The Indo-Burma Detachment Geometry Constrained by an Updated Vertical and Horizontal GPS Velocity Field in Bangladesh

The Indian plate and the Eurasian plate started colliding about 50 Ma, forming the Himalayas and the Tibetan Plateau, two of the most prominent topographic features on Earth. The current plate boundary between the two plates stretches from northwestern India to eastern India, where it bends around the eastern syntaxis in Assam into the Naga thrust belt. It continues southwards where it transitions from continental collision to subaerial subduction along the Indo-Burma subduction zone.

The Indo-Burma subduction zone is characterized by the extreme thickness of sediments of the Bengal Basin (15-20 km) on the downgoing plate. The Ganges and Brahmaputra Rivers drain considerable parts of the Himalayas and the Tibetan Plateau, carrying ~8% of the world's sediments to the Ganges-Brahmaputra Delta (GBD) , making it the world's largest. Subduction and deformation of the Bengal Basin and GBD sediments create the Indo-Burman Ranges (IBR), the surface expression of an extremely wide forearc and 375 km wide accretionary prism.

While the northern section of the Indo-Burma subduction zone has not experienced a great earthquake in the past 400 years, the southern segment ruptured in 1762. Moreover, recent geodetic surveys indicate that the northern segment of the subduction zone is currently locked and accumulating strain. This poses a major threat to the surrounding megacities, such as Dhaka, the capital Bangladesh and one of the most densely populated cities in the world.

Here we compute an updated GPS velocity field for Bangladesh and its adjacent region using the latest available dataset from a suite of 30 GPS receivers. Previous GPS velocity field models used data obtained in 2003-2013 from Bangladesh. We use an up-to-date dataset through 2020, including preliminary results from stations installed in 2018 from the flanks of the IBR. We compare the horizontal and vertical GPS velocity field with the expected displacement rates for different detachment geometries to better estimate the megathrust geometry and seismic hazard in the region.