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High-resolution boomer seismic-reflection profiles of the shelf off southern California from cruise A-1-00-SC: Santa Monica Bay to San Diego

Data Acquisition Method

Most of the survey time in 2000 concentrated on the area within the California State three-mile limit from Port Hueneme to the Mexican border. Trackline naming conventions were complicated in order to keep some continuity with those assigned during previous cruises. Trackline designations were considered extensions to lines already run, or that might be run in the future using larger sound sources in areas seaward of state waters. For example, on cruise A-1-00-SC we ran an inshore addition to line 128 from cruise O-1-99-SC, and named the addition 128X. The short dogleg between 2 tracklines is commonly indicated with the addition of DL to the name; in this case the dogleg after 128X was named 128XD. A-1-00-SC lines run in the harbor were generally named with an H, as in H824. In some cases, a line name ends with A, B, C, generally indicating that data collection was interrupted by equipment failure or by a system shutdown to stay within the permits for operating where marine mammals were present. As a result, the data segments created were given successive letter designations in addition to the basic line number.

As reported in Gutmacher and others, 2000, the Geopulse sound source consisted of two ORE Geopulse 5813A boomer plates mounted on a catamaran sled built by the USGS. The sled was towed at the water surface, and most of the survey was conducted in water depths of 20-300m. The outgoing power level used was 350 Joules. The firing rate depended on water depth: we used 0.5-1 sec for work within the 3-mile limit, and 0.25 sec for work in the Los Angeles/Long Beach harbor. Signals were received by a 5-m-long SIG streamer towed from a boom on the side of the vessel. This streamer had 8 hydrophones spaced at 0.5-m intervals. To monitor data acquisition, the data were displayed in real-time on an EPC recorder as well as being recorded by Triton-Elics International ‘Delph Seismic’ software, in SEG-Y format, where we generally used a sample frequency of 16 kHz and a record length of 200-300 msec. We recorded the data without use of bandpass filters or gain algorithms. The data were also backed up to CD-ROM on board ship.

Data collected from JD 164 through JD 167 were lost as a result of a hard-disk crash, but were recovered by using the near-channel of the multichannel streamer that was being recorded by a Geometrics seismic controller. These “recovered” lines were recorded with a 2-sec fire rate, an 8-kHz sample rate and 750-msec record length.