Workshop to cultivate and coordinate GeoPRISMS studies of the Hikurangi subduction margin

Introduction

9:00 | Introductory remarks and logistics – Laura Wallace

9:15 | Recap of science priorities defined for Hikurangi in the GeoPRISMS implementation planb – Mike Underwood

9:30-10:30 | Ongoing and already proposed projects – Chair: Samer Naif

• Status of IODP drilling and observatory proposals at North Hikurangi – Demian Saffer
• OBS and seafloor pressure sensor deployments (HOBITSS project) – Laura Wallace
• Hikurangi Heatflow – Laura Wallace to overview on behalf of Rob Harris and Anne Trehu
• Hikurangi fluid budgets | Susan Ellis
• Current offshore Hikurangi research – Phil Barnes
• Hikurangi seismological studies | Bill Fry, Donna Eberhart-Phillips, Martha Savage
  
• Japan-led seismological and seafloor geodetic efforts – Yoshihiro Ito
• Hikurangi 3D Seismic proposal – Nathan Bangs
• Physical controls on variations in slip behavior at Hikurangi- interdisciplinary proposal to do 2D seismic, CSEM, paleoseismology, GPS, and numerical modeling – Kirk Mcintosh

10:30-10:45 | Open discussion of additional ongoing/proposed projects not discussed above

10:45-11:00 | Short break

11:00-12:30 | Discussion: Studies that should be proposed at the Hikurangi margin – Chairs: Mike Underwood and Laura Wallace

Discussion will focus on studies that are needed to fill existing science/dataset gaps in the implementation plan. Discussion will also include leveraging existing datasets, and on linking in with other planned/proposed studies. Coordinating logistics, such as taking advantage of ships that will be in the area, should also be discussed. Participants are welcome to come with a few slides if appropriate—please let us know in advance if you plan to bring slides, so we can be sure to fit this in. We will develop a short listing of potential projects that prioritizes the science gaps that need to be filled.

MVUW contributions to Hikurangi research proposed or in process – Martha Savage

The Hikurangi subduction margin in New Zealand offers an outstanding opportunity to address many fundamental questions on subduction margin deformation and megathrust behavior. The objectives of the Hikurangi mini-workshop will be to foster new relationships among researchers who will develop amphibious projects across a spectrum of geophysical, geological, and geochemical approaches. Discussion will occur within the context of existing planned projects, including a proposed IODP transect. Data acquisition activities are ongoing by New Zealand, United States, Japanese and European scientists. We will discuss ways of leveraging and coordinating these existing efforts with new efforts to maximize potential GeoPRISMS outcomes at the Hikurangi focus site.

We encourage all researchers interested in subduction processes at the Hikurangi margin to attend. We also encourage attendees interested in subduction deformation and megathrust processes in Cascadia and Alaska, to cross-fertilize ideas and implementation strategies among all three of the GeoPRISMS primary sites. Some of the topics to be discussed include:

1. the state of the incoming plate and the role of incoming sediment properties in subduction thrust behavior and margin evolution;
2. physical properties of the megathrust and the influence of this on megathrust behavior;
3. fluid sources and fluxes, with emphasis on the forearc;
4. microseismicity, episodic slip, and tremor.

Attendees will collectively identify new research activities that address these topics most effectively, with an emphasis on leveraging existing studies/datasets.

Workshop to cultivate and coordinate GeoPRISMS studies of the Hikurangi subduction margin (9am-12 pm, December 14, 2014)

On Sunday, December 14, 2014, an enthusiastic group of more than 70 international researchers from a variety of disciplines met in San Francisco at AGU to discuss studies that should be proposed at the Hikurangi subduction margin (part of the New Zealand focus site) for the upcoming GeoPRISMS funding rounds. The meeting began with a brief overview of the GeoPRISMS program by Peter van Keken, which was followed by Mike Underwood’s review of the Hikurangi margin science priorities, which are based largely on discussions at the New Zealand Focus site workshop that was held in April 2013. The objective of the mini-workshop was to promote and coordinate new collaborations to fill critical gaps in the GeoPRISMS Implementation Plan. To that end, a series of short talks highlighted projects that are either ongoing, already proposed, or soon to be proposed. The last half of the meeting was focused on open discussion during which participants identified new research opportunities.

The community has already made major progress in advancing key science objectives identified for the Hikurangi margin. Demian Saffer overviewed the IODP drilling proposals to investigate shallow slow slip events (SSEs) at the northern Hikurangi margin; the proposal for riserless drilling has passed through panel reviews and now awaits scheduling by the JOIDES Resolution Facilities Board. A proposal for riser drilling also reviewed well and has been forwarded to the Chikyu Facilities Board. Already underway is the Hikurangi Ocean Bottom Investigation of Tremor and Slow Slip (HOBITSS) to investigate vertical deformation of the seafloor and seismicity related to the shallow SSEs, supported by funding from NSF, New Zealand, and Japanese sources. An NSF-funded heat-flow survey led by Rob Harris is scheduled for May/June 2015 to constrain the thermal regime of the subduction interface. Proposals have been submitted to NSF to (1) acquire 3-D seismic data of the shallow SSE source, (2) conduct onshore and offshore geophysical investigation of megathrust properties along-strike, and (3) to install long-term borehole observatories at the proposed IODP sites.

Numerous representatives from the New Zealand geoscience community introduced ongoing and planned geophysical, geological, and modeling initiatives that dovetail nicely with GeoPRISMS goals. In particular, there are a large number of seismological, electromagnetic (onshore), numerical modeling, and paleoseismological investigations conducted by New Zealand-based researchers. To leverage these existing and planned studies (and not duplicate efforts), it is particularly important for GeoPRISMS-funded investigators to collaborate with and communicate with their New Zealand-based counterparts. David Johnston of GNS Science informed participants about a New Zealand-based initiative called “East Coast Life at the Boundary (LAB)”, part of which is targeted at communication of research results on the Hikurangi margin to the general public and local policymakers. This offers an excellent opportunity for GeoPRISMS researchers at Hikurangi to work with the East Coast LAB to coordinate outreach activities in New Zealand. We also heard about ongoing and already funded efforts by Japanese and European researchers focused on the offshore Hikurangi margin over the next four years.

The last half of the mini workshop was dedicated to discussion of critical science gaps. The main discussion focused on:

1. microseismicity, episodic slow slip, and tremor;
2. the state of the incoming plate and the role of incoming sediment properties in subduction thrust behavior and margin evolution;
3. past and present megathrust slip behavior and the physical controls on that behavior;
4. fluid and volatile fluxes in the forearc.

From this discussion we identified some of the most critical studies that are needed to fill gaps. Paleoseismology studies will help resolve the past earthquake behavior of the subduction thrust and whether or not the modern-day geodetic locking pattern is static or varies with time. Increased efforts towards sampling and geochemical analysis of onshore and offshore fluid seeps will yield important insights into volatile cycling and hydrogeology above a shallow subduction thrust. A new idea was raised to use the seafloor drill rig MeBo for coring at numerous points on the Hikurangi Plateau (a Large Igneous Province) where the sedimentary cover is thin (<200 m). Such sampling would address the role of 3-D stratigraphic variability in modulating subduction-interface slip behavior. Controlled-source electromagnetic (CSEM) transects in the offshore forearc and incoming plate will evaluate the role of fluids in megathrust slip behavior and margin evolution. Seafloor (GPS-Acoustic) geodetic studies will help resolve the slip behavior of the shallow subduction thrust. Densification of onshore geodetic instrumentation, and addition of strain meters, tiltmeters, and borehole seismometers will lower the threshold of slow slip event detection, enabling higher-resolution investigation of SSEs and seismicity, and detection of smaller events. Modeling of Hikurangi SSEs assuming a rate-state friction framework, as well as other approaches, will help resolve the physical controls on the diversity of SSE behavior.
The conveners appreciate the participants’ contributions, and thank them for their help in achieving the goals of the mini-workshop.