The origin of folding remains one of the oldest and most complex unsolved problems of geotectonics and structural geology. In tectonophysics, the formation mechanism of folded structures is understood as a description of the geometry and rheological properties of the stratified medium in combination with the external load (and internal forces) or quantitative characteristic of changes in the shape from the initial one to the present-day. In the recent dominant paradigm (plate tectonics), researchers avoid rather than solve this problem, because the generally accepted collision-related models of folding allow only a general interpretation of particular structures. In so doing, they ignore extensive information on deformations, which is recorded in folds and fractures and can be obtained during field work. The diversity of structures existing in nature is reduced to simple schemes. Correspondingly, strain mechanisms of entire folded structures or their segments are not studied in detail and the obtained geodynamic model of the particular region may include substantial errors and gaps. The use of structures, which are traditionally defined for geological mapping as objects for special studies, is one of the causes responsible for lack of progress in solution of the problem of folding. Tectonophysical description of their formation mechanism encounters difficulties, since the boundaries of the traditional object are either vague or inconsistent with the domains of the studied mechanisms. This paper presents a new reliable approach, in which boundaries of study objects coincide with domains of acting mechanisms. The study of foothills and intermontane troughs with their fold‐thrust structures (hereafter, nappes), which have received adequate interpretation and quantitative assessment of their deformations owing to the well-known method of balanced sections [13], is one of the clear methodological achievements of the past few decades. Unlike foothills, the inner parts of nappe belts have a sedimentary cover of substantially thicker flysch and shaly sequences deformed into numerous small folds and their basement is subjected to significant plastic deformations. The method of balanced sections cannot be applied to these structures for several reasons. The most important and evident among them is probable or certain changes in the length of beds in the course of deformation. Another less evident reason is the impossibility to extrapolate correctly the fold‐fracture structure downward to depths of more than 3‐4 km and its eroded part. This extrapolation is possible only if the type and scale of structure deformation are known. The available publications show that the correct quantitative assessment of deformations in internal parts of folded structures is based on the methods of strain analysis [12] and usually restricted to very small segments of the structure. As was mentioned, the models of foothills are most frequently used for interpreting the structure of inner parts of folded structures: large folds combined with thrusts are united in the lower part of the structure into a gentle detachment surface. We should note the strangeness of this widely used approach from the standpoint of methodology: the structure with the competent thick-bedded cover underlain by a rigid undeformed basement is used, in fact, as a tectonotype for the structure with different mechanical properties of the cover and basement. All these methodological problems prevent us from defining the real structure of inner parts of folded structures and determining its formation mechanisms.