Seismic study of subduction zones, rifted margins and mid-ocean ridges

The proposed research program is focused on three of the Earth's major boundaries: subduction zones, rifted margins and mid-ocean ridges, all of which form as part of the Earth's plate tectonic cycle. Subduction zones are places where oceanic and continental plates converge, and where the thinner but denser oceanic plate "ducks" under the continental plate to eventually become recycled into the Earth's mantle. Rifted continental margins form by extension and breakup of the continental lithosphere, a process that opens up new ocean basins. 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 on planet Earth. The proposed research program relies on applying an innovative combination of state-of-the-art data analysis methods to new multichannel seismic and ocean bottom seismometer data. The goal is to image the targeted subsurface structures at unprecedented resolution in order to test leading scientific hypothesis and questions that have the potential to transform the fields of study this program focuses on. The selected study areas are: Alaska subduction zone, Juan de Fuca plate and Cascadia subduction zone, rifted margins of eastern Canada, and Southwest Indian ridge. The study areas and problems to be addressed by this program are chosen based on their suitability for achieving my short- and long-term science goals, the potential for high-impact discoveries, and interest to a broad group of earth scientists and general public. Volcanic eruptions and earthquakes at the Cascadia and Alaska subduction zones pose significant risk in the heavily populated areas of northwestern United States and southwestern Canada. How oceanic crust evolves from ridge to trench 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 societal impacts (subduction earthquake hazards). An expected outcome of this program are improved constraints on the downdip limit of maximum coseismic slip during subduction earthquakes or, in other words, better understanding of how close to the coastal cities can these large offshore earthquakes occur. Another outcome of this research program is more detailed information on lateral variations in subduction thrust (megathrust) coupling or, in simpler terms, which sections of subduction zones are strongly jammed and therefore likely to release most of the destructive seismic energy during subduction earthquakes. This knowledge will lead to advances in accuracy of probabilistic seismic hazards maps for megathrust events and improved building codes, our primary means used to mitigate against these damaging earthquakes. Better understanding of the inner workings of active magmatic systems, which are the least challenging to investigate at mid-ocean ridges because of the thin crust and relatively simple tectonic setting, will lead to better prediction of future undersea eruptions and to improved understanding of volcanoes in general. New constraints on the deep structures at rifted margins, that are also the site of major sedimentary basins that host the largest recently drilled hydrocarbon deposits, will help guide future petroleum exploration to new discoveries. All of the projects that comprise the proposed research program are high-profile international collaborations because investigations of structures deep below the seabed, which is one of the Earth's last frontiers, require major resources, both human and material.