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16 July 2015

Güralp Systems customer, Australian Geophysical Observing System (AGOS) has published initial findings from an active marine seismic survey off the coast of Australia showing the benefits of using ocean bottom seismometers (OBS) in addition to hydrophone streamer based surveys.

Güralp provided 20 OBS instruments, engineered to withstand ocean depths to 6000m. Each OBS incorporated a Güralp 6T-OBS 3-component broadband (0.0167 Hz–100 Hz) seismometer, with a titanium housing; a hydrophone (1Hz–30KHz) attached to the fourth channel and a high precision Güralp Real Time clock with accuracy of better than a microsecond. The instruments can remain on the seafloor continuously recording for up to 12 months and can be commanded to return to the surface using an acoustic communication link.Recovery of AGOS deployed Guralp Ocean Bottom Seismometers

AGOS found that the Güralp OBS allowed for recovery of information from much deeper crustal features which would not typically be recovered via streamer based surveys during marine seismic acquisition. In addition they found that the hydrophone records considerably less information and appears to be more sensitive to water-born multiples than the seismometer.

AGOS identified a number of findings from their recent surveys for the future of OBS technology development which include:

  • The possibility to image whole crust and upper mantle velocity distributions and unequivocally define the Moho boundary from analysis of both reflected and refracted phases, generated by an industry standard airgun array with certain specifications.
  • Extension of 3D imaging capability, utilising OBS-recorded signal from 3D surveys at larger offsets than achievable with streamer survey configurations.
  • Analysis of background noise and understanding the interaction of broadband airgun generated signal and the ocean/Earth system.

Further possible uses of the OBS instruments identified by AGOS include:

  • passive seismology and plate tectonic reconstructions
  • earthquake and geo-hazard studies
  • monitoring of energy from construction on the ocean floor and its impact on marine life
  • monitoring sub-seafloor CO2 injection for long term storage.

Dr Alexey Goncharov, Australian Ocean Bottom Seismograph Science Coordinator, commented:

“Australian National OBS Fleet instruments that were built by Güralp have proven their capability to record high quality data from commercial seismic surveys airguns to very large offsets.

There is significant interest from industry, government and researchers for future OBS surveys. We are currently processing data from the Shell DAB survey and have obtained fantastic results for some long refraction lines, including high-quality first arrivals at large offsets. Moho refractions are clearly visible in the majority of the refraction profiles. We are also processing ‘eavesdropped’ signal from nearby 3D reflection shots and exploring the full capability of this unique dataset.

Nothing comparable in data quality and coverage exists anywhere in the world at the moment.”

Chris Potts Executive Chairman at Güralp added: “We are very pleased that our instruments have produced such excellent quality data for AGOS, and that this innovative use of deep ocean instruments with airgun sources has proved so effective. We are continuing to develop our Ocean Bottom Seismometers and intend to remain a global leader in the design, build and deployment of these complex instruments.”

You can read the full AGOS article here.

These results follow earlier success on the same project where the Güralp OBS were used to increase the aperture of the streamer survey from eight to thirty kilometres. You can read more about this here.

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