Seismic refraction studies of the upper igneous crust in the North Atlantic and porosity estimates for Layer 2 |
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| Authors: | RB Whitmarsh |
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| Institution: | Institute of Oceanographic Sciences, Wormley, Surrey GU8 5UB England |
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| Abstract: | A number of unreversed refraction profiles up to 40 km long and with closely spaced shots has been interpreted to provide the structure of oceanic Layer 2. Different velocity/depth models based on a homogeneous layered structure and on a gradient structure have been obtained for each profile. The gradient models are believed to be a better representation of the real earth. They are all remarkably similar with a predominant velocity gradient of 0.85–1.35 km s?1 km?1 ending with a slowly downward increasing velocity of about 6 km s?1 at about 2 km depth. The positive gradient can be reasonably explained by the reduction downwards of bulk porosity, particularly due to the closure of cracks, in a simple two-component, basalt plus voids, model. The model takes account of weathering but not of metamorphism. A theory, based on oversimplified assumptions about the rocks in Layer 2, allows rough estimates of porosity at different depths to be made. |
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