What tectonic structures delineate the split between the Australian and Indian tectonic plates?
The structures are not mature or well defined and deformation was thought to be diffused, i.e., distributed over a large area. Earthquakes such as the M8.6 2012 Indian Ocean earthquake (largest strike-slip earthquake on record) appear to accommodate some, if not all, of the deformation. 

Seafloor geodesy is relatively a new field. Most studies are limited to areas near the coast, e.g., US (Cascadia), Japan etc.