Numerical Simulation on Ramp Initiation and Propagation in a Fold-and-thrust Belt and Accretionary Wedge

Abstract:

Fold-and-thrust belts and accretionary wedge develop along compressive plate boundaries, both in hinterland and foreland. Under the long-term compressive tectonic loading, a series ramps will initiate and propagate along the wedge. How do the ramps initiate? What are the timing and spacing intervals between the ramps? How many patterns are there for the ramp propagation? These questions are basic for the study of ramp initiation and propagation. Many scholars used three different methods, critical coulomb wedge theory, analogue sandbox models, and numerical simulation to research the initiation and propagation of the ramps, respectively. In this paper, we set up a 2-D elastic-plastic finite element model, with a frictional contact plane, to simulate the initiation and propagation of the ramps. In this model, the material in upper wedge is homogenous, but considering the effects of gravity and long-term tectonic loading. The model is very simple but simulated results are very interesting. The simulated results indicate that the cohesion of upper wedge and dip angle of detachment plane have strong effects on the initiation and propagation of ramps. There are three different patterns of ramp initiation and propagation for different values of the cohesion. The results are different from those by previous analogue sandbox models, and numerical simulation, in which there is usually only one pattern for the ramp initiation and propagation. The results are consistent with geological survey for the ramp formation in an accretionary wedge. This study will provide more knowledge of mechanism of the ramp initiation and propagation in Tibetan Plateau and central Taiwan.