They develop from a series of vertically aligned, subparallel systematic joints that, crosscutting many beds, may form a multilayer brittle structure.
A preexisting systematic joint can represent, in certain cases, a mechanical layer boundary, which is characterized by a homogeneous rheological behaviour .
To calculate the density of fractures in studied area in some stations that have plenty of systematic joints
, a circle whit 5m diameter is drown and the length of each joint in this area is measured.
Because the measurement of such distance is prone to error as a result of the curved and non-linear nature of the surfaces, error in the premises of + 3cm was entertained, with this, J9 & J8, J11 & J12, J16 & J18, and J20 & J21 were categorised as systematic joints
with average perpendicular distance of ~62cm between them others are non-systematic joints (Table.