The evolution of deformation mechanisms, physical conditions and physical properties in the seismogenic Alpine Fault zone: a pilot study

Lead Research Organisation: University of Liverpool
Department Name: Earth, Ocean and Ecological Sciences

Abstract

The movement of large faults in the Earth's crust is controlled by the physical properties of the fault rocks: these are materials formed within the zone of fault movement. Earthquakes are generated in the top 10-20 km of the earth's crust (known as the seismogenic zone). The fault rocks in the seismogenic zone (brittle fault rocks) are formed by processes that produce material made up of lots of small particles that roll-around and slide past each other, with fluids playing an important role in controlling these processes. Understanding the physics of brittle fault rocks is crucial to understanding both the long-term movement of faults, on a time scale of millions of years, and to understanding the nucleation, rupture and cessation of large earthquakes. The Alpine Fault zone of New Zealand is a major plate-boundary fault that produces great earthquakes every 200-400 years. The fault movement involves a large component of dextral strike-slip - when one stands on one side of the fault the other side moves to the right (at about 35mm per year averaged over hundreds of thousands of years). It also involves reverse movement, so that the east side is sliding upwards and over the west side, at about 10 mm per year. There is a very-high rainfall on the west coast of the South Island and the uplifted material is eroded quickly so that the action of the fault over tens of thousands to millions of years is to bring materials from depth up to the Earth's surface. Materials from 10km get to the surface in a million years. What is unique about the Alpine Fault zone is that fault rocks at the surface have come from all depths in the fault zone and that equivalent fault rocks are being generated by the active fault today. We can sample brittle fault rocks at the surface that were formed at 5km depth and we can use geophysics (remote sensing into the Earth) to find out about what conditions exist today in the active fault at 5km depth, where equivalent fault rocks are being created. There is nowhere else where we can do this. In this proposal we aim to collect the first complete section of brittle fault rocks from the Alpine Fault zone and to use these to better understand the physics of processes in the seismogenic zone. The brittle fault rocks are often covered by river gravels and no complete section is exposed at the surface. So to collect the samples we plan to drill through about 150m of rock and collect cores from the drill hole. The core samples will be analysed in the laboratory so that we know their physical properties and can model better their behaviour on earthquake timescales and longer timescales. This project will involve significant international research collaboration and provides a stepping stone towards a more ambitious programme of deeper drilling and allied science supported by International Continental Drilling Programme. The ultimate goal is use the Alpine Fault Zone as a natural laboratory to understand the physics of rock deformation in the seismogenic zone and the physics of earthquake rupture.

Publications

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Faulkner D (2018) Pore Fluid Pressure Development in Compacting Fault Gouge in Theory, Experiments, and Nature in Journal of Geophysical Research: Solid Earth

 
Title X-ray Computed Tomography and borehole televiewer images of the Alpine Fault's hanging-wall, New Zealand: Deep Fault Drilling Project phase 1 (DFDP-1) and Amethyst Hydro Project (AHP) 
Description The orientations and densities of fractures in the foliated hanging-wall of the Alpine Fault provide insights into the role of a mechanical anisotropy in upper crustal deformation, and the extent to which existing models of fault zone structure can be applied to active plate-boundary faults. Three datasets were used to quantify fracture damage at different distances from the Alpine Fault principal slip zones (PSZs): (1) X-ray computed tomography (CT) images of drill-core collected within 25 m of the PSZs during the first phase of the Deep Fault Drilling Project that were reoriented with respect to borehole televiewer (BHTV) images, (2) field measurements from creek sections at <500 m from the PSZs, and (3) CT images of oriented drill-core collected during the Amethyst Hydro Project at distances of ~500-1400 m from the PSZs. Results show that within 160 m of the PSZs in foliated cataclasites and ultramylonites, gouge-filled fractures exhibit a wide range of orientations. At these distances, fractures are interpreted to form at high confining pressures and/or in rocks that have a weak mechanical anisotropy. Conversley, at distances greater than 160 m from the PSZs, fractures are typically open and subparallel to the mylonitic foliation or schistosity, implying that fracturing occurred at low confining pressures and/or in rocks that are mechanically anisotropic. Fracture density is similar across the ~500 m width of the hanging-wall datasets, indicating that the Alpine Fault does not have a typical â??damage zoneâ? defined by decreasing fracture density with distance. Instead, we conclude that the ~160 m-wide zone of intensive gouge-filled fractures provides the best estimate for the width of brittle fault-related damage. This estimate is similar to the 60-200 m wide Alpine Fault low-velocity zone detected through fault zone guided waves, indicating that a majority of its brittle damage occurs within its hanging-wall. The data provided here include CT scan 'core logs' for drill-core from both boreholes of the first phase of the Deep Fault Drilling Project (DFDP-1A and DFDP-1B) and from the Amethyst Hydro Project (AHP), the code to generate 'unrolled' CT images (which is to be run on imageJ), and an overview image of the integration of unrolled DFDP-1B CT images and BHTV images (DFDP-1B_BHTV-CT-Intergration.pdf). The header for the scan log images indicate 'core run-core section-upper depth-lower depth' for DFDP and 'borehole-core run-core section-upper depth-lower depth' for AHP boreholes. CT scan core logs cover the depth range 67.5-91.1 m in DFDP-1A drill-core and all of DFDP-1B drill-core. A classification of fracture type is given in Williams et al (2016). For DFDP-1 CT scan logs, title of each page labelled by: core run - core section - depth range. For AHP CT scan log, header of each page gives: borehole - core run - core section - depth. These are supplementary material to Williams et al. (submitted), in which a methodology for matching unrolled CT and BHTV images is given in Appendix A. 
Type Of Art Film/Video/Animation 
Year Produced 2017 
URL http://dataservices.gfz-potsdam.de/icdp/showshort.php?id=escidoc:2604902
 
Description Fluid control on architecture and rupture of Apline Fault Zone;
Discovery of new lithologies and their architecture in Alpine Fault Zone; Exceptionally high geothermal gradient of the Alpine Fault, published in Nature.
Exploitation Route Could be presented to local authorities for consideration with respect to seismic hazard and earthquake risk assessment; Ways of exploiting geothermal energy on the west coast of New Zealand South Island along the Alpine Fault could be explored.
Sectors Construction

Education

Energy

Environment

URL http://theconversation.com/new-zealands-alpine-fault-reveals-extreme-underground-heat-and-fluid-pressure-77868
 
Description Standard joint grant
Amount £600,000 (GBP)
Funding ID NE/J024449/1 
Organisation Natural Environment Research Council 
Sector Public
Country United Kingdom
Start 06/2012 
End 10/2016
 
Description DFDP-1 GFZ 
Organisation Helmholtz Association of German Research Centres
Department German Research Centre for Geosciences
Country Germany 
Sector Private 
PI Contribution We contributed to the drilling operations through the central Alpine Fault within the DFDP-1 iternational initiative. We are also carrying out in depth systematic analyses of core sample recovered.
Collaborator Contribution Our Partner contributed to the drilling operations through the central Alpine Fault within the DFDP-1 iternational initiative.
Impact For outputs see Publications in My Portfolio. The project is multi-disciplinary and involves: Geology, Geophysics and Geochemistry.
Start Year 2010
 
Description DFDP-1 GNS 
Organisation GNS Science
Country New Zealand 
Sector Public 
PI Contribution We contributed to funding the drilling operations to investigate the central Alpine Fault at depth within phase 1 of the Deep Fault Drilling Project (DFDP1)
Collaborator Contribution Our Partner contributed to funding the drilling operations to investigate the central Alpine Fault at depth within phase 1 of the Deep Fault Drilling Project (DFDP1)
Impact For outputs see Grant NE/H012486/1 Disciplines involved: Geology, Geophysics, Geochemistry
Start Year 2010
 
Description NERC - Ion Microprobe Facility - University of Edinburgh 
Organisation Natural Environment Research Council
Department NERC Ion Micro-Probe Facility
Country United Kingdom 
Sector Academic/University 
PI Contribution My research team provided the material for study, undertook the measurements using the Ion Microprobe and preformed the subsequent data analysis.
Collaborator Contribution The NERC IMF provided equipment and technical support for trace element and stable isotope analysis of carbonate material collected during the Deep Fault Drilling Project - Phase 1.
Impact The data collected during this study has been presented in a number of conferences, as both poster and oral presentations. The work covers a number disciplines including; microstructural analysis in the SEM and geochemical measurements in the Ion Microprobe.
Start Year 2015
 
Title Generating circumferential images of tomographic drill-core scans 
Description This code (nwrap.ijm) can be used to generate an 'unrolled' circumferential image of a tomographic drill-core scan, such as an X-ray Computed Tomography (CT) scan. The resulting image is analogous to those produced by a DMT CoreScan system®. By comparing such images to geographically references borehole televiewer data, it may be used to reorientate drill-core back into geographic space (Williams et al. submitted). This code should be installed and run as a plugin on ImageJ/Fiji. Full instructions are given in the code and in the Appendix A of Williams et al. (submitted). Examples of unrolled CT scans can be found at Williams et al (2017, http://doi.org/10.5880/ICDP.5052.004). 
Type Of Technology Software 
Year Produced 2017 
URL http://dataservices.gfz-potsdam.de/icdp/showshort.php?id=escidoc:2611892
 
Description "Implications of wet pseudotachylyte formation: Insights from the Alpine Fault Zone, New Zealand". L.J Scott, M.J. Allen and E. Mariani. Department of Earth, Ocean and Ecological Sciences, University of Liverpool. 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Study participants or study members
Results and Impact DRT conference 2019 - up to 100 participants. Talk topics are on deformation, rheology and tectonics. Laura is going to communicate our results on pseudotachylytes from the Alpine Fault Zone. Each pseudotachylyte is thought to represent an earthquake event. We expect good feedback to aid writing and publication of a planned manuscript.
Year(s) Of Engagement Activity 2019
URL https://drt-2019.net/
 
Description The Christchurch earthquake 2011 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Media (as a channel to the public)
Results and Impact Radio interview on the effects of the Christchurch earthquake in February 2011

Radio interview on Materials World, with Quentin Cooper, by BBC radio 4
Year(s) Of Engagement Activity 2011