High-resolution chirp seismic reflection data acquired from the Cap de Creus shelf and canyon area, Gulf of Lions, Spain in 2004

This report consists of high-resolution chirp seismic reflection profiledata
from the northern Gulf of Lions, Spain. These data were acquired in2004 using
the Research Vessel Oceanus (USGS Cruise ID: O-1-04-MS). Thedata are available
in binary and JPEG image formats. Binary data arein Society of Exploration
Geologists (SEG) SEG-Y format and may bedownloaded for further processing or
display. Reference maps andJPEG images of the profiles may be viewed with your
Web browser.

Marine seismic reflection data are used to image and mapsedimentary and
structural features of the seafloor and subsurface.These data were acquired
across the shelf and canyon area of the Gulfof Lions, Spain as part of a
multinational effort to characterize thegeologic framework and sedimentary
environment of the region.The specific objective of this seismic survey is to
provide seismicreflection images of the depositional geometry of the upper 50
meters ofsubbottom stratigraphy in order to better understand the mechanisms
ofsediment transport and deposition. These chirp seismic profiles
providehigh-quality images with approximately 20 cm of verticalresolution and
up to 80 m of subbottom penetration.

Chirp seismic reflection profiles are acquired by means of anacoustic source
and a hydrophone array, both contained in a single unittowed in the water
behind a survey vessel. The sound source emits ashort (30 ms) swept-frequency
(500 to 7200 Hz)acoustic pulse,which propagates through the water and sediment
columns. The acousticenergy is reflected at density boundaries (such as the
seafloor orsediment layers beneath the seafloor), and detected by the
hydrophonearray, and digitally recorded by the onboard PC-based acquisition
system.As the vessel moves, this process is repeated multiple times per
second,producing a two-dimensional image of the shallow geologic
structurebeneath the ship track.

[Summary provided by the USGS.]