Echelon cracks are a related series of cracks in a planar structure and are a response to shearing forces in the plane of the surface. Such cracks are typically found in asphalt roadways due to
aseismic creep
In geology, aseismic creep or fault creep is measurable surface displacement along a fault in the absence of notable earthquakes. Aseismic creep may also occur as "after-slip" days to years after an earthquake. Notable examples of aseismic slip i ...
and in other planar structures such as walls and building facades due to non-uniform settlement into soft soil.
Such cracks in a uniform surface will form at a uniform angle to the general direction of shear and will progress with more-or-less uniform spacing, length, and offset, thus forming the echelon.
On a larger scale, a zone between offset
strike slip fault
In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...
s may have minor ''en echelon'' fault strands that accommodate the shearing motion induced in the region. On rock undergoing these shearing stresses
en echelon veins may occur as
fracture
Fracture is the appearance of a crack or complete separation of an object or material into two or more pieces under the action of stress (mechanics), stress. The fracture of a solid usually occurs due to the development of certain displacemen ...
fillings.
[Davis, G. H., and Reynolds, S. J., ''Structural Geology of Rocks and Regions.'' 2nd Ed. 1996 ]
References
Structural geology
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