Abstract
The Rakhine (Arakan)-Bangladesh megathrust, along which the Indian and Burma plates collide, is assumed by some to be inactive/aseismic due to the lack of notable interplate earthquakes in the modern instrumental catalog. However, geological and historical evidence of the great 1762 Arakan earthquake suggest the megathrust can produce M similar to 8 events that could adversely affect the lives of millions of people in the region. To investigate the seismogenic potential and determine the slip budget of the megathrust, we first need to solve for India-Burma-Sunda relative plate motions. We present a new set of 24 GPS velocities (2011-2017) from the Myanmar-India-Bangladesh-Bhutan continuous GPS network. We use the new velocities and those from previously published studies to explore the geometries and slip rates of three major faults (Rakhine-Bangladesh megathrust, Churachandpur-Mao Fault, and Sagaing Fault) that accommodate the India-Burma-Sunda plate motion. Our results suggest that the three major faults we studied are likely fully coupled; the modern shortening rate across the Burma plate is 12-24mm/year, while the total dextral shear rate is 25-32mm/year. The possibly fully coupled shallow megathrust, and splay faults that may sole into it, are geodetically invisible while they are not slipping. However, we can identify the transition from coupling to steady creep on the deeper extension of the megathrust; we use this to show active oblique India-Burma convergence and to map along-strike and along-dip variations in dip-slip and strike-slip motion. This implies that the megathrust is currently accumulating strain which will eventually be released in earthquakes.