Collaborative Research: Along Strike Variation in Shallow, Offshore Strain Accumulation and Slow Slip at Hikurangi Subduction Margin, New Zealand

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Subduction zones are regions where one of Earth's tectonic plates slides beneath another. The zone of slip between the two plates is a geologic fault where the motion of the lower plate is imperfectly transferred to the overlying plate through frictional processes allowing for unreleased strain to build up in the upper plate. The abrupt release of built-up strain in the upper plate causes earthquakes, which can be large on subduction zones because of the size of the slip region. These great earthquakes cause damage both from the shaking itself but also because of the flooding of seawater from a tsunami. Recent events in Sumatra in 2004, Chile in 2010, and Japan in 2011 all demonstrate the devastating hazard associated with these events. Subduction zones also lie offshore the US coasts along Northern California, Oregon and Washington State and another along Alaska and the Aleutian Islands. Both of these subduction zones have experienced great earthquakes in the past and will do so again in the future. A goal of this project is to better understand the geophysical processes at work at subduction zones and to improve the quantitative assessment of potential hazard. This project will deploy a combination of seafloor geodetic sensors to track the slow buildup and possible release of seafloor motion offshore of a New Zealand subduction zone. The New Zealand Hikurangi site was picked because the subduction zone is shallow and can be imaged more effectively with seafloor geodetic instruments. This site also has a history of rapidly repeating slow slip earthquakes that provide insight into the slip process. Broader impacts of this project include training and support for a graduate student in the research. The project leverages international efforts by New Zealand and Japanese research teams who will occupy adjacent seafloor geodetic sites. The project will also transfer operational know-how for how to conduct seafloor geodesy experiments to NZ research counterparts, enabling them to collect measurements at these critical sites during this proposed project and continue in the future past the end of the project.This project will measure deformation near the trench of the New Zealand Hikuangi subduction margin over a four year period using the GPS-Acoustic (GPS-A) method. The GPS-A site will be established in the Hawkes Bay area to provide critical measurements centered between GPS-A sites in the northern and southern parts of the margin established using Japanese and New Zealand funding. This central site is near the transition from an apparently strongly coupled margin to the South, and a nearly uncoupled margin in the North. The project will implement the more efficient and cost-saving Wave Glider platform for the GPS-Acoustic measurements. Permanent seafloor benchmarks will be installed for horizontal positioning to ensure the time series of positions can be continued into the future, past the end of this project. An array of absolute pressure gauges will also be deployed for two years to measure the offshore extent of slow slip events observed from land arrays beneath the Hawkes Bay area, a region thought to have experienced many 8 magnitude earthquakes in the past based on paleoseismology. The array is expected to detect vertical uplift and hence the spatial extent of at least one large slow slip event in this region during the deployment.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.