Deep Fault Drilling Project (DFDP) — Alpine Fault ... - GNS Science

Workshop Proposal to the International Continental Scientific Drilling Program 

Deep Fault Drilling Project (DFDP) — Alpine Fault, NZ 

Active deformation processes in the seismogenic zone 

of a major transpressional plate boundary fault 

John Townend 1 , Rupert Sutherland 2 , Susan Ellis 2 , Richard Norris 3 , Tim Little 1 , Rick Sibson 3 , 

Cliff Thurber 4 , Stephen Cox 5 , Tim Stern 1 , Tim Davies 6 , Dave Prior 7 , Dan Faulkner 7 , Peter Malin 8 

1 2 3 4 

Victoria Univ. of Wellington, GNS Science, Univ. of Otago, Univ. of Wisconsin-Madison, 

5 6 7 8 

Australian National Univ., Univ. of Canterbury, Univ. of Liverpool, Univ. of Auckland, 

1 Summary 

The mid-crust is the locus of several fundamental geological and geophysical 

phenomena: these include the transitions from brittle to ductile behaviour and from 

unstable to stable frictional sliding; earthquake nucleation and predominant moment 

release; the peak in the crustal stress envelope; the transition from predominantly 

cataclastic to mylonitic fault rocks; and mineralisation associated with fracture 

permeability. Our current understanding of faulting and seismogenesis in this 

tectonically important zone is largely based on remote geophysical observations of 

active faults and direct geological observations of fossil faults. 

The Alpine Fault, New Zealand, is a globally significant dextral-reverse fault that is 

thought to fail in large earthquakes (c. Mw 7.9) every 200–400 years and last ruptured 

in 1717 AD. Ongoing uplift has rapidly exhumed a crustal section from c. 20 km, 

providing a young (

The meeting was attended by 46 local scientists and San Andreas Fault Observatory at Depth 

(SAFOD) principal investigators Prof Mark Zoback (Stanford University) and Dr William Ellsworth 

(US Geological Survey). 

A key theme that emerged at the meeting was the possibility of calibrating geological predictions 

based on surface exposures to rocks at >4 km depth. This would yield a wealth of information about 

near-surface fluid alteration and fluid processes; localisation with depth; rheological mechanisms; and 

involvement and deformation of the footwall. This proposal stems from those discussions and the 

Science Advisory Group’s comments on the 2007 proposal. 

3 Motivation 

Figure 1. Block model 

illustrating the setting of the 

Alpine Fault [Modified after 

Cox and Sutherland, 2007]. 

High exhumation and 

geothermal gradients have led to 

a relatively shallow (

Figure 2. Map of the South 

Island showing principal 

features of the Australia–Pacific 

plate boundary, including the 

Alpine Fault, Puysegur 

subduction zone, and 

Marlborough fault system 

(Wairau, Awatere, Clarence, 

and Hope Faults), and key 

locations referred to in the text 

“A” and “B” mark the ends of 

the along-fault illustration in 

Fig. 6. The thick grey lines 

indicate the inferred extent of 

past Alpine Fault ruptures. 

Light grey shading demarcates 

topography higher than 800 m. 

[Modified after Sutherland, et 

al., 2007]. 

3.2 The Alpine Fault 

The Alpine Fault is the primary structure accommodating Australia–Pacific plate motion in South 

Island (Figs 1, 2). It is a mature dextral-reverse fault that offsets basement rocks laterally by ~470 km, 

with estimated late Quaternary horizontal displacement rates of 21–27 mm/yr [Berryman, et al., 1992; 

Norris and Cooper, 2001; Sutherland, et al., 2006; Wellman, 1953]. Paleoseismic evidence near the 

Alpine Fault identifies earthquakes in 1717 AD, 1620 AD, and 1430 AD; the estimated moment 

magnitudes are 7.9±0.3, 7.6±0.3, and 7.9±0.4, respectively [Sutherland, et al., 2007]. 

In central South Island, the Alpine Fault is transpressive and the surface trace bounds the western edge 

of the mountains [Norris, et al., 1990]. Rapid exhumation due to high rates of erosion has produced 

rapid cooling, as indicated by the decreasing metamorphic grade and increasing thermochronological 

age with distance from the fault [Adams and Gabites, 1985; Batt, et al., 2004; Batt and Braun, 1999; 

Little, et al., 2005; Tippett and Kamp, 1993]. The rapid exhumation of material up the Alpine Fault 

ramp produces a spectacular exposure of the crustal section (Fig. 3) from >20 km depths [Little, et al., 

2002b; Norris and Cooper, 2003]. Along its central segment (dashed zone in Fig. 2), the fault 

juxtaposes a hanging wall of lithologically uniform high-grade (up to garnet-oligoclase) foliated 

Alpine Schists (the metamorphosed equivalent of the Mesozoic Torlesse greywacke terrane) against a 

footwall comprising a basement (Buller Terrane) of Paleozoic greywackes (Greenland Group) 

intruded by Devonian–Cretaceous granites and overlain by a Cretaceous–Cenozoic cover sequence. 

Due to the high exhumation rates [~6–9 mm yr–1; Little, et al., 2005] and uniform hanging wall 

lithology, the exposed section may serve as a young proxy for deformation currently occurring at midcrustal 

depths, allowing unprecedented ground-truthing of geophysical data and enabling us to 

interpret borehole observations in terms of recent fault products — and vice versa. An exhumed 1–2 

km-wide Plio–Pleistocene mylonite zone demonstrates that localized ductile deformation occurs 

beneath the brittle part of the Alpine Fault [Norris, 2004; Norris and Cooper, 2001; Norris and 

Cooper, 2003; Sibson, et al., 1979; Toy, et al., 2008]. In many areas the Alpine Fault separates Alpine 

Schist in the southeast from granitoid basement to the northwest but although portions of the ~1 kmthick 

fault zone are exposed in numerous river sections, no complete fault-rock sequence from hardrock 

hanging wall to hard-rock footwall has so far been located. One principal goal of site 

Deep Fault Drilling Project (DFDP) — Alpine Fault, NZ Page 3 of 15

Figure 3. Schematic cross 

section of an oblique thrust 

segment within the central 

section of the Alpine Fault 

[Norris and Cooper, 2007]. 

Figure 4. Map of earthquake 

epicentres recorded since 2001 

in the central South Island. The 

gray symbols mark 

seismographs deployed during 

the SIGHT experiment; black 

squares represent continuous 

GPS stations; and white 

triangles mark broadband 

seismographs operated by 

GeoNet. “A” and “B” mark the 

ends of the along-fault 

illustration in Fig. 6. 

characterisation ahead of a deep drilling project would be to obtain a continuous hard-rock coresection 

across the fault zone, as discussed further in Section 5. 

About 7 km structurally above the Alpine Fault lies a brittle–ductile shear array inferred to have 

formed at 15–22 km depths, with evidence for complex, transient semi-brittle behaviour at high strainrates 

and fluid pressure cycling on relatively short, possibly seismic, timescales [Wightman and Little, 

2007]. The base of the seismogenic zone is relatively shallow (c. 8–12 km) , and when similar 

magnitude ranges are considered, the seismicity rate of the Alpine Fault is comparable with seismicity 

rates along locked sections of the San Andreas fault [Leitner, et al., 2001] (Fig. 4). Geodetic studies 

are consistent with a shallow (5–10 km) depth for full fault locking [Beavan, et al., 1999; Pearson, et 

al., 2000], though some degree of interseismic coupling may persist to as deep as c. 18 km [Wallace, 

et al., 2007]. The fault zone exhibits low seismic wave speeds and high attenuation [Eberhart-Phillips 

and Bannister, 2002; Norris and Cooper, 2007; Smith, et al., 1995; Stern, et al., 2001; Stern, et al., 

2007] and high electrical conductivity [Wannamaker, et al., 2002], suggesting interconnected fluids at 

high pressures (Fig. 5). 

3.3 Global significance of drilling the Alpine Fault 

1. The >300 km along-strike exposure of a uniform-lithology hanging wall and derived fault rocks 

that formed during the current tectonic regime and which provide an exceptional reference for 

interpreting observations of the processes and structures operating at depth; 

2. A shallow seismogenic zone that is relatively accessible to drilling by international standards; 


3. A non-vertical fault orientation enabling fault penetration with one or more subvertical holes; 

4. Geologically well-determined rapid slip rates (20–25 mm yr –1 ); 

5. The potential to obtain continuous hard-rock sections through the fault zone; 

6. An existing, extensive body of geological and geophysical knowledge, and a modern, 

nationwide geophysical monitoring network (GeoNet 1 ); 

7. A relatively benign political and physical environment to operate in with existing petroleum 

industry onshore drilling activity and supporting infrastructure; 

8. Well-established and globally-credible scientists and science funding system — an Alpine Fault 

drilling program was one of 36 projects identified in a recent review of New Zealand’s largescale 

research infrastructure needs in the coming five years [Metson, et al., 2007]. 

There are, of course, a number of complicating factors, both scientific and logistical. The steep 

topography, high rainfall, and active erosion make access to the hanging wall difficult (in fact, only 

three graded roads extend more than 1 km from the fault trace in the central region of most rapid 

uplift) and field conditions are often difficult. These factors and recent glaciation affect the upper 

crustal hydrological regime and thermal structure, making estimates of the temperatures prevailing at 

mid-crustal depths complicated. Near-surface segmentation of the fault and the penetrative schist 

foliation may likewise complicate drilling. 

In the following section we describe how the present knowledge of the Alpine Fault’s surface geology 

and regional geometry can be combined to design a globally unique experiment linking outcrop and 

borehole observations of genetically linked rock masses. 

4 Fault-rock and fault zone evolution experiment 

4.1 Motivation and scientific objectives 

Drawing inferences about conditions and processes prevailing at depth based on outcrop observations 

is complicated by the fact that rocks exposed at the surface may have undergone modifications — 

structural, mineralogical, and geochemical — at shallow depths [Zoback, et al., 2007]. Any such 

modifications may have overprinted and obscured the record of deeper phenomena and conditions to a 

poorly known degree. One way of examining and accounting for the character and extent of upper 

crustal modifications is to examine a rock mass at depth whose future exhumation trajectory intersects 

a present-day surface outcrop: in other words, to treat the rock mass at depth as the protolith of the 

1 http://www.geonet.org.nz/ 

Figure 5. Migrated seismic 

section and contours of P-wave 

speed (km/s) showing a lowspeed 

region in the crust 

adjacent to the Alpine Fault 

inferred from seismic data 

[Stern, et al., 2001; Stern, et al., 

2007]. 


modified rocks now observed at the surface, and thereby investigate the accumulation of geological 

deformation as a function of space and time along the transport path. 

Note that evaluating fault rock evolution by means of paired borehole and surface outcrop 

observations is only feasible when the two rock masses in question can be reasonably presumed to 

have had similar geological histories. What is hugely advantageous in the case of the Alpine Fault, 

and globally rare if not unique, is the along-strike homogeneity (for >300 km) of the hanging wall 

rocks. This enables observations made at different points along-strike to be amalgamated laterally 

more simply than if the lithologies varied appreciably, and moreover enables vertical correlations — 

such as the upstream/downstream experiment proposed here — to be made. 

The fundamental questions that paired up- and downstream observations of the Alpine Fault could 

elucidate in conjunction with regional geological, geophysical, and geochemical studies include: 

1. How do fault rock properties such as quartz lattice-preferred orientations, microcrack density, 

fracture permeability, porosity, chloritic alteration etc. evolve during exhumation? 

2. How does strain localise within the fault core and surrounding damage zone, and what 

deformation mechanisms govern this? 

3. How do meteoric and metamorphic fluids interact with fault rocks? 

4. How does thermochronometric “age” accumulate with depth and temperature along the 

exhumation path (with implications for calibrating geochronometers and diffusion/closure 

parameters for application elsewhere, and estimates of long-term slip rates)? 

5. What is the thickness of the active slip zone and accompanying damage zone? 

6. What are the stresses, fluid pressures, and temperatures acting on the fault plane at depths 

relevant to earthquake nucleation and propagation, and how do these parameters fluctuate 

spatiotemporally and affect fault strength? 

7. Do creep, episodic slow-slip, or low-frequency tremor occur and, if so, where in the 

rheological system? 

8. How is seismic slip recorded at different depths within the fault zone? 

9. How common (or rare) are pseudotachylytes in a continuous across-fault section? 

These questions form two natural groupings, which underline this proposal and serve as this project’s 

principal objectives: 

A. To determine via integrated surface and borehole observations what deformation mechanisms 

and mineralogical processes govern fault rock evolution and fault rheology in the brittle crust 

and the brittle–ductile transition (Questions 1–5); 

B. To determine what factors govern seismic and aseismic deformation (Questions 6–9). 

4.2 Site selection 

In Figure 6, we illustrate the idealised geometry of the Alpine Fault in the central Southern Alps (inset 

stereogram) and a schematic view of the fault plane (as viewed along its pole) with the surface 

outcrops and fault-crossing roads marked. The regional fault plane strikes northeast and dips at 

approximately 50° to the southeast, and northeast-plunging striations and ductile slip vectors define a 

mean rake of ~38°NE [Little, et al., 2002a; Norris and Cooper, 1995; 1997]. This geometry 

corresponds to an average horizontal transport direction for the footwall of 070–090°, similar to the 

Nuvel-1 Australia–Pacific angle of 071±2° [DeMets, et al., 1990]. This means, for example, that a 

vertical borehole drilled approximately 3.5 km southeast of the Alpine Fault would intersect the 

Alpine Fault at a depth of ~4 km. Most importantly, however, the point at which the borehole 

intersected the fault plane would lie on the exhumation trajectory of rocks that are now exposed at the 

surface. The time taken for hanging wall rocks outcropping today to travel from the borehole 

intersection point is estimated to be 350 kyr. Options for borehole site locations require further 

discussion and this is a key outcome from the workshop. 


The experiment outlined here is well suited to a multi-phase drilling program conducted over several 

years and involving a number of boreholes commencing with shallow instrumentation holes (as 

already under construction; see Section 5.1) and 1-2 km-deep exploratory holes (Section 5.2), and 

going progressively deeper. This would enable the final and technologically most challenging phases 

of drilling and monitoring to be directly informed by sub-surface measurements in a similar manner to 

that used in the SAFOD project described below. 

4.3 Relation of an Alpine Fault drilling project to other ICDP projects 

The key difference of an Alpine Fault project from other such projects overseas is that, first, our target 

is the rheological mid-crust at greater structural depths (i.e. mid-crust, and the middle or even lower 

portions of the seismogenic zone) and, second, the well-studied but incomplete exhumed crustal 

section outcropping at the surface will directly inform interpretation of the borehole observations. 

Here we review how an Alpine Fault project would complement active fault drilling studies elsewhere. 

San Andreas Fault Observatory at Depth (SAFOD) 

Figure 6. Schematic view 

normal to the mean fault plane 

in the central Alpine Fault 

region showing rock uplift 

trajectories. “T” and “R” denote 

tracks and roads crossing the 

fault trace, respectively. “A” 

and “B” are marked on Fig. 1 

for reference. The short red 

lines mark strike-slip portions of 

the fault trace. The inset 

summarises the mean fault 

geometry in stereographic 

projection. 

The active fault zone drilling experiment with which an Alpine Fault project would have closest 

affinity is SAFOD, which was designed to directly sample fault zone materials (rock and fluids), 

measure a wide variety of fault zone properties, and monitor a creeping and seismically active fault 

zone at depth [Zoback, et al., 2007]. The experiment’s location, at the northwestern end of the 1966 

M6 Parkfield earthquake, corresponds to the transition between locked and creeping sections of the 

fault. This area has been the focus of extensive geophysical monitoring for several decades, and 

SAFOD represents the latest phase of a long-term natural laboratory experiment. SAFOD was 

designed to address both generic questions about fault zone properties and earthquake behaviour, and 

more specific questions related to the apparent weakness of plate-boundary faults. 

The drilling itself was conducted in three phases, between 2004 and 2007 following the successful 

drilling and instrumentation of a 2.2 km-deep pilot hole in 2002 [Hickman, et al., 2004]. The key 

benefit of this approach was that each phase of drilling, which reached a maximum depth during Phase 

of 3.0 km, could be used to inform the following phases, both technically and scientifically. A diverse 

range of geophysical and geochemical observations were made — and continue to be made as SAFOD 

enters the monitoring phase — including real-time gas chemistry measurements, cuttings analysis, 

spot and continuous core measurements, and extensive seismic monitoring using surface and 

downhole instruments. The advantage of this multi-technique, multi-phase approach was clearly seen 

when active faults detected by casing deformation at 2.7 km depth following Phase 2 drilling could be 

correlated with nearby M~2 seismicity and low Vp/Vs and resistivity in geophysical logs, and then 

directly cored in Phase 3. 

A key distinction between what is under consideration for the central Alpine Fault and the SAFOD 

experiment is the close integration in the Alpine Fault case of surface and borehole data along a well- 


constrained exhumation trajectory. This will enable a relatively direct examination of fault rock 

evolution through time and depth, which in turn will permit an evaluation of the rates of fault zone 

processes. 

North Anatolian Fault Project 

Planning is underway for a deep borehole geophysical observatory near the intersection of strike-slip 

and normal fault segments of the North Anatolia Fault Zone. Key questions to be addressed include 

the strength of the fault zone; orientation of stresses near the fault; variation in stresses and other 

properties in time; and mechanics of earthquake rupture [Dresen, et al., 2007]. The North Anatolian 

fault is comparable to the Alpine Fault in terms of length (1400 km) and Holocene slip rate (25–35 km 

yr –1 ) but is notably different in having ruptured over 900 km of its length in the last century. The 

planned drill site, ~20 km south of Istanbul and immediately west of the most recent M>7 earthquakes 

(Izmit and Düzce, 1999), is at the eastern end of a ~100 km-long segment of the fault that has 

accumulated 4–5 m of slip deficit since last rupturing in 1766. A 2 km-deep borehole adjacent to (but 

not intersecting) the North Anatolian fault will be instrumented with a range of instruments in order to 

serve as a long-term fault monitoring site. 

Unlike the North Anatolian Fault Project, which focuses on near-fault monitoring of an area 

reasonably likely to experience a major earthquake in the coming decades, the Alpine Fault project 

will focus more directly on sampling the fault itself and placing constraints on the rates and structural 

positions (depths) at which different deformation processes operate. 

Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) and associated onshore drilling 

NanTroSEIZE is a complex ocean drilling project that will attempt for the first time to drill, sample, 

and instrument the up-dip end of a seismogenic thrust interface and shed light on how water and rock 

interact in subduction zones to influence earthquake occurrence. Stage 1 drilling began in 2007: 

samples will be collected in order to study the frictional properties of the rock and sensors will be 

installed deep beneath the sea floor to record earthquakes and yield insight into the processes 

responsible for earthquakes and tsunami. The fundamental objective of the onshore (ICDP-supported) 

component of Nankai Trough drilling is similarly to elucidate the processes governing megathrust 

earthquakes, but the key contribution of the onshore boreholes will be to link NanTroSEIZE to surface 

geophysical arrays (geodetic and seismological). The onshore boreholes do not target active faults 

themselves: they serve a similar role to outcrops along the Alpine Fault and the GeoNet network in 

providing a surface observation-based context in which to interpret deeper observations. 

Corinth Rift Laboratory (CRL) and the planned Sevier Basin and Central Appenines projects 

The Corinth Rift Laboratory was established within a rapidly extending rift and focussed on active 

normal faulting. A key goal of this project was to establish the geometric relationships between 

steeply-dipping outcropping faults which have given rise to historic M>6 earthquakes and gentlydipping 

microseismically active structures at depth, with an emphasis on hydro-thermo-mechanical 

interactions and geochemical processes and the seismic hazard posed by the major normal faults. The 

Aigion fault was intersected at a depth of 760 m: it comprises a ~7 m-thick zone of brecciated 

limestone surrounding a 50 cm-thick clay core, offsets basement rocks by ~150 m, and currently 

sustains a 0.5 MPa pressure difference [Cornet, et al., 2004]. Preliminary dating suggests that this 

fault is young (~50 kyr) with a mean slip rate of ~3.5 mm yr –1 , in marked contrast to the Alpine Fault. 

The Sevier Basin and Central Appenines projects, both now in the workshop phase, are likewise 

intended to ultimately address the mechanics of low-angle normal faulting, and specifically the 

unresolved questions of whether brittle deformation can occur on ostensibly misoriented faults and 

whether such deformation can occur seismically. In the Sevier Basin case, this will involve drilling to 

2–4 km to intersect the Sevier Desert detachment, which separates Paleozoic basement from Cenozoic 

basin fill; measuring fluid pressure, permeability, fluid chemistry, temperature and stress; determining 

whether the Paleozoic–Cenozoic contact is fault-related, unconformable, or a combination; and 

documenting the history of hanging wall sedimentation (and hence the detachment’s movement 

history). The Central Appenines project will focus on intersecting the moderately dipping Colfiorito 

fault at a depth of 2–3 km and the shallowly dipping Alto Tiberina fault at 5–6 km. 


Nojima Fault Project and Taiwan Chelungpu Fault Drilling Project 

These two projects were post-seismic fault zone characterisation experiments. Several medium-depth 

boreholes (~750–1800 m) were drilled into strands of the Nojima fault following the 1995 M 6.9 Kobe 

earthquake with the overall objective of determining the physical characteristics and post-seismic 

recovery of a seismogenic fault as soon as possible after a major earthquake. The combined aims of 

the different projects were to characterise the structure and properties of the Nojima fault at depth; 

conduct geophysical examinations of the fault zone; and carry out borehole tests in order to investigate 

temporal changes (“healing”) [Oshiman, et al., 2001 and references therein]. The TCDP was 

conducted in response the 1999 M 7.7 Chi-Chi earthquake. Two deep boreholes (1.3 km and 2.0 km) 

were drilled to address fundamental questions about earthquake nucleation and rupture, notably the 

character and seismogenic significance of a large-slip-magnitude (>10 m) asperity inferred from 

seismic waveform modelling, and the role of the Chelungpu thrust fault in regional tectonics [Ma, et 

al., 2006]. 

Although the Alpine Fault is thought to be late in the earthquake cycle [Sutherland, et al., 2007], the 

emphasis of a deep drilling experiment would clearly be on the fault’s long-term evolution in both the 

brittle and ductile fields rather than on short-term processes associated with individual earthquakes. 

Natural Earthquake Laboratory in South African Mines (NELSAM) 

In the same way that drilling into the Alpine Fault would take advantage of ongoing uplift and erosion 

to target rocks exhumed from the mid-crust, the NELSAM experiment exploits ~4 km-deep South 

African gold mines to access depths rendered seismogenic by ongoing mining operations. The 

laboratory is built 2.9 km below the surface within the >10 km-long, 30–200 m-displacement Pretorius 

fault zone in the Tautona mine, Witswatersrand Basin. NELSAM consists of a number of geophysical 

and geochemical instruments and is situated in order to obtain near-field observations of mininginduced 

earthquakes (M>2) on reactivated Archean faults. The emphasis of NELSAM is therefore on 

the mechanisms and products of small-scale, purely brittle deformation. 

To date no active fault drilling experiment has been targeted at the mid-crustal roots of a long-lived 

active fault, or addressed fault zone evolution throughout the seismogenic zone and towards the 

brittle-ductile transition. 

5 Recent and current, and planned Alpine Fault research 

5.1 Seismicity studies 

Funding has recently been received from the Royal Society of New Zealand’s Marsden Fund for a 

three-year borehole seismology program in the central region of the Alpine Fault. This project 

involves researchers from Victoria and Auckland universities and GNS Science, and is led by Tim 

Stern. One 250 m-deep borehole (near Franz Josef) and up to thirteen 2–25 m-deep holes (including 

four within ~10 km of Gaunt Creek and the Whataroa River site) will be drilled in the central Alpine 

Fault region and fitted with three-component sondes to record earthquakes to an estimated lower 

magnitude threshold of approximately M0.5 This study extends current work by Bronwyn O’Keefe 

(Victoria) and colleagues, who are using a surface network of eight portable instruments and three 

GeoNet stations to better characterise seismicity in the central Alpine fault region. 

Research by GNS Science (Stephen Bannister and colleagues) is improving on existing seismic 

tomography models [Eberhart-Phillips and Bannister, 2002] at the regional scale and yielding 3D 

images of velocity, Vp/Vs and attenuation. Ongoing work focuses on double-difference relocation 

analysis of the seismicity catalogue using the improved seismic velocity models. Infill seismometer 

deployments are planned for the northern Alpine Fault during 2009–2010 to complement the 

downhole monitoring array described above. Two new GeoNet seismograph stations will be installed 

adjacent to the Alpine Fault in late 2008. 


5.2 Structural geology 

The Mt Cook [Cox and Barrel, 2008], Greymouth [Nathan, et al., 2002], and Haast [Rattenbury and 

others, in preparation] geological sheets span the central Southern Alps and the Alpine Fault. These 

recently revised and updated map sheets delineate the regional geological context, including the 

distribution of active faults, for the regions surrounding the proposed drill sites on the Alpine Fault. 

The data are compiled in a GIS database at 1:50,000 scale and published at 1:250,000 scale. Simon 

Cox is continuing work on distributed deformation east of the Alpine Fault and attempting to constrain 

the kinematics, location and amount of deformation that may occur in the central Southern Alps. 

The University of Otago’s structural geology group (Richard Norris, Alan Cooper, Rick Sibson, Dave 

Craw, Phaedra Upton, Virginia Toy, and students) has systematically mapped the fault zone from the 

Hokitika River to Milford Sound [Norris and Cooper, 2007] and made particularly detailed studies in 

the central part of the fault [Toy, et al., 2008]. Further structural and petrological investigation of fault 

rocks along the length of the Alpine Fault is ongoing, with an emphasis in the coming years on 

locating and describing all surface outcrops of the fault and fault rocks and determining the fault’s 

kinematics, especially to the south of the Whataroa River, as part of the site characterisation work. 

Work is also continuing on the structural and petrological characteristics of pseudotachylytes and their 

distribution [Sibson and Toy, 2006], and in collaboration with Dave Prior (University of Liverpool) a 

detailed study of mylonite microstructures, deformation mechanisms, and rock strength is underway. 

Tim Little (Victoria University of Wellington) and colleagues at GNS Science and the University of 

Liverpool are conducting detailed structural geological studies of the Alpine Schists that comprise the 

hanging wall of the Alpine Fault. Current research is focused on describing and modelling the 

rheology of quartz veins that were naturally deformed by shearing in the past several million years at 

depths of ~20 km in the Alpine Fault’s hanging wall [Wightman and Little, 2007; Wightman, et al., 

2006]. In collaboration with the Otago team, further research is planned for the regions surrounding 

the several alternate proposed drill sites in the central Southern Alps. The field- and laboratory-based 

research will focus on ductile deformational fabrics in the Alpine Fault’s hanging wall, in particular, 

the nature and rheological significance of transition between non-mylonitic and mylonitic zones. 

As noted above, obtaining a continuous core through the footwall and hanging wall in the central 

portion of the Alpine Fault should form a key task of site characterisation and be seen as an important 

goal in its own right. One location at which such a core could be obtained using relatively cheap 

diamond exploration coring methods is Saddle Creek, in the upper Kokatahi River valley. At this site, 

a semi-continuous section of mylonites is exposed, with a transition from granitoid-derived (footwall) 

to Alpine Schist-derived (hanging wall) mylonites midway through the transect [Reed, 1964]. 

5.3 Active source seismology 

Determining the shallow (0–10 km) orientation and seismic characteristics of the Alpine Fault will be 

a key task in site characterisation, as emphasised in discussions at the November 2007 meeting. In 

2008, GNS Science researchers will reprocess the SIGHT98 seismic line (Line 2), which crosses the 

Alpine Fault, and a University of Otago team led by Andrew Gorman will conduct a seismic reflection 

study across the Alpine Fault at Haast. A Victoria University of Wellington MSc student supervised 

by Tim Stern will be working on a cross-line seismic tomography study (to lower crustal depths) of 

the Alpine Fault Zone, using the onshore-offshore, active-source, seismic data collected during SIGHT 

in 1996. 

Alan Green (ETH Zürich) and students are processing high-resolution 3D seismic reflection surveys 

collected at Maruia (northeastern Alpine Fault) to image fault zone structure in the sedimentary cover 

and basement to ~200 m depth. 

5.4 Hydrological and thermal modelling 

The November 2007 meeting identified the need for better thermal models of the central Alpine Fault. 

Current thermal and hydrological models of the shallow to mid-crust in the vicinity of the Alpine Fault, 

particularly on the hanging wall, are limited because of uncertainties in the maximum depth and 

pattern of topographically-induced fluid flow, the permeability structure, and shear heating effects. 


The present-day shallow thermal regime west of the Alpine Fault can be inferred reasonably directly 

from petroleum exploration wells [Townend, 1999], but data from the immediate vicinity of the Alpine 

Fault’s surface trace and further east are sparse. Significant differences exist between models: some 

show a maximum upward deflection of 100–300°C isotherms east of the surface trace of the Alpine 

Fault, matched by a downward perturbation of higher temperatures to the west and at greater depths as 

material is deflected downwards into a thickening crustal root [Allis and Shi, 1995; Gerbault, et al., 

2003]; whereas others place the elevated 400°C isotherm directly above the Alpine Fault at extremely 

shallow (

Wanganui rock avalanche, which appears to be associated with the c. 1420 AD earthquake; and the 

Waiho Loop terminal moraine (Franz Josef). Davies and colleagues at NIWA are also determining the 

frequency–magnitude relationships of rock-fall and delta-front avalanches at Milford Sound. 

5.7 Geoelectrical observations 

On completion of a current magnetotelluric profile through the Marlborough region, Grant Caldwell 

(GNS Science) will collect infill data and complete a 3D MT conductivity survey between the 

Karangarua and Whataroa rivers. 

5.8 Geochemistry 

The geochemistry of hot springs in the central portion of the Southern Alps is currently being analysed 

by Agnes Reyes and Simon Cox (GNS Science). In collaboration with Rupert Sutherland (GNS 

Science), they are developing a program for continuously monitoring changes in hot spring 

temperature and chemistry in conjunction with rainfall data measurements. Cox and colleagues at the 

University of Southampton are also investigating the nature of low-temperature alteration in Alpine 

Fault rocks using chemical and isotopic analyses (stable isotopes and 87 Sr) to infer conditions at depth. 

Dave Craw, Richard Norris, and Virginia Toy (University of Otago) are using fluid inclusions to 

determine pressure, temperature and fluid chemistry of quartz veins in the mylonites. Norris is also 

working on oxygen isotope measurements to document changing fluid circulation during exhumation. 

6 ICDP-sponsored international workshop, New Zealand, 2009 

We wish to hold a five-day workshop in New Zealand in early 2009 at which we assemble an 

international group of experts to discuss an Alpine Fault drilling project and compress our existing 

knowledge into a specific research plan. 

In addition to the purely scientific questions to be resolved during the workshop, there are several key 

logistical issues to be addressed. These include the advisory structure required for a multi-year 

program of site characterisation, drilling, and science, both on the surface and down-hole; the 

membership of technical focus groups; and the attraction of adequate long-term, high-level funding. 

As noted above, a deep drilling project on the Alpine Fault has been identified in a recent 

governmental review of large-scale research infrastructure demands in the coming five years [Metson, 

et al., 2007], and New Zealand researchers have a strong track record of leveraging international 

funding for large geoscience projects (including the SIGHT program described above and the 

ANDRILL Antarctic Drilling Program). New Zealand and the United Kingdom have both expressed 

interest in joining ICDP, and one of the key tasks of this workshop will be to develop a timeline and 

strategy for finalising this. 

We plan to involve approximately 40 researchers from New Zealand and overseas with 

complementary experience in pertinent fields, and particularly structural geology, tectonics, 

hydrological and thermal modelling, geophysics, earthquake physics, and drilling. 

The principal outcome of this workshop will be a draft science plan for the coming years that 

encompasses further site characterisation, deep drilling, and ongoing monitoring. 

In order to familiarise workshop participants with the central Alpine Fault’s geology and field 

relationships during a short mid-workshop fieldtrip, we will hold the workshop in Franz Josef, 

approximately five hours’ drive from Christchurch International Airport. 

Day 1 — Background and scientific rationale; review of recent regional and local studies; summary of 

current understanding; update on fault zone drilling projects elsewhere; 

Day 2 — Break into working groups — site characterisation, core handling and analysis; fluidsampling 

and analysis; downhole measurements; fault zone monitoring; 

Day 3 — Fieldtrip to Whataroa, Gaunt Creek and nearby outcrops; 

Day 4 — Reports from working groups; identification of key scientific goals; discussion of finance 

plan; identification of project leaders, organisational structure, and external advisors; 


Day 5 — Preparation of draft science plan; preparation of workshop report. 

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Deep Fault Drilling Project (DFDP) — Alpine Fault ... - GNS Science

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