Collaborative Research: Slow-Slip and Fluid Flow Response Offshore New Zealand -Probing The Nature Of The Margin Hydrogeochemical System

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Observations at subduction zones over the past two decades have revealed a range of modes by which stress is released on the plate boundary, including periodic slow slip behavior. Slow slip events occur at a rate intermediate between long-term tectonic plate motion and the fast slip velocity that occurs during earthquakes. Thus, slow slip is thought to span the transition between stable slip and the stick-slip process that generates earthquakes. An important mechanism that could cause the transitions in slip style is the evolution of pressure along the fault that is generated by the accumulation and release of fluids. There is a concerted and extensive international sampling and monitoring effort to understand slow slip at the Hikurangi margin offshore New Zealand. A missing piece in this effort is the sampling and monitoring of fluids along seafloor fault zones over a long enough period of time to capture a slip event. This project will address this problem and will provide a two-year continuous record of fluid flow rate and composition over the time frame of the next expected large slow slip event. The project will add value to other ongoing NSF-funded programs at this margin such as scientific ocean drilling and seismic surveys aimed at understanding slow slip events. From both the scientific and societal perspectives, results from this project will contribute to our understanding of earthquake activity not only offshore New Zealand but worldwide. This project has a large component of international collaboration. The project supports the training of graduate and undergraduate students. This project addresses the GeoPRISMS Program's Subduction Cycles and Deformation Initiative Science Plan by testing interrelationships between fluid production, fluid flow, and slow slip at the Hikurangi margin off New Zealand. At the Hikurangi margin, the recognition of dramatic changes in the along-strike depth distributions of slow-slip events (SSEs) and their recurrence intervals, interseismic coupling, inferred pore pressure, and other subduction-related parameters have resulted in a concerted international effort to acquire seismological, geodetic, other geophysical, and geomechanical data. This project will complement and extend these efforts by providing 1) a two-year continuous record of fluid flow rate and composition over the timeframe of the next expected large SSE; 2) information on the present background state of fluid flow and how it relates to inferred overpressure along the plate boundary; and 3) comparative geochemical and hydrologic data between the northern and southern sections of the margin. The work plan combines ship operations and Remotely Operated Vehicle (ROV) surveys in a nested approach to constrain the margin-wide fluid flow distribution. Coring, heat flow measurements, and benthic fluid flow meter deployments will target fault zones and off-fault locations from the deformation front to the shelf-break. Continuous fluid flow rate measurements at off-fault locations will quantify the fluid flow response to local volumetric strain during slip, and comparative data at fault zones will provide information on the hydrologic responses to slip.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.