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Seismic Metadata v.1

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General Information

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

5,355 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

Dataset Information

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.

Navigation Information

Datum

World Geodetic System 1984 (WGS84)

Location

Tracklines 20 total

Name Length (km) First SP Last SP First CDP Last CDP
L0911-01 207 924 3,188 156 18,882
L0911-02A 99 922 2,002 653 9,921
L0911-02B 37 2,354 2,767 12,109 16,041
L0911-02C 252 2,961 5,798 16,965 40,289
L0911-02D 34 6,134 6,527 42,425 45,610
L0911-03 147 986 2,645 653 14,553
L0911-04 257 1,076 3,973 653 24,457
L0911-05 816 920 10,194 653 9,937
L0911-06 125 952 2,362 414 12,322
L0911-07 299 1,072 4,492 653 28,641
L0911-08 306 1,017 4,631 653 30,193
L0911-09 196 915 3,250 653 19,961
L0911-10 60 1,031 1,740 653 6,953
L0911-11 340 1,091 5,104 156 33,385
L0911-12 149 1,155 2,900 877 15,465
L0911-13 638 1,050 8,027 485 56,761
L0911-14 598 1,028 7,695 485 54,281
L0911-15 345 918 4,798 485 31,985
L0911-OBS01 294 1,025 2,178 1,313 28,985
L0911-OBS2B 156 2,010 2,589 953 14,849

Acquisition Parameters

Name Value
Field Activity Identifiers L-09-11-GA, MGL1109
Vessels R/V Marcus G. Langseth
Navigation System C-Nav 3050
Horizontal Datum World Geodetic System 1984
Recording System Sercel Syntrak 960
Antenna to source 223 meters
Source to near channel 176 meters
Near channel number 636
Number of channels recorded 636
Number of cables 1
Number of channels each cable 636
Source to far channel 13 meters
Cable length 8,000 meters
Cable receiver depth 9 meters
Cable receiver depth recorded Yes
Number of sources 36
Source array separation 8 meters
Source Depth 9 meters
Source volume 6,600 cubic inches
Source pressure 138 bars
Shot interval 50 meters
Sample interval 2,000 microseconds
Record length 15 seconds
Nominal fold 80
Recording delay No
Compass birds Yes
Tailbuoy positioning Yes
Flip-flop shooting No