Analysis of high-resolution geophysical data collected over 253 blocks tentatively selected for proposed OCS Oil and Gas Lease Sale 59 revealed potential geologic hazards to oil and gas exploration and development activities. These potential hazards are shallow recent faults and massmovement areas on the continental slope. Relatively recent faulting and movement of shallow diapirs may have triggered some of the slumps and slides mapped. No potential hazards were observed on any blocks on the continental shelf.Other geologic features, classified as constraints because they pose a relatively low degree of risk, can be dealt with using existing technology.Constraints found in the proposed Lease Sale 59 area are filled channels, erosion, sand waves, deep and shallow faulting, and gassy sediments.Piston cores were collected for geotechnical analyses at selected locations on the continental slope in the proposed lease sale area. The core locations were selected to provide information on geotechnical properties of slumps, slides, and undisturbed sediments. The results indicate that localized areas of underconsolidated sediments exist primarily on valley walls and ridges of the upper slope.

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A multi-parameter high-resolution seismic survey covering 253 offshore lease blocks was undertaken for analysis of critical structural and depositional features and a suite of piston cores was examined for geotechnical properties on the Mid-Atlantic continental slope in the OCS Lease Sale 59 area. The analysis of this data revealed complex interrelationships between a number of buried structural and depositional features indicating the existence of a variety of slope environments in the proposed lease sale area. The relationship these depositional features have to fault scarps and other topographic irregularities is critical to hazards assessment in this area. Southwest of the Hudson Canyon area, a major slump complex was partially delineated and numerous drape structures, which in some cases appear to have developed into contemporaneous down-to-the-basin faults, are associated with topographic irregularities. Southwest of the Baltimore Canyon area, slumps may be a result of the formation of mud diapers. These diapers? are the first reported in the Mid-Atlantic continental slope. Piston cores were collected at selected locations to provide information on geotechnical strength parameters of slumps, slides, and undisturbed sediments. These data indicate that localized areas of under consolidated sediments are found on valley walls and ridges of the upper slope. These zones may represent discrete areas where either mass movement has occurred or the potential for mass movement may exist. Many of the mass-movement features identified in the OCS Lease Sale 59 area may be Pleistocene in age and are related to' conditions prevailing during low sea stands. Since these conditions are presently absent, the potential for sediment mass movement does not appear to present a major problem to oil and gas operations within the proposed OCS Lease Sale 59 area. Introduction A recently completed study by the U.S. Geological Survey assessed the existence of potential geologic hazards and constraints which might adversely affect oil and gas exploration and development in the Mid-Atlantic OCS Lease Sale 59 area. The 253 blocks in the study area total some 1,440,376 acres, and are located in the Baltimore Canyon Trough in water depths of 85 m to 2,455 m (figure 1). Seventy of these blocks were previously surveyed for geohazards in connection with OCS Lease Sales 40 and 49. It was not considered cost effective or necessary to resurvey these blocks, but tie lines were run into these blocks at approximately 8,000-m intervals in order to facilitate merging the different data sets. The assessment of geologic hazards was partially based on the interpretation of high-resolution seismic- reflection profiles collected by Inter sea Research Corporation under contract to the U.S. Geological Survey. A total of 7,574 km of multi-spectral high-resolution acoustic data were collected from June to September 1980 over 183 blocks aboard the RV Albert using an 800 by 2,400-m grid. The data were collected using a 24-kHz narrow-beam (100 cone) fathometer, a single-channel (l/Z-ms sampling rate) digital seismic profiler, and a broad-band analog acquisition system. The analog data were played back through a 450-Hz low-cut filter. A single 15cubic inch water gun was used as the sound source for the seismic system.

Shallow seismic reflection techniques were successful in delineating stratigraphic units and bedding geometries significant to the hydrologic modeling of unconsolidated sediments less than 60 m deep at Cherry Point Marine Air Base near Havelock, North Carolina. Discontinuous confining units beneath an industrialized portion of this major aircraft overhaul facility were thought to be due the erosion by a river that had cm through this area. Land shallow seismic reflection techniques provided images of alternating sand and clay sequences with average thicknesses on the order of 6 to 9 m. The land data have a dominant frequency of about 200 Hz, providing a minimum vertical bed resolution of about 2 m. Continuous seismic reflection data collected in the Neuse River directly north of the base have a dominant frequency around 600 Hz, providing a resolution potential of less than 1 m. Well defined cut and fill features that appear to have removed portions of the confining units are evident on the processed marine data. Correlation of the land CDP stacked seismic section with the drillholedefined lithology was enhanced by incorporating electric logs and VSPs acquired in three strategically placed monitor wells. Some processed VSPs have interpretable reflections from within the upper 70 m that are consistent with the geologic section as inferred from drilling and electric logs. Subtle stratigraphic contacts, such as shell layers within sand or changes in the grain size of sand, were not easily interpretable on the CDP stacked sections. The land seismic reflection data provided the very high horizontal and vertical resolution necessary for determining continuity of confining units and stratigraphic variations between 10 and 60 m at this site.