Seismic Reflection and Refraction Acquisition and Processing

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Seismic Reflection and Refraction Acquisition and
Processing

• Andrew M. Goodliffe
• Department of Geological Sciences
• University of Alabama

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R/V Maurice Ewing in Yokohama, Japan, August 1999
R/V Maurice Ewing Length - 70.2 m Width
-14.1 m Range - 15,000 Nautical miles
Personnel 28 scientists, 22 crew Operated by
the Lamont-Doherty Earth Observatory, owned by
the US National Science Foundation
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R/V Maurice Ewing in Athens, Greece, July 2001
The rear of the R/V Maurice Ewing shows the
airguns in their stowed position.
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R/V Maurice Ewing in the Gulf of Corinth, Greece,
July 2001. Courtesy LDEO
When deployed, each 12 m boom tows 8 airguns. The
remaining four are towed from the rear
A-frame. In the water, each airgun is suspended
from a Norwegian Buoy.
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From http//www.ldeo.columbia.edu/res/fac/oma/sss/
index.html
A typical array for deep seismic penetration
seismic profiling consists of 20 Bolt airguns
varying in volume from 1.3 to 13.9 liters (80-850
cu.in), with a total volume of 140 liters (8580
cu.in).
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From http//www.ldeo.columbia.edu/res/fac/oma/sss/
bubble.html
From http//www.ldeo.columbia.edu/res/fac/oma/sss/
tuning.html
The large number of airguns allows the array to
be tuned. In the example above the collapsing and
expanding air bubble creates a series of bubble
pulses. Summing the signature of six individual
guns results in a tuned signature in which the
bubble pulse is supressed. This produces a much
improved seismic section
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The streamer is stored on a large reel on the
fantail of the R/V Maurice Ewing. The reel can
accommodate a total of 6 km of streamer,
consisting of 100 m sections. The streamer can
be configured with a group interval of 12.5 or 25
m depending on the survey requirements (240 or
480 channels)
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Attached to the end of the streamer is a tail
buoy. Instrumentation includes GPS for streamer
navigation. A strobe light is included as a
safety precaution.
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Birds are attached to the streamer to help it
maintain a constant depth. Every other bird also
contains a compass. By knowing the position of
the ship, the tail buoy, and the bearing of the
streamer at known points, the position of the
streamer can be derived. Inputting this
information into an onboard navigation computer
running Spectra allows navigation to be output
in standard UKOOA format. Post processing of the
navigation data can be carried out with Sprint
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Once we start shooting the emphasis shifts to the
main lab. On the right is the watchstander
station. Here, navigation, logging and seismic
quality control computers are monitored. Survey
parameters such as sample rate, number of
channels, etc are also set here
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The raw seismic data is recorded in SEG-D format
on two 3490E tape drives simultaneously. Each
3490E contains up to 810 MB of data and has to be
changed approximately every 20 minutes (assuming
sample rate 2 ms, 480 channels). Initial
processing can include copying the SEG-D tapes to
SEG-Y format, re-sampling, and writing out to DLT
tape and hard drive.

• Typically shipboard processing is carried out on
  the ships Sun server or scientist supplied
  workstations (Sun, Linux). Shipboard processing
  software consists of
• ProMAX a commercial seismic processing package
  by Landmark Graphics.
• SIOSeis a freely available processing package
  that runs on Unix/Linux based computers (written
  by Paul Henkart at Scripps Oceanographic
  Institute).

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• Shipboard processing typically includes
• Read raw data from SEG-D tape.
• Resample (typically from 2 ms to 4 ms).
• Navigation quality control and loading of
  navigation data into trace headers.
• Brute stacks and near trace plots for initial
  quality control.
• Bandpass filter to remove noise.
• Trace statistics to remove dead traces, noisy
  shots, etc.
• Pre-stack deconvolution.
• Velocity analysis.
• Inside mute to attenuate the multiple
• Outside mute to remove excessive NMO stretch
• Normal Moveout correction and stack.
• Post-stack deconvolution.
• Migration.
• If time allows, processes such as Dip Moveout and
  Radon Analysis can also be applied at sea.
• A realistic goal is to walk off the ship with an
  initial version of the processed seismic data.

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An example of data collected with the R/V Maurice
Ewing in the Gulf of Corinth, Greece, July 2001.
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• Scripps ocean bottom hydrophone/seismometer.
• Yellow area contains flotation.
• Black tubes contain electronics/batteries,
  pinger.
• Black weight holds the instrument on the seafloor

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OBS/H electronics, batteries, hard drive.
Acoustic release
Top view with floats removed.
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When not in use the OBS/H instruments are stored
in specially designed shipping frames. The R/V
Maurice Ewing has held up to 55 instruments on
deck at one time
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The OBS/H instruments have a dedicated group of
typically 3-4 technicians who maintain, deploy,
and retrieve them. They also download the data
from the instruments and do initial processing on
the raw seismic data. A vital role of the
technicians is to train shipboard scientists to
carry out all these steps.
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From Kerr et al., 2002
Data from a single OBS in the Mariana region
From Tischer et al., 2002
Data from a single OBS on the Exmouth margin of
NW Australia
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From Tischer et al., 2002
2-D Velocity models obtained for the Exmouth
margin. These were derived using freely available
software (e.g. RayGUI, Loss et al., 1998
rayinvr, Zelt and Smith, 1992).
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An example of 3 D first-arrival traveltime
tomography from the Woodlark Basin, Papua New
Guinea. This was carried out using freely
available software from Zelt and Barton (1998).
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• Software Availability and Training
• As part of our planned proposal we want to ensure
  that NRIAG has access to software to process both
  the raw seismic reflection and refraction data.
• Seismic Reflection Processing
• ProMAX (by Landmark) is a commercial, oil
  industry standard, seismic reflection processing
  package.
• Runs on Unix (e.g. Sun) or Linux (P.C based)
  computers
• NRIAG does not meet the criteria for an academic
  grant from Landmark
• In discussions with Landmark I have found that
  NRIAG may qualify for a very substantial sales
  discount as Landmark is looking for opportunities
  to expand in the Egyptian market.
• Under such an agreement Landmark would restrict
  the use of the software to non-commercial
  applications.
• We can assist NRIAG in exploring the possibility
  of obtaining this software package through
  contacts at Landmark (a useful person would be
  Rasha El-Waraky, REl-Waraky_at_lgc.com)
• I am still trying to get cost estimates from
  Landmark. We would like to include these costs in
  our proposal budget.
• ProMAX training
• In our proposal we can include the cost incurred
  for some NRIAG personnel to attend ProMAX
  classes. This would cost approx. US2,750/day
  (not including instructor travel costs) if
  Landmark were to give a class at NRIAG, or
  US3,700/day is NRIAG personnel were to travel to
  a Landmark office.

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• SIOSeis
• Runs on Unix/Linux based computer
• Disadvantage not as user friendly as ProMAX, no
  formal training available.
• Advantage Free, comprehensive seismic processing
  package.
• Seismic Refraction Processing
• All software is freely available.
• Additional Training Opportunities
• Senior graduate students from LDEO/Alabama/Hawaii
  could visit NRIAG for extended periods to work
  on the data with NRIAG personnel.
• This would give us the opportunity to carry out
  additional processing on the raw data (e.g.
  pre-stack depth migration) in Egypt.
• This would give NRIAG personnel an opportunity to
  become proficient with some of the freely
  available processing software with which we are
  familiar.
• The students would also benefit greatly from
  expertise at NRIAG.
• NRIAG visits to US?
• Hardware
• We could also include the cost of a workstation
  in our proposal that would be capable of running
  all the software mentioned in this presentation.
• I am exploring the logistics involved in this.