Tectonic geomorphology and seismic hazard of the east boundary thrust in northern segment of the Sunda–Andaman subduction zone

The East Boundary Thrust (EBT) is a ~ 500 km long linear to curvilinear deformation zone that accommodates the bulk of present crustal deformation along the Sunda–Andaman plate edge convergent margin. EBT is the main active tectonic structure responsible for accretionary prism formation in the outerarc ridge of the Andaman and Nicobar subduction zone. The EBT marks the up dip expression of subduction megathrust progressing toward the Andaman trench in the form of actively accreting the frontal prism and deforming the trench sediment sequences above the detachment. We conducted paleoseismic trench investigations of the Jarawa Thrust (JT) (northern 300 km segment of EBT) at two specific sites between Ferrargunj in the south and the Radhanagar in the north Andaman. Structural and stratigraphic relationships exposed in a trench excavated across the 6 m high scarp at Ferrargunj show the scarp to be the result of single earthquake. Dating of sediment offset by the fault with optical luminescence indicates that the displacement occurred between 2160 ± 300 BP and 400 ± 50 BP. Complex structural deformation is observed in the trench excavated across 10 m high scarp at Radhanagar similarly indicates that the scarp is due to single earthquake. The present findings are helpful for seismic hazard evaluation of the Andaman and Nicobar region, where greater slip deficit and no great earthquake (M ≥ 8) have been accounted so far which suggests that the region is potential for earthquakes larger than the observed one historically.