Alaska Amphibious Community Seismic Experiment

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This innovative, large shoreline-crossing seismic experiment investigates the processes that govern subduction, earthquakes, and volcanism along the Alaska Peninsula. The Alaskan subduction system is one of the best places in the world to study these processes, because earthquakes and volcanic eruptions are large and frequent. It has generated more magnitude 8+ earthquakes during the past century than any other subduction zone in the world, as well as thousands of small earthquakes that will allow the research to produce geophysical "sonograms" of the Earth's crust, mantle and beneath its volcanoes. There is also much systematic variability in earthquake and volcano behavior, which has been hypothesized to be influenced by the tremendous variability in the nature of the Pacific tectonic plate which subducts here beneath Alaska. Earthquakes and volcanic eruptions have significant impacts on the security and well-being of regional populations; eruptions impact trans-Pacific air travel and transport, and tsunamis from this region are focused toward Hawaii and the west coast of North America so pose a danger to a large population. Our understanding of these hazards is severely hampered by a lack of seismometers in the region that produces these events -- thus the need to deploy seismometers onland and particularly offshore. This is a community experiment: after completion of the data collection, all data will be made immediately available to the broader scientific community to spur discovery and innovation. Understanding the relationships between the observed earthquakes and the physical properties of interacting plates will enhance our ability to characterize seismic and volcanic hazards in Alaska, as well as globally in similar geologic settings. The data and project will provide a fertile training ground for the next generation of earth scientists in a broad range of disciplines.The selection of Alaska as a GeoPRISMS primary site, deployment of Alaskan EarthScope Transportable Array (TA) seismic stations, and the recent development of a large pool of both shallow and deep-water ocean bottom seismographs (OBSs) provide a unique opportunity to advance understanding of subduction zones. This project funds onshore and offshore seismicity data collection and rapid release to the community. The deployment will include 75  broadband OBSs and 30 land broadband sensors, recording for 15 months in 2018-19. The array covers a broad area that spans the incoming plate, the megathrust and volcanic arc to the distal backarc, and includes a dense transect in the Kodiak/Katmai region. When integrated with the TA, the array extends 1500 km from incoming plate to the Arctic coast and spans 700 km along strike. The OBSs include 20 shielded sensors for deployment in shallow water. All shallow-water and nine deep-water instruments will include absolute pressure gauges to capture possible slow slip events, while five OBSs and six land sites will include accelerometers to record large local earthquakes without clipping.The project is likely to revolutionize our understanding of subduction zones. Much of the Alaskan subduction system is dominated by megathrust events, hosting more M8 events in the past century than any other subduction system, yet some sections show aseismic creep. It also hosts a world-class magmatic arc displaying a range of systematic along-strike variations in chemistry and a subducting plate exhibiting along-strike variations in hydration, structure, and sediment thickness. The proposed experiment is designed to provide a critical data set addressing several broad questions: (1) What changes in seismic properties cause variation in seismic coupling, the occurrence of great earthquakes and aseismic creep on subduction megathrusts? (2) Is the subducting uppermost mantle hydrated and what controls variations in hydration along strike? (3) What controls variations in volcanic arc crust/mantle structure, volcanic composition and the geometry of the arc melt production region? (4) How does the flow and volatile release generated by subduction zones interact with large-scale plate flow and the evolution of sub-continental mantle?Data collected by this community experiment will be made publically available immediately via the IRIS Data Management Center, allowing the geophysical community to use them in research of fundamental questions about subduction processes as well as seismic and volcanic hazards. Experiment design was constructed to leverage contemporaneous deployment of the Alaska TA to encourage maximal use of both datasets. During three cruises, graduate students and early to mid career scientists will be selected to join the science crew, learning about OBS data collection, to encourage the widespread use of the data from new sectors of the community. During the fourth cruise, a group of ten undergraduates will join the science team following a five-day intensive preparatory short course. An additional 10 undergraduate students from Alaskan universities will participate in the workshop. To extend the educational opportunities of this experiment to local communities, two K-12 teachers from Alaskan or Native schools will be selected to participate in OBS deployment cruise and use their experiences to design lesson plans for public distribution. The 10-member PI team was chosen through an open application process and includes multiple early-career scientists benefitting from this leadership opportunity.