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

Stern, T. A.; Okaya, D. A.; Scherwath, Martin

doi:10.1186/bf03353294

Cited by 21 publications

(8 citation statements)

References 40 publications

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“…Nearly half of the relative motion between the Australian and Pacific plates is distributed over a distance of up to 200 km to the southeast of the Alpine Fault (Beavan et al, 1999;Beavan and Haines, 2001;Leitner et al, 2001). These breaks may contribute to the very low effective elastic thickness (T e ≈ 5 km) estimated for the interior of the central South Island (Stern et al, 2002).…”

Section: New Zealand Southern Alpsmentioning

confidence: 99%

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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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Section: New Zealand Southern Alpsmentioning

confidence: 99%

“…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%

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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“…Northward towards Banks Peninsula the heat flow steadily decreases to 'normal' values for continental crust (Godfrey et al, 2001). Based on seismic imaging, the lithospheric thickness beneath Zealandia is generally between 70 and 100 km (Molnar et al, 1999;Stern et al, 2002;Liu and Bird, 2006), but an orogenic root extends up to ∼140 km beneath the Southern Alps (Stern et al, 2002).…”

Section: Geodynamic Background Of Zealandia Since the Late Cretaceousmentioning

confidence: 99%

Temporal and geochemical evolution of the Cenozoic intraplate volcanism of Zealandia

Timm¹,

Hoernle²,

Werner³

et al. 2010

Earth-Science Reviews

144

136

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Ar and geochemical (major and trace element and Sr-Nd-Hf-Pb isotope) data from offshore (Chatham Rise, Campbell and Challenger Plateaus) and onland (North, South, Auckland, Campbell, Chatham and Antipodes Islands of New Zealand) volcanism on Zealandia. The samples include nephelinite, basanite through phonolite, alkali basalt through trachyte/rhyolite, and minor tholeiite and basaltic andesite, all of which have ocean island basalt (OIB)-type trace element signatures and which range in age from 64.8 to 0.17 Ma. Isotope ratios show a wide range in composition (

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“…[] suggest that a fluid‐rich facture system extends to depth of 5–6 km in the central Southern Alps. Overpressured fluids at depth ≥6 km have been inferred from the reduction of seismic wave‐speeds in wide‐angle reflection and teleseismic P‐wave arrival data on SIGHT transect 2 [ Stern et al ., ], while low resistivities indicate interconnected fluids at these depths [ Wannamaker et al ., ]. A distinct transition between seismic (≤7.5 km) and aseismic depths can be seen in Figures c and d.…”

Section: Discussionmentioning

confidence: 99%

Background and delayed-triggered swarms in the central Southern Alps, South Island, New Zealand

Boese

Jacobs

Smith

et al. 2014

Geochem. Geophys. Geosyst.

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Low-magnitude earthquake swarms (M L 2.8), consisting of up to 47 events of similar waveforms, have been observed repeatedly in the central Southern Alps, a rapidly uplifting orogen bounded by the transpressive Alpine Fault in the South Island of New Zealand. We compare nine background swarms recorded between November 2008 and April 2010 with five delayed-triggered swarms that occurred after the M W 7.8 Dusky Sound and the M W 7.1 Darfield (Canterbury) earthquakes. The two types of swarms are similar in terms of the magnitudes, depths, focal mechanisms, and interevent times of the constituent microearthquakes, and appear to both involve the rupture of steeply dipping faults in highly fractured crust in a 10 km 3 12 km area in the center of the SAMBA network. The delayed-triggered swarms occurred at similar epicentral distances (c. 4.53 the rupture length of the mainshocks) to the Dusky Sound and Darfield earthquakes, commenced shortly after the passage of the surface waves, continued for 5 and 2 days, respectively, and were followed in each case by a 2 day long quiescent period, which may suggest clockadvanced of faults in their failure-cycle. Triggering thresholds of 0.01 MPa proposed elsewhere are similar to the dynamic stress changes computed for the Southern Alps (0.09 MPa). However, as 98% of the locatable triggered events occurred several hours after the surface waves had passed, the dynamic stress changes associated with the surface waves themselves are unlikely to have triggered the earthquakes directly. Instead, we suggest that the locations and delays of the triggered swarms are more consistent with triggering by pore pressure diffusion.

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

Cited by 21 publications

References 40 publications

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

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

Temporal and geochemical evolution of the Cenozoic intraplate volcanism of Zealandia

Background and delayed-triggered swarms in the central Southern Alps, South Island, New Zealand

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