in effect are microfaults, instead of joints. Shear fractures do not form as the result of the perpendicular opening of a fracture due to tensile stress, but through the shearing of fractures that causes lateral movement of its faces. Shear fractures can be confused with joints, because the lateral offset of the fracture faces is not visible at the scale of outcrop or hand specimen. Because of the absence of diagnostic ornamentation or the lack of any discernible movement or offset, they can be indistinguishable from joints. Joints: Planar discontinuities involving no relative displacement of the adjacent blocks. Joints develop during the exhumation of rocks following erosion of the overburden. Joints result from contraction and expansion due to cooling and decompression respectively. Fractures are discontinuities with limited displacement. They form when applied stress reaches the yielding threshold, i.e. the stress at which rock fractures. A fault is a fracture across which two blocks have slipped; the displacement of adjacent blocks is parallel to the fault plane. Faulting corresponds to the brittle failure of an undeformed rock formation or, alternatively, involves frictional sliding on a pre-existing fault plane. Faulting occurs when the maximum differential stress (i.e., maximum stress !1 minus minimum stress !3) exceeds the shear strength of an intact rock formation, or the frictional strength of a pre-existing fault. When rocks break in response to stress, the resulting break is called a fracture. If rocks on one side of the break shift relative to rocks on the other side, then the fracture is a fault. If there is no movement of one side relative to the other, and if there are many other fractures with the same orientation, then the fractures are called joints. Joints with a common orientation make up a joint set . Joints are more or less regular groups of fractures paralleled by little or no movement or orientation of rock components. Fractures paralleled by movement are, of course, faults, and those paralleled by considerable or pervasive orientation of minerals or other rock components are cleavage of one sort or another. Small, irregular, and inconsistently oriented
