Seismic exploration of the sub-ice continental shelf using ... · A vibroseis source and a 1.5 km...
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Yngve Kristoffersen, University of Bergen, Allegaten 41, Bergen, 5007 Norway, [email protected] Coen Hofstede, AWI, Bremerhaven, Germany Olaf Eisen, AWI, Bremerhaven, Germany Lomonosov Canada Basin Makarov Basin Ridge Siberian shelf 2 Ellesmere Isl. 4 disturbed area Mendeleev Ridge Alpha Ridge Arctic Ocean ACEX drill site 1 3 Seismic exploration of the sub-ice continental shelf using a vibroseis source, Dronning Maud Land, Antarctica Yngve Kristoffersen, Dept.of Earth Science, University of Bergen, Norway Coen Hofstede, AWI, Bremerhaven, Germany Olaf Eisen, AWI, Bremerhaven, Germany Richard Blenkner, Dept. of Earth Science, University of Bergen, Norway Abstract A vibroseis source and a 1.5 km snow streamer pulled by a track vehicle have been used to acquire a 90 km long transect of multichannel seismic reflection data across the continental shelf at the location of Neumayer Station, Dronning Maud Land. The 2.5 sq.m. pad of the 12 ton peak force truck mounted vibrator on skies rarely sank more than 15 cm into the snow for 10-100 Hz sweeps of 10 second duration. and yielded useful signal/noise ratios down to 2 seconds two-way travel time. We maintained a production rate of ca. 20 km/day for 8-fold data. The sea bed below the Ekstrøm Ice Shelf is an erosional surface with no resolvable cover of younger sediments except irregular < 100 meter thick accumulations within 5 km of the grounding line. A strong reflection event at about 2 sec. depth (TWT) below the outer continental shelf can be associated with the top of the volcanic Explora Wedge and followed to outcrop about 13 km south of Neumayer Station. The vibroseis method The vibrator generates a known signal which is cross correlated with the recorded trace to obtain a zero phase image of reflecting interfaces Conclusions Use of vibrators for exploration of the sub-ice geology on the Antarctic continent have the advantage of low environmental impact and reduced data acquisition costs. The operation of a vibrator and snowstreamer pulled by a snow cat require 3-4 persons and can achieve a production rate of > 20 km/day for 8 fold data. Future vibroseis operations may have objectives such as: i) exploring for sub-ice sediment accumulations suitable for sampling by scientific drilling, ii) tying together offshore and onshore geology iii) the physical properties of the ice-bedrock interface, iv) grounding line processes, basal debris layers and marine ice, v) surveys of sub-glacial lake settings, Results Signal characteristics The dynamite signal is richer in higher frequencies compared to the band limited vibroseis signal Changes in signal to noise vary little with Increasing sweep lengths Changing the sweep length Acknowledgements The field work has been funded under the LIMPICS project by a grant from DFG EI 672/5-1 to Olaf Eisen and AWI. Norwegian participation was funded by the University of Bergen and the NPD.
Transcript of Seismic exploration of the sub-ice continental shelf using ... · A vibroseis source and a 1.5 km...
Yngve Kristoffersen, University of Bergen, Allegaten 41, Bergen, 5007 Norway, [email protected] Hofstede, AWI, Bremerhaven, GermanyOlaf Eisen, AWI, Bremerhaven, Germany
Lomonosov
Canada
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Makarov Basin
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Siberian
shelf
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Elle
sm
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Isl.
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disturbed area
Men
dele
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Alpha Ridge
Arctic
Ocean
ACEX drill site
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Seismic exploration of the sub-ice continental shelf using a vibroseis source,Dronning Maud Land, Antarctica
Yngve Kristoffersen, Dept.of Earth Science, University of Bergen, NorwayCoen Hofstede, AWI, Bremerhaven, GermanyOlaf Eisen, AWI, Bremerhaven, GermanyRichard Blenkner, Dept. of Earth Science, University of Bergen, Norway
AbstractA vibroseis source and a 1.5 km snow streamer pulled by a track vehicle have been used to acquire a 90 km long transect of multichannel seismic reflection data across the continental shelf at the location of Neumayer Station, Dronning Maud Land. The 2.5 sq.m. pad of the 12 ton peak force truck mounted vibrator on skies rarely sank more than 15 cm into the snow for 10-100 Hz sweeps of 10 second duration. and yielded useful signal/noise ratios down to 2 seconds two-way travel time. We maintained a production rate of ca. 20 km/day for 8-fold data.The sea bed below the Ekstrøm Ice Shelf is an erosionalsurface with no resolvable cover of younger sediments except irregular < 100 meter thick accumulations within 5 km of the grounding line. A strong reflection event at about 2 sec. depth (TWT) below the outer continental shelf can be associated with the top of the volcanic Explora Wedge and followed to outcrop about 13 km south of Neumayer Station.
The vibroseis method
The vibrator generates a known signal which is cross correlated with the recorded trace to obtain a zero phaseimage of reflecting interfaces
ConclusionsUse of vibrators for exploration of the sub-ice geology on theAntarctic continent have the advantage of low environmental impactand reduced data acquisition costs. The operation of a vibrator and snowstreamer pulled by a snow cat require 3-4 persons and canachieve a production rate of > 20 km/day for8 fold data.
Future vibroseis operations may have objectives such as:i) exploring for sub-ice sediment accumulations suitable for
sampling by scientific drilling, ii) tying together offshore and onshore geologyiii) the physical properties of the ice-bedrock interface, iv) grounding line processes, basal debris layers and marine ice,v) surveys of sub-glacial lake settings,
ResultsSignal characteristics
The dynamite signal is richer in higher frequenciescompared to the band limited vibroseis signal
Changes in signal to noise vary little withIncreasing sweep lengths
Changing the sweep length
AcknowledgementsThe field work has been funded under the LIMPICS project by a grant from DFG EI 672/5-1 to Olaf Eisen and AWI. Norwegian participation was funded by theUniversity of Bergen and the NPD.
