Evolution of the physical, geochemical and mechanical properties of the Alpine Fault Zone: A journey through an active plate boundary

Lead Research Organisation: University of Southampton
Department Name: School of Ocean and Earth Science

Abstract

This proposal is the UK component of a major international campaign, the Deep Fault Drilling Project (DFDP) to drill a series of holes into the Alpine Fault, New Zealand. The overarching aim of the DFDP to understand better the processes that lead to major earthquakes by taking cores and observing a major continental fault during its build up to a large seismic event. The next stage of this project will be to drill and instrument a 1.5 km hole into the Alpine Fault.

Earthquakes are major geohazards. Although scientists can predict where on the Earth's surface earthquakes are most likely to occur, principally along plate boundaries, we have only imperfect knowledge. We also don't know when earthquakes will occur. This is well illustrated by recent events on the South Island of NZ. Two earthquakes in Christchurch in Sept 2010 and Feb 2011 caused 181 deaths and £7-10 billion of damage (~10% NZ GDP). Yet Christchurch had previously been considered of relatively low seismic risk. In contrast, the western side of the South Island is defined by the Southern Alps, a major mountain chain (>3700 m) formed along the Australian-Pacific Plate boundary. Until a few million years ago this plate boundary was a strike-slip fault like the San Andreas Fault in California, but subtle changes in plate motion has led to the collision of the Pacific and Australian Plates. This caused uplift of the mountains and due to very high rates of rainfall and erosion, rapid exhumation of rocks that until recently had been deep within the Earth. Although these plates are moving past each other at ~30 mm/y and the uplift rate in the Southern Alps approaches 10 mm/y, there has not been a major earthquake along the Alpine Fault in NZ's, albeit short, written history. However, there is palaeo-seismic evidence that major earthquakes do occur along the Alpine Fault with magnitude ~8 earthquakes occurring every 200-400 years, with the latest event in 1717 AD.

Earthquake occur because stresses build-up wthin the relatively strong brittle upper crust. At greater depths (>15 km) rocks can flow plastically and plates can move past each other without building up dangerous stresses. On some faults, the brittle crust "creeps" in numerous small micro-earthquake events and this inhibits the build up of stress. Unfortunately there are few even micro-earthquake events along the Alpine Fault or surface evidence for deformation, suggesting that the stresses along this plate boundary have been building up since 1717 - if that stress was released in a single earthquake it would result in a horizontal offset across the fault of >8 m!

A major hindrance to earthquake research is a lack of fault rock samples from the depths where stresses build up before an earthquake. Fault rocks exposed at the surface tend to be strongly altered. The strength of fault rocks will depend on a number of factors include pressure, temperature and the nature of the materials, but also whether there are geothermal fluids present. The geometry of the Alpine Fault is special in that the fault rocks that were recently deforming at depth within the crust are exposed close to the surface. Also because of rapid uplift and erosion the local geothermal gradients are high and relatively hot rocks are near the surface. This results in a relatively shallow depth (5-8 km) for the transition from brittle to plastic behaviour. This provides a unique opportunity to drill into the fault zone to recover cores of the fault, to undertake tests of the borehole strata, and to install within the borehole instruments to measure temperature, fluid pressures, and seismic activity. Once core samples are recovered we will perform geochemical and microstructural analyses on the fault rocks to understand the conditions at which they were deformed. We will subject them to geomechanical testing to see how changes in their environment affects the strength of the rocks and their ability to accommodate stresses before breaking.

Planned Impact

This project will make significant advancement towards understanding the behaviour of fault rocks within a major continental plate boundary, the Alpine Fault of New Zealand, and give broad insight into why earthquakes occur.

The following communities will principally benefit from this research:
-Local Government Agencies in New Zealand: The Alpine Fault is at a late stage of its inter-seismic cycle. Its rupture in a large earthquake will have major consequences on the population of the West Coast of the South Island, on all infrastructures as well as on tourism and the environment. Regional Councils, the NZ Transport Agency, the Department of Conservation (Te Papa Atawhai), and the Earthquake Commission of NZ (the government agency providing natural disaster insurance) are identified as primary users of knowledge relevant to earthquake hazards, which will inform existing and new/adapted regulations and policies. Parallel Agencies worldwide may also benefit from this research. Our engagement efforts will be undertaken in collaboration with NZ project partners (GNS Science; Univ. Otago, Auckland, Victoria), to best package our technical findings for local, regional and national geohazards professionals and the wider New Zealand community. Our aim is to develop published materials that are directly focused on geohazards issues. We will ensure our UK project website links effectively with existing and new NZ-based geohazard information.

-School children are inspired by earthquakes, their societal impacts, and the dynamics of our planet. Our gained knowledge, communicated at appropriate levels for different ages of children, will raise awareness of natural hazards and provide renewed interest in STEM subjects and technical careers related to Earth and its environment.

-The general public are interested in the devastating effects of natural disasters and become engaged when Earth processes and hazards are clearly explained through mass media.

Engagement and Dissemination:
-The project will engage for 6 h/w a Knowledge Exchange Officer (KEO) to establish and keep updated the "Journey through a Plate Boundary - DFDP-2" Website. The KEO will liaise with our international partners and programs (e.g., ICDP), stake holders, NZ Local Government Agencies, industrial end-users, schools and the wider public. The KEO with PIs and researchers will develop digestible scientific explanations of the project aims and findings for schools and the wider public than can be accessed from the website. They will deliver outreach materials and presentations on the project and its outcomes to schools in the UK. The website will detail drilling operations of DFDP2 and report scientific outputs from the borehole observatory and from collaborating research groups. It will enable open-source access to abstracts, peer-reviewed publications, and reports. It will be linked with relevant existing websites at the GNS Science NZ (drill.gns.cri.nz) and GeoNet NZ that monitors geological hazards. The KEO will help organize the project end symposium with project partners and end-users.

-Public Lectures will be organised in local communities during the drilling operations, to inform and communicate with the general public and policy-makers on the scientific relevance of the drilling and its outcomes. DFDP Phase 1 sparked major media attention in NZ and we anticipate that Phase 2 will have even greater impact. The P.I.s, PDRAs and PhD student and the KEO will all engage UK Science Week, University Open Days, and other UK public engagement lectures.

-Communication with mass media will be organised through the Science Media Centre (SMC), London. Faulkner, Mariani and Teagle are part of the SMC existing database of scientists for breaking news. The P.I.s and DFDP Team have excellent track records of public and media engagement.

Training: PDRAs and PhD student will attend the "Communicating science to the public" training course organised by NERC.

Publications

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Menzies C (2014) Incursion of meteoric waters into the ductile regime in an active orogen in Earth and Planetary Science Letters

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Pitcairn I (2014) Metabasalts as sources of metals in orogenic gold deposits in Mineralium Deposita

 
Description Meteoric water penetrates very deeply down to the brittle-ductile transition in mountain belts and can influence the behaviour of major fault zones
Exploitation Route Risk analysis of major fault zones
Potential geothermal energy resource
Sectors Energy,Environment,Government, Democracy and Justice

 
Description NERC Isotope Geoscience Facility
Amount £50,000 (GBP)
Funding ID IP-1601-1115 
Organisation Natural Environment Research Council 
Department Isotope Community Support Facility
Sector Public
Country United Kingdom
Start 03/2016 
End 03/2018
 
Description GNS Science, New Zealand 
Organisation GNS Science
Country New Zealand 
Sector Public 
PI Contribution Collaboration with Alpine Fault geothermal systems and ICDP deep drilling
Collaborator Contribution Led the ICDP Alpine Fault Deep Drilling project
Impact Numerous scientific papers
Start Year 2008