Active faulting along the Noa Dihing River, easternmost Himalaya

Abstract:

The eastern terminus of the Himalayan arc is defined by the intersection of three active, seismogenic plate-bounding fault systems: the Himalayan Frontal Thrust accommodating India-Eurasia convergence, the Naga Thrust accommodating convergence between India and the Burma sliver plate in the Indo Burman Ranges, and the dextral Sagaing Transform Fault dividing the Burma sliver plate from southeast Asia. While each fault system has been well studied independently, the kinematics of their intersection remain poorly constrained. We present preliminary field mapping and remote sensing of a ~100 km east-west striking fault at the center of this intersection in the vicinity of the Noa Dihing River. Field mapping constrains the fault trace where it crosses the Noa Dihing river, consistent with north-side uplift of an active, reverse-sense structure that cuts the Naga Thrust. At this location C-band Sentinel-1 InSAR measurements between 2015 and 2020 indicate a change in surface uplift across the fault trace and DEM analysis indicates evidence for at least 6 distinct periods of terrace incision in the hanging wall. Despite clear evidence of activity, the fault has little recorded seismicity, potentially indicative of locked or aseismic slip behavior. We propose that the fault kinematics may be explained by either of two models: southward propagation of a shallowly dipping splay of the Himalayan Frontal Thrust or a steeply dipping dextral-oblique reverse fault continuous with the Sagaing system cutting both the Himalayan wedge and Indo-Burman fold-thrust belt. As this fault delineates Himalayan tectono-stratigraphic units from sedimentary rocks of the Indo-Burman Ranges, determination of the fault kinematics is key to predicting the evolution of this continental fault intersection. Thermo-kinematic modeling of hanging wall exhumation demonstrates that low-temperature thermochronology may distinguish between these models, guiding the future direction of this research.