The destructive 1994 earthquake in Northridge, Los Angeles, California, was caused by a previously undiscovered blind thrust fault.
With continued displacement on the thrust, higher stresses are developed in the footwall of the ramp due to the bend on the fault.
This process may repeat many times, forming a series of fault-bounded thrust slices known as imbricates or horses, each with the geometry of a fault-bend fold of small displacement.
Duplexing is a very efficient mechanism of accommodating the shortening of the crust by thickening the section rather than by folding and deformation.
These conditions exist in the orogenic belts that result from either two continental tectonic collisions or from subduction zone accretion.
The Himalayas, the Alps, and the Appalachians are prominent examples of compressional orogenies with numerous overthrust faults.
Here, ramp flat geometries are not usually observed because the compressional force is at a steep angle to the sedimentary layering.
Thrust faults were unrecognised until the work of Arnold Escher von der Linth, Albert Heim and Marcel Alexandre Bertrand in the Alps working on the Glarus Thrust; Charles Lapworth, Ben Peach and John Horne working on parts of the Moine Thrust in the Scottish Highlands; Alfred Elis Törnebohm in the Scandinavian Caledonides and R. G. McConnell in the Canadian Rockies.
He wrote: By a system of reversed faults, a group of strata is made to cover a great breadth of ground and actually to overlie higher members of the same series.
They are strictly reversed faults, but with so low a hade that the rocks on their upthrown side have been, as it were, pushed horizontally forward.