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Akaroa, New Zealand

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. Source

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. Source

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. Source

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. Source

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. Source

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