Archive of Digitized Analog Boomer Seismic-Reflection Data Collected During U.S. Geological Survey Cruises Erda 92-2 and Erda 92-4 in Mississippi Sound, June and August 1992

The USGS Saint Petersburg Coastal and Marine Science Center (SPCMSC) currently holds data from 13 major geophysical surveys from the northern Gulf of Mexico in its paper repository. A conservative estimate of 2,000 line-kilometers (km) of data are available. Paper copies of data are difficult and expensive to duplicate and share with other facilities, and cannot be analyzed using standard GIS and interpretative software. Conversion of this data into a usable digital format is necessary to archive the geologic information that otherwise might be lost, requiring additional redundant and expensive marine geophysical surveys. The USGS NGGDPP addresses the need to preserve, catalog, and provide access to geological and geophysical data for scientific research and economic development. In addition to the current efforts under the NGGDPP, four geophysical investigations from the 1980s and 1990s were previously archived through a preservation project in collaboration with the Bureau of Ocean Energy Management (Harrison and others, 2007; Sanford and others, 2009a, b, c). The USGS SPCMSC scans its analog HRSP holdings using a large-format continuous scanner. The analog to digital conversion process used for this dataset is similar to the processes used previously in Harrison and others (2007) and Sanford and others (2009a, b, c) and is described in detail in Bosse and others (2017). The digital files were converted into Tagged Image File Format (TIFF) for standard accessibility by raster image processors. The TIFF images of the seismic profiles were then converted into SEG-Y format. This standard non-proprietary format is the accepted industry standard for seismic data, and can be accessed by all major seismic data processing and interpretation systems. Navigation and metadata files, which are generated for use in GIS, database, and Internet Message Access Protocol (IMAP) services as well as processed seismic profile images are also provided. The processed profiles provided in this data release are Portable Document Format (PDF) files that were created using Seismic Unix and/or Imagemagick software. The northern Gulf of Mexico is a passive continental margin, where minimal structural change to the shallow stratigraphy has occurred during the last few thousand years (Anderson and others, 2004). Therefore, subsurface data collected from this environment for the purposes of geologic assessment can be considered useful in perpetuity. The geologic information collected by the USGS in the northern Gulf of Mexico remains a valuable resource for sea floor and stratigraphic investigations, and is continuously revisited by researchers interested in Holocene and recent earth processes. For example, decades-old geologic data is commonly used in sediment resource studies in coastal Louisiana (for example, Kindinger and others, 2001; Kulp and others, 2002; Rogers and others, 2009) and previously collected datasets across the Mississippi-Alabama shelf have been used in recent geologic-framework assessments (Roberts and others, 2004; Greene and others, 2007; Flocks and others, 2011). The seismic data were collected using a single-channel Huntec boomer/benthos hydrophone system with Ocean Research Equipment (ORE) Geopulse power supply. The system consists of an electromechanical sound source mounted on a catamaran sled towed behind the vessel at the water surface. The signal emitted from the sound source is received by a 5 meter- (m) long hydrophone streamer towed alongside the sled. The received signal was recorded in one of two ways. For older cruises, the signal went to a graphic recorder, while in the most recent cruises, the signal is processed into response amplitudes via a topside computer running the acquisition software; the settings varied by cruise for both methods. The seismic returns were printed onto paper rolls as two-dimensional profiles representing shots horizontally (time along track) and depth (two-way travel time). Geographic positioning of the system was collected using a Global Positioning System (GPS) and a long-range navigation (LORAN) system and annotated onto the paper copies. This data release is an addition to the work that Sanford and others (2009c) completed in a previous USGS Data Series.