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National Geophysical Data Center

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 subsequent editing.

* "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 ordering).

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.

Please contact NGDC for prices.