Seismic Anisotropy in the Earth

Babuška, Vladislav; Cara, Michel

doi:10.1007/978-94-011-3600-6

Cited by 527 publications

(378 citation statements)

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“…We use the elastic stiffness proposed by MacBeth (1999) for Transverse Isotropic (TI) conditions, which includes a first order perturbation to the isotropic elastic constants, to simulate the general 3-D mechanical properties of the fractured solid. By evaluating the eigenvalues and eigenvectors of the corresponding Christoffel matrix, which depend on the medium stiffness and direction of wave propagation, synthetic fast shear-wave polarizations, shear-wave phase velocities, and associated differential time delays can be calculated for prescribed transversely isotropic models (Babuska and Cara, 1991;Tsvankin, 2001). …”

Section: Preliminary Inversion Resultsmentioning

confidence: 99%

Seismic imaging of the geothermal field at Krafla, Iceland using shear-wave splitting

Tang

Rial

Lees

2008

Journal of Volcanology and Geothermal Research

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During the summer of 2004 we recorded the seismicity at the Krafla geothermal field for forty days with an array of twenty PASSCAL L-28 4.5-Hz sensors. The Krafla field is located approximately 60 km East of Akureyri in northern Iceland. The array covered an area approximately 5 km N-S by 4 km E-W. The field area is located on Holocene lava flows on the Mid-Atlantic Ridge. The array recorded approximately 5 micro-earthquakes per day at a sampling rate of 500 Hz. This high sampling rate is required to exploit newly developed theories on the frequency-dependence of shear-wave splitting (SWS). During the experiment, the injection well was stopped for ten days to study the response of the subsurface crack system to changes in water pressure. SWS is an exploration method based on the analyses of polarizations and time delays of shear waves that have been distorted by the anisotropy of the medium through which the seismic waves have propagated. Epicenters roughly align along the E-W direction, while hypocenters are shallow around the injection well and appear to be related to the on-going injection. Observations of SWS at Krafla have provided evidence for at least two major crack systems oriented approximately N-S and E-W. This last, rather unexpected direction is consistent with results from a simultaneous MT (magneto-telluric) survey. Further SWS study will lead to a more detailed understanding of the fracture locations, sizes, and orientations in the geothermal field.

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Section: Preliminary Inversion Resultsmentioning

confidence: 99%

Seismic imaging of the geothermal field at Krafla, Iceland using shear-wave splitting

Tang

Rial

Lees

2008

Journal of Volcanology and Geothermal Research

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“…The reflection response illuminates finer-scale elasticity con- trasts, whereas the teleseismic signature identifies the presence of an anisotropic mantle lid within the subducted lithosphere. In this section we shall examine candidate mechanisms by which this localized (10 -15 km thick) zone of mantle material, AM, may acquire its anisotropy, under the assumption that it represents lattice preferred orientation of olivine [Babuška and Cara, 1991]. We proceed then to examine its relation to the structure H observed beneath the Slave province and implications thereof for models of continental evolution.…”

Section: Discussionmentioning

confidence: 99%

The teleseismic signature of fossil subduction: Northwestern Canada

Mercier¹,

Bostock²,

Audet³

et al. 2008

J. Geophys. Res.

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broadband, three-component seismometers were deployed along the MacKenzie-Liard Highway in Canada's Northwest Territories as part of the joint Lithoprobe-IRIS Canada Northwest Experiment (CANOE). These stations traverse a paleo-Proterozoic suture and subduction zone that has been previously documented to mantle depths using seismic reflection profiling. Teleseismic receiver functions computed from $250 earthquakes clearly reveal the response of the ancient subduction zone. On the radial component, the suture is evident as a direct conversion from the Moho, the depth of which increases from $30 km to $50 km over a horizontal distance of $70 km before its signature disappears. The structure is still better defined on the transverse component where the Moho appears as the upper boundary of a 10 km thick layer of anisotropy that can be traced from 30 km to at least 90 km depth. The seismic response of this layer is characterized by a frequency dependence that can be modeled by upper and lower boundaries that are discontinuous in material properties and their gradients, respectively. Anisotropy can be characterized by a ±5% variation in shear velocity and hexagonal symmetry with a fast axis that plunges at an oblique angle to the subduction plane. The identification of this structure provides an unambiguous connection between fossil subduction and fine-scale, anisotropic mantle layering. Previous documentation of similar layering below the adjacent Slave province and from a range of Precambrian terranes across the globe provides strong support for the thesis that early cratonic blocks were stabilized through processes of shallow subduction.

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“…It is generally accepted that LPO of anisotropic olivine and orthopyroxene crystals in the upper mantle is the primary cause of the observed splitting [Mainprice et al, 2000], and straininduced LPO is considered to be a valuable indicator of either past or present tectonics [Babuska and Cara, 1991;Kay et al, 1999]. In this paper, we present the first shear wave splitting measurements in the NCC to understand the characteristics of upper mantle deformation beneath the region.…”

Section: Introductionmentioning

confidence: 93%

Using shear wave splitting measurements to investigate the upper mantle anisotropy beneath the North China Craton: Distinct variation from east to west

Zhao

Zheng

2005

Geophysical Research Letters

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A compilation of shear wave splitting measurements in the North China Craton (NCC) is presented to investigate the upper mantle anisotropy beneath the region. By applying the method of Silver and Chan (1991), the splitting parameters of fast polarization direction and delay time are determined from SKS waveforms for 38 broadband stations. The results reveal the presence of small to large seismic anisotropy in the mantle beneath the NCC. The most striking result is the distinct difference of fast polarization directions between the Eastern Block (EB) and the Central Zone (CZ) of the NCC. The fast polarization directions trend SE beneath the EB, which implies that northwestward mantle flow has played a significant role in the reactivating of the EB during Late Mesozoic to Early Cenozoic, and the boundary between the CZ and the EB was possibly a west limit where the mantle flow was deflected. However, a collision event occurred in Early Proterozoic was also a possible cause for the anisotropy of the lithosphere beneath the CZ, depending on the craton lithosphere beneath the region had not been completely reformed by later tectonic activities.

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Seismic Anisotropy in the Earth

Cited by 527 publications

References 0 publications

Seismic imaging of the geothermal field at Krafla, Iceland using shear-wave splitting

Seismic imaging of the geothermal field at Krafla, Iceland using shear-wave splitting

The teleseismic signature of fossil subduction: Northwestern Canada

Using shear wave splitting measurements to investigate the upper mantle anisotropy beneath the North China Craton: Distinct variation from east to west

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