Continuous Deformation Versus Faulting Through the Continental Lithosphere of New Zealand

Molnár, Péter; Anderson, Helén; Audoine, Etienne; Eberhart‐Phillips, Donna; Gledhill, Ken; Klosko, Eryn; McEvilly, T. V.; Okaya, D. A.; Savage, Martha K.; Stern, T. A.; Wu, Francis T.

doi:10.1126/science.286.5439.516

Cited by 145 publications

(143 citation statements)

References 42 publications

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“…This result is similar to the observations in New Zealand [e.g., Molnar et al, 1999] [Holt, 2000]. In our case, the anisotropy correlates well with the present-day extension, which we assume is constant during the Pliocene but differs significantly from previous deformation.…”

Section: Implication For the Geodynamicssupporting

confidence: 92%

Shear wave anisotropy in the upper mantle beneath the Aegean related to internal deformation

Hatzfeld¹,

Karagianni²,

Kassaras³

et al. 2001

J. Geophys. Res.

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Abstract. Seismic anisotropy, deduced from SKS splitting measured at 25 stations installed in the Aegean, does not show a homogeneous pattern. It is not restricted to the North Anatolian Fault but is distributed over a region several hundreds kilometers wide. Little anisotropy is observed in continental Greece or along the Hellenic arc; however, significant anisotropy is observed in the north Aegean Sea. Large values of delay times suggest that anisotropy is due to a long path within the upper mantle and to strong intrinsic anisotropy. Our results, both in fast polarization directions and in values of delay time, do not support the idea that anisotropy is associated with inherited tectonic fabric nor are they consistent with the present-day Aegean motion relative to an absolute frame. In contrast, the direction of fast polarization and the magnitude of delay times correlate well with the present-day strain rate observed at the surface deduced from both geodetic measurements and seismicity. This anisotropy is not horizontally restricted to major surface faults but is spread over a wide region.

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Section: Implication For the Geodynamicssupporting

confidence: 92%

Shear wave anisotropy in the upper mantle beneath the Aegean related to internal deformation

Hatzfeld¹,

Karagianni²,

Kassaras³

et al. 2001

J. Geophys. Res.

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“…Sutherland et al, 2000;Turnbull et al, 1993). Molnar et al (1999) have argued from seismic data that the mantle beneath the South Island is deforming by distributed shear without a zone of highly localised creep. If this is accepted, the localisation of deformation on the Alpine Fault is unlikely to derive directly from the mantle.…”

Section: Discussionmentioning

confidence: 99%

“…at least 23 mm/yr) indicate that this can only be true near surface for, at most, the remaining 14 mm/yr, or c. 35% of the predicted plate motion. Based on mantle anisotropy, Molnar et al (1999) and Stern et al (2000) have suggested that New Zealand overlies a broad zone of shear some 200 km wide and localisation onto faults only occurs in the brittle crust.…”

Section: °Ementioning

confidence: 99%

Strain localisation within ductile shear zones beneath active faults: The Alpine Fault contrasted with the adjacent Otago fault system, New Zealand

Norris

2014

Earth Planet Sp

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The Alpine Fault accommodates around 60-70% of the 37 mm/yr oblique motion between the Australian and Pacific plates in the South Island of New Zealand. Uplift on the fault over the past 5 Ma has led to the exhumation of the deep-seated mylonite zone alongside the present surface trace. Shear strain estimates in the mylonites reach 200-300 in the most highly strained rocks, and provide an integrated displacement across the zone of 60-120 km. This is consistent with the amount of displacement during the last 5 Ma, suggesting that displacement on the fault is localised within a 1-2 km wide ductile shear zone to depths of 25-30 km. Existing geodetic data, together with Late Quaternary slip rate and paleoseismic data, are consistent with the steady build-up and release of elastic strain in the upper crust driven by ductile creep within a narrow mylonite zone at depth. Faults of the Otago Fault System form a parallel array east of the Alpine Fault and accommodate c. 2 mm/yr contraction. Long periods of quiescence on individual structures suggest episodic, or "intermittently characteristic", behaviour. This is more consistent with failure on faults within an elastico-frictional upper crust above a ductile lower crust. Localisation of crustal deformation may be initiated by inherited weaknesses in the upper crust, with downward propagation of slip causing strain weakening within the ductile zone immediately beneath. Inherited structures of great length focus a greater amount of displacement and hence more rapidly develop underlying zones of ductile shear.

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“…As we know the loading distribution, and the restoring force can be deduced from the surface geology, Te remains the sole variable to resolve from trial and error modeling. The choice of a continuous plate, rather than a broken one is based on there being a wide zone of deformation in the mantle and lower crust, rather than a fault (Molnar et al, 1999). A continuous plate also permits a more general solution, as the ability of the finite difference technique to reduce Te to near zero values effectively permits us to approach the broken plate situation.…”

Section: A Flexure Model For the Central South Islandmentioning

confidence: 99%

Structure and strength of a continental transform from onshore-offshore seismic profiling of South Island, New Zealand

2014

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Seismic images of deformation beneath South Island, New Zealand, are provided by a form of seismic exploration uniquely suited to the study of "continental islands"-double-sided, onshore-offshore seismic methods in conjunction with onshore refraction and teleseismic P-wave delay data. Four sets of independent observations and analysis are use to infer rock properties within this plate boundary zone: seismic and electrical indications of highfluid pressures within the crust; P-wave delays from teleseismic anisotropy to show a high-speed zone in the mantle directly below the crustal root; Pn anisotropy of 11 ± 3% distributed over a region > 100 km-wide; and an effective elastic thickness (Te) that is vanishingly small beneath the Southern Alps and surface outcrop of the Alpine Fault, but increases to values of Te > 20 km beyond the coastlines of the South Island. Together, these observations show that deformation in the crust and mantle becomes progressively wider with depth. A region of distributed deformation > 200 km wide is inferred for the upper mantle. We propose that the weakness and the wide zone of deformation are phenomena of plate boundaries where both strike-slip and convergence have persisted for several millions of years.

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Continuous Deformation Versus Faulting Through the Continental Lithosphere of New Zealand

Cited by 145 publications

References 42 publications

Shear wave anisotropy in the upper mantle beneath the Aegean related to internal deformation

Shear wave anisotropy in the upper mantle beneath the Aegean related to internal deformation

Strain localisation within ductile shear zones beneath active faults: The Alpine Fault contrasted with the adjacent Otago fault system, New Zealand

Structure and strength of a continental transform from onshore-offshore seismic profiling of South Island, New Zealand

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