STRAIN PARTITIONING AND STRUCTURAL OVERPRINTING WITHIN THE NAGA AND INDO-BURMAN FOLD-THRUST BELTS

The ~400 km long Naga Fold-Thrust Belt (NFTB) formed due to the collision of the Burma sliver terrane with the trailing edge of the Indian plate in the Assam Valley. In this region, major continental fault systems that bound the Burma sliver terrane interact with the accretionary wedge of the Indo-Burman Ranges (IBR) and the NFTB. Oblique convergence between India and Eurasia is partitioned within the IBR south of 25° N, however the nature of strain accommodation between the major fault systems that bound the Burma sliver terrane and the NFTB north of 25°N is poorly understood. Geodetic studies of the NFTB suggest that it is locked at the range front and capable of producing a Mw 7.7–8.5 earthquake. This study utilizes field mapping, structural analyses, fault kinematic analyses, and cross-section construction to investigate how strain is accommodated within the NFTB and inform future seismic hazard assessments in the region. Structural and fault slip analyses indicate the NFTB is partitioned, with frontal structures absorbing NW-directed shortening related to the Burma-India collision and hinterland structures absorbing right-lateral transpressional shearing between Burma and India. Fault slip data reveal three kinematically compatible groups that record structural overprinting where IBR structures are refolded and faulted as they are transported northward into the NFTB. Structural analyses further indicate that the Naga Fault is segmented along strike and occurs at varying stratigraphic intervals between 4.2 km and 3.2 km. Geological shortening rates calculated from this study agree with previously reported GPS convergence rates of ~1 mm/yr for the SW NFTB. Future geodetic studies must consider fault normal convergence and a segmented geometry for the Naga Fault when conducting seismic hazard modeling in the region.