Disasters can occur without warning and severely test society’s capacity to cope, significantly altering the relationship between society and the built and natural environments. The scale of a disaster is a direct function of the pre-event actions and decisions taken by society. Poor pre-event planning is a major contributor to disaster, while effective pre-event planning can substantially reduce, and perhaps even avoid, the disaster. Developing and undertaking effective planning is therefore a vital component of disaster risk management in order to achieve meaningful societal resilience. Disaster scenarios present arguably the best and most effective basis to plan an effective emergency response to future disasters. For effective emergency response planning, disaster scenarios must be as realistic as possible. Yet for disasters resulting from natural hazards, intricately linked secondary hazards and effects make development of realistic scenarios difficult. This is specially true for large earthquakes in mountainous terrain. The primary aim of this thesis is therefore to establish a detailed and realistic disaster scenario for a Mw8.0 earthquake on the plate boundary Alpine fault in the South Island of New Zealand with specific emphasis on secondary effects. Geologic evidence of re-historic earthquakes on this fault suggest widespread and large-scale landsliding has resulted throughout the Southern Alps, yet, currently, no attempts to quantitatively model this landsliding have been undertaken. This thesis therefore provides a first attempt at quantitative assessments of the likely scale and impacts of landsliding from a future Mw8.0 Alpine fault earthquake. Modelling coseismic landsliding in regions lacking historic inventories and geotechnical data (e.g. New Zealand) is challenging. The regional factors that control the spatial distribution of landsliding however, are shown herein to be similar across different environments. Observations from the 1994 Northridge, 1999 Chi-Chi, and 2008 Wenchuan earthquakes identified MM intensity, slope angle and position, and distance from active faults and streams as factors controlling the spatial distribution of landsliding. Using fuzzy logic in GIS, these factors are able to successfully model the spatial distribution of coseismic landsliding from both the 2003 and 2009 Fiordland earthquakes in New Zealand. This method can therefore be applied to estimate the scale of landsliding from scenario earthquakes such as an Alpine fault event. Applied to an Mw8.0 Alpine fault earthquake, this suggests that coseismic landsliding could affect an area >50,000 km2 with likely between 40,000 and 110,000 landslides occurring. Between 1,400 and 4,000 of these are expected to present a major hazard. The environmental impacts from this landsliding would be severe, particularly in west-draining river catchments, and sediment supply to rivers in some catchments may exceed 50 years of background rates. Up to 2 km3 of total landslide debris is expected, and this will have serious and long-term consequences. Fluvial remobilisation of this material could result in average aggradation depths on active alluvial fans and floodplains of 1 m, with maximum depths substantially larger. This is of particular concern to the agriculture industry, which relies on the fertile soils on many of the active alluvial fans affected. This thesis also investigated the potential impacts from such landsliding on critical infrastructure. The State Highway and electrical transmission networks are shown to be particularly exposed. Up to 2,000 wooden pole and 30 steel pylon supports for the transmission network are highly exposed, resulting in >23,000 people in the West Coast region being exposed to power loss. At least 240 km of road also has high exposure, primarily on SH6 between Hokitika and Haast, and on Arthur’s and Lewis Passes. More than 2,750 local residents in Westland District are exposed to isolation by road as a result. The Grey River valley region is identified as the most critical section of the State Highway network and pre-event mitigation is strongly recommended to ensure the road and bridges here can withstand strong shaking and liquefaction hazards. If this section of the network can remain functional post-earthquake, the emergency response could be based out of Wellington using Nelson as a forward operating base with direct road access to some of the worst-affected locations. However, loss of functionality of this section of road will result in >24,000 people becoming isolated across almost the entire West Coast region. This thesis demonstrates the importance and potential value of pre-event emergency response planning, both for the South Island community for an Alpine fault earthquake, and globally for all such hazards. The case study presented demonstrates that realistic estimates of potential coseismic landsliding and its impacts are possible, and the methods developed herein can be applied to other large mountainous earthquakes. A model for developing disaster scenarios in collaboration with a wide range of societal groups is presented and shown to be an effective method for emergency response planning, and is applicable to any hazard and location globally. This thesis is therefore a significant contribution towards understanding mountainous earthquake hazards and emergency response planning.

An Alpine Fault Earthquake has the potential to cause significant disruption across the Southern Alps of the South Island New Zealand. In particular, South Island river systems may be chronically disturbed by the addition of large volumes of sediment sourced from coseismic landsliding. The Taramakau River is no exception to this; located north of Otira, in the South Island of New Zealand, it is exposed to natural hazards resulting from an earthquake on the Alpine Fault, the trace of which crosses the river within the study reach. The effects of an Alpine Fault Earthquake (AFE) have been extensively studied, however, little attention has been paid to the effects of such an event on the Taramakau River as addressed herein. Three research methods were utilised to better understand the implications of an Alpine Fault Earthquake on the Taramakau River: (1) hydraulic and landslide data analyses, (2) aerial photograph interpretation and (3) micro-scale modelling. Data provided by the National Institute of Water and Atmospheric Research were reworked, establishing relationships between hydraulic parameters for the Taramakau River. Estimates of landslide volume were compared with data from the Poerua landslide dam, a historic New Zealand natural event, to indicate how landslide sediment may be reworked through the Taramakau valley. Aerial photographs were compared with current satellite images of the area, highlighting trends of avulsion and areas at risk of flooding. Micro-scale model experiments indicated how a braided fluvial system may respond to dextral strike-slip and thrust displacement and an increase in sediment load from coseismic landslides. An Alpine Fault Earthquake will generate a maximum credible volume of approximately 3.0 x 108 m3 of landslide material in the Taramakau catchment. Approximately 15% of this volume will be deposited on the Taramakau study area floodplain within nine years of the next Alpine Fault Earthquake. This amounts to 4.4 x 107 m3 of sediment input, causing an average of 0.5 m of aggradation across the river floodplains within the study area. An average aggradation of 0.5 m will likely increase the stream height of a one-in-100 year flood with a flow rate of 3200 m3/s from seven metres to 7.5 m overtopping the road and rail bridges that cross the Taramakau River within the study area – if they have survived the earthquake. Since 1943 the Taramakau River has shifted 500 m away from State Highway 73 near Inchbonnie, moving 430 m closer to the road and rail. Paleo channels recognised across the land surrounding Inchbonnie between the Taramakau River and Lake Brunner may be reoccupied after an earthquake on the Alpine Fault. Micro-scale modelling showed that the dominant response to dextral strike-slip and increased ‘landslide’ sediment addition was up- and downstream aggradation separated by a localised zone of degradation over the fault trace. Following an Alpine Fault Earthquake the Taramakau River will be disturbed by the initial surface rupture along the fault trace, closely followed by coseismic landsliding. Landslide material will migrate down the Taramakau valley and onto the floodplain. Aggradation will raise the elevation of the river bed promoting channel avulsion with consequent flooding and sediment deposition particularly on low lying farmland near Inchbonnie. To manage the damage of these hazards, systematically raising the low lying sections of road and rail may be implemented, strengthening (or pre-planning the replacement of) the bridges is recommended and actively involving the community in critical decision making should minimise the risks of AFE induced fluvial hazards. The response of the Taramakau River relative to an Alpine Fault Earthquake might be worse, or less severe or significantly different in some way, to that assumed herein.

The Wanganui-Wilberg landslide lies between Hokitika and Franz Josef townships, at the entrance of Harihari, on the true left bank of the Wanganui River, by State Highway 6. This apparently co-seismic landslide belongs to the class of events called rock avalanches - powerful destructive agents (Keefer, 1984) in the landscape. Other rock avalanches are numerous (Whitehouse, 1983), and widespread over the Southern Alps of New Zealand, and many appear to be co-seismic. De Mets et al. (1994) used the model NUVEL-1A to characterize the motion of the Alpine fault: 37 mm/year at an azimuth of 071° for the strike-slip and a dip-slip of 10 mm/year normal to the strike direction. Although linear when seen from the sky, the detailed morphology of the fault is more complex, called en échelon (Norris and Cooper, 1997). It exhibits metamorphosed schists (mylonite series) in its hanging wall (McCahon, 2007; Korup, 2004). Earthquakes on the Alpine fault have a recurrence time of c. 200-300 years and a probability of occurrence within 100 years of 88% (Rhoades and Van Dissen, 2002). Thought to have been triggered by the AD1220 event (determined by dendrochronology), the Wanganui-Wilberg rock avalanche deposit represents only 20% of its original volume, which was c. 33 million cubic metres. The deposit probably dammed the Wanganui River and, as a result, created a small and short-lived lake upstream. The next earthquake capable of triggering such events is likely to occur fairly soon (Yetton, 1998). Knowledge of historic catastrophic events such as the Wanganui-Wilberg rock avalanche is of crucial importance in the development of future hazard and management plans.

The Alpine Fault is the major structure of the Pacific-Australian plate boundary through New Zealand�s South Island. During dextral reverse fault slip, a <5 million year old, ~1 km thick mylonite zone has been exhumed in the hanging-wall, providing unique exposure of material deformed to very high strains at deep crustal levels under boundary conditions constrained by present-day plate motions. The purpose of this study was to investigate the fault zone rheology and mechanisms of strain localisation, to obtain further information about how the structural development of this shear zone relates to the kinematic and thermal boundary constraints, and to investigate the mechanisms by which the viscously deforming mylonite zone is linked to the brittle structure, that fails episodically causing large earthquakes. This study has focussed on the central section of the fault from Harihari to Fox Glacier. In this area, mylonites derived from a quartzofeldspathic Alpine Schist protolith are most common, but slivers of Western Province-derived footwall material, which can be differentiated using mineralogy and bulk rock geochemistry, were also incorporated into the fault zone. These footwall-derived mylonites are increasingly common towards the north. At amphibolite-facies conditions mylonitic deformation was localised to the mylonite and ultramylonite subzones of the schist-derived mylonites. Most deformation was accommodated by dislocation creep of quartz, which developed strong Y-maximum crystallographic preferred orientation (CPO) patterns by prism (a) dominant slip. Formation of this highly-oriented fabric would have led to significant geometric softening and enhanced strain localisation. During this high strain deformation, pre-existing Alpine Schist fabrics in polyphase rocks were reconstituted to relatively well-mixed, finer-grained aggregates. As a result of this fabric homogenisation, strong syn-mylonitic object lineations were not formed. Strain models show that weak lineations trending towards ~090� and kinematic directions indicated by asymmetric fabrics and CPO pattern symmetry could have formed during pure shear stretches up-dip of the fault of ~3.5, coupled with simple shear strains [greater than or equal to]30. The preferred estimate of simple:pure shear strain gives a kinematc vorticity number, W[k] [greater than or equal to]̲ 0.9997. Rapid exhumation due to fault slip resulted in advection of crustal isotherms. New thermobarometric and fluid inclusion analyses from fault zone materials allow the thermal gradient along an uplift path in the fault rocks to be more precisely defined than previously. Fluid inclusion data indicate temperatures of 325+̲15�C were experienced at depths of ~45 km, so that a high thermal gradient of ~75�C km⁻� is indicated in the near-surface. This gradient must fall off to [ less than approximately]l0�C km⁻� below the brittle-viscous transition since feldspar thermobarometry, Ti-inbiotite thermometry and the absence of prism(c)-slip quartz CPO fabrics indicate deformation temperatures did not exceed ~ 650�C at [greater than or equal to] 7.0-8.5�1.5 kbar, ie. 26-33 km depth. During exhumation, the strongly oriented quartzite fabrics were not favourably oriented for activation of the lower temperature basal(a) slip system, which should have dominated at depths [less than approximately]20 km. Quartz continued to deform by crystal-plastic mechanisms to shallow levels. However, pure dislocation creep of quartz was replaced by a frictional-viscous deformation mechanism of sliding on weak mica basal planes coupled with dislocation creep of quartz. Such frictional-viscous flow is particularly favoured during high-strain rate events as might be expected during rupture of the overlying brittle fault zone. Maximum flow stresses supported by this mechanism are ~65 Mpa, similar to those indicated by recrystallised grain size paleopiezometry of quartz (D>25[mu]m, indicating [Delta][sigma][max] ~55 MPa for most mylonites). It is likely that the preferentially oriented prism (a) slip system was activated during these events, so the Y-maximum CPO fabrics were preserved. Simple numerical models show that activation of this slip system is favoured over the basal (a) system, which has a lower critical resolved shear stress (CRSS) at low temperatures, for aggregates with strong Y-maximum orientations. Absence of pervasive crystal-plastic deformation of micas and feldspars during activation of this mechanism also resulted in preservation of mineral chemistries from the highest grades of mylonitic deformation (ie. amphibolite-facies). Retrograde, epidote-amphibolite to greenschist-facies mineral assemblages were pervasively developed in ultramylonites and cataclasites immediately adjacent to the fault core and in footwall-derived mylonites, perhaps during episodic transfer of this material into and subsequently out of the cooler footwall block. In the more distal protomylonites, retrograde assemblages were locally developed along shear bands that also accommodated most of the mylonitic deformation in these rocks. Ti-in-biotite thermometry suggests biotite in these shear bands equilibrated down to ~500+̲50�C, suggesting crystal-plastic deformation of this mineral continued to these temperatures. Crossed-girdle quartz CPO fabrics were formed in these protomylonites by basal (a) dominant slip, indicating a strongly oriented fabric had not previously formed at depth due to the relatively small strains, and that dislocation creep of quartz continued at depths [less than or equal to]20 km. Lineation orientations, CPO fabric symmetry and shear-band fabrics in these protomylonites are consistent with a smaller simple:pure shear strain ratio than that observed closer to the fault core (W[k] [greater than approximately] 0.98), but require a similar total pure shear component. Furthermore, they indicate an increase in the simple shear component with time, consistent with incorporation of new hanging-wall material into the fault zone. Pre-existing lineations were only slowly rotated into coincidence with the mylonitic simple shear direction in the shear bands since they lay close to the simple shear plane, and inherited orientations were not destroyed until large finite strains (<100) were achieved. As the fault rocks were exhumed through the brittle-viscous transition, they experienced localised brittle shear failures. These small-scale seismic events formed friction melts (ie. pseudotachylytes). The volume of pseudotachylyte produced is related to host rock mineralogy (more melt in host rocks containing hydrated minerals), and fabric (more melt in isotropic host rocks). Frictional melting also occurred within cataclastic hosts, indicating the cataclasites around the principal slip surface of the Alpine Fault were produced by multiple episodes of discrete shear rather than distributed cataclastic flow. Pseudotachylytes were also formed in the presence of fluids, suggesting relatively high fault gouge permeabilities were transiently attained, probably during large earthquakes. Frictional melting contributed to formation of phyllosilicate-rich fault gouges, weakening the brittle structure and promoting slip localisation. The location of faulting and pseudotachylyte formation, and the strength of the fault in the brittle regime were strongly influenced by cyclic hydrothermal cementation processes. A thermomechanical model of the central Alpine Fault zone has been defined using the results of this study. The mylonites represent a localised zone of high simple shear strain, embedded in a crustal block that underwent bulk pure shear. The boundaries of the simple shear zone moved into the surrounding material with time. This means that the exhumed sequence does not represent a simple 'time slice' illustrating progressive fault rock development during increasing simple shear strains. The deformation history of the mylonites at deep crustal P-T conditions had a profound influence on subsequent deformation mechanisms and fabric development during exhumation.

Two examples of Pacific rim plate boundary deformation are presented. In the first part of the thesis crustal models are derived for the northwestern part of the Vizcaino block in California using marine seismic and gravity data collected by the Mendocino Triple Junction Seismic Experiment. A northwest-southeast trending kink in the Moho is imaged and interpreted to have formed under compression by reactivation of preexisting thrust faults in the paleoaccretionary prism at the seaward margin of the Vizcaino block. The study suggests that the deformation resulted from mainly north-south compression between the Pacific-Juan de Fuca plates across the Mendocino transform fault and predates late Pliocene Pacific-North America plate convergence. In the second part, 195 earthquakes recorded during the duration of the Southern Alps Passive Seismic Experiment (SAPSE) are analysed. Precise earthquake locations and focal mechanisms provide unprecedented detail of the seismotectonics in the central South Island. The short term (6 month) SAPSE seismicity is compared with long term (8 years) seismicity recorded by the New Zealand National Seismic network and the Lake Pukaki network. The seismicity rate of the Alpine fault is low, but comparable to locked sections of the San Andreas fault, with large earthquakes expected. Changes of the depth of the seismogenic zone, generally uniform at about 10-12 km, occur only localised over distances smaller than 30 km, suggesting that thermal perturbations must be of similar scale. This implies that the thermal effects of the uplift of the Southern Alps do not change the seismogenic depth significantly and are not in accordance with most of the present thermal models. Both the Hope and Porters Pass fault zones are seismically active and deformation is accommodated near the fault zones and in the adjacent crust. North of Mt Cook, a triangular shaped region along the Alpine fault is characterised by absence of earthquakes. We interpret this as the result of the plate boundary shift from the Alpine fault to the Hope and Porters Pass fault zones. The study region shows distributed deformation in a 60-100 km wide zone on NNE-SSW trending thrust faults and strike-slip mechanisms on transfer faults. / Graduation date: 2000 / Best scan available for black and white figures.

The Alpine Fault in western South Island ruptures every 300±100 years in large magnitude (7.8 ± 3) earthquakes and presents a major seismic hazard to New Zealand. The Deep Alpine Fault Drilling Project (DFDP) aims to drill, sample, and monitor the Alpine Fault in order to investigate the processes of earthquake genesis, rock deformation, and fault gouge formation for a tectonically active fault late in the seismic cycle. Rapid dextral reverse movements and exhumation rates on the central section of the Alpine Fault at Whataroa Valley make this a geologically favourable setting to drill and sample fault rocks at depth that can be correlated with surface exposures. The suitability of a site for stationing a major drilling operation depends upon practical issues such as the engineering geological characteristics of the proposed site, possible geohazards, and drilling logistics. This thesis presents new engineering geological, geophysical, and geomorphic investigations of the Whataroa Valley for the DFDP-2 drill site in order to provide a framework for proposed future operations. MASW, GPR and basic geotechnical methods such as test pits and face logs were conducted at various locations at the site to gain geotechnical properties and attempt to find depth to bedrock. Results showed bedrock is at least 25m deep as it was not seen in any of the GPR surveys. Correlation of the MASW and GPR profiles with freshly eroded and face logged outcrops permitted assignment of s-wave velocities to each of the gravels present and confirmation of features seen in the geophysical surveys. Vs30 values gained from the MASW classed the gravels as a soft soil in Site Class D in NZS 1170.5. Expected peak ground accelerations at the study site during an Alpine Fault earthquake are estimated at ≥0.8g. The Whataroa River is actively eroding the southern edge of the investigation area. Comparison of historic aerial photos and newly obtained LiDAR showed the river bank has moved a total of 165 m since 1948, a majority of that occurring in the past decade, 35 m of erosion occurring over a few days during early January 2011. Little correlation between heavy rainfall periods and increased erosion rates suggest changing channel dynamics play a major part in the channel migration. Modelling of the threshold discharges required to overtop the Whataroa terraces results in return periods several orders of magnitude larger than Alpine Fault earthquake recurrence intervals that result in major sediment pulses, implying that inundation from river flooding under current channel conditions is highly unlikely. Debris flows originating from the west valley wall have been identified as a possible hazard to drilling operations. Recent debris flows were easily mapped due to the changes in vegetation, whereas the remnants of historic debris flows were able to be mapped using the LiDAR. Studies of these show that they have a minimal run out distance (<100 m), and can be easily avoided by ensuring the drill site is located outside the proposed debris flow risk zone plus a 50 m buffer that has been added for caution. Current uncertainty of the fault dip and target depth of the hole causes large variation in proposed drill rig locations at the surface. All of the investigations are summarised on a hazard map used to suggest a range of favoured drill sites based on varied angle dips and drilling depths, minimizing flood, erosion and sediment inundation hazards, and specifying access routes.

The Alpine Fault is the major structure of the Pacific-Australian plate boundary through New Zealand�s South Island. During dextral reverse fault slip, a <5 million year old, ~1 km thick mylonite zone has been exhumed in the hanging-wall, providing unique exposure of material deformed to very high strains at deep crustal levels under boundary conditions constrained by present-day plate motions. The purpose of this study was to investigate the fault zone rheology and mechanisms of strain localisation, to obtain further information about how the structural development of this shear zone relates to the kinematic and thermal boundary constraints, and to investigate the mechanisms by which the viscously deforming mylonite zone is linked to the brittle structure, that fails episodically causing large earthquakes. This study has focussed on the central section of the fault from Harihari to Fox Glacier. In this area, mylonites derived from a quartzofeldspathic Alpine Schist protolith are most common, but slivers of Western Province-derived footwall material, which can be differentiated using mineralogy and bulk rock geochemistry, were also incorporated into the fault zone. These footwall-derived mylonites are increasingly common towards the north. At amphibolite-facies conditions mylonitic deformation was localised to the mylonite and ultramylonite subzones of the schist-derived mylonites. Most deformation was accommodated by dislocation creep of quartz, which developed strong Y-maximum crystallographic preferred orientation (CPO) patterns by prism (a) dominant slip. Formation of this highly-oriented fabric would have led to significant geometric softening and enhanced strain localisation. During this high strain deformation, pre-existing Alpine Schist fabrics in polyphase rocks were reconstituted to relatively well-mixed, finer-grained aggregates. As a result of this fabric homogenisation, strong syn-mylonitic object lineations were not formed. Strain models show that weak lineations trending towards ~090� and kinematic directions indicated by asymmetric fabrics and CPO pattern symmetry could have formed during pure shear stretches up-dip of the fault of ~3.5, coupled with simple shear strains [greater than or equal to]30. The preferred estimate of simple:pure shear strain gives a kinematc vorticity number, W[k] [greater than or equal to]̲ 0.9997. Rapid exhumation due to fault slip resulted in advection of crustal isotherms. New thermobarometric and fluid inclusion analyses from fault zone materials allow the thermal gradient along an uplift path in the fault rocks to be more precisely defined than previously. Fluid inclusion data indicate temperatures of 325+̲15�C were experienced at depths of ~45 km, so that a high thermal gradient of ~75�C km⁻� is indicated in the near-surface. This gradient must fall off to [ less than approximately]l0�C km⁻� below the brittle-viscous transition since feldspar thermobarometry, Ti-inbiotite thermometry and the absence of prism(c)-slip quartz CPO fabrics indicate deformation temperatures did not exceed ~ 650�C at [greater than or equal to] 7.0-8.5�1.5 kbar, ie. 26-33 km depth. During exhumation, the strongly oriented quartzite fabrics were not favourably oriented for activation of the lower temperature basal(a) slip system, which should have dominated at depths [less than approximately]20 km. Quartz continued to deform by crystal-plastic mechanisms to shallow levels. However, pure dislocation creep of quartz was replaced by a frictional-viscous deformation mechanism of sliding on weak mica basal planes coupled with dislocation creep of quartz. Such frictional-viscous flow is particularly favoured during high-strain rate events as might be expected during rupture of the overlying brittle fault zone. Maximum flow stresses supported by this mechanism are ~65 Mpa, similar to those indicated by recrystallised grain size paleopiezometry of quartz (D>25[mu]m, indicating [Delta][sigma][max] ~55 MPa for most mylonites). It is likely that the preferentially oriented prism (a) slip system was activated during these events, so the Y-maximum CPO fabrics were preserved. Simple numerical models show that activation of this slip system is favoured over the basal (a) system, which has a lower critical resolved shear stress (CRSS) at low temperatures, for aggregates with strong Y-maximum orientations. Absence of pervasive crystal-plastic deformation of micas and feldspars during activation of this mechanism also resulted in preservation of mineral chemistries from the highest grades of mylonitic deformation (ie. amphibolite-facies). Retrograde, epidote-amphibolite to greenschist-facies mineral assemblages were pervasively developed in ultramylonites and cataclasites immediately adjacent to the fault core and in footwall-derived mylonites, perhaps during episodic transfer of this material into and subsequently out of the cooler footwall block. In the more distal protomylonites, retrograde assemblages were locally developed along shear bands that also accommodated most of the mylonitic deformation in these rocks. Ti-in-biotite thermometry suggests biotite in these shear bands equilibrated down to ~500+̲50�C, suggesting crystal-plastic deformation of this mineral continued to these temperatures. Crossed-girdle quartz CPO fabrics were formed in these protomylonites by basal (a) dominant slip, indicating a strongly oriented fabric had not previously formed at depth due to the relatively small strains, and that dislocation creep of quartz continued at depths [less than or equal to]20 km. Lineation orientations, CPO fabric symmetry and shear-band fabrics in these protomylonites are consistent with a smaller simple:pure shear strain ratio than that observed closer to the fault core (W[k] [greater than approximately] 0.98), but require a similar total pure shear component. Furthermore, they indicate an increase in the simple shear component with time, consistent with incorporation of new hanging-wall material into the fault zone. Pre-existing lineations were only slowly rotated into coincidence with the mylonitic simple shear direction in the shear bands since they lay close to the simple shear plane, and inherited orientations were not destroyed until large finite strains (<100) were achieved. As the fault rocks were exhumed through the brittle-viscous transition, they experienced localised brittle shear failures. These small-scale seismic events formed friction melts (ie. pseudotachylytes). The volume of pseudotachylyte produced is related to host rock mineralogy (more melt in host rocks containing hydrated minerals), and fabric (more melt in isotropic host rocks). Frictional melting also occurred within cataclastic hosts, indicating the cataclasites around the principal slip surface of the Alpine Fault were produced by multiple episodes of discrete shear rather than distributed cataclastic flow. Pseudotachylytes were also formed in the presence of fluids, suggesting relatively high fault gouge permeabilities were transiently attained, probably during large earthquakes. Frictional melting contributed to formation of phyllosilicate-rich fault gouges, weakening the brittle structure and promoting slip localisation. The location of faulting and pseudotachylyte formation, and the strength of the fault in the brittle regime were strongly influenced by cyclic hydrothermal cementation processes. A thermomechanical model of the central Alpine Fault zone has been defined using the results of this study. The mylonites represent a localised zone of high simple shear strain, embedded in a crustal block that underwent bulk pure shear. The boundaries of the simple shear zone moved into the surrounding material with time. This means that the exhumed sequence does not represent a simple 'time slice' illustrating progressive fault rock development during increasing simple shear strains. The deformation history of the mylonites at deep crustal P-T conditions had a profound influence on subsequent deformation mechanisms and fabric development during exhumation.

The Wanganui-Wilberg landslide lies between Hokitika and Franz Josef townships, at the entrance of Harihari, on the true left bank of the Wanganui River, by State Highway 6. This apparently co-seismic landslide belongs to the class of events called rock avalanches - powerful destructive agents (Keefer, 1984) in the landscape. Other rock avalanches are numerous (Whitehouse, 1983), and widespread over the Southern Alps of New Zealand, and many appear to be co-seismic. De Mets et al. (1994) used the model NUVEL-1A to characterize the motion of the Alpine fault: 37 mm/year at an azimuth of 071° for the strike-slip and a dip-slip of 10 mm/year normal to the strike direction. Although linear when seen from the sky, the detailed morphology of the fault is more complex, called en échelon (Norris and Cooper, 1997). It exhibits metamorphosed schists (mylonite series) in its hanging wall (McCahon, 2007; Korup, 2004). Earthquakes on the Alpine fault have a recurrence time of c. 200-300 years and a probability of occurrence within 100 years of 88% (Rhoades and Van Dissen, 2002). Thought to have been triggered by the AD1220 event (determined by dendrochronology), the Wanganui-Wilberg rock avalanche deposit represents only 20% of its original volume, which was c. 33 million cubic metres. The deposit probably dammed the Wanganui River and, as a result, created a small and short-lived lake upstream. The next earthquake capable of triggering such events is likely to occur fairly soon (Yetton, 1998). Knowledge of historic catastrophic events such as the Wanganui-Wilberg rock avalanche is of crucial importance in the development of future hazard and management plans.

<p dir="ltr">The Alpine Fault, located in the South Island, New Zealand, is a subject of intense geological study due to its potential to trigger large earthquakes. It encompasses a complex system with the interplay of mechanics, thermodynamics, and fluid. Gaining insights into these systems not only enhances our understanding of the fault but also holds the potential to guide risk mitigation efforts.</p><p dir="ltr">The damage extent and fracture networks within the metamorphic rock mass adjacent to the fault can be effectively characterized by seismic anisotropy, an elastic property of rock, where seismic waves travel at different speeds with variation directions. This thesis presents a comprehensive exploration of seismic anisotropy in the hanging wall immediately adjacent to the principal slip zone of the Alpine Fault in New Zealand. Leveraging the borehole seismic data from a unique scientific drilling project and advanced numerical modeling techniques, the ultimate goal is to invert and parameterize the bulk seismic anisotropy.</p><p dir="ltr">Motivated by these challenges, the thesis undertakes several key initiatives: The first effort focuses on gaining a comprehensive understanding of an innovative method for seismic measurement: Distributed Acoustic Sensing (DAS) – examining its operational principles, factors influencing observed wavelets, and how it contrasts with traditional point sensors for accurate interpretation. Subsequently, the research introduces the implementation of an open-source seismic wave solver designed for modeling elastic wave propagation in complicated anisotropic media. This solver is further optimized for computational efficiency with its performance rigorously benchmarked.</p><p dir="ltr">With this preparedness, the inversion is further facilitated by high-performance computing (HPC) and a deep-learning algorithm specifically designed for automatically picking transit times. The inverted bulk elastic constants, compared to the intact rock, reveal 28% to 35% reductions in qP-wave velocity, characterizing the damage due to mesoscale fracture. Further analysis sheds light on the existence of orthogonal fracture sets and an intricate geometrical arrangement that agree with the previous borehole image log. This represents an advancement in our ability to characterize and understand the geologic processes with seismic anisotropy.</p>

The Alpine Fault is a major plate boundary structure, which accommodates up to 50-80% of the total plate boundary motion across the South Island of New Zealand. The fault has not ruptured historically although limited off-fault shaking records and on-fault dating suggest large to great (~ Mw 8) earthquakes (every ~100-480 years; most recently in 1717), making it potentially one of the largest onshore sources of seismic hazard in New Zealand. The central section of the Alpine Fault, which bounds the highest elevations in the Southern Alps, is one of the most poorly characterised sections along the fault. On-fault earthquake timing in addition to the amount of dextral slip during major earthquakes was unknown along a 200-km-long section of the central Alpine Fault, while the amount of co-seismic hanging wall uplift was poorly known, prior to the present work. In this thesis I address these knowledge gaps through a combination of light detection and ranging (lidar), field, and stratigraphic mapping along with sample dating to constrain earthquake timing, style of faulting, and hanging wall rock uplift rates. Using lidar data coupled with field mapping I delineated the main trace of the Alpine Fault at Gaunt Creek as a north-striking fault scarp that was excavated and logged; this is part of a 2-km-wide restraining bend dominated by low-angle thrust faulting and without the clear strike-slip displacements that are present nearby (<5 km distant along strike in both directions). Where exposed in this scarp, the fault-zone is characterized by a distinct 5-50 cm thick clay fault-gouge layer juxtaposing hanging wall bedrock (mylonites and cataclasites) over unconsolidated late-Holocene footwall colluvium. An unfaulted peat at the base of the scarp is buried by post-most recent event (MRE) alluvium and yields a radiocarbon age of A.D. 1710–1930, consistent with sparse on-fault data, validating earlier off-fault records that suggest a 1717 MRE with a moment magnitude of Mw 8.1 ± 0.1, based on the 380-km-long surface rupture. Lidar and field mapping also enabled the identification and measurement of short (<30 m), previously unrecognized dextral offsets along the central section of the Alpine Fault. Single-event displacements of 7.5 ± 1 m for the 1717 earthquake and cumulative displacements of 12.9 ± 2 m and 22 ± 2.7 m for earlier ruptures can be binned into 7.1 ± 2.1 m increments of repeated dextral (uniform) slip along the central Alpine Fault. A comparison of these offsets with the local paleoseismic record and known plate kinematics suggests that the central Alpine Fault earthquakes in the past 1.1 ka may have: (i) bimodal character, with major surface ruptures (!Mw 7.9) every 270 ± 70 years (e.g. the 1717 event) and with moderate to large earthquakes (!Mw 7) occurring between these ruptures (e.g. the 1600 event); or (ii) that some shaking data may record earthquakes on other faults. If (i) is true, the uniform slip model (USM) perhaps best represents central Alpine Fault earthquake recurrence, and argues against the applicability of the characteristic earthquake model (CEM) there. Alternatively, if (ii) is true, perhaps the fault is “characteristic” and some shaking records proximal to plate boundary faults do not necessarily reflect plate-boundary surface ruptures. Paleoseismic and slip data suggest that (i) is the most plausible interpretation, which has implications for the understanding of major plate-boundary faults worldwide. Field mapping, geological characterisation, geophysical mapping, and optically stimulated luminescence (OSL) dating of on-fault hanging wall sediments were used to better constrain the geometry and kinematics of Holocene deformation along the rangefront of the Southern Alps at the Alpine Fault near the Whataroa River. The fault here is dextral-reverse, although primarily strike-slip with clear fault traces cutting across older surfaces of varying elevations. Deformational bulges are observed along these traces that are likely thrust-bounded. A terrace of Whataroa River sediments was found on the hanging wall of the Alpine Fault approximately ~ 55-75 m (when considering uncertainties) above the floodplain of the Whataroa River. OSL ages for a hanging wall sediments of 10.9 ± 1.0 ka for the aforementioned terrace, 2.8 ± 0.3 ka for Whataroa River terrace deposits in a deformational bulge, and 11.1 ± 1.2 ka for a rangefront derived fan indicate Holocene aggradation along the rangefront and hanging wall uplift rates of 6.0 ± 1.1 mm/yr. The sub-horizontal, laterally continuous, and planar-bedded Whataroa-sourced terrace deposits suggest that the adjacent bounding faults are steeply-dipping faults without geometries in the shallow subsurface that would tend to cause sedimentary bed rotation and tilting. Using data from the approximately 100-m deep pilot DFDP boreholes together with lidar and field mapping, I present a review of the Quaternary geology, geomorphology, and structure of the fault at Gaunt Creek, and estimate new minimum Late-Pleistocene hanging wall rock uplift rates of 5.7 ± 1.0 mm/yr to 6.3 ± 1.1 mm/yr (without considering local erosion) that suggest that the Southern Alps are in a dynamic steady state here. GPS-derived “interseismic” vertical uplift rates are < 1 mm/yr at the Alpine Fault, so the majority of rock uplift at the rangefront happens during episodic major earthquakes, confirming with on-fault data that slip occurs coseismically. Notably the uplift rates from both Mint and Gaunt Creek are consistent between the two sites although the primary style of faulting at the surface is different between the two sites, suggesting consistent coseisimc uplift of the Southern Alps rangefront along the Alpine Fault in major earthquakes. This thesis collected new on-fault datasets that confirm earlier inferences of plate-boundary fault behaviour. This study of the high-uplift central section of the Alpine Fault provides the first on-fault evidence for the MRE (i.e. 1717) and repeated of dextral slip during the MRE and previous events as well as new hanging wall uplift data which suggests that the majority of rangefront uplift occurs in earthquakes along the Alpine Fault. Because the fault has not ruptured for ~300 years, it poses a significant seismic hazard to southern New Zealand.