Three-dimensional seismic analysis of high-amplitude anomalies in the shallow subsurface of the northern Indus Fan: Sedimentary and/or fluid origin

Abstract

We report on a detailed analysis of amplitude anomalies in three-dimensional (3D) seismic reflection data and their surrounding strata in the shallow subsurface of the northern part of the Indus Submarine Fan, Arabian Sea. Our analysis reveals the presence of distributary lobe complexes and a relict fluid migration system, including a buried mud volcano, linked to contractional anticlines overlying deep-seated strike-slip faults buried below the Indus slope. Building on a regional tectonic and stratigraphic framework, we have used a 3D seismic survey to map in detail the occurrence of high-amplitude anomalies in the shallow subsurface. We link these to gas hydrate and free gas accumulations hosted within distal distributary lobes deposited on the Indus slope and supplied by underlying focused fluid flow system along a fault zone. Our results suggest that the seismic amplitude anomalies may be classified as a weak "bottom-simulating reflection" (BSR) formed during a paleofluid flow event in the northern Indus Fan (∼5-1.8 Ma). Present-day fluid influx is low. Copyright 2008 by the American Geophysical Union.