Constraints on the configuration of Andaman-Nicobar Subduction zone from EM modeling

Abstract

The electrical conductivity structures, using Long period Magneto Telluric data at three sites: NBG (Nabagram) & HAV (Havelock) in Andaman and CBY (Campbell Bay) in Nicobar region are investigated. After obtaining 1D responses, 2D forward models of electrical structure are constructed along profiles across North Andaman, Middle Andaman and Nicobar Islands. The initial configuration along each profile is constrained from models based on seismic reflection data. The responses obtained after iterative forward computations match the observed data at respective sites reasonably well. New structures within the forearc high are discerned: from north to south we delineate a moderately conductive body beneath North Andaman, which is associated with the presence of ophiolites around this location, in the Middle Andaman, a highly conductive body below the island is interpreted as presence of fluids along the active Diligent Fault, facilitated by the barrier of the Invisible Bank. A complex geometry of resistive material embedded in a highly conductive body inferred beneath at Great Nicobar at CBY is commensurate with the presence of a layered magmatic body, possibly linked to the volcanic seamount to the east, near the tear of the subducting plate.