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Minisparker seismic-reflection data collected between Point Sur and Morro Bay, offshore of central California, from 2011-09-12 to 2011-09-26 (USGS field activity B-05-11-CC)

July 20, 2017

This data release includes marine geophysical data collected on cruise B-05-11-CC between Point Sur and Morro Bay, California. The overall goal of this research is to understand the shallow geologic framework of this area as a contribution to the California Seafloor Mapping Program (Johnson and others, 2017). Particular focus is on mapping active faults and documenting the distribution and thickness of offshore, unconsolidated sediment.

Approximately 700 km of single-channel, seismic-reflection data between Point Sur and Morro Bay were collected during the cruise. Seismic profiles were collected at 1 km line spacing between Point Sur and Piedras Blancas, crossing the Hosgri-San Gregorio fault system 60 times. Data were also collected to the south on the south flank of Piedras Blancas (south of San Simeon) crossing the Hosgri-San Gregorio fault 13 times at 800 m line spacing. Farther south, additional data were collected offshore of Morro Bay with a focus on crossing the Los Osos fault zone. Data collected in the southern two areas overlap with and supplement data available in Sliter and others (2009).

Seismic-reflection data were collected using a minisparker system that creates an acoustic signal by discharging an electrical pulse between electrodes and a ground that generates a frequency spectrum roughly between 200 and 1600 Hz. At boat speeds of 4 to 4.5 nm/hour, seismic traces were collected roughly every 1 to 2 meters. Water depths were between 20 m and 600 m. Acoustic pulses were generated at 0.5-second intervals on profiles where maximum depth was about 300 m; a 1-second interval was used on the deeper water profiles. Standard SEG-Y files were generated using a Triton Subbottom Logger (SBL). Seismic data processing was accomplished using Sioseis, a public-domain software developed at Scripps Institute of Oceanography (part of the University of California at San Diego), and SeismicUnix developed at the Colorado School of Mines. The processing of these data consisted of a bandpass filter, mute function, automatic gain control, water bottom detect, swell correction, and scaling/plotting. Both raw data in SEG-Y format and processed (corrected) data are provided here.