Seismic anisotropy in the fore-arc region of the Hikurangi subduction zone, New Zealand

Gledhill, Ken; Stuart, G. W.

doi:10.1016/0031-9201(95)03117-0

Cited by 62 publications

(105 citation statements)

References 34 publications

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“…Our results suggest that the backazimuthal variation may be due instead to laterally varying anisotropy. Local events recorded on the array yielded f = 51°± 18°F with 4% pervasive shear wave velocity anisotropy for the crust of the overlying plate, and f = 41°± 15°with 1.4% shear wave velocity anisotropy for the mantle (down to at least 260 km depth) [Gledhill and Stuart, 1996]. We note that, particularly for intermediate depth events, Gledhill and Stuart [1996] found a striking f alignment on the LTN arm, but that the LTW arm did not show as consistent an alignment.…”

Section: Discussionmentioning

confidence: 67%

“…We examine deep teleseismic S and regional ScS recorded on the Leeds Tararua array [Stuart et al, 1995] (Figure 1). At this array, shear wave splitting from high frequency local phases yields station to station differences, suggesting variations in near surface anisotropy [Gledhill and Stuart, 1996], while low frequency stacked SKS yields long delay times (dt) [Gledhill and Gubbins, 1996]. Frequency dependent anisotropy has also been observed at SNZO, $70 km SW of the Tararua array Savage, 1997, 2004].…”

Section: Introductionmentioning

confidence: 83%

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Shear‐wave splitting variations across an array in the southern North Island, New Zealand

Marson-Pidgeon

Savage

2004

Geophysical Research Letters

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[1] We observe significant spatial variations in shear wave splitting from deep teleseismic S and regional ScS recorded on an array in the fore-arc region of the Hikurangi subduction zone, New Zealand. We also observe variations from different events recorded at the same station. The fast polarization directions range between 23°and 72°and the delay times range between 0.75 s and 1.80 s. These observations contrast with previous SKS studies in New Zealand where little spatial variation is seen, and highlights the importance of using a variety of phases with different periods. Our observations are consistent with a model in which a lateral anisotropic boundary runs $NE-SW in a zone between Kapiti Island and $40 km east of the Tararua mountain range. The anisotropic boundary is possibly related to a prominent vertical velocity feature near Kapiti Island.

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Section: Discussionmentioning

confidence: 67%

Section: Introductionmentioning

confidence: 83%

Shear‐wave splitting variations across an array in the southern North Island, New Zealand

Marson-Pidgeon

Savage

2004

Geophysical Research Letters

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“…A study of local earthquakes that included two of the southeastern stations suggested shear wave velocity anisotropy of 1.4% in the subslab mantle [Gledhill and Stuart, 1996]. Rays arriving at the northwestern stations travel through both the mantle wedge and subslab mantle, yet give similar results to rays arriving at the southeastern stations, which travel through the subslab mantle but not the mantle wedge.…”

Section: Asthenospheric Flow Above and Below The Slabmentioning

confidence: 99%

Seismic anisotropy beneath the lower half of the North Island, New Zealand

Marson-Pidgeon¹,

Savage²,

Gledhill³

et al. 1999

J. Geophys. Res.

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Abstract. Teleseismic ScS and SKS events recorded on nine broadband seismograph stations have been used to investigate seismic anisotropy beneath the lower half of the North Island, New Zealand. This area lies above the Hikurangi subduction zone, and the array provides ray paths which sample the mantle both above and below the slab. Shear wave splitting measurements give similar fast polarizations and delay times at each station. The average SKS fast polarization is approximately NE-SW, subparallel to the strike of subduction and the major geological features, with an average SKS delay time of 1.6 + 0.1 s. This lack of.variation in splitting parameters suggests that similar fast polarizations are found in both the mantle wedge and the subslab mantle. The anisotropy in the lithospheric portion of the mantle wedge is most likely caused by the preferred orientation of olivine due to the shear deformation associated with oblique convergence. Any anisotropy in the slab is probably due to fossil mineral alignment. Anisotropy in the asthenosphere is most likely caused by the preferred orientation of olivine due to asthenospheric flow. The similar NE-SW fast polarizations found in the asthenosphere both above and below the slab suggest that the mantle flow is in a trench-parallel direction in both regions. IntroductionShear wave splitting of teleseismic phases such as ScS and SKS is now a common method used to investigate mantle anisotropy, which can in turn be related to deformation of the upper mantle [e.g., Silver, 1996]. This phenomenon occurs when a shear wave enters an anisotropic medium, upon which it is split into two orthogonally polarized waves which travel with different velocities [e.g., Crampin, 1981 ]. Shear wave splitting measurements can be characterized by two parameters; the polarization direction of the fast shear wave, q•, can be related to the symmetry of the anisotropic system, and the time separation between the two waves, fit, can be related to the strength of anisotropy and the path length through the anisotropic material. Thus, if the cause of the anisotropy is known, the splitting parameters can be related to the deformation and tectonic structure of a region. For example, mantle anisotropy is usually assumed to be due to straininduced lattice-preferred orientation of olivine. The polarization direction of the fast shear wave is then assumed to align parallel to the mantle flow direction, if it is in the form of

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“…Cycle skipping is the phenomenon whereby instead of fitting the correct arrivals, the algorithm fits the first fast peak with the and Chan, 1991] calculates the covariance matrix for the two horizontal seismogram components over all possible values of • and St. Splitting parameters are defined to be the values that yield the most nearly singular covariance matrix. Alternatively, fast directions can be determined using the aspect ratio method [Shih et al, 1989], and delay times can be determined using a crosscorrelation technique [e.g., Gledhill and Stuart, 1996].…”

Section: Data Processingmentioning

confidence: 99%

Seismic anisotropy from local earthquakes in the transition region from a subduction to a strike‐slip plate boundary, New Zealand

Audoine¹,

Savage²,

Gledhill³

2000

J. Geophys. Res.

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Seismic anisotropy in the fore-arc region of the Hikurangi subduction zone, New Zealand

Cited by 62 publications

References 34 publications

Shear‐wave splitting variations across an array in the southern North Island, New Zealand

Shear‐wave splitting variations across an array in the southern North Island, New Zealand

Seismic anisotropy beneath the lower half of the North Island, New Zealand

Seismic anisotropy from local earthquakes in the transition region from a subduction to a strike‐slip plate boundary, New Zealand

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