EGU General Assembly 2020
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the Creative Commons Attribution 4.0 License.

Scientific basis for definition of a fault rupture hazard in Franz Josef Glacier, West Coast, New Zealand, and the fight to see use made of this information.

Virginia Toy1,2, Bernhard Schuck1,3, Risa Matsumura2, Caroline Orchiston3, Nicolas Barth5, and Mark Stirling2
Virginia Toy et al.
  • 1Institut für Geowissenschaften, Johannes Gutenberg-Universität Mainz, Germany (
  • 2Department of Geology, University of Otago, Dunedin, New Zealand
  • 3Helmholtz Centre, GFZ-Potsdam, Germany
  • 5Earth and Planetary Sciences, University of California – Riverside, USA

There is currently around a 30% probability New Zealand’s Alpine Fault will accommodate another M~8 earthquake in the next 50 years. The fault passes through Franz Josef Glacier town, a popular tourist destination attracting up to 6,000 visitors per day during peak season. The township straddles the fault, with building stock and infrastructure likely to be affected by at least 8m horizontal and 1.5m vertical ground displacements in this coming event. New Alpine Fault science is presented here that adds to the strong evidence in support of moving the township northward and out of a 200m zone of deformation across the fault zone to mitigate future losses.

In 2011 two shallow boreholes were drilled at Gaunt Creek, as part of the Alpine Fault Drilling Project, DFDP. In cores collected from the deeper of these boreholes (DFDP-1B), two ‘principal slip zones (PSZ)’ were sampled, indicating the fault is not a simple geometrical structure. Subsequent studies of the recovered cores have demonstrated:

  1. The lower of the two PSZ in DFDP-1B has particle size distributions indicating it accommodated more coseismic strain than the shallower PSZ
  2. The PSZs sampled in the two boreholes have authigenic clay mineralogies diagnostic of different temperatures

These studies, combined with other recent outcrop studies nearby, highlight that the central Alpine Fault zone is a complex structure comprising multiple PSZ in the near surface, some of which may have been simultaneously active in past earthquakes. The results support previous studies (e.g. lidar mapping of offset Quaternary features) that underpinned definition of an ‘avoidance zone’ around the fault trace in the town. Sadly, local government has failed to acknowledge this risk in public legislature in a way that adequately protects tourism and community infrastructure, and the >1.3 million visitors passing through the region each year. We will explain other actions consequently taken to build awareness and resilience to this hazard.

How to cite: Toy, V., Schuck, B., Matsumura, R., Orchiston, C., Barth, N., and Stirling, M.: Scientific basis for definition of a fault rupture hazard in Franz Josef Glacier, West Coast, New Zealand, and the fight to see use made of this information. , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5316,, 2020

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Presentation version 1 – uploaded on 04 May 2020
  • CC1: Comment on EGU2020-5316, Solmaz Mohadjer, 08 May 2020

    Dear  Virginia and colleagues,

    Thanks for your display. Interesting work. Quick question- Why do you think the regional authority felt challenged by your proposal, and what do you think scientists can do (or should be doing) to effectively engage policymakers instead of challenging them? 

    Many thanks,

    Solmaz Mohadjer