Geophysical Characterisation of the Active Fault Geometry and Trends in Tectonic Deformation in the Shallow Stratigraphy along Active Faults, South Andaman, India

摘要

A comprehensive Ground Penetrating Radar (GPR) profiling with high resolution was done and complemented with total station surveys along an active faults in the South Andaman Island (near Bathubasti) to reveal the sub-surface fault geometry and trends in tectonic deformation in shallow stratigraphy. The surface manifestation of deformation along the investigated active faults is expressed in the form of explicit tectonic scarps of various levels related to persistent tectonic uplift of the area and frontal scarps expressed in younger sediments were meticulously examined with GPR profiling. The surface displacement (scarp height) was calculated by using high resolution GPR data and total station data that may be correlated to the vertical displacement component of palaeoseismic faulting. Two active fault sites were carefully chosen for the systematic profiling with high resolution GPR profiling to examine the efficacy of GPR in elucidating the complicated near surface tectonic deformation. The surface deformation of site-1 is manifested in a form of a 6 m high abrupt tectonic scarp expressed in quaternary sediments. Site-2 is piggy back basin with corresponding pop-up structures with two antithetic scarps of 10 m height each. The high resolution GPR data vividly reveals the complicated sub-surface fault geometry and tectonic deformation in the form of an inclined and distorted radar reflections upto several meters of depth in the shallow stratigraphy and upward fault termination related to the active deformation. The high resolution GPR profiling demonstrates severe near surface tectonic deformation in the form of buckling, truncation, offsetting of recent sediments and warped radar reflections suggesting the propagation of tectonic activity in a compressive stress regime whose dynamics is related to the continuous oblique subduction of Indian plate under the Burmese micro plate.