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Introduction
Published in Hector Estrada, Luke S. Lee, Introduction to Earthquake Engineering, 2017
This theory, however, does not fully explain all phenomena associated with lithospheric plate movement. The current view is that plate movement is driven by additional forces, known as ridge push and slab pull, which also derive their energy from the dissipation of heat from the earth’s core through convection currents (this theory is still being debated). These forces are generated at the mid-oceanic ridge (divergent zones) and at the subduction zones. At the divergent zones, lava cools at the surface creating new oceanic ridge; as this new material moves away from the divergent zones, it continues to cool, becoming denser. At the other end of the plate, the oceanic lithosphere becomes even denser with age as it continues to cool and thicken. This causes the lithospheric plate to tilt toward the subduction zones, like an unbalanced boat in water. The mid-oceanic ridge then rises above the rest of the seafloor, and as the new material rises to the top of the ridge, gravity pulls it down; this is called ridge push. Also, the greater density of old oceanic lithosphere at the subduction zones, relative to the underlying asthenosphere, allows gravity to pull these rocks (known as slabs) down into the mantle. This is believed to be the source of the driving force for the majority of plate movement.
An XFEM Model for Seismic Activity in Indian Plate
Published in Journal of Earthquake Engineering, 2018
S. Jayalakshmi, S. T. G. Raghukanth, B. N. Rao
The geometry and boundaries of the Indian Plate with all its geological features like cratons and tectonic faults being broadly known, it is desirable to develop a mechanistic model for the plate. There are several analytical techniques available in literature to model plate with cracks. The FE method is a powerful technique in computational mechanics that can be used to analyze structures of complex shape with complicated boundary conditions. The analysis of Indian Plate requires prior identification of forces and boundary conditions on the plate. Various estimates for the plate driving forces are attempted in previous studies on plate modeling [Dyksterhuis et al., 2005; Jayalakshmi and Raghukanth, 2013]. It is also well established that the historic collision of India with Eurasia decreased the convergence rate of Indian Plate by almost half and hence the plate driving forces play an important role in the dynamics of Indian Plate [Molnar and Tapponnier, 1975]. The ridge push force arises from the elevated topography at the Mid Oceanic Ridge. The direction of this force is applied normally to the strike of the ridge [Wilson, 1993]. Among the various forces that drive tectonic plates [Forsyth and Uyeda, 1975], the ridge push and the slab pull forces are identified as important for the dynamics of the Indian Plate. Therefore in the FE model, the ridge push is defined to act along the Mid-Oceanic Ridge. The expression for the ridge push is given by the relation [Turcotte and Schubert, 2002].