The origin of overthrust faults widely distributed between basins and folded mountain ranges in the west and central part of China has been explained by Luo Zhili in the theory of buried subduction.It is believed that these overthrust faults were normal ones which controlled half graben-like basins in their earlier stage.The filling of the thickest terrestrial sediments in the mountain front depressions later

and the buried subduction along sliding layer slopes of the buried muddy rocks type by gravity force that have made the surface of earlier normal faults above mentioned overturn and then become overthrust faults.Therefore

it is impossible for the newly-deposited soft formation to subduct toward the well-consolidated and folded mountain ranges.These overthrust faults

with the exception of a few from gravitation gliding structure

have resulted mainly from the process of lateral shear stress of vertical flexural fold

namely

multiple folds and compressed basins

which then can be attributed to the group of fan overthrust fault.The distribution and development of lateral shear stress within vertical flexural folds in both space and time has been studied in the concept of vertical flexural rod of material mechanics.The results from calculating in theory show that the maximum value of the vertical shear stress within the flanks of vertical folds is much stronger than that of the horizontal shear stress

as 3 times as that of later.