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Modern Industrial Technology and Methodology Used in the Acquisition of High-Resolution 3D PCable Seismic Reflection Data, Offshore Central California

​Extensive three-dimensional (3D) low-energy offshore seismic reflection surveys were undertaken in 2011 and 2012 for Pacific Gas and Electric Company (PG&E) to image faults and piercing points for constraining slip rates of the Shoreline and the Hosgri Fault Zones.

04 May 2015
Hogan, P., Greene, H. G., and Nishenko, S.


Interpretations of the 3D/2D datasets are being used by PG&E in its ongoing efforts to characterize seismic hazards at the DCPP. The major components of the 3D multichannel data acquisition system were a digital recording system (CNT-2 Controller), 12 to 14 PCable-configured GeoEel solid digital streamers, CSP-D power supplies, and a triple-plate boomer acoustic source. The streamers were connected to a single PCable that was pulled taut from each end by port and starboard paravanes. Very high-resolution data were collected using state-of-the-art high-precision navigation, acoustic sound source, receivers, and recorders. The low-energy (1.5 kJ), high-resolution 3D PCable seismic-reflection profiling system has a frequency range of 100-700 hertz [Hz], with a 200-225 Hz fundamental frequency. A 3D navigation binning system was used. The streamer separation on the P-Cable was 6.25 m; each streamer consisted of eight active channels, with a group interval of 6.25 m. This allowed for tight control of bin spacing by using individual channels or summation of adjacent channels to increase the signal-to-noise ratio. With this configuration, a total of 96 channels (12 streamers) or 112 channels (14 streamers) of data were acquired at a sampling rate of 250 microseconds and a record length of 750 milliseconds (ms). The GeoEel streamer configuration used in this investigation provided a Nyquist frequency of 2 kilohertz. Survey sail-lines for 3D data collection in all surveyed areas used a trackline spacing of 37 to 40 m. The 3D swath width of this spread was 37.5 m or 43.75 m, depending on the number of streamers deployed. Shot spacing was at 3.125 m, with a CDP interval of 3.125 m and a 0.25 ms sample interval. Vertical resolution for all the seismic data is estimated to be 2 m; horizontal resolution is approximately 3 m. Processed 3D seismic-reflection amplitude and attribute volumes provide imaging of faults, stratigraphic horizons and geomorphologic features in unprecedented detail that were used to map fault geometry and evaluate slip-rates. The slip rate for the Shoreline fault zone is estimated to be less than 0.1 mm/yr., an order-of-magnitude less than that for the Hosgri Fault Zone. 


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