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Accommodating ~9 m of dextral slip on the Kekerengu Fault through ground deformation during the Mw 7.8 Kaikōura Earthquake, November 2016
<p>The Mw 7.8 Kaikōura earthquake of November 14th 2016 provided unprecedented opportunities to understand how the ground deforms during large magnitude strike-slip earthquakes. The re-excavation and extension of both halves of a displaced paleoseismic trench following this earthquake provided an opportunity to test, refine, and extend back in time the known late Holocene chronology of surface rupturing earthquakes on the Kekerengu Fault. As part of this thesis, 28 organic-bearing samples were collected from a suite of new paleoseismic trenches. Six of these samples were added to the preferred age model from Little et al. (2018); this updated age model is now based on 16 total samples. Including the 2016 earthquake, six surface rupturing earthquakes since ~2000 cal. B.P. are now identified and dated on the Kekerengu Fault. Based on the latest five events (E0 to E4), this analysis yields an updated mean recurrence interval estimate for the Kekerengu Fault of 375 ± 32 yrs (1σ) since ~1650 cal. B.P. The older, sixth event (E5) is not included in the preferred model, as it may not have directly preceded E4; however, if this additional event is incorporated into an alternative age model that embraces all six identified events, the mean recurrence interval estimate (considered a maximum) calculated is 433 ± 22 yrs (1σ) since ~2000 cal. B.P. Comparison of structures on an identical trench wall logged both before and after the 2016 earthquake, and analysis of pre- and post-earthquake high resolution imagery and Digital Surface Models (DSMs), has allowed the quantification of where and how ~9 m of dextral-oblique slip was accommodated at this site during the earthquake. In addition to this, I analyse the coseismic structure of the adjoining segment of the 2016 ground rupture using detailed post-earthquake aerial orthophotography, to further investigate how geological surface structures (bulged-up moletrack structures) accommodated slip in the rupture zone. These combined analyses allowed me to identify two primary deformation mechanisms that accommodated the large coseismic slip of this earthquake, and the incremental effect of that slip on the structural geology of the rupture zone. These processes include: a) discrete slip along strike-slip faults that bound a narrow, highly deformed inner rupture zone; and b), distributed deformation within this inner rupture zone. The latter includes coseismic clockwise rotation of cohesive rafts of turf, soil and near-surface clay-rich sediment. During this process, these “turf rafts” detach from the underlying soil at a mean depth of ~0.7 m, shorten by ~2.5 m (in addition to shortening introduced by any local contractional heave), bulge upwards by < 1 m, and rotate clockwise by ~19° - while also separating from one another along fissures bounded by former (now rotated) synthetic Riedel faults. This rotational deformation accommodated ~3 m of dextral strike-slip (of a total of ~9 m), after which this rotation apparently ceased, regardless of the total slip or the local kinematics (degree of transpression) at any site. The remaining slip was transferred onto later forming, throughgoing faults as discrete displacement. Analysis of the morphology and amplitude of these moletracks suggests that an increase in the degree of transpression (value of contractional heave) at a site increases the magnitude of shortening and the finite longitudinal strain absorbed by the rotated turf rafts, but does not necessarily contribute to an increase in height (generally 0.33-0.53 m on all parts of the fault). Rather, the comparison of these moletracks with those described by other authors suggests that a more controlling factor on their height is the clay content and cohesion of material deformed into the moletracks. Finally, comparison of the before and after cross-sections of the displaced paleoseismic trench has provided, for the first time, insight into how large magnitude strike-slip ruptures are expressed in the fault-orthogonal view typical of paleoseismic trenches. Although this rupture involved ~9 m of dextral strike-slip, the cross-sectional view of the re-excavated trenches was dominated by the much lesser component of fault-perpendicular contractional heave (~1.3 m) that occurred in 2016, which did not occur in previous paleoearthquakes at the same site (these were, by contrast, transtensional). This heave was expressed as up to ~2 m of fault-transverse shortening in the inner rupture zone of the trenches, while the ~9 m of strike-slip only created cm-scale offsets across faults. Previous earthquakes at the site were expressed as cm-dm scale, mostly normal dip-separations of sub-horizontal stratigraphic units across faults, suggesting that a change in local kinematics (of ~8°) must have occurred in 2016. Such a small kinematic change may drastically impact the overall ground expression of strike-slip earthquakes - producing also complicated structures including overprinting fault strands in the rupture zone (to a few metres depth). This information poses challenges for structural geologists and paleoseismologists when interpreting (the significance of) structures in future trench walls.</p>
<p>The Mw 7.8 Kaikōura earthquake of November 14th 2016 provided unprecedented opportunities to understand how the ground deforms during large magnitude strike-slip earthquakes. The re-excavation and extension of both halves of a displaced paleoseismic trench following this earthquake provided an opportunity to test, refine, and extend back in time the known late Holocene chronology of surface rupturing earthquakes on the Kekerengu Fault. As part of this thesis, 28 organic-bearing samples were collected from a suite of new paleoseismic trenches. Six of these samples were added to the preferred age model from Little et al. (2018); this updated age model is now based on 16 total samples. Including the 2016 earthquake, six surface rupturing earthquakes since ~2000 cal. B.P. are now identified and dated on the Kekerengu Fault. Based on the latest five events (E0 to E4), this analysis yields an updated mean recurrence interval estimate for the Kekerengu Fault of 375 ± 32 yrs (1σ) since ~1650 cal. B.P. The older, sixth event (E5) is not included in the preferred model, as it may not have directly preceded E4; however, if this additional event is incorporated into an alternative age model that embraces all six identified events, the mean recurrence interval estimate (considered a maximum) calculated is 433 ± 22 yrs (1σ) since ~2000 cal. B.P. Comparison of structures on an identical trench wall logged both before and after the 2016 earthquake, and analysis of pre- and post-earthquake high resolution imagery and Digital Surface Models (DSMs), has allowed the quantification of where and how ~9 m of dextral-oblique slip was accommodated at this site during the earthquake. In addition to this, I analyse the coseismic structure of the adjoining segment of the 2016 ground rupture using detailed post-earthquake aerial orthophotography, to further investigate how geological surface structures (bulged-up moletrack structures) accommodated slip in the rupture zone. These combined analyses allowed me to identify two primary deformation mechanisms that accommodated the large coseismic slip of this earthquake, and the incremental effect of that slip on the structural geology of the rupture zone. These processes include: a) discrete slip along strike-slip faults that bound a narrow, highly deformed inner rupture zone; and b), distributed deformation within this inner rupture zone. The latter includes coseismic clockwise rotation of cohesive rafts of turf, soil and near-surface clay-rich sediment. During this process, these “turf rafts” detach from the underlying soil at a mean depth of ~0.7 m, shorten by ~2.5 m (in addition to shortening introduced by any local contractional heave), bulge upwards by < 1 m, and rotate clockwise by ~19° - while also separating from one another along fissures bounded by former (now rotated) synthetic Riedel faults. This rotational deformation accommodated ~3 m of dextral strike-slip (of a total of ~9 m), after which this rotation apparently ceased, regardless of the total slip or the local kinematics (degree of transpression) at any site. The remaining slip was transferred onto later forming, throughgoing faults as discrete displacement. Analysis of the morphology and amplitude of these moletracks suggests that an increase in the degree of transpression (value of contractional heave) at a site increases the magnitude of shortening and the finite longitudinal strain absorbed by the rotated turf rafts, but does not necessarily contribute to an increase in height (generally 0.33-0.53 m on all parts of the fault). Rather, the comparison of these moletracks with those described by other authors suggests that a more controlling factor on their height is the clay content and cohesion of material deformed into the moletracks. Finally, comparison of the before and after cross-sections of the displaced paleoseismic trench has provided, for the first time, insight into how large magnitude strike-slip ruptures are expressed in the fault-orthogonal view typical of paleoseismic trenches. Although this rupture involved ~9 m of dextral strike-slip, the cross-sectional view of the re-excavated trenches was dominated by the much lesser component of fault-perpendicular contractional heave (~1.3 m) that occurred in 2016, which did not occur in previous paleoearthquakes at the same site (these were, by contrast, transtensional). This heave was expressed as up to ~2 m of fault-transverse shortening in the inner rupture zone of the trenches, while the ~9 m of strike-slip only created cm-scale offsets across faults. Previous earthquakes at the site were expressed as cm-dm scale, mostly normal dip-separations of sub-horizontal stratigraphic units across faults, suggesting that a change in local kinematics (of ~8°) must have occurred in 2016. Such a small kinematic change may drastically impact the overall ground expression of strike-slip earthquakes - producing also complicated structures including overprinting fault strands in the rupture zone (to a few metres depth). This information poses challenges for structural geologists and paleoseismologists when interpreting (the significance of) structures in future trench walls.</p>
<p>A comprehensive traffic monitoring system can assist authorities in identifying parts of a road transportation network that exhibit poor performance. In addition to monitoring, it is essential to develop a localized and efficient analytical transportation model that reflects various network scenarios and conditions. A comprehensive transportation model must consider various components such as vehicles and their different mechanical characteristics, human and their diverse behaviours, urban layouts and structures, and communication and transportation infrastructure and their limitations. Development of such a system requires a bringing together of ideas, tools, and techniques from multiple overlapping disciplines such as traffic and computer engineers, statistics, urban planning, and behavioural modelling. In addition to modelling of the urban traffic for a typical day, development of a large-scale emergency evacuation modelling is a critical task for an urban area as this assists traffic operation teams and local authorities to identify the limitations of traffic infrastructure during an evacuation process through examining various parameters such as evacuation time. In an evacuation, there may be severe and unpredictable damage to the infrastructure of a city such as the loss of power, telecommunications and transportation links. Traffic modelling of a large-scale evacuation is more challenging than modelling the traffic for a typical day as historical data is usually available for typical days, whereas each disaster and evacuation are typically one-off or rare events. Damage due to a disaster, combined with a sudden increase of demand due to the evacuation of people will likely result in increased pressure on the remaining, potentially fragmented, infrastructure. The lessons learnt from evacuation modelling can assist traffic operation teams and local authorities to provide safer and more efficient planning. The development of pervasive personal digital devices such as phones, watches, and headphones which can be interconnected with technologies such as Bluetooth, has led to a disruptive change in the ways in which local governments can monitor traffic flows within their cities. Moreover, modern vehicles and navigation systems can interconnect to the personal devices of drivers and passengers primarily via Bluetooth technologies. By continuously monitoring such devices when they are discoverable and in range, traffic patterns can be estimated based on, not only the volume of detection, but also other characteristics of the devices that can be used to give more refined estimates of the real underlying traffic flows. This thesis examines Bluetooth traffic data collected from Bluetooth Traffic Monitoring Systems (BTMS) for modelling and monitoring the urban traffic. BTMS can monitor and track individual detected vehicles through a city. Installation, processing, data transmission, and maintenance of BTMS are easier, quicker and cheaper than existing standard monitoring systems such as CCTV cameras and inductive loops. Inductive loops are typically point-wise traffic monitoring systems that are installed in the roads and can measure the traffic flow. However, the use of BTMS devices presents several challenges: not every vehicle has a detectable device, some have many, and there are devices carried by pedestrians and non-motor vehicles as well as stationary devices. This thesis enumerates and investigates these challenges through statistical modelling, various protocols for cleaning and data preparation, dynamic estimation of the detection rate, and simulation through the case study of the city of Wellington, New Zealand. The city of Wellington experienced damage from the 2016 Kaikoura earthquake (a magnitude 7.8 earthquake), which led to road closures and other infrastructure damage. As part of modelling, performance evaluation, and identifying impacted routes by the 2016 Kaikoura earthquake, this thesis analyses three weeks of BTMS data from the periods before and after the earthquake. Furthermore, this thesis proposes a multi-disciplinary dynamic traffic modelling (TFDA2M) framework and evaluates the performance of TFDA2M on various large-scale evacuation scenarios. These scenarios cover a wide range of real-world use cases which may occur during a disaster such as power failure, an abrupt increase in demand, and damage to the main transportation infrastructure. The findings of this thesis highlight an immediate need for preparations of a large-scale evacuation planning for Wellington to mitigate the consequences of a large-scale evacuation due to a future disaster. Moreover, TFDA2M can assist traffic operation managers and authorities in making smarter decisions (both quantitative and spatially) through the simulation process. Since TFDA2M has a flexible schema, it can be set to monitor, assess, and manage the traffic flow on a daily basis and disaster occasions.</p>
<p>A comprehensive traffic monitoring system can assist authorities in identifying parts of a road transportation network that exhibit poor performance. In addition to monitoring, it is essential to develop a localized and efficient analytical transportation model that reflects various network scenarios and conditions. A comprehensive transportation model must consider various components such as vehicles and their different mechanical characteristics, human and their diverse behaviours, urban layouts and structures, and communication and transportation infrastructure and their limitations. Development of such a system requires a bringing together of ideas, tools, and techniques from multiple overlapping disciplines such as traffic and computer engineers, statistics, urban planning, and behavioural modelling. In addition to modelling of the urban traffic for a typical day, development of a large-scale emergency evacuation modelling is a critical task for an urban area as this assists traffic operation teams and local authorities to identify the limitations of traffic infrastructure during an evacuation process through examining various parameters such as evacuation time. In an evacuation, there may be severe and unpredictable damage to the infrastructure of a city such as the loss of power, telecommunications and transportation links. Traffic modelling of a large-scale evacuation is more challenging than modelling the traffic for a typical day as historical data is usually available for typical days, whereas each disaster and evacuation are typically one-off or rare events. Damage due to a disaster, combined with a sudden increase of demand due to the evacuation of people will likely result in increased pressure on the remaining, potentially fragmented, infrastructure. The lessons learnt from evacuation modelling can assist traffic operation teams and local authorities to provide safer and more efficient planning. The development of pervasive personal digital devices such as phones, watches, and headphones which can be interconnected with technologies such as Bluetooth, has led to a disruptive change in the ways in which local governments can monitor traffic flows within their cities. Moreover, modern vehicles and navigation systems can interconnect to the personal devices of drivers and passengers primarily via Bluetooth technologies. By continuously monitoring such devices when they are discoverable and in range, traffic patterns can be estimated based on, not only the volume of detection, but also other characteristics of the devices that can be used to give more refined estimates of the real underlying traffic flows. This thesis examines Bluetooth traffic data collected from Bluetooth Traffic Monitoring Systems (BTMS) for modelling and monitoring the urban traffic. BTMS can monitor and track individual detected vehicles through a city. Installation, processing, data transmission, and maintenance of BTMS are easier, quicker and cheaper than existing standard monitoring systems such as CCTV cameras and inductive loops. Inductive loops are typically point-wise traffic monitoring systems that are installed in the roads and can measure the traffic flow. However, the use of BTMS devices presents several challenges: not every vehicle has a detectable device, some have many, and there are devices carried by pedestrians and non-motor vehicles as well as stationary devices. This thesis enumerates and investigates these challenges through statistical modelling, various protocols for cleaning and data preparation, dynamic estimation of the detection rate, and simulation through the case study of the city of Wellington, New Zealand. The city of Wellington experienced damage from the 2016 Kaikoura earthquake (a magnitude 7.8 earthquake), which led to road closures and other infrastructure damage. As part of modelling, performance evaluation, and identifying impacted routes by the 2016 Kaikoura earthquake, this thesis analyses three weeks of BTMS data from the periods before and after the earthquake. Furthermore, this thesis proposes a multi-disciplinary dynamic traffic modelling (TFDA2M) framework and evaluates the performance of TFDA2M on various large-scale evacuation scenarios. These scenarios cover a wide range of real-world use cases which may occur during a disaster such as power failure, an abrupt increase in demand, and damage to the main transportation infrastructure. The findings of this thesis highlight an immediate need for preparations of a large-scale evacuation planning for Wellington to mitigate the consequences of a large-scale evacuation due to a future disaster. Moreover, TFDA2M can assist traffic operation managers and authorities in making smarter decisions (both quantitative and spatially) through the simulation process. Since TFDA2M has a flexible schema, it can be set to monitor, assess, and manage the traffic flow on a daily basis and disaster occasions.</p>
<p>Seismic velocity changes before and after large magnitude earthquakes carry information about damage present within the faults in the surrounding region. In this thesis, temporal velocity changes are measured before and after the 2016 Kaikōura earthquake using ambient noise interferometry between 2012 - 2018. This period contains the Mw 7.8 2016 Kaikoura earthquake as well as the 2013 Cook Strait earthquake sequence and a few deep large magnitude earthquakes in 2015 - 2016. Three primary objectives are identified: (1) investigate seismic velocity changes in the Kaikōura region and their connection to the 2016 Kaikōura earthquake to try and determine if there was a change before/after the earthquake, (2) determine how this change varied across the region, and (3) consider if ambient noise can lead to improved detection and understanding of geological hazard. The primary approach used to measure velocity changes in the Kaikōura region involved cross correlating noise recorded by seismic stations across the region. Velocity changes are sought by averaging the best result from multiple onshore station pairs. A secondary approach was also used, in which specific station pairs were averaged to determine if there were more localised velocity changes over more specific regions. This was to determine if the velocity changes observed following the 2016 Kaikōura earthquake occurred over the entire ruptured region. Following the 2016 Kaikōura earthquake a velocity decrease of 0.24±0.02% was observed on the average of the vertical-vertical components for eight stations. The remaining eight cross-component pairs showed a smaller seismic decrease with an average value of 0.22±0.05%. After the decrease following the Kaikōura earthquake, there is a steady velocity increase of 0.13±0.02% over a one-and-a-half-year period. This indicates that prior to the earthquake, seismic velocity was at a steady state until it was perturbed by the Kaikōura earthquake, and seismic velocities rapidly decreased over all stations. Across the region, stations with a longer interstation distance and further away from ruptured faults had a smaller decrease in velocity than station pairs with a smaller interstation distance that were closer to ruptured faults. We interpret the velocity decrease following the Kaikōura earthquake as a result of cracks opening during the earthquake. The velocity increase following the earthquake is indicative of the cracks slowly healing. The Cook Strait earthquake sequence that occurred in 2013 did not cause any velocity changes at the stations used in this thesis. This has been interpreted to be because the changes were too small compared to the background noise or the stations were not recording during the time of the earthquake sequence. Two other decreases were also observed in the region following two deep earthquakes in April 2015 (Mw 6.2, depth = 52km) and February 2016 (Mw 5.7, depth = 48km). Both of these events resulted in a small seismic decrease of 0.1±0.02%. Although these earthquakes were close to seismic stations when they occurred, they were much deeper and had a smaller magnitude than the Kaikōura earthquake so did not cause a large velocity decrease. By understanding what causes velocity changes it is possible to have an improved understanding of the geological hazard in the region.</p>
<p>Conventional logic suggests that businesses should look inwards following natural disasters to ensure employee welfare, and minimise disruptions to operations. However, disasters afford the opportunity to administer corporate philanthropy to affected communities, providing a non- reciprocal gift of money or in-kind services. Philanthropic aid results in commercial benefits for firms, including strengthened financial performance, employee motivation, and reputation. While businesses are increasingly cognisant of their moral responsibilities, few studies examine consumer reactions to corporate philanthropy during a disaster. This research aims to address gaps in extant knowledge, examining the impact of non-reciprocal giving on consumer perceptions of corporate reputation. Further, it seeks to better understand the effect of consumer scepticism and ethnocentrism on evaluations of giving. Three studies were employed to satisfy the research objectives, utilising a between-subjects experimental design. Study 1A manipulates types of corporate responses after the 2016 Kaikōura 7.8-magnitude earthquake (monetary, voluntary time, forgoing giving to recover internally), and measures consumer scepticism. The results demonstrate that monetary and employee time donations have an equivalent positive impact on perceptions of reputation. Forgoing philanthropy is viewed significantly worse, leading to negative evaluations of reputation. Low scepticism consumers assess reputation more positively than those suspicious of the corporate motives for giving. Focusing on employee voluntary time, Study 1B shows that philanthropy administered by companies suffering adverse impacts to operations garner more positive evaluations of reputation than uninterrupted organisations. Study 2 compares domestic (2016 Kaikōura earthquake) and overseas relief (2018 New Caledonia earthquake), measuring the impact of ethnocentrism on preferences for giving. Interestingly, there are no differences in evaluations between high and low ethnocentrism consumers in each geographic context. The overall findings suggest that companies should look beyond their own interests following disasters, administering non-reciprocal giving to generate reputational benefits. Moreover, firms suffering direct adverse impacts are uniquely positioned to generate the strongest reputation gains from giving, fostering moral capital through selfless offerings. Although, sceptical consumer predispositions dilute such benefits, suggesting that businesses cannot simply rely on giving as a panacea to reputational concerns. A natural disaster context also suspends the influence of ethnocentrism on geographic preferences for philanthropy, meaning managers should assess the perceived needs of benefactors when determining where to give.</p>
<p>Conventional logic suggests that businesses should look inwards following natural disasters to ensure employee welfare, and minimise disruptions to operations. However, disasters afford the opportunity to administer corporate philanthropy to affected communities, providing a non- reciprocal gift of money or in-kind services. Philanthropic aid results in commercial benefits for firms, including strengthened financial performance, employee motivation, and reputation. While businesses are increasingly cognisant of their moral responsibilities, few studies examine consumer reactions to corporate philanthropy during a disaster. This research aims to address gaps in extant knowledge, examining the impact of non-reciprocal giving on consumer perceptions of corporate reputation. Further, it seeks to better understand the effect of consumer scepticism and ethnocentrism on evaluations of giving. Three studies were employed to satisfy the research objectives, utilising a between-subjects experimental design. Study 1A manipulates types of corporate responses after the 2016 Kaikōura 7.8-magnitude earthquake (monetary, voluntary time, forgoing giving to recover internally), and measures consumer scepticism. The results demonstrate that monetary and employee time donations have an equivalent positive impact on perceptions of reputation. Forgoing philanthropy is viewed significantly worse, leading to negative evaluations of reputation. Low scepticism consumers assess reputation more positively than those suspicious of the corporate motives for giving. Focusing on employee voluntary time, Study 1B shows that philanthropy administered by companies suffering adverse impacts to operations garner more positive evaluations of reputation than uninterrupted organisations. Study 2 compares domestic (2016 Kaikōura earthquake) and overseas relief (2018 New Caledonia earthquake), measuring the impact of ethnocentrism on preferences for giving. Interestingly, there are no differences in evaluations between high and low ethnocentrism consumers in each geographic context. The overall findings suggest that companies should look beyond their own interests following disasters, administering non-reciprocal giving to generate reputational benefits. Moreover, firms suffering direct adverse impacts are uniquely positioned to generate the strongest reputation gains from giving, fostering moral capital through selfless offerings. Although, sceptical consumer predispositions dilute such benefits, suggesting that businesses cannot simply rely on giving as a panacea to reputational concerns. A natural disaster context also suspends the influence of ethnocentrism on geographic preferences for philanthropy, meaning managers should assess the perceived needs of benefactors when determining where to give.</p>
<p>Seismic velocity changes before and after large magnitude earthquakes carry information about damage present within the faults in the surrounding region. In this thesis, temporal velocity changes are measured before and after the 2016 Kaikōura earthquake using ambient noise interferometry between 2012 - 2018. This period contains the Mw 7.8 2016 Kaikoura earthquake as well as the 2013 Cook Strait earthquake sequence and a few deep large magnitude earthquakes in 2015 - 2016. Three primary objectives are identified: (1) investigate seismic velocity changes in the Kaikōura region and their connection to the 2016 Kaikōura earthquake to try and determine if there was a change before/after the earthquake, (2) determine how this change varied across the region, and (3) consider if ambient noise can lead to improved detection and understanding of geological hazard. The primary approach used to measure velocity changes in the Kaikōura region involved cross correlating noise recorded by seismic stations across the region. Velocity changes are sought by averaging the best result from multiple onshore station pairs. A secondary approach was also used, in which specific station pairs were averaged to determine if there were more localised velocity changes over more specific regions. This was to determine if the velocity changes observed following the 2016 Kaikōura earthquake occurred over the entire ruptured region. Following the 2016 Kaikōura earthquake a velocity decrease of 0.24±0.02% was observed on the average of the vertical-vertical components for eight stations. The remaining eight cross-component pairs showed a smaller seismic decrease with an average value of 0.22±0.05%. After the decrease following the Kaikōura earthquake, there is a steady velocity increase of 0.13±0.02% over a one-and-a-half-year period. This indicates that prior to the earthquake, seismic velocity was at a steady state until it was perturbed by the Kaikōura earthquake, and seismic velocities rapidly decreased over all stations. Across the region, stations with a longer interstation distance and further away from ruptured faults had a smaller decrease in velocity than station pairs with a smaller interstation distance that were closer to ruptured faults. We interpret the velocity decrease following the Kaikōura earthquake as a result of cracks opening during the earthquake. The velocity increase following the earthquake is indicative of the cracks slowly healing. The Cook Strait earthquake sequence that occurred in 2013 did not cause any velocity changes at the stations used in this thesis. This has been interpreted to be because the changes were too small compared to the background noise or the stations were not recording during the time of the earthquake sequence. Two other decreases were also observed in the region following two deep earthquakes in April 2015 (Mw 6.2, depth = 52km) and February 2016 (Mw 5.7, depth = 48km). Both of these events resulted in a small seismic decrease of 0.1±0.02%. Although these earthquakes were close to seismic stations when they occurred, they were much deeper and had a smaller magnitude than the Kaikōura earthquake so did not cause a large velocity decrease. By understanding what causes velocity changes it is possible to have an improved understanding of the geological hazard in the region.</p>
There is a coupling relationship between surrounding rock stress, deformation, and fracture evolution, especially in the microdynamics of the crust caused by mining activities and earthquakes. Previous research has investigated many cases regarding the coseismal water level responses and proposed a method to calculate the aquifer parameters by tidal analysis. However, to date, measurement of the degree of rock damage in the field has not been reported. Quantifying the fracture characteristics is essential for accurate evaluation of rock stability. This study has analyzed the relationship between the seismograms and hydroseismograms in response to the Mw 7.8 Solomon Islands earthquake and the Mw 7.8 Kaikōura earthquake, both events occurring in 2016. The calculated and measured changes in water level in the X10 well were fitted in order to study the relationships among the volumetric strain, the deviatoric strain, and the oscillations in the pore pressure. Then, we further estimate the degree of rock damage and the hydraulic characteristics of the aquifer. The results showed that the values for the rock damage parameter, 0.662 < αD < 0.754, and the Skempton coefficient, −0.100 < A < 0.026, estimated for the Solomon Islands earthquake signified higher damage and dilatancy in the X10 well. Also, the respective values for the parameters, 0.293 < αD < 0.363 and 0.226 < A < 0.251, calculated for the Kaikōura earthquake signified a lower degree of rock damage. It is concluded that the changes in the pore pressure were influenced by both the volumetric strain and the deviatoric strain. The degree of rock damage and the hydraulic properties of the aquifer estimated from the water level fluctuations in the wells which were induced by the seismic waves represent the actual aquifer characteristics.
<p>During the 2016, Mw 7.8 Kaikōura earthquake the Kekerengu fault ruptured the ground surface producing a maximum of ~12 m of net displacement (dextral-slip with minor reverse- slip), one of the largest five co-seismic surface rupture displacements so far observed globally. This thesis presents the first combined onshore to offshore dataset of co-seismic ground-surface and vertical seabed displacements along a near-continuous ~83 km long strike-slip dominated earthquake surface rupture of large slip magnitude. Onshore on the Kekerengu, Jordan Thrust, Upper Kowhai, and Manakau faults, we measured the displacement of 117 cultural and natural markers in the field and using airborne LiDAR data. Offshore on the dextral-reverse Needles fault, multibeam bathymetric and high-resolution seismic reflection data image a throw of the seabed of up to 3.5±0.2 m. Mean net slip on the total ~83 km rupture was 5.5±1 m, this is an unusually large mean slip for the rupture length compared to global strike-slip surface ruptures. Surveyed linear features that extend across the entire surface rupture zone show that it varies in width from 13 to 122 m. These cultural features also reveal the across-strike distribution of lateral displacement, 80% of which is, on average, concentrated within the central 43% of the rupture zone. Combining the near-field measurements of fault offset with published, far-field InSAR, continuous GPS, and coastal deformation data, suggests partitioning of oblique plate convergence, with a significant portion of co-seismic contractional deformation (and uplift) being accommodated off-fault in the hanging-wall crust to the northwest of the main rupturing faults. This thesis also documents in detail the onshore extent of surface fault rupture on the Kekerengu, Jordan Thrust, Upper Kowhai and Manakau faults. I present large-scale maps (up to 1:3,000) and documentary field photographs of this 53 km-long onshore surface rupture zone utilizing field data, post-earthquake LiDAR-derived Digital Elevation Models (DEMs), and post-earthquake ortho-rectified aerial photography. Ground deformation data is most detailed near the Marlborough coast where the 2016 rupture trace is well-exposed on agricultural grassland on the Kekerengu fault. In the southwest, where surface fault rupture traversed the alpine slopes of the Seaward Kaikoura ranges, fault mapping relied heavily on the LiDAR-derived DEMs. At 24 sites along the Kekerengu fault, I document co-seismic wear striae that were formed during the earthquake and were preserved on free face fault exposures. Nearly all of these striae were distinctly curved along their length, demonstrating that the direction of near-surface fault slip changed with time during rupture of the Kekerengu fault. Co-seismic displacement on the Kekerengu fault initiated as oblique-dextral (mainly dextral-reverse), and subsequently rotated to become nearly-pure dextral slip. These slip trajectories agree with directions of net displacements derived from offset linear features at nearby sites. Temporal rotation of the slip direction may suggest a state of low shear stress on the Kekerengu fault before the earthquake, and a near-complete reduction in stress during the earthquake, as has been inferred for other historic earthquakes that show evidence for changing slip direction with time.</p>
