Seismic imaging of mid-ocean ridges and passive margins

The proposed work is focused on two of the first order tectonic boundaries found on the Earth's surface: Mid-ocean ridges and their flanks, and passive continental margins. The mid-ocean ridges are a divergent plate tectonic boundary where new oceanic crust is being continuously generated. They make up the most extensive mountain system and the longest chain of volcanoes in the world. The thin crust and relatively simple tectonic setting of mid-ocean ridges make them ideal settings to investigate the magma plumbing system of an active volcano. How oceanic crust evolves along the mid-ocean ridge flanks is important from the perspectives of both basic science (e.g., energy and mass exchange between the Earth's solid interior and the oceans) and subduction earthquake hazards as they may be influenced by the plate hydration processes. Passive continental margins located at the boundary between old, thick continental crust and young, thin oceanic crust are one of the Earth's major transitions. They are formed when continental lithosphere is rifted apart to form new ocean basins. The continent-ocean boundary is also the site of major sedimentary basins created during subsidence of the thinned continental crust and the newly formed oceanic crust. These marginal basins are potentially of great economic importance because they can host large hydrocarbon reservoirs. All of the investigations proposed here rely on using multichannel seismic (MCS) data. MCS data are analyzed to form reflection images, determine physical properties of the imaged structures, and construct velocity profiles by applying shallow seismic tomography. Wide-angle refraction data will also be used for the study of passive margins to independently form deep velocity models, and in combination with the MCS data to extract maximum possible information about the targeted structures. The key goals of the proposed program are to: 1) Investigate mid-ocean ridge processes at unprecedented detail by producing the first 3D prestack time and depth migrated images of a mid-ocean ridge environment; 2) Characterize large variations in the ocean-continent transitions that appear to occur over small margin-lateral distances within just one rift segment.