East Breaks Slump, Northwest Gulf of Mexico
Authors: Trabant Peter , Watts Philip , Lettieri Frederick  L. , Jamieson George A. 
Published: October 2008

The East Breaks slump in the northwestern Gulf of Mexico was mapped using 2D and 3D seismic and multibeam bathymetry data. Its morphology extends over a large area of the seafloor and comprises a tremendous volume of sediments. Detailed seafloor bathymetry shows a rough surface with evidence of friction-induced drag folds. Volume of the slumped material is 50-60 cubic kilometers with a maximum thickness of 70 meters. An eroded chute and accumulation zone extends 160 km down slope from the shelf break and encompasses an area of 3,200 km2; the main depositional lobe is located 145 km downslope of the head scarp. This volume of displaced material would have generated a tsunami wave on the order of 7.6 meters above sea level that would have impacted the entire south Texas coast.

The occurrence of a slump of similar magnitude at the present shelf edge could become a hazard to deep-water hydrocarbon production facilities and coastal communities as a result of mass slope failure and tsunami impact of the coastline.

Introduction

Evidence of large shelf edge slumps of recent age (past 30,000 years) is ubiquitous throughout the world. Large scale slumps described to date include the Walker-Massingill slump originating near the Mississippi River Delta and extending hundreds of kilometers across the Mississippi Fan (1), and the Storegga Slide offshore Norway (2). The presence of the East Breaks slump in the northwest corner of the GOM has been recognized since the 1960's when it was identified by the petroleum industry and subsequently surveyed by the U.S.G.S EEZ mapping program in 1985. While these initial studies recognized the feature as the product of mass wasting, no detailed mapping or sampling programs have yet been undertaken and the feature remains a mere curiosity. However, it has all the properties of induced mass gravity flows and slumps that could have serious impact on the petroleum industry's deep-water field development. In parallel with petroleum exploration activities, 3D seismic data sets have been acquired throughout most of the northern Gulf of Mexico and these data sets can provide an effective tool for investigating recent geological depositional features including mass slope failures.

This paper describes the dimensions and morphology of the East Breaks slump extracted from 3D seismic and looks at the effect slope failures might have on present day subsea production facilities and coastal towns.

Previous Studies

The presence of a large shelf edge slump in the northwest corner of the GOM has been recognized since the 1960's (5). Petroleum industry research labs mapped the slump's overall extent in the 1960's (3 & 4), and the USGS using sparker and the Gloria long-range side scan sonar systems in the mid 1980's (6). While these studies recognized the feature to be the product of slope failure and mass wasting, no detailed mapping with modern tools or sampling programs have been undertaken. Its head scarp is situated within the northwest corner of the Gulf of Mexico where it is identified by a 20 km indentation of the shelf edge along the 150-meter isobath