Upper crustal velocity structure beneath the central Lucky Strike Segment from seismic refraction measurements

Seher, Tim and Singh, Satish C. and Crawford, Wayne C. and Escartín, Javier (2010) Upper crustal velocity structure beneath the central Lucky Strike Segment from seismic refraction measurements. Geochemistry Geophysics Geosystems, 11. 21 PP.. DOI 10.1029/2009GC002894

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Abstract

We present a three-dimensional velocity model of the upper crust around the central volcano of the Lucky Strike Segment, Mid-Atlantic Ridge. The model, constructed from a 3-D array of air gun shots (37.5 m spacing along line and 100 m between lines) to ocean bottom seismometers fired during a 3-D seismic reflection survey, shows an off-axis velocity increase (∼1 km/s), a low-velocity region within the median valley, and a low-velocity anomaly underneath the Lucky Strike volcano. Our observations indicate a porosity decrease of 1%–9% (corresponding to a velocity increase of ∼0.5–1 km/s) over a distance of 8 km from the ridge axis (∼0.7 Ma) and a porosity decrease of 4%–11% (corresponding to a velocity increase of ∼2 km/s) between a depth of 0.5 and 1.75 km below seafloor. A sinusoidal variation in the traveltime residuals indicates the presence of azimuthal anisotropy with cracks aligned approximately along the ridge axis. We favor an interpretation in which upper crustal porosities are created by a combination of magmatic accretion (lava–sheeted dike boundary) and active extension (faults, fractures, and fissures). The porosity variation with depth probably depends on pore space collapse, hydrothermal alteration, and a change of stress accommodation. The off-axis porosities are possibly influenced by both hydrothermal precipitation and the aging of the crust.

Item Type:	Article
Uncontrolled Keywords:	2010AREP; IA
Subjects:	02 - Geodynamics, Geophysics and Tectonics
Divisions:	02 - Geodynamics, Geophysics and Tectonics
Journal or Publication Title:	Geochemistry Geophysics Geosystems
Volume:	11
Page Range:	21 PP.
Identification Number:	10.1029/2009GC002894
Depositing User:	Sarah Humbert
Date Deposited:	15 Dec 2011 17:01
Last Modified:	23 Jul 2013 10:03
URI:	http://eprints.esc.cam.ac.uk/id/eprint/2284

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