A Low-Velocity Zone Within the Layer 3 Region of 118 Myr Old Oceanic Crust in the Western North Atlantic
During the North Atlantic transect (NAT) experiment 11 expanding spread profiles (ESPs) were acquired using a 3300 cubic inch, 30-element tuned airgun array (S/V Prospekta ) and a 48-channel seismic streamer (R/V Moore ). Extremely high-density seismograms were obtained that have allowed us to trans...
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1989
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fthighwire:oai:open-archive.highwire.org:gji:97/2/275 2023-05-15T17:32:07+02:00 A Low-Velocity Zone Within the Layer 3 Region of 118 Myr Old Oceanic Crust in the Western North Atlantic Mithal, Rakesh Mutter, John C. 1989-05-01 00:00:00.0 text/html http://gji.oxfordjournals.org/cgi/content/short/97/2/275 https://doi.org/10.1111/j.1365-246X.1989.tb00501.x en eng Oxford University Press http://gji.oxfordjournals.org/cgi/content/short/97/2/275 http://dx.doi.org/10.1111/j.1365-246X.1989.tb00501.x Copyright (C) 1989, Oxford University Press Articles TEXT 1989 fthighwire https://doi.org/10.1111/j.1365-246X.1989.tb00501.x 2015-02-28T17:58:17Z During the North Atlantic transect (NAT) experiment 11 expanding spread profiles (ESPs) were acquired using a 3300 cubic inch, 30-element tuned airgun array (S/V Prospekta ) and a 48-channel seismic streamer (R/V Moore ). Extremely high-density seismograms were obtained that have allowed us to transform the observed data to the domain of intercept time and ray parameter (tau- p ) with high precision. Velocity structures have been obtained by tau-sum inversion, ray tracing, and synthetic WKBJ and reflectivity seismogram methods both in tau- p and x-t domains. A detailed analysis of ESP 5 suggests the presence of a low-velocity zone within the lower oceanic crust at the location of magnetic anomaly MO (118 Ma). It is apparently 2.86 km thick, has a P -wave velocity of 6.5 km s−1, S-wave velocity of 3.6 km s−1, and occupies much of the depth interval normally associated with oceanic layer 3. Converted shear wave arrivals have been used to obtain the shear velocity structure. We find that the V p / V s ratio in the uppermost part of the crust is about 1.9, and much of the crustal section has a V p / V s ratio greater than √3. Attenuation of P - and S -waves has been studied by amplitude analysis, and we find that in most of the lower crust Q s is equal to Q p . Comparison with solutions from ESPs in younger and older parts of the basin suggests that ESP 5 is unique in displaying a low-velocity zone. Despite this the total thickness at ESP 5 is not significantly different than at other locations. We suggest that this provides strong evidence that the low-velocity zone occurs within the lower crust, and does not result from serpentinization of the upper mantle beneath thin oceanic crust. Text North Atlantic HighWire Press (Stanford University) Geophysical Journal International 97 2 275 294 |
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English |
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Articles Mithal, Rakesh Mutter, John C. A Low-Velocity Zone Within the Layer 3 Region of 118 Myr Old Oceanic Crust in the Western North Atlantic |
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Articles |
description |
During the North Atlantic transect (NAT) experiment 11 expanding spread profiles (ESPs) were acquired using a 3300 cubic inch, 30-element tuned airgun array (S/V Prospekta ) and a 48-channel seismic streamer (R/V Moore ). Extremely high-density seismograms were obtained that have allowed us to transform the observed data to the domain of intercept time and ray parameter (tau- p ) with high precision. Velocity structures have been obtained by tau-sum inversion, ray tracing, and synthetic WKBJ and reflectivity seismogram methods both in tau- p and x-t domains. A detailed analysis of ESP 5 suggests the presence of a low-velocity zone within the lower oceanic crust at the location of magnetic anomaly MO (118 Ma). It is apparently 2.86 km thick, has a P -wave velocity of 6.5 km s−1, S-wave velocity of 3.6 km s−1, and occupies much of the depth interval normally associated with oceanic layer 3. Converted shear wave arrivals have been used to obtain the shear velocity structure. We find that the V p / V s ratio in the uppermost part of the crust is about 1.9, and much of the crustal section has a V p / V s ratio greater than √3. Attenuation of P - and S -waves has been studied by amplitude analysis, and we find that in most of the lower crust Q s is equal to Q p . Comparison with solutions from ESPs in younger and older parts of the basin suggests that ESP 5 is unique in displaying a low-velocity zone. Despite this the total thickness at ESP 5 is not significantly different than at other locations. We suggest that this provides strong evidence that the low-velocity zone occurs within the lower crust, and does not result from serpentinization of the upper mantle beneath thin oceanic crust. |
format |
Text |
author |
Mithal, Rakesh Mutter, John C. |
author_facet |
Mithal, Rakesh Mutter, John C. |
author_sort |
Mithal, Rakesh |
title |
A Low-Velocity Zone Within the Layer 3 Region of 118 Myr Old Oceanic Crust in the Western North Atlantic |
title_short |
A Low-Velocity Zone Within the Layer 3 Region of 118 Myr Old Oceanic Crust in the Western North Atlantic |
title_full |
A Low-Velocity Zone Within the Layer 3 Region of 118 Myr Old Oceanic Crust in the Western North Atlantic |
title_fullStr |
A Low-Velocity Zone Within the Layer 3 Region of 118 Myr Old Oceanic Crust in the Western North Atlantic |
title_full_unstemmed |
A Low-Velocity Zone Within the Layer 3 Region of 118 Myr Old Oceanic Crust in the Western North Atlantic |
title_sort |
low-velocity zone within the layer 3 region of 118 myr old oceanic crust in the western north atlantic |
publisher |
Oxford University Press |
publishDate |
1989 |
url |
http://gji.oxfordjournals.org/cgi/content/short/97/2/275 https://doi.org/10.1111/j.1365-246X.1989.tb00501.x |
genre |
North Atlantic |
genre_facet |
North Atlantic |
op_relation |
http://gji.oxfordjournals.org/cgi/content/short/97/2/275 http://dx.doi.org/10.1111/j.1365-246X.1989.tb00501.x |
op_rights |
Copyright (C) 1989, Oxford University Press |
op_doi |
https://doi.org/10.1111/j.1365-246X.1989.tb00501.x |
container_title |
Geophysical Journal International |
container_volume |
97 |
container_issue |
2 |
container_start_page |
275 |
op_container_end_page |
294 |
_version_ |
1766130066934202368 |