Knapp, Camelia C.¹, James H. Knapp¹, Christopher Mitchell¹ 
(1) University of South Carolina, Columbia, SC

ABSTRACT: Absheron Allochton of the South Caspian Sea: Evidence for Slope Instability in Response to Gas Hydrate Dissociation

Seismic reflection profiles from the petroleum rich Absheron Ridge of the South Caspian Sea, Azerbaijan, were analyzed with the aim of identifying the occurrence of deep water gas hydrates. Processing of these profiles was focused on noise reduction and preservation of true amplitudes, necessary for the evaluation of the elastic properties of gas hydrates, including possible “blanking” effects, identification of Bottom Simulating Reflectors (BSRs), and amplitude vs. offset (AVO) effects for examination of possible free gas accumulations beneath the gas hydrate layer. These data document the occurrence of gas hydrates well beneath the seafloor (~300 m) where the water depth varies between ~400 and 650 m. Development of these gas hydrates near the base of the continental rise and in the vicinity of a mud volcano appears to control a large region (200 sq. km) of shallow deformation. Due to the complexity of disruption, the relatively sharp boundaries to the zone of deformation, the discontinuity of stratigraphy across these boundaries, and the shallow level of detachment, this confined zone appears to be allocthonous in origin, and it was named the Absheron Allochton. Shallow structural disruption, evident on the detailed bathymetry of the seafloor, appears to be controlled by the base of the gas hydrate layer, while the zone of gas hydrate appears to be continuous across shallow inverse faults, implying rapid and dynamic re-equilibration of the gas hydrate stability field following very recent faulting. From the AVO analysis, these gas hydrates show accumulation of free gas within the underlying sediment.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.