USGS CMG 2009-037-FA Metadata

Complete high-resolution seismic survey of pockmark field.  Sub-bottom only with 
EdgeTech 424 in primary study area.

Seismic stratigrapic framework of pockmark field

From July 24-31, 2009 the USGS Woods Hole Science Centers Sea Floor Mapping 
Group, aboard the R/V RAFAEL, collected 66 lines (totaling 192 km) of seismic 
reflection profile data in the Belfast Bay, ME pockmark field.
Personnel included Emile Bergeron, William Danforth, Barry Irwin, and USGS
volunteer and Principal Investigator Laura Brothers.  Lines were collected
with an east-west orientation every 200 m over 29 km2.  Tie lines were
collected perpendicular to the survey lines.  In the northwest quadrant of the
survey area, tie lines were collected at 200 m spacing to further resolve the
geometry of seismic reflectors of interest (i.e. a proposed methane sourcebed,
and paleo pockmarks).  Seismic reflection profile data were collected using an
EdgeTech FSSB 424 seismic profiling system operating at frequencies of 4-24 kHz. 
 The data were acquired in EdgeTech Discover program, and saved in EdgeTech's 
JSF format.
The data were then converted to SEG-Y format using custom USGS software.
Data were processed in SioSeis, SeismicUnix, and will later be interpreted in
Landmark Graphics software. Our objective was to gather seismic data where we
had already acquired swath bathymetry data, but did not have corresponding
subsurface data.  In this latest initiative we identified seismic reflectors
observed in other previously surveyed portions of the field. We found that
recently mapped surficial flute-like features located in the southern portion
of the field are structurally controlled by irregular bedrock.  We observed
the southern terminus of a proposed organic layer, potentially representing a
sea-level lowstand, and identified potential coring sites.
Also, subsurface data suggest that paleo pockmarks or failure features may
exist at the Holocene/Pleistocene unconformity in the periphery of the main
channel.  This is the first time any such features have been observed and the
geometry of the reflectors must be further examined to confirm the validity of
this interpretation. With survey 09037 we completed a multiyear project that
characterizes the spatial, morphological, and subsurface variability of the 
field.

Platform Owner:
USGS-Woods Hole, MA
Platform Captain:
Barry Irwin
Sponsoring Office:
Woods Hole Coastal and Marine Science Center
Affiliate Principal and Organization (if any):
Laura Brothers, University of Maine
Number of days at sea:
7
 Major Center Equipment Required:
Navigation - DGPS, Navigation - HYPACK, EdgeTech 424 chirp
Navigation Methods:
dgps;
Data Types:
Location/Navigation, Notes/Logs, Seismic,
Degree of Certainty:
Certain
Continuous Data (in km):
192
Number of Stations Occupied:
0
Number of Submersible Dives:
0
Science Strategy:
Hazards;Climate;
Submitted By:
Walter Barnhardt
Report Date:
2010-12-02

2921-AWW80

USGS