L-09-11-GA MCS

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Data Type

2D Multichannel Seismic

Data Acquisition System

Bolt Airgun and Sentry Solid Streamer

Contributor

U.S. Geological Survey

Dates

Started on June 5, 2011, and ended on June 25, 2011.

Number of Tracklines

20

Distance Shot

3,042 km

Description

In 2011, the U.S. Geological Survey (USGS) conducted a 2D MCS survey in support of U.S. extended continental shelf (ECS) assessments in the Gulf of Alaska. The survey was conducted with the R/V Marcus G. Langseth, a geophysical research vessel owned by the National Science Foundation and operated by Lamont-Doherty Earth Observatory of Columbia University.

Purpose

This field survey were designed to determine sediment thickness and acoustic velocity in support of extended continental shelf maritime zone definition, conducted on behalf of the interagency U.S. Extended Continental Shelf Project, and are being released without restriction or warranty.

Notes

The final 4 MCS lines on L-09-11-GA, collected after June 21 (day 172/04:46 UTM), were collected using the offsets to the near 6 km of the streamer with 468 channels total due to a streamer malfunction.

Other Survey Identifiers

MGL1109 was used by Lamont-Doherty Earth Observatory.

Geographic Features

Gulf of Alaska

Processed Methods

Seismic Reflection

Processed Data Classes

Migration, Stack

Data File Formats

SEG-Y

Embedded Navigation

No

Data Class

Processed

Seismic Data Provenances

Digitally Acquired Digital SEG

Data Media

Online

Data Quality

The quality of the MCS data was excellent on the cruise. The only significant problem was encountered on L-09-11-GA (Gulf of Alaska) during data acquisition when a telemetry failure of the far 2 km of streamer occurred near the end of the survey (June 21). The airguns were powered down 18 times during L-09-11-GA, but these power-downs introduced significant data gaps only in line L0911-02. Most power-downs lasted 30 minutes or less. In these cases, with an 8 km streamer, the fold was reduced but no gap in the profile section resulted. During the survey, some variability in gun array volume and streamer depth occurred due to weather and maintenance requirements. This is documented in the observer logs for each acquisition line.

Processing

Field data were recorded in demultiplexed SEG-D format. Upon completion of an MCS profile line, SEG-D data files (one per shot) were posted to the ship’s server. These were concatenated into a single SEG-D file and imported to Paradigm’s Focus software for processing. Products of shipboard processing included raw shot gathers, CDP gathers processed through gapped predictive deconvolution, preliminary unmigrated stacked sections, post-stack FK-migrated sections, and stacking velocity fields. All MCS processing was reviewed and finalized post-cruise.

Datum

World Geodetic System 1984 (WGS84)