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

Audoine, Etienne; Savage, M. K.; Gledhill, Ken

doi:10.1029/1999jb900444

Cited by 75 publications

(102 citation statements)

References 51 publications

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“…Wittlinger et al [1998] image a low velocity zone of ∼40 km width in the upper mantle beneath the Altyn Tagh fault that they interpret as a shear zone; this result, also supported by a shear wave splitting study by Herquel et al [2004], is comparable to our observation, which hints at the presence of a ∼30 km wide shear zone beneath the NNAF. Estimates for the San Andreas fault on the other hand range from a ∼50 km shear zone (Ford et al [2014]) to a broader, ∼130 km wide, zone of shear in the upper mantle (Titus et al [2007]), more similar to what has been observed in New Zealand (Audoine et al [2000]; Wilson et al [2004]). Interestingly, as has been observed by Molnar and Dayem [2010], all of these faults appear to be bounded by a stronger block to one side and a deforming block on the other side, perhaps suggesting that the presence of heterogeneous lithosphere may favour the formation of strike slip faults.…”

Section: Comparison With Other Major Fault Zonessupporting

confidence: 58%

Constraints on North Anatolian Fault zone width in the crust and upper mantle from S-wave teleseismic tomography

Papaleo¹,

Cornwell²,

Rawlinson³

2018

Preprint

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Abstract.We present high resolution S-wave teleseismic tomography images of the western segment of the North Anatolian Fault (NAFZ) in Turkey using teleseismic data recorded during the deployment period of the DANA array. The array comprised 66 stations with a nominal station spacing of 7 km, thus permitting a horizontal and vertical resolution of approximately 15 km. We use the current S-wave results with previously published P-wave teleseismic tomography to produce maps of relative V P /V S anomalies, which we use to highlight the difference in overall composition of the three terranes separated by the northern (NNAF) and southern (SNAF) branches of the NAFZ. Our results show a narrow S-wave low velocity anomaly beneath the northern branch of the NAFZ extending from the upper crust, where it has a width of ∼10 km, to the lower crust, where it widens to ∼30 km. This low velocity zone most likely extends into the upper mantle, where we constrain its width to be ≤50 km and interpret it as indicative of localised shear beneath the NNAF; this structure is similar to what has been observed for the NAFZ west of 32• and therefore we propose that the structure of the NNAF is similar to that of the NAFZ in the east. The SNAF does not show a very strong signature in our images and we conclude that it is most likely rooted in the crust, possibly accommodating deformation related to rotation of the Armutlu/Almacik Blocks situated between the two NAFZ branches. Keypoints:• An ∼15-km resolution teleseismic S-wave velocity model constrains width and depth of the North Anatolian Fault in the crust and upper mantle

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Section: Comparison With Other Major Fault Zonessupporting

confidence: 58%

Constraints on North Anatolian Fault zone width in the crust and upper mantle from S-wave teleseismic tomography

Papaleo¹,

Cornwell²,

Rawlinson³

2018

Preprint

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“…Eberhart-Phillips and Henderson (2004) conducted Vp azimuthal-anisotropy tomography for the central New Zealand. They used the fast polarization directions from localearthquake SWS (Audoine et al, 2000) to define an initial anisotropy model. The ray paths are estimated for each of the SWS observations and the 3-D initial model is determined via an averaging process and a coherence analysis.…”

Section: New Zealandmentioning

confidence: 99%

Seismic anisotropy tomography: New insight into subduction dynamics

2016

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Body-wave and surface-wave tomography, receiver-function imaging, and shear-wave splitting measurements have shown that seismic anisotropy and heterogeneity coexist in all parts of subduction zones, providing important constraints on the mantle flow and subduction dynamics. P-wave anisotropy tomography is a new but powerful tool for mapping three-dimensional variations of azimuthal and radial seismic anisotropy in the crust and mantle. P-wave azimuthal-anisotropy tomography has been applied widely to the Circum-Pacific subduction zones, Mainland China and North America, whereas P-wave radial-anisotropy tomography was applied to only a few areas including Northeast Japan, Southwest Japan and North China Craton. These studies have revealed complex anisotropy in the crust and mantle lithosphere associated with the surface geology and tectonics, anisotropy reflecting subduction-driven corner flow in the mantle wedge, frozen-in fossil anisotropy in the subducting slabs formed at the mid-ocean ridge, as well as olivine fabric transitions due to changes in water content, stress and temperature. Shear-wave splitting tomography methods have been also proposed, but their applications are still limited and preliminary. There is a discrepancy between the surface-wave and body-wave tomographic models in radial anisotropy of the mantle wedge beneath Japan, which is a puzzle but an intriguing topic for future studies.

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“…Regions of strike-slip faulting or shear have one or more layers of anisotropy with f parallel to the strike of the structures [Savage and Silver, 1993;Barruol and Hoffman, 1999;Audoine et al, 2000]. Because temperatures required to significantly modify a lattice preferred orientation of olivine under typical deviatoric stresses are generally thought to be higher than those found throughout the lithosphere [Vauchez et al, 1999], it is probable that f in cratons reflect paleoshortening directions that were fossilized during subsequent lithospheric cooling.…”

Section: Fossilized Anisotropy In the Lithosphere 431 Tanzania Cratonmentioning

confidence: 99%

On the relationship between extension and anisotropy: Constraints from shear wave splitting across the East African Plateau

et al. 2004

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[1] East Africa is a tectonically complex region owing to the presence of a rigid craton, paleothrust belts and shear zones, active magmatism and rifting, and possibly even a mantle plume. We present new splitting results of teleseismic shear phases recorded by 21 broadband seismic stations in Tanzania, seven broadband stations in Kenya, and three permanent broadband Global Seismic Network stations in Kenya and Uganda. Inconsistent apparent splitting is observed beneath the craton and along its southern and southeastern flank in Tanzania. Splitting at stations elsewhere in the rifts and orogenic belts is more consistent. We test between different models of anisotropy for stations with inconsistent splitting (single layer with horizontal fast axis, single layer with dipping fast axis, and two layers with horizontal fast axes). However, we show that these more complicated models do not reasonably explain the data. The data are explained better by a laterally (and/or in some places vertically) varying single-layer model with a horizontal fast axis. We arrive at a conceptual model of anisotropy in Tanzania and Kenya that is controlled by (1) active shear along the base of the plate associated with asthenospheric flow beneath and around the moving craton keel, (2) asthenospheric flow from a plume north of central Kenya, (3) fossilized anisotropy in the lithosphere due to past orogenic events, and possibly (4) aligned magma-filled lenses beneath the rifts. Our most robust conclusion is that we can rule out an extension-induced lattice preferred orientation of olivine as a dominant factor, which is surprising given the long history of extension in the region. This indicates that mantle-lithospheric extension in East Africa occurs via dikeintrusion and/or ductile thinning within narrow rift zones and is possibly facilitated by a mechanical lithospheric anisotropy imparted by fossilized north/south structural or mineralogical fabrics.

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

Cited by 75 publications

References 51 publications

Constraints on North Anatolian Fault zone width in the crust and upper mantle from S-wave teleseismic tomography

Constraints on North Anatolian Fault zone width in the crust and upper mantle from S-wave teleseismic tomography

Seismic anisotropy tomography: New insight into subduction dynamics

On the relationship between extension and anisotropy: Constraints from shear wave splitting across the East African Plateau

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