Low seismic-wave speeds and enhanced fluid pressure beneath the Southern Alps of New Zealand

Stern, T. A.; Kleffmann, Stefan; Okaya, D. A.; Scherwath, Martin; Bannister, Stephen

doi:10.1130/0091-7613(2001)029<0679:lswsae>2.0.co;2

Cited by 97 publications

(150 citation statements)

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“…The Alpine Fault marks the western boundary of the Southern Alps, and presently accommodates about 70% of relative plate motion in the central South Island (Norris and Cooper, 2001;Beavan et al, 1999). Seismic velocity anomalies and wide angle reflections along the down-dip trend of the surface fault have been imaged in a geophysical transect across the central Southern Alps (Stern et al, 2001), suggesting that the Alpine Fault is a major crustal structure that continues as a localized shear zone at depths of more than 30 km. Studies of high strain mylonites exhumed structurally above the Alpine Fault also indicate that strain is localized at depths of 20 km or more along a narrow mylonitic shear zone .…”

Section: Implications For the Seismic Cycle Of The Alpine Fault New mentioning

confidence: 99%

“…Strain analysis in mylonites exhumed from mid and lower crustal depths indicates significant localization (e.g., Norris and Cooper, 2003) and major faults such as the Alpine Fault of New Zealand can be traced to the lower crust using geophysical observations (Davey et al, 1995;Stern et al, 2001). However, in general it has not been possible to establish how much of the plate boundary motion is accommodated along ductile shear zones in the lower crust.…”

Section: Introductionmentioning

confidence: 99%

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Imposed strain localization in the lower crust on seismic timescales

Ellis

Stöckhert

2014

Earth Planet Sp

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We show using numerical model experiments that upper crustal faults can impose ductile localization in the mid and lower crust over the seismic cycle, with strain-rates and integrated creep strain enhanced by a factor of 10, or a factor of 100 if lower crust is also thermally weakened. Imposed ductile localization is caused by the transfer in stress from the lower tip of the frictional fault to the mid-crust. Within the weak ductile mid-lower crust, this stress transfer also promotes significantly enhanced creep rates in a lobe that extends down-dip from the lower end of the fault. Comparison of model results with the Alpine Fault of New Zealand, shows how the interaction of faulting with other localization mechanisms can account for key aspects of the geodetic strain accumulating across the Alpine Fault. Localization of ductile strain in the lower crust imposed by faulting in the upper crust could explain the extension of major faults into the lower crust observed in seismic imaging.

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Section: Implications For the Seismic Cycle Of The Alpine Fault New mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Imposed strain localization in the lower crust on seismic timescales

Ellis

Stöckhert

2014

Earth Planet Sp

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“…Geodetic studies are consistent with a shallow (5-10 km) depth for full fault locking (Beavan et al, 1999), though some degree of interseismic coupling may persist to as deep as ~18 km . In the mid-crust, the fault zone exhibits low seismic wave speeds and high attenuation (Stern et al, 2001;Eberhart-Phillips and Bannister, 2002;Stern et al, 2007 and references therein) and high electrical conductivity (Wannamaker et al, 2002), suggesting interconnected saline fluids at high pressures within the ductile regime.…”

Section: Tectonic Settingmentioning

confidence: 99%

Deep Fault Drilling ProjectAlpine Fault, New Zealand

Townend

Sutherland

Toy

2009

Scientific Drilling

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The Alpine Fault, South Island, New Zealand, constitutes a globally significant natural laboratory for research into how active plate-bounding continental faults work and, in particular, how rocks exposed at the surface today relate to deep-seated processes of tectonic deformation, seismogenesis, and mineralization. The along-strike homogeneity of the hanging wall, rapid rate of dextral-reverse slip on an inclined fault plane, and relatively shallow depths to mechanical and chemical transitions make the Alpine Fault and the broader South Island plate boundary an important international site for multi-disciplinary research and a realistic target for an ambitious long-term program of scientific drilling investigations.

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“…However, a nearly coincident low velocity zone is seen in the same area and appears to persist at least 50 km to the southwest (Stern et al, 2001(Stern et al, , 2002. Moreover, followup MT soundings taken by the New Zealand IGNS (T. G. Caldwell, pers.…”

Section: New Zealand Southern Alpsmentioning

confidence: 99%

“…Substantially influenced by Craw (1997) and Sibson and Scott (1998). P-wave velocity contours in km/s in upper panel after Stern et al (2001).…”

Section: Introductionmentioning

confidence: 99%

Fault zone fluids and seismicity in compressional and extensional environmen inferred from electrical conductivity: the New Zealand Southern Alps and U. S. Great Basin

Wannamaker

Caldwell

Doerner³

et al. 2014

Earth Planet Sp

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Seismicity in both compressional and extensional settings is a function of local and regional stresses, rheological contrasts, and the distribution of fluids. The influence of these factors can be illustrated through their effects on electrical geophysical structure, since this structure reflects fluid composition, porosity, interconnection and pathways. In the compressional, amagmatic New Zealand South Island, magnetotelluric (MT) data imply a concave-upward ("U"-shaped), middle to lower crustal conductive zone beneath the west-central portion of the island due to fluids generated from prograde metamorphism within a thickening crust. Change of the conductor to near-vertical orientation at middle-upper crustal depths is interpreted to occur as fluids cross the brittle-ductile transition during uplift, and approach the surface through induced hydrofractures. The central South Island is relatively weak in seismicity compared to its more subduction-related northern and southern ends, and the production of deep crustal fluids through metamorphism may promote slip before high stresses are built up. The deep crustal conductivity is highly anisotropic, with the greater conductivity along strike, consistent with fault zone models of long-range interconnection versus degree of deformation. The central Great Basin province of the western U.S. by contrast is extensional at present although it has experienced diverse tectonic events throughout the Paleozoic. MT profiling throughout the province reveals a quasi one-dimensional conductor spanning the lower half of the crust which is interpreted to reflect high temperature fluids and perhaps melting caused ultimately by exsolution from crystallizing underplated basalts. The brittle, upper half of the crust is generally resistive, but also characterized by numerous steep, narrow conductors extending from near-surface to the middle crust where they contact the deep crustal conductive layer. These are suggested to represent fluidised/altered fault zones, with at least some fluids contributed from the deeper magmatic exsolution. The best-known faults imaged geophysically before this have been the listric normal faults bounding graben sediments as imaged by reflection seismology. However, the major damaging earthquakes of the Great Basin appear to nucleate near mid-crustal depths on near-vertical fault planes, which we suggest are being imaged with the MT transect data, and where triggering fluids from the ductile lower crust are available. In both compressional and extensional examples, the fluidised fault zones are hypothesized to act to concentrate slip, with major earthquakes resulting in asperities along the fault surface.

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Low seismic-wave speeds and enhanced fluid pressure beneath the Southern Alps of New Zealand

Cited by 97 publications

References 22 publications

Imposed strain localization in the lower crust on seismic timescales

Imposed strain localization in the lower crust on seismic timescales

Deep Fault Drilling ProjectAlpine Fault, New Zealand

Fault zone fluids and seismicity in compressional and extensional environmen inferred from electrical conductivity: the New Zealand Southern Alps and U. S. Great Basin

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Low seismic-wave speeds and enhanced fluid pressure beneath the Southern Alps of New Zealand

Cited by 97 publications

References 22 publications

Imposed strain localization in the lower crust on seismic timescales

Imposed strain localization in the lower crust on seismic timescales

Deep Fault Drilling ProjectAlpine Fault, New Zealand

Fault zone fluids and seismicity in compressional and extensional environmen inferred from electrical conductivity: the New Zealand Southern Alps and U. S. Great Basin

Contact Info

Product

Resources

About

Deep Fault Drilling ProjectAlpine Fault, New Zealand