Three-dimensional attenuation structure beneath North Island, New Zealand

Satake, Kenji; Hashida, Toshihiko

doi:10.1016/0040-1951(89)90127-3

Cited by 32 publications

(15 citation statements)

References 20 publications

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“…The presence of water within the upper-mantle acts to reduce seismic velocities in a manner consistent with our observations from beneath the TVZ and to increase seismic attenuation (Karato 1995). The location of the region of lowered mantle velocities also correlates well with seismic attenuation observations, which require a region of high attenuation within the mantle wedge beneath the TVZ and northwestern North Island (Mooney 1970;Satake & Hashida 1989).…”

Section: The Mantle Wedgesupporting

confidence: 84%

Lithospheric structure of an active backarc basin: the Taupo Volcanic Zone, New Zealand

Harrison

White

2006

Geophysical Journal International

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S U M M A R YSeismic data from both explosive and earthquake sources have been used to model the crustal and upper-mantle velocity structure beneath the Taupo Volcanic Zone (TVZ), an active backarc basin in central North Island, New Zealand. Volcanic sediments with P-wave velocities of 2.0-3.5 km s −1 reach a maximum thickness of 3 km beneath the central TVZ. Underlying these sediments to 16 km depth is material with velocities of 5.0-6.5 km s −1 , interpreted as quartzo-feldspathic crust. East and west of the TVZ, crust with similar velocities is found to depths of 30 and 25 km, respectively. Beneath the TVZ, material with P-wave velocities of 6.9-7.3 km s −1 is found from 16 to 30 km depth and is interpreted as heavily intruded or underplated lower crust. The base of the crust at 30 km depth under the TVZ is marked by a strong seismic reflector, interpreted as the Moho. Modelling of arrivals from deep (>40 km) earthquakes near the top of the underlying subducting Pacific Plate reveals a region with low mantle velocities of 7.4-7.8 km s −1 beneath the crust of the TVZ. This region of low mantle velocities is best explained by the presence of partially hydrated upper mantle, resulting from dehydration of hydrous minerals (e.g. serpentinite) carried down by the underlying subducting plate. Within the lower crust beneath the TVZ, a region of high (0.34) Poisson's ratio is observed, indicating the presence of at least 1 per cent partial melt. This melt probably fractionates and assimilates crustal material before some of it migrates into the upper crust, where it provides a source for the voluminous rhyolitic magmas of the TVZ.

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Section: The Mantle Wedgesupporting

confidence: 84%

Lithospheric structure of an active backarc basin: the Taupo Volcanic Zone, New Zealand

Harrison

White

2006

Geophysical Journal International

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“…For directions between NE and SE the beamformer results reveal a paucity of strong sources. For directions between NE and east this may be attributed to the Taupo Volcanic Zone (TVZ), a volcanic area in the central North Island, which is known for its strong seismic attenuation [ Satake and Hashida , ; Behr et al ., ].…”

Section: Resultsmentioning

confidence: 99%

Source directionality of ambient seismic noise inferred from three‐component beamforming

et al. 2013

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[1] The increased use of ambient seismic noise for seismic imaging requires better understanding of the ambient seismic noise wavefield and its source locations and mechanisms. Although the source regions and mechanisms of Rayleigh waves have been studied extensively, characterization of Love wave source processes are sparse or absent. We present here the first systematic comparison of ambient seismic noise source directions within the primary (~10-20 s period) and secondary (~5-10 s period) microseism bands for both Rayleigh and Love waves in the Southern Hemisphere using vertical-and horizontalcomponent ambient seismic noise recordings from a dense temporary network of 68 broadband seismometers in New Zealand. Our analysis indicates that Rayleigh and Love waves within the primary microseism band appear to be mostly generated in different areas, whereas in the secondary microseism band they arrive from similar backazimuths. Furthermore, the source areas of surface waves within the secondary microseism band correlate well with modeled deep-water and near-coastal source regions.Citation: Behr Y., J. Townend, M. Bowen, L. Carter, R. Gorman, L. Brooks, and S. Bannister (2013), Source directionality of ambient seismic noise inferred from three-component beamforming,

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“…Permanent stations had somewhat better response, with 196 out of 381 shallow and 287 out of 331 deep traces used. Part of the problem is likely due to the high scattering and attenuation of S waves in this volcanic region [e.g., Satake and Hashida , 1989; Salmon et al , 2003]. Both scattering and attenuation reduces the signal quality of S waves.…”

Section: Data and Analysismentioning

confidence: 99%

Anisotropic structure under a back arc spreading region, the Taupo Volcanic Zone, New Zealand

2004

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We investigate anisotropy surrounding a continental back arc spreading region, the Central Volcanic Region (CVR), in the North Island of New Zealand and present a simple method for spatial averaging to examine heterogeneous anisotropy. S phases from local earthquakes yield consistent trench‐parallel fast directions (ϕ) in the southern, compressional region but varied directions in the northern, extensional region. In the forearc east of the CVR, ϕ is nearly trench‐parallel, suggesting shear in the mantle or trench‐parallel flow. In the western CVR, local phases from 50 to 80 km depth give ϕ parallel to extension (120°), and phases from 150 to 220 km depth yield similar ϕ (150°). These results suggest asthenospheric flow with olivine a axes oriented in the extension direction down to 100–150 km depth. In the eastern CVR, local phases show mixed ϕ, suggesting that it is a transition between the western CVR and the forearc. Trench‐parallel ϕ for shallow local events within the CVR may be caused by fluid‐filled cracks. Trench‐parallel ϕ for deeper local events and for SKS phases can be explained by standard olivine fabrics developed by lithospheric shearing, by trench‐parallel flow, and by fossil anisotropy in the subducting oceanic lithosphere. Alternatively, in the CVR they could be caused in part by hydrous minerals at the slab‐mantle upper interface, which could cause olivine a axes to orient parallel to the trench due to a maximum shear stress oriented perpendicular to the trench along the slab. We suggest that trench‐perpendicular flow in the extensional region helps to drive fluids away from the slab, while in the compressional region, trench‐parallel flow fails to distribute the fluids, explaining the location of changes in geophysical properties.

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Three-dimensional attenuation structure beneath North Island, New Zealand

Cited by 32 publications

References 20 publications

Lithospheric structure of an active backarc basin: the Taupo Volcanic Zone, New Zealand

Lithospheric structure of an active backarc basin: the Taupo Volcanic Zone, New Zealand

Source directionality of ambient seismic noise inferred from three‐component beamforming

Anisotropic structure under a back arc spreading region, the Taupo Volcanic Zone, New Zealand

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