Research Projects

The Indian Ocean Geoid Low, a prominent global anomaly, is a long wavelength feature exceeding 4,000 km across the central Indian Ocean, with a significant low of -106 m south of Sri Lanka, yet despite numerous studies, its origin remains unclear and a conclusive explanation elusive. Early studies suggested that undulations on the core-mantle boundary (CMB) could explain the Indian Ocean Geoid Low (IOGL), linking it to large wavelength geopotential anomalies. The authors suggest that large wavelength regional gravity anomalies are modelled by negative density contrasts at various depths, indicating the Indian Ocean Geoid Low (IOGL) is due to low-density subducted rocks from the Indian/Tethyan lithosphere concentrated in the upper and middle mantle below the 660 km discontinuity. Further investigations using ScS phase travel times and anisotropy confirmed the presence of highvelocity slab graveyards in the lower mantle, which, alongside low-velocity upwellings in the upper mantle, may explain the IOGL. Recent high-resolution tomographic studies have identified a massive ancient subducted tectonic slab in the south-eastern Indian Ocean, termed the southeast Indian slab (SEIS), which is adjacent to the Indian Ocean Geoid Low (IOGL), suggesting that the IOGL may extend from south of India to southeast Australia. The presence of SEIS could mask the effects of this long-wavelength feature. The authors propose that water from ancient slabs contributes to low mantle velocities, explaining the observed low geoid anomaly. Discrepancies between models lead to ambiguous interpretations, while insufficient data coverage and reliance on assumptions hinder accuracy. Additionally, these models struggle to resolve small-scale features and anisotropic structures, highlighting the need for improved methods in ongoing research. However, there is a need for direct studies to explain density changes at greater depths and resolve tomography ambiguity. Thus, gravity, gravity gradients, and geoid can be used to estimate density distribution and its effects at different depths of the upper and lower mantle. By combining gravity, gravity gradients, and geoid data with other geophysical observations like tomography models, one can better understand the Earth's internal structure and dynamics. This integrated approach can help to estimate density distribution in the upper mantle, resolve tomography ambiguity, and provide new insights into the Earth's mantle and its evolution over time to resolve the existing shortcomings. An integrated geodynamic modelling approach is essential to address unresolved questions regarding the Indian Ocean Geoid Low (IOGL). Key issues include the causative source and extent of the IOGL, the interplay between the Southeast Indian Slab (SEIS) and mantle dynamics, and the relationship of the IOGL to plate tectonic mechanisms and seismic activity in the India-Australia region.