Velocity structure of upper ocean crust at Ocean Drilling Program Site 1256

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doi: 10.1029/2008GC002188
Author(s): Swift, Stephen; Reichow, Marc; Tikku, Anahita; Tominaga, Masako; Gilbert, Lisa A.
Author Affiliation(s): Primary:
Woods Hole Oceanographic Institution, Department of Geology and Geophysics, Woods Hole, MA, United States
University of Leicester, United Kingdom
ExxonMobil Upstream Research Company, United States
Texas A&M University, United States
Williams College, United States
Volume Title: Geochemistry, Geophysics, Geosystems - G<sup>3</sup>
Source: Geochemistry, Geophysics, Geosystems - G>3`, 9(10). Publisher: American Geophysical Union and The Geochemical Society, United States. ISSN: 1525-2027
Note: In English. 62 refs.; illus., incl. sketch map
Summary: We examine shipboard physical property measurements, wireline logs, and vertical seismic profiles (VSP) from Ocean Drilling Program/Integrated Ocean Drilling Program Hole 1256D in 15 Ma ocean crust formed at superfast spreading rates to investigate lateral and vertical variations in compressional velocity. In general, velocities from all methods agree. Porosity is inversely related to velocity in both the logging and laboratory data. We infer that microfracturing during drilling is minor in the upper 1 km of basement, probably due to connected pores and, thus, low effective stress. The closure of porosity to very low values coincides with the depth below which laboratory velocities diverge from logging velocities. We infer that porosity controls velocity in layer 2, lithostatic pressure controls the thickness of seismic layer 2, and the distribution of flow types determines seismic velocity in the upper 200 m of basement. In the sheeted dikes, changes in physical properties, mineralogy, and chemistry define clusters of dikes.
Year of Publication: 2008
Research Program: IODP Integrated Ocean Drilling Program
ODP Ocean Drilling Program
Key Words: 18 Geophysics, Solid-Earth; 20 Geophysics, Applied; Chemical composition; Crust; Deep-seated structures; Dike swarms; Dikes; East Pacific; Elastic waves; Equatorial Pacific; Expeditions 309/312; Fractured materials; Geophysical methods; Geophysical profiles; Geophysical surveys; Guatemala Basin; Integrated Ocean Drilling Program; Intrusions; Mineral composition; North Pacific; Northeast Pacific; ODP Site 1256; Ocean Drilling Program; Oceanic crust; Pacific Ocean; Physical properties; Porosity; Seismic methods; Seismic profiles; Seismic waves; Sheeted dikes; Surveys; Velocity structure; Vertical seismic profiles
Coordinates: N000000 N100000 W0800000 W1050000
N064400 N064400 W0915600 W0915600
Record ID: 2009080444
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