Imbricate thrust spacing: experimental and theoretical analyses

Abstract

With the help of model experiments and theoretical analyses we evaluate the relationships of imbricate thrust spacing (a) with the bed thickness (H), basal friction (μ_b), initial taper (m_w), and the magnitude (normalized to bed-weight per unit area) of horizontal stress (n). Imbricate thrust spacing increases linearly with bed thickness when m_w = 0 and initial-stage thrust imbricates are taken into account. For general cases (m_w≠0) the variations are nonlinear. In nonlinear variations thrust spacing steadily increases but approaches a stable value. The variations for large m_w are complex, where thrust spacing increases to a maximum and then decreases down to a near-stable value. Thrust spacing shows a positive relationship with the dynamic factor, n. With increase in basal friction, thrust spacing decreases. Steepening of early frontal thrusts and formation of back-thrust also depend on the basal friction.

Acknowledgements: We are grateful to Professor S.K. Ghosh for his comments on an early version of the manuscript. We wish to thank Dr Sudipta Sengupta for her constructive suggestions in preparing the manuscript. Dr Gautam Mitra and Dr Malay Mukul critically reviewed the manuscript and provided many suggestions to improve the paper. Their contribution to this paper are gratefully acknowledged. The DST, India and Jadavpur University provided the financial assistance.