ACTIVE TECTONICS OF THE INDO-BURMAN FOREARC, A REVISED PERSPECTIVE FROM NEW STRUCTURAL AND GEODETIC MODELING

The Indo-Burma Ranges are a highly oblique (70°) subduction system where the Indian plate is converging with the Eurasian plate. Recent geodetic studies indicate that the megathrust is locked and an active zone of convergence that can host great (≥8M) earthquakes. Despite growing interest in the seismic potential of the region, the structure and kinematic evolution of the active forearc fault systems that absorb India–Eurasia convergence remain poorly understood and widely debated. To help resolve conflicting tectonic interpretations of the IBR forearc, we synthesize the results of several geologic mapping campaigns in the IBR since 2015 with published and new geo- and thermo-chronology data. A train of detachment folds and fault-cored antiforms fold late Miocene–Quaternary strata and absorb the component of convergence normal to the deformation front within the outer belt of the IBR. Within the inner belt, deeply rooted (up to ~10 km) out-of-sequence thrusts initiated ca. 7 Ma and uplifted Miocene and Oligocene strata, thickening the thrust wedge. Inboard of the thin-skinned thrust wedge, an ~80 km wide zone of dextral transpression absorbs the margin parallel component of oblique convergence between the Churachandpur-Mao (CMF) and Kabaw Fault systems. West of the CMF, northwest-striking left-lateral faults bound ~20 km wide fault blocks that have rotated up to ~45° clockwise based on the misorientation of fold-axes within the blocks. East of the CMF, Triassic to Oligocene strata are intensely deformed by oblique, dextral-reverse faults and upright tight to isoclinal folds. Thermokinematic and geodetic modeling of the Kabaw Fault indicate that it is a locked crustal structure that initiated ca. 20 Ma and uplifted ultramafic rocks of the Burman crust. The Kabaw Fault presently accommodates ~7 mm/yr of right-lateral strike-slip motion and ~10 mm/yr of convergence and is capable of generating 7M earthquakes, absorbing a portion of the convergence previously ascribed to the Indo-Burma megathrust. Our results illuminate active structures within the IBR forearc and reveal a previously unrecognized seismic hazard associated with the Kabaw Fault.