Strain analysis using structural elements and geometry of surfaces of no finite longitudinal strain

Abstract

In this research, using structural elements and the geometry of surfaces of no finite longitudinal strain, crustal shortening and strain analyses have been carried out between two thrust faults in the Khon-Khoreh area in the north of Dehbid. The direction of the principal axes of the finite strain ellipsoid was defined using stereographic analyses of pole of foliation and lineation. With separation of shortening and longitudinal strain domains, the geometry of surfaces of no finite longitudinal strain was determined in 3D. The results of stereographic analyses and angular relations of surfaces of no finite longitudinal strain on the XZ and XY principal planes of strain ellipsoid show the amounts of 2Φ angle as: 48° < 2ΦXZ < 58° and 75° < 2ΦXY < 82°. Results show three axial prolate strain ellipsoids in the study area. Using calculated angles and R/2Φ nomogram, the amount of finite strain in the principal planes of strain ellipsoid (RXZ and RXY) and natural logarithmic strain (e) was determined in the study area. With application of kinematic vorticity analysis, the amount of crustal shortening was determined to be about 30 to 60 % in the study area. Finally, it reveals that the amounts of finite strain ratios, natural logarithmic strain, and increment in the prolate shapes of strain ellipsoid increased with decrease in distance from the thrust faults.