A proposed study of the dynamics of the Hikurangi New Zealand margin.

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This multi-disciplinary study will investigate the processes that trigger submarine slope failures on the New Zealand continental margin. The investigation will explore how many failures occur and their frequency, whether small landslides in an area make the slope resistant to large landslides, and what types of landslides generate tsunamis. Recent work off the northwest coast of the U.S. has shown that small landslides on continental margins occur more frequently than previously thought. The small landslides are caused by shaking generated by both local and remote earthquakes. Changes in the overlying water column were also found to be important in generating the small landslides. In this new study off New Zealand, seafloor sensor data will be combined with other available geophysical, water column, and meteorological data, to evaluate whether the results of the Cascadia work on the stability of submarine slopes can be generalized to other subduction zone margins. The results of this study will improve the capability to identify past large earthquakes in the sedimentary record. In addition, this study will provide constraints for models of submarine landslides and aid in predicting areas of potential slope failure. The study supports the training of a postdoctoral investigator.Accretionary margins that overlie active subduction zones undergo continuous re-surfacing by repeated sediment slope failures and gravity flows. Studies done off Cascadia show that slope failures can occur either spontaneously or be triggered by identifiable events that include oceanographic processes or by seismic waves generated by local or remote earthquakes. The mechanisms and key attributes of these triggering seismic waves (e.g., frequency content, duration, etc.) remain speculative. Preliminary results also indicate that the geologic structure and topography of the accretionary wedge have profound impacts on the seismic loading. Sediment slope failures and flows also can be triggered by storms, tides, upper water column eddies and circulation changes. This study tests these ideas by analyzing new data from seafloor sensors that were deployed on the Hikurangi margin off New Zealand in 2015. These data will also be used to examine the signature of slow slip events on the shallow plate interface. A Regional Ocean Modeling System hindcast will provide insight into the nature of signals at the seafloor that originate from ocean surface forcing in this area. By combining seafloor pressure, temperature and seismic ground motion measurements, with other available geophysical, water column and meteorological data, and the oceanographic context provided by the regional model, it will be possible to improve the fidelity of seafloor temperature and pressure signals associated with sediment slope failures and flows, with the side-benefit of characterizing near-surface eddies and ocean circulation changesThis 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.