Quantitative assessment of active tectonics of Chittagong-Tripura Fold Belt, Bengal Basin, Bangladesh

Abstract

The Chittagong-Tripura Fold Belt (CTFB) is part of the active accretionary wedge of the Indo-Burman Ranges (IBR), spanning more than 100 km in width. Although the tectonic evolution and signature of active tectonics are evident from tectonogeomorphic and structural features, the assessment of active tectonics in the CTFB area—especially along the Chittagong Coastal Fault (CCF) and Kaladan Fault—remains limited. The present study attempts to comprehensively analyze fracture orientations and geomorphic features of the area to assess the level of active tectonics. The WSW-ENE generalized compressional direction, deciphered from the fracture set analysis, represents the normal component of present-day Indian Plate motion. Different morphometric parameter values of the seven watresheds in the CTFB area assign the range of the index of active tectonics (IAT): Class 1 is highly active (1.375–1.500), Class 2 is moderately active (1.501–1.875), and Class 3 is low/less active (1.876–2.250). The best-fit curves with the power-law (R² values) for linear, exponential, logarithmic, and power functions for seven master streams from seven watersheds and sixteen other streams from four different regions reflect the relative levels of active tectonics. Overall, the western margin of the CTFB along the Frontal Thrust/CCF appears to be relatively more active than the eastern margin along the Kaladan Fault and is therefore more prone to seismic hazards.