National Centers for Environmental Information (NCEI)
MULTICHANNEL SEISMIC-REFLECTION PROFILES
Offshore of Northern California and Southern Oregon
USGS Open File Report 89-222*
Data Announcement 90-MGG-02
During May 1981 the U.S. Geological Survey (USGS) collected
approximately 1005 km of 24-channel seismic-reflection data
across the continental margin in the eastern Pacific Ocean off of
the California and Oregon coast. This survey area includes the
Eel River sedimentary offshore of northern California.
The data were collected on the USGS Research Vessel S.P. Lee
(cruise identifier L5-81-NC). Seismic energy was provided by a
tuned array of five airguns with a total volume of 1311 cubic
inches of air compressed to approximately 1800 psi. The
recording system consisted of a 24-channel streamer 2400 m long,
and a GUS (Global Universal Science) model 4200 digital recording
instrument. Records were sampled in the field at a 2-millisecond
rate and later processed at a 4-millisecond rate. Record lengths
vary from 8 to 10 seconds, depending on water depth, in order to
obtain 6 to 7 seconds of data below the seafloor. Navigational
control for the survey was provided by a Marconi integrated
navigation system using transit satellites and doppler-sonar
augmented by Loran C (Rho-Rho).
The data were processed at the USGS Marine Seismic
Processing Center in Menlo Park, California. Processing was done
in the following sequence: editing-demultiplexing, trace-
balancing, deconvolution-filtering, velocity analysis and normal-
moveout correction, muting, normalized stacking, time-varying
bandpass-filtering, automatic gain control, and finally plotting
on an electrostatic plotter. In areas of shallow seafloor, early
arrivals on far-offset traces were muted before stacking to
remove refracted energy and the direct-arrival of the outgoing
pulse. In deeper water, the near-offset traces were muted before
stacking at and below approximately twice the water-bottom time
to suppress the water-bottom multiples on the stacked traces.
A reflection geometry of 50-m shotpoint intervals and 100-m
group intervals resulted in optimally 24-fold data collection.
However, twelve of the included seismic lines are nominally 22-
fold after trace editing, and the remaining five lines are 10- to
12-fold, due to reconfiguration of the streamer in the field and
* "Multichannel Seismic-Reflection Profiles Collected in May
1981, Between Latitudes 4040' and 4500' North, Offshore of
Northern California and Southern Oregon" By S.H. Clarke, Jr. and
P.H. McClellan, U.S.G.S. Open File Report 89-222, U.S. Geological
Survey, Menlo Park, California.
DATA AVAILABLE (please refer to 9-digit product numbers when
multichannel seismic-reflection profiles (17 lines, 17 sections)
(plastic sepia) Product #976F20176
(paper sepia) Product #976F19176
(blackline) Product #976F18176
2 trackline charts (scale: 1:500,000). Product #976A18176.
1 magnetic tape containing shotpoint navigation and magnetics
data. Product #976A18176. This data is also available on CD-
ROM, Product #129F27001.
17 digital magnetic stack tapes. Product #976L07176.