Andy Nicol - Academia.edu (original) (raw)

Papers by Andy Nicol

&lt;p&gt;Fault surfaces and networks have been shown to have complex geometries. ... more &lt;p&gt;Fault surfaces and networks have been shown to have complex geometries. Outcrop observations are typically two-dimensional and limited in size by the exposure dimensions, while three-dimensional (3D) seismic data lack the resolution to characterize and quantify fault complexities on length scales less than a decameter. Defining the geometries of faults and their networks (high-resolution in 3D) is critical for understanding the interactions between faults and fluids. This presentation will examine the geometries of a network of small-scale normal faults displacing (by &lt;1 cm) well bedded sand and silt layers in the Mount Messenger and Mohakatino formations in Taranaki, New Zealand. A 3D model of faulting was produced from high-resolution multi-band CT scanner (&lt;em&gt;MARS Bioimaging Ltd.&lt;/em&gt;) imagery of a 10x8x3 cm rock sample. The digitally sectioned rock contains calcified fault rock that is distinguishable from wall rock and mapped throughout the rock volume at sub-millimeter scale. Fault-rock thicknesses vary by in excess of an order of magnitude, with greatest thicknesses at fault steps and fault bends. Fault zones comprise a series of lenses that have strike lengths greater than dip lengths and lens shapes that are often elongate parallel to bedding. The fault network is highly connected with branch lines, fault steps and fault bends most often sub-parallel to bedding. These observations suggest that mechanical heterogeneity of beds may partly control the geometries of both fault zones and the fault network. At the time of formation, the interconnected fault network likely increased bedding-parallel permeability (at scales from sub-millimeter and above) along fault zones.&lt;/p&gt;

faults: An alternative model from

Submarine Landslides, 2019

Bulletin of the New Zealand Society for Earthquake Engineering, 2017

We provide a summary of the surface fault ruptures produced by the Mw7.8 14 November 2016 Kaikōur... more We provide a summary of the surface fault ruptures produced by the Mw7.8 14 November 2016 Kaikōura earthquake, including examples of damage to engineered structures, transportation networks and farming infrastructure produced by direct fault surface rupture displacement. We also provide an overview of the earthquake in the context of the earthquake source model and estimated ground motions from the current (2010) version of the National Seismic Hazard Model (NSHM) for New Zealand. A total of 21 faults ruptured along a c.180 km long zone during the earthquake, including some that were unknown prior to the event. The 2010 version of the NSHM had considered multi-fault ruptures in the Kaikōura area, but not to the degree observed in the earthquake. The number of faults involved a combination of known and unknown faults, a mix of complete and partial ruptures of the known faults, and the non-involvement of a major fault within the rupture zone (i.e. the Hope Fault) makes this rupture an...

Energy Procedia, 2017

Faults comprise zones of crushed, sheared and fractured rock that have the potential to influence... more Faults comprise zones of crushed, sheared and fractured rock that have the potential to influence the migration of stored CO 2. Fault-zone permeabilities of 10-9 to 10-19 m 2 are controlled by many interdependent factors including; fault-zone architecture and rock types, mechanical strength and permeability of host rock, orientation and magnitude of in situ stresses, fracture aperture size and connectivity, fluid properties and burial history. Mitigating the risk of CO 2 migration via faults to the atmosphere or into economically valuable resources requires an understanding of the conditions under which they promote fluid flow from the reservoir. In situ flow data from natural seeps indicate that faults can promote the upward flow of CO 2 , with flux rates being greatest where the highest densities of fractures occur. Flow simulation modelling suggests that low-permeability fault rock may compartmentalise reservoirs giving rise to increased pressures and promoting upward flow of CO 2. Migration rates along faults of up to 1000 m/yr are possible and could produce leakage rates of up to 15000 t/yr at natural seeps. These rates are likely to be site specific and positively related to reservoir pressures. Present understanding of fault hydraulic properties is generally not sufficiently complete to predict when and where faults will influence CO 2 migration. To improve understanding of fault hydraulic properties, studies of outcrop, analogue and numerical models are required. In situ flow measurements are critical for testing site-specific and generic fault fluid-flow models that are important in establishing guidelines for the inclusion of faults in risk assessment and determining what mitigation measures are most appropriate.

The Taranaki Fault is a crustal scale thrust of at least 400 km in length that lies at the easter... more The Taranaki Fault is a crustal scale thrust of at least 400 km in length that lies at the eastern margin of the Taranaki Basin. Interpretation of seismic-reflection data (including pre-stacked depth migrated lines), tied to recently drilled wells, indicates that the dip of the principal fault surface ranges from 25 to 45° and increases southwards. The principal fault is corrugated on length scales of 10’s to 100’s of kilometres and is accompanied by multiple slip surfaces which often splay from the main fault within 2-5 km of the upper tip. Splays can be entirely within Tertiary or basement rocks, or may produce inter-fingering of basement and CretaceousTertiary strata. These splays are discontinuous and, in the main, appear to extend for no more than 10-50 km along strike. The fault has accommodated at least 12-15 km of dip-slip displacement in the last ca. 80 Myr. Analysis of displacement data indicates at least two periods of accelerated shortening and displacement on the fault, during the Mid-Late Eocene (ca. 43-35 Ma) and the Early Miocene (ca. 23-18 Ma). These periods of more rapid deformation are interspersed with intervals during which contraction was either slow or absent. The relative importance of Eocene and Miocene displacements varies along the length of the fault with a greater proportion of Eocene and Miocene displacement north and south of Pukearuhe-1 well respectively. This distribution of displacement reflects a southward migration of fault activity which is mirrored by an apparent southward migration of basin depocenters adjacent to the fault. Deformation and associated movement of the Taranaki Fault has produced changes in fault dip, anastomosing fault splays and corrugations in the principal thrust surface together with tilting and folding of sedimentary strata adjacent to the fault. Therefore, petroleum accumulations underneath the fault are most likely to be spatially discontinuous, but potentially stacked within the fault zone.

Volcanoes and normal faults are, by definition, both present within volcanic rifts. Despite this ... more Volcanoes and normal faults are, by definition, both present within volcanic rifts. Despite this association the causal relationships between volcanism and normal faulting can be unclear and are poorly understood. One of the principal challenges for investigations of the links between faulting and volcanic activity, is the definition of the detailed temporal relationships between these two processes. The northern Taranaki

A recent model of fault growth suggests that many faults establish their lengths rapidly and for ... more A recent model of fault growth suggests that many faults establish their lengths rapidly and for much of the duration of deformation grow principally by the accumulation of displacement. For faults consistent with this model we investigate the factors controlling displacement rates and average recurrence intervals using the lengths and displacement rates for 274 normal faults from 4 extensional regions.

Over the last ~15 years we have excavated 73 trenches across active normal faults in the Taupo an... more Over the last ~15 years we have excavated 73 trenches across active normal faults in the Taupo and Hauraki Rifts, North Island, New Zealand. The stratigraphy in these trenches is quite similar because of the predominance of volcanic and volcanic-derived deposits, sourced from the active Taupo Volcanic Zone. These deposits, whether alluvial (reworked, mainly volcanics) or volcanic (tephra), are all

Energy Procedia, 2013

Seismicity produced by human activities (i.e. induced seismicity) has been widely reported over t... more Seismicity produced by human activities (i.e. induced seismicity) has been widely reported over the last 40 years. To date few induced earthquakes have been recorded at CO 2 storage sites, however, the volumes of injected CO 2 and the number of operational sites are small. A review of induced seismicity from different types of fluid injection and extraction sites confirms that these events are typically magnitude (M) and in many cases have no reported earthquakes. Although the size (and associated risks) of induced earthquakes at CO 2 storage sites is most likely to be small, these events could decrease seal integrity or raise public concerns, while rare larger events (>M5) could also have ramifications for CCS beyond a single site. These risks can be reduced by careful site selection and development of site-specific risk reduction and mitigation programmes. Forecasts of induced seismicity using physical and statistical models and real-time monitoring will be key planning and decision making tools. The utility of monitoring and mitigation programmes will be maximized by establishing prior to injection, site performance and management guidelines for acceptable levels of induced seismicity, and agreed control measures. Further improvements to risk management practices, understanding induced seismicity processes and stakeholder confidence may be achieved by; a) increasing the number of publically available induced earthquake catalogues for development and testing of physical and statistical models, b) undertaking more systematic studies of individual sites populated by well constrained sub-surface geomechanical information and seismicity data complete down to small magnitudes (e.g., M-3), c) enhancing the physical reality of numerical dynamic models, d) studying the scaling effects of seismicity associated with moving from pilot projects to full commercial implementation of CO 2 storage, e) developing standard risk management procedures and guidelines for induced seismicity at CCS sites and, f) filling induced seismicity knowledge gaps in the CCS community by collaborating with seismologists and modellers working in other industries.

Tectonophysics, 1995

The relationships between folding and small (1060 km long, &amp;amp;lt; 30 km wide and &... more The relationships between folding and small (1060 km long, &amp;amp;lt; 30 km wide and &amp;amp;lt; 2 km deep) sedimentary basins are examined using outcrop and seismic reflection data from the New Zealand plate boundary. Folding has a significant effect on the geometry and formation of ...

Tectonophysics, 2013

The Taranaki Basin in the west of New Zealand's North Island has evolved from a rifted Mesozoic G... more The Taranaki Basin in the west of New Zealand's North Island has evolved from a rifted Mesozoic Gondwana margin to a basin straddling the Neogene convergent Australian-Pacific plate margin. However, given its proximity to the modern subduction front, Taranaki Basin is surprisingly cold when compared to other convergent margins. To investigate the effects of active margin evolution on the thermal regime of the Taranaki Basin we developed a 3D crustal-scale forward model using the petroleum industry-standard basinmodelling software Petromod™. The crustal structure inherited from Mesozoic Gondwana margin breakup and processes related to modern Hikurangi convergent margin initiation are identified to be the main controls on the thermal regime of the Taranaki Basin. Present-day surface heat flow across Taranaki on average is 59 mW/m 2 , but varies by as much as 30 mW/m 2 due to the difference in crustal heat generation between mafic and felsic basement terranes alone. In addition, changes in mantle heat advection, tectonic subsidence, crustal thickening and basin inversion, together with related sedimentary processes result in variability of up to 10 mW/m 2. Modelling suggests that increased heating of the upper crust due to additional mantle heat advection following the onset of subduction is an ongoing process and heating has only recently begun to reach the surface, explaining the relatively low surface heat flow. We propose that the depth of the subducted slab and related mantle convection processes control the thermal and structural regimes in the Taranaki Basin. The thermal effects of the subduction initiation process are modified and overprinted by the thickness, structure and composition of the lithosphere.

Tectonics, 2007

Deformation across the active Hikurangi subduction margin, New Zealand, including shortening, ext... more Deformation across the active Hikurangi subduction margin, New Zealand, including shortening, extension, vertical‐axis rotations, and strike‐slip faulting in the upper plate, has been estimated for the last ∼24 Myr using margin‐normal seismic reflection lines and cross sections, strike‐slip fault displacements, paleomagnetic declinations, bending of Mesozoic terranes, and seafloor spreading information. Post‐Oligocene shortening in the upper plate increased southward, reaching a maximum rate of 3–8 mm/year in the southern North Island. Upper plate shortening is a small proportion of the rate of plate convergence, most of which (>80%) accrued on the subduction thrust. The uniformity of these shortening rates is consistent with the near‐constant rate of displacement transfer (averaged over ≥5 Myr) from the subduction thrust into the upper plate. In contrast, the rates of clockwise vertical‐axis rotations of the eastern Hikurangi Margin were temporally variable, with ∼3°/Myr since 1...

New Zealand Journal of Geology and Geophysics, 2003

Southeastern Marlborough, New Zealand, preserves many complete sections through the Cretaceous/ T... more Southeastern Marlborough, New Zealand, preserves many complete sections through the Cretaceous/ Tertiary (K/T) boundary. Attempts to understand the paleogeography of these sections are hampered by the pervasive, Neogene deformation of the area associated with the propagation of the modern Pacific/Australian plate boundary through New Zealand. In this paper, we produce palinspastic maps of southeastern Marlborough for five intervals of Cretaceous and Paleogene time, based on a retrodeformed, pre-Neogene geographic model. Retrodeformation takes account of: displacements on five major faults; distributed, between-fault shortening; and a uniform, vertical axis, clockwise rotation of 100°. The mapped intervals are: (1) part of the Urutawan-Motuan (middle-late Albian, c. 105-102 Ma); (2) the Piripauan (latest Coniacian to late Santonian, 86.5-84.5 Ma); (3) the Early to early Late Haumurian (late Santonian-Campanian, 84.5-72 Ma); (4) the late Late Haumurian to late Teurian (late Maastrichtian to late Paleocene, 68-58 Ma); and (5) the Waipawan-Mangaorapan (early Eocene, 55-51 Ma). During the Cretaceous and Paleogene, southeastern Marlborough lay on the generally north-facing, Pacific margin of proto-New Zealand. The palinspastic maps record the progressive drowning of what we infer to be a faulted platform, the "Marlborough paleo-platform", that formed the eastern boundary of a large embayment, the "Marlborough paleo-embayment". In the late Early and early Late Cretaceous, terrigenous clastic sediments were deposited on the platform at mostly shelf to upper bathyal depths. Ngaterian (late Albian-Cenomanian) and Piripauan (latest G02025;

New Zealand Journal of Geology and Geophysics, 2002

Growth histories of contractional structures at the southern end of New Zealand's Hikurangi forea... more Growth histories of contractional structures at the southern end of New Zealand's Hikurangi forearc basin have been analysed for the last c. 10 m.y. Growth data are from outcrop and seismic-reflection profiles that contain syntectonic strata and angular unconformities, and from deformed fluvial terrace surfaces. Deformation is described for up to eight intervals of time, spanning c. 12 000 yr to 5 m.y., the ages of which were determined by biostratigraphy and tephrochronology. Reverse faults and related asymmetric folds, which strike parallel to the subduction margin and verge troughwards, experienced variable rates of shortening through time. The current period of deformation commenced at c. 1.8 Ma with displacement rates of c. 0.1-0.7 mm/yr on the main faults (i.e., Martinborough, Huangarua, and Mangaopari Faults). Before this time there were periods of accelerated deformation during the mid Pliocene (c. 3.4-2.4 Ma) and latest Miocene (c. 8.0-6.0 Ma). Therefore, shortening since 10 Ma accumulated mainly during three periods of 1-2 m.y., with structures active in the Quaternary forming in the late Miocene or earlier. Local intervals of accelerated deformation are coincident with the timing of intervals of uplift and faulting along much of the emergent forearc and cannot be attributed to local transfer of displacements between faults. Instead, these intervals of deformation appear to reflect regional changes in the kinematics of the upper plate. These changes could arise due to margin-normal migration of strain to regions outside the forearc basin or may indicate temporal variations in the dynamics of subduction.

New Zealand Journal of Geology and Geophysics, 1990

In the Marlborough Sounds area near Picton. multiple deformation during the Miocene produced earl... more In the Marlborough Sounds area near Picton. multiple deformation during the Miocene produced early (D 1) north-northeast-trending folds, and north-and east-striking thrusts. Later folding (D0 about east-west axes led to the formation of basin and dome interference structures. During D 1 • Mesozoic rocks of the Marlborough Schist and Permian-Triassic Pelorus Group were thrust over an Oligocene sedimentary sequence. which is now exposed as erosional inliers. Thrust transport from west to east is inferred from fibre striations. Striation-derived M-axis data, calcite grain fabric studies, and the maximwn shortening direction of northnortheast-trending folds suggest that thrusting developed in association with approximate west-east compression. Thrust motion resulted in progressive late Cenozoic stacking of the basement sequence in this area, with considerable shortening and thickening of the Marlborough Sounds region.

Journal of Volcanology and Geothermal Research, 2010

Okataina Caldera is located within the Taupo Rift and formed due to collapse following eruptions ... more Okataina Caldera is located within the Taupo Rift and formed due to collapse following eruptions at 325 and 61 ka. Gravity, seismic reflection, topographic and geological data indicate that active rift faults pass into the caldera and have influenced its location and geometry. The caldera has a minimum gravity anomaly of −50 mGal, is elongate north–south with an inferred minimum depth to

Journal of Structural Geology, 2012

ABSTRACT