Lateral heterogeneity in the seismic structure of upper oceanic crust, western North Atlantic

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doi: 10.1029/JB094iB07p09303
Author(s): Swift, Stephen A.; Stephen, Ralph A.
Author Affiliation(s): Primary:
Woods Hole Oceanogr. Inst., Woods Hole, MA, United States
Volume Title: Journal of Geophysical Research
Source: Journal of Geophysical Research, 94(B7), p.9303-9322. Publisher: American Geophysical Union, Washington, DC, United States. ISSN: 0148-0227
Note: In English. Woods Hole Oceanogr. Inst., Contrib. No. 6534. 40 refs.; illus. incl. 7 tables, sketch maps
Summary: We carried out a borehole seismic experiment at Deep Sea Drilling Project hole 418A in order to study the vertical and lateral velocity variations in 100-m.y.-old oceanic crust. We clamped a seismometer successively at five depths between 41m and 430 m within the extrusive basalt layer while air gun and explosive sources were fired on eight radial lines and four concentric circles to 8 km range. Our travel time data do not give consistent evidence of anisotropy. However, our experimental error may mask anisotropy of up to 0.2-0.3 km/s. Velocities from inflection point analysis, sonic log, and reflectivity synthetic seismograms support results of τ-ζ inversion of radial line P arrival times. Velocity increases with an almost linear gradient of 1.3 s-1 from 4.6 km/s at the top of basement to 1.8 km depth. The τ-ζ velocity profile at 418A does not differ significantly at the 95% confidence level from that at 417D located ∼7.5 km away. Seismic velocities at shorter-length scales do vary laterally. Travel time anomalies indicate that seismic velocity in the upper 0.5 km increases laterally northwest to 3 km range. Other data indicate that this velocity anomaly in the extrusive layer may be due to alteration controlled by topography or to primary porosity variations. Copyright 1989 by the American Geophysical Union.
Year of Publication: 1989
Research Program: DSDP Deep Sea Drilling Project
Key Words: 18 Geophysics, Solid-Earth; 20 Geophysics, Applied; Anisotropy; Atlantic Ocean; Crust; DSDP Site 418A; Deep Sea Drilling Project; Geophysical methods; Geophysical surveys; Lateral heterogeneity; North Atlantic; Northwest Atlantic; Oceanic crust; Seismic methods; Surveys; Tectonophysics; Upper crust; Velocity structure
Coordinates: N200000 N330000 W0640000 W0750000
Record ID: 1989063674
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