Akaroa, New Zealand
Akaroa, New Zealand

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Ghisetti F.C.,TerraGeoLogica | Ghisetti F.C.,University of Canterbury | Barnes P.M.,NIWA - National Institute of Water and Atmospheric Research | Sibson R.H.,University of Otago
New Zealand Journal of Geology and Geophysics | Year: 2014

Geometry of the Top Basement Unconformity (TBU) west of the Alpine Fault has been reconstructed through a set of cross-sections linking surface and subsurface geology. Onshore, the TBU shows tectonic relief of several kilometres between antiformal pop-ups and synformal depressions in contrast with a smoother topography offshore. This geometry arises from reverse slip on sets of north-south to NNE-SSW faults, mostly dipping 50-66° both west and east, that control folding of the TBU and overlying cover sequence. Some of these faults are inherited Upper Cretaceous-Palaeogene normal faults that displaced the TBU during the extensional phases and were later reactivated as reverse faults under compression, whereas others appear to be newly propagated Neogene reverse faults. The faults that deform the TBU have vertical displacements of 3-5 km and lengths of >150 km, and have the potential of being reactivated in the present stress field. Currently active faults comprise a set of blind reverse faults that propagate upsection from pre-existing extensional fault fabric in the basement, imposing a short-wavelength undulation on the TBU. © 2014 The Royal Society of New Zealand.


Barnes P.M.,NIWA - National Institute of Water and Atmospheric Research | Ghisetti F.C.,TerraGeoLogica
New Zealand Journal of Geology and Geophysics | Year: 2016

The North Westland deformation front runs offshore for 320 km between Cape Farewell and Hokitika at a distance of 3–30 km from the coast. From marine seismic reflection profiles integrated with published sediment core and coastal uplift data, we infer late Quaternary activity on six major reverse faults. The principal structures are the Cape Foulwind, Kahurangi and Kongahu faults and the newly named Farewell, Elizabeth and Razorback faults. They include Late Cretaceous and Paleogene rift faults that were reactivated as reverse faults during the late Cenozoic. Best estimates of late Quaternary (<120 ka) slip rates for different faults range from 0.05–0.75 mm a–1. Nine potential earthquake sources are identified, including four segments of the Cape Foulwind Fault. They are of length c. 20–120 km, are potentially capable of producing moderate- to large-magnitude earthquakes of Mw 6.7–7.8 and represent a seismic risk to coastal communities. Best estimates of recurrence intervals for individual fault sources range from about 7600 years to 30,400 years, with large uncertainties in slip rates of up to –0.4, +1.0 mm a–1 reflected by the wide range of recurrence intervals. © 2016 The Royal Society of New Zealand.


Vezzani L.,University of Turin | Festa A.,University of Turin | Festa A.,Miami University Ohio | Ghisetti F.C.,TerraGeoLogica | Ghisetti F.C.,University of Canterbury
Special Paper of the Geological Society of America | Year: 2010

The Geological-Structural Map of the Central-Southern Apennines (Italy)1 provides entirely revised and original cartography for a large sector of the orogenic belt that stretches along peninsular Italy. New data collected by the authors over the past 20 years, together with field revisions of published data, and available subsurface data are synthesized in two geological map sheets at scale 1:250,000 giving a regional overview of the stratigraphy, geometry, and structure of the Apenninic fold-and-thrust belt. The Apennines comprise a variety of lithotectonic assemblages that evolved through interaction between the African and European plates in the central Mediterranean, with: (i) Mesozoic development of the Tethyan domain; (ii) Cretaceous-Eocene oceanic subduction; (iii) Oligocene-Miocene and Pliocene convergence, continental collision and shortening; and (iv) late Miocene-present extensional collapse of the contractional edifice. The geological maps and this paper illustrate a number of critical orogenic processes, including: (1) control of paleogeographic position and stratigraphy on the finite geometry of the thrust belt; (2) the history of progressive deformation and translation of far-traveled tectonic units; (3) selective reactivation of inherited structures during the sequence of superposed tectonic events; (4) the evolution of syntectonic and posttectonic sedimentary basins; and, (5) the propagation paths of thrust faults. The paper, together with the geological map and cross sections, provide a regional overview of the progressive tectono-stratigraphic evolution of the thrust belt, with focus on the geometry of the imbricate wedge and its subsurface geometry. Emphasis is also given to the relationships between active faulting and historical seismicity. © 2010 The Geological Society of America. All rights reserved.


Festa A.,University of Turin | Festa A.,Miami University Ohio | Pini G.A.,University of Bologna | Dilek Y.,Miami University Ohio | And 5 more authors.
International Geology Review | Year: 2010

In the peri-Adriatic region, mélanges represent a significant component of the Apennine and Dinaride-Albanide-Hellenide orogenic belts as well as ancient and present-day accretionary wedges. Different mélange types in this broad region provide an excellent case study to investigate the mode and nature of main processes (tectonic, sedimentary, and diapiric) involved in mélange formation in contrasting geodynamic settings. We present a preliminary subdivision and classification of the peri-Adriatic melanges based on several years of field studies on chaotic rock bodies, including detailed structural and stratigraphic analyses. Six main categories of melanges are distinguished on the basis of the processes and geodynamic settings of their formation. These mélange types are spatially and temporally associated with extensional tectonics, passive margin evolution, strike-slip tectonics, oceanic crust subduction, continental collision, and deformation. There appears to have been a strong interplay and some overlap between tectonic, sedimentary, and diapiric processes during mélange formation; however, in highly deformed regions, it is still possible to distinguish those melanges that formed in different geodynamic environments and their main processes of formation. This study shows that a strong relationship exists between melange-forming processes and the palaeogeographic settings and conditions of mélange formation. Given the differences in age, geographic location, and evolutionary patterns, we document the relative importance of mélanges and broken formations in the tectonic evolution of the peri-Adriatic mountain belts.


Campbell F.M.,ETH Zurich | Ghisetti F.,TerraGeoLogica | Ghisetti F.,University of Canterbury | Kaiser A.E.,ETH Zurich | And 3 more authors.
Tectonophysics | Year: 2010

To improve our understanding of active faulting away from the main plate boundary on New Zealand's South Island, we have acquired high resolution seismic data across the Ostler Fault Zone Twelve 1.2. km long lines perpendicular to fault strike and a 1.6. km long crossline were collected in a region of the MacKenzie Basin where surface mapping delineates significant complexity in the form of two non-overlapping reverse fault strands separated by a transfer zone characterised by multiple smaller strands and increased folding. Interpretation of the resultant images includes a 45-55° west-dipping principal fault and two 25-30° west-dipping subsidiary faults, one in the hanging wall and one in the footwall of the principal fault. The geologically mapped complexities are shown to be caused by shallow variations in the structure of the principal fault, which breaks the surface in the north and south but not within the transfer zone, where it forms a triangle zone with associated backthrusting and minor faulting. These complexities only extend to ~. 300. m depth. Structures below this level are markedly simpler and much more 2D in nature, with the principal fault strand extending over a much longer distance than the individual strands observed at the surface. Since longer faults are susceptible to larger earthquakes than shorter ones, seismic hazard at the study site may be higher than previously thought. Multiple surface fault strands that give way to a single more major stand at relatively shallow depths may be a common feature of segmented fault systems.The deepest layered reflections at our site are consistent with the presence of a Late Cretaceous (?)-Tertiary basin underlying the present-day MacKenzie Basin. Structural restoration of the seismic images back to the base of Quaternary fluvioglacial terraces and back to the top of a Late Pliocene-Pleistocene fluviolacustrine unit indicate that compression was initiated prior to the Late Pliocene and that it has continued at a comparatively steady rate of about a millimetre per year to the present day. The fluviolacustrine unit has experienced 440-800. m of along-fault vertical offset and 870-1080. m of horizontal shortening since that time. Our study demonstrates that structural reconstructions based on high resolution seismic reflection data provide critical displacement information that can be used to estimate slip rates. © 2010 Elsevier B.V.


Campbell F.M.,ETH Zurich | Kaiser A.,ETH Zurich | Horstmeyer H.,ETH Zurich | Green A.G.,ETH Zurich | And 4 more authors.
Journal of Applied Geophysics | Year: 2010

In an attempt to understand the structure of active faults as they emerge from bedrock into shallow semi-consolidated and unconsolidated sediments, we have recorded a comprehensive high-resolution seismic reflection/refraction data set across the Ostler Fault zone on the central South Island of New Zealand. This fault zone, which absorbs 1-2 mm/yr of compression associated with oblique convergence of the Pacific and Australian tectonic plates, consists of a series of surface-rupturing N-S trending, west-dipping reverse faults that offset a thick sequence of Quaternary glacial outwash and late Neogene fluvio-lacustrine sediments of the Mackenzie Basin. Our study focuses on a region of the basin where two non-overlapping fault segments are separated by a transfer zone. Deformation in this area is accommodated by offsets on multiple small faults and by folding in their hanging walls. The seismic data with source and receiver spacing of 6 and 3 m and nominal CMP fold of 60 was acquired along twelve 1.2 km long lines orthogonal to fault strike and an additional 1.6 km long tie-line parallel to fault strike. The combination of active deformation and shallow glacial outwash sediments results in particularly complicated seismic data, such that application of relatively standard processing schemes yields only poor quality images. We have designed a pre- and post-stack reflection/refraction processing scheme that focuses on minimising random and source-generated noise, determining appropriate static corrections and resolving contrasting reflection dips. Application of this processing scheme to the Ostler Fault data provides critical information on fault geometry and offset and on sedimentary structures from the surface to ~800 m depth. Our preliminary interpretation of one of the lines includes complex deformation structures with folding and multiple subsidiary fault splays on either side of a ~50° west-dipping primary fault plane. © 2009 Elsevier B.V.


Sibson R.H.,University of Otago | Ghisetti F.C.,Terrageologica | Crookbain R.A.,Royal Dutch Shell
Geological Society Special Publication | Year: 2012

The initial Mw7.1 Darfield earthquake sequence was centred west of Christchurch City in the South Island of New Zealand but aftershocks, including a highly destructive Mw6.3 event, eventually extended eastwards across the city to the coast. The mainshock gave rise to rightlateral strike-slip of up to 5 m along the segmented rupture trace of a subvertical fault trending 085 ± 5 ° across the Canterbury Plains for c. 30 km, in agreement with teleseismic focal mechanisms. Near-field data however suggest that the mainshock was composite, initiating with reverseslip north of the surface rupture. Stress determinations for the central South Island show maximum compressive stress s1 to be horizontal and oriented 115 ± 5°. The principal dextral rupture therefore lies at c. 30° to regional σ1, the classic 'Andersonian' orientation for a low-displacement wrench fault. An aftershock lineament trending c. 145° possibly represents a conjugate leftlateral strike-slip structure. This stress field is also consistent with predominantly reverse-slip reactivation of NNE-NE faults along the Southern Alps range front. The main strike-slip fault appears to have a low cumulative displacement and may represent either a fairly newly formed fault in the regional stress field, or an existing subvertical fault that happens to be optimally oriented for frictional reactivation. © The Geological Society of London 2012.


Ghisetti F.C.,TerraGeoLogica | Sibson R.H.,University of Otago
New Zealand Journal of Geology and Geophysics | Year: 2012

Earthquake ruptures of the 2010-2011 Canterbury sequence exploit a varying mixture of optimally oriented newly formed faults and inherited discontinuities that are favourably oriented for reactivation within the prevailing tectonic stress field. Reinterpretation of subsurface data shows that the Torlesse basement is imprinted with an E-W fault fabric inherited from Late Cretaceous-Eocene rifting. The prevailing E-W band of rupturing illuminated by seismicity lies at the southern boundary of a Late Cretaceous basin, terminating against the Banks Peninsula structural high. Analysis of a set of seismic lines in the Ashley River region (c. 30 km north of the Greendale fault) demonstrates compressional inversion of inherited high-angle E-W normal faults and folding and detachment of the Neogene cover sequence, together with propagation of new faults through the Pliocene and Quaternary cover sequences. These structures provide an analogue to deformation in the epicentral region of the Greendale fault. © 2012 The Royal Society of New Zealand.

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