Velocity structure of upper ocean crust at Ocean Drilling Program Site 1256
Table S1: One-way travel times for compressional waves recorded during the VSP shot at the end of ODP Leg 206 and interval velocities computed by inversion. (1.572Kb)
Swift, Stephen A.
Gilbert, Lisa A.
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KeywordUpper ocean crust; Seismic structure; Integrated Ocean Drilling Program; D/V JOIDES Resolution; Expedition 309/312; Site 1256
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.
Author Posting. © American Geophysical Union, 2008. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 9 (2008): Q10O13, doi:10.1029/2008GC002188.
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