3–D FINITE ELEMENT MODELLING OF INDIAN TECTONIC PLATE TO INVESTIGATE THE INTRAPLATE STRESS DISTRIBUTION AND DEFORMATION

Abstract

Plate tectonic models are the essential tools that allow us to explore and understand the working mechanism of plate tectonics and its related events in geological time. These models are complex as it includes integrating many concepts and data of different fields of science. Based on the plate tectonic hypotheses the Earth’s lithosphere is made up of some large and small rigid plates which are moving with respect to each other, and most of the seismic activity and crustal deformation is localised at the plate boundaries. However, there have been various historical earthquake events reported away from the plate boundaries called intraplate earthquakes; these earthquakes may reflect significant deformation of plate interiors. Although the occurrence of these earthquakes is less as compared to the interplate earthquakes, however, the death toll in intraplate earthquakes is much more as compared to interplate earthquakes. These intraplate earthquakes occur due to the increase in stress beyond the local rock strength. Therefore the regional and local stress pattern within the plate has a significant relation with the seismic activity of the plate interior, which indicates that intraplate stress distribution of the tectonic plate can be useful to visualise the potential active seismicity within the plate tectonic, consequently the seismic sources can be identified. In the present study, the intraplate stress field has been estimated using an isotropic elastic plate for the Indian plate with the aid of numerical analysis. Most approaches for modelling the intraplate stresses have been typically based on applying plate driving forces to a homogeneous elastic plate. However, a tectonic plate comprises of continental and oceanic lithosphere with sedimentary basins, cratons, and fold belts with varying significant differences in elastic properties. Present studies differ from the previous studies mainly: (1) it is centralized on the Indian plate with a covered area from 34◦ N – 7.6◦ S to 52◦ E–100◦ E (2) in-homogeneity of the Indian plate are incorporated that are correlated with the elastic strength parameter of the various geological province such as cratons, trap-rocks and fold belts. However, the topographic and gravity potential energy difference effect in the local and regional stress fields is not simulated since it requires a comprehensive, detailed structural model of the lithosphere. Moreover, the Finite Element Method (FEM) based software package, ABAQUS is used to estimate the intraplate stresses and internal deformation of the plate using a 3–D mechanical model incorporating the elastic properties of the 19 geological regions of the Indian subcontinent and oceanic region. The element size of the model is considered as 35×35×10 km. First, two basic models are developed with the homogeneous and regional heterogeneity of the Indian plate to simulate the intraplate stress distribution. Further, the GPS velocity data is used to validate both heterogeneous and homogeneous models which show reasonable agreement with the data. In addition, based on the elastic heterogeneous finite element model of the Indian tectonic plate, the effect of the rheology of the crust and mantle layers is also studied with three rheological models, viz. elastic, elastic-plastic and viscoelastic. Based on these three rheological models, four models of India plate are analysed within the FEM platform. In Model–A and Model–B the crust is considered as elastic, whereas the mantle layer is assumed to be elastic-plastic and viscoelastic in Model-A and Model-B, respectively. Similarly in Model-C and Model-D, the crust is elastic-plastic. At the same time, the mantle is considered elastic-plastic and viscoelastic in Model-C and Model-D, respectively. Furthermore, based on Model-D, the effect of slip and separation is also incorporated in Model-E at the interface of the geological region using the Coulombs friction model. Results show that rheology and frictional properties significantly affect the spatial stress distribution of the plate tectonics.