Seismic Anisotropy of the Subcrustal Lithosphere in Europe: Another Clue to Recognition of Accreted Terranes?

ABSTRACT. Reverse time migration (RTM) is one of the most powerful methods used to generate images of the subsurface. The RTM was proposed in the early 1980s, but only recently it has been routinely used in exploratory projects involving complex geology – Brazilian pre-salt, for example. Because the method uses the two-way wave equation, RTM is able to correctly image any kind of geological environment (simple or complex), including those with anisotropy. On the other hand, RTM is computationally expensive and requires the use of computer clusters. This paper proposes to investigate the influence of anisotropy on seismic imaging through the application of RTM for tilted transversely isotropic (TTI) media in pre-stack synthetic data. This work presents in detail how to implement RTM for TTI media, addressing the main issues and specific details, e.g., the computational resources required. A couple of simple models results are presented, including the application to a BP TTI 2007 benchmark model.Keywords: finite differences, wave numerical modeling, seismic anisotropy. Migração reversa no tempo em meios transversalmente isotrópicos inclinadosRESUMO. A migração reversa no tempo (RTM) é um dos mais poderosos métodos utilizados para gerar imagens da subsuperfície. A RTM foi proposta no início da década de 80, mas apenas recentemente tem sido rotineiramente utilizada em projetos exploratórios envolvendo geologia complexa, em especial no pré-sal brasileiro. Por ser um método que utiliza a equação completa da onda, qualquer configuração do meio geológico pode ser corretamente tratada, em especial na presença de anisotropia. Por outro lado, a RTM é dispendiosa computacionalmente e requer o uso de clusters de computadores por parte da indústria. Este artigo apresenta em detalhes uma implementação da RTM para meios transversalmente isotrópicos inclinados (TTI), abordando as principais dificuldades na sua implementação, além dos recursos computacionais exigidos. O algoritmo desenvolvido é aplicado a casos simples e a um benchmark padrão, conhecido como BP TTI 2007.Palavras-chave: diferenças finitas, modelagem numérica de ondas, anisotropia sísmica.

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LINKING LITHOLOGY, STRUCTURE, AND ROCK PROPERTIES TO OBSERVED SEISMIC ANISOTROPY IN COLORADO ROCKY MOUNTAIN CRUST

10.1130/abs/2019am-333204 ◽

2019 ◽

Author(s):

Michael G. Frothingham ◽

◽

Kevin H. Mahan ◽

Vera Schulte-Pelkum ◽

Jonathan S. Caine

Keyword(s):

Seismic Anisotropy ◽

Rocky Mountain ◽

Rock Properties

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Geneses of Two Contrasting Antigorite Crystal Preferred Orientations and Their Implications for Seismic Anisotropy in the Forearc Mantle

Journal of Geophysical Research Solid Earth ◽

10.1029/2020jb019354 ◽

2020 ◽

Vol 125 (9) ◽

Cited By ~ 1

Author(s):

Wenlong Liu ◽

Junfeng Zhang ◽

Yi Cao ◽

Zhenmin Jin

Keyword(s):

Seismic Anisotropy ◽

Forearc Mantle

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The competing effects of olivine and orthopyroxene CPO on seismic anisotropy

Tectonophysics ◽

10.1016/j.tecto.2021.228954 ◽

2021 ◽

pp. 228954

Author(s):

Rachel E. Bernard ◽

Vera Schulte-Pelkum ◽

Whitney M. Behr

Keyword(s):

Seismic Anisotropy

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Oceanic crustal flow in Iceland observed using seismic anisotropy

Nature Geoscience ◽

10.1038/s41561-021-00702-7 ◽

2021 ◽

Vol 14 (3) ◽

pp. 168-173

Author(s):

Omry Volk ◽

Robert S. White ◽

Simone Pilia ◽

Robert G. Green ◽

John Maclennan ◽

...

Keyword(s):

Seismic Anisotropy

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Anomalous azimuthal variations with 360° periodicity of Rayleigh phase velocities observed in Scandinavia

Geophysical Journal International ◽

10.1093/gji/ggaa553 ◽

2020 ◽

Vol 224 (3) ◽

pp. 1684-1704

Author(s):

Alexandra Mauerberger ◽

Valérie Maupin ◽

Ólafur Gudmundsson ◽

Frederik Tilmann

Keyword(s):

Seismic Anisotropy ◽

Broad Band ◽

Shear Velocity ◽

Velocity Variation ◽

The South ◽

Study Region ◽

Lithospheric Thickness ◽

Phase Velocities ◽

The North ◽

Southern Norway

SUMMARY We use the recently deployed ScanArray network of broad-band stations covering most of Norway and Sweden as well as parts of Finland to analyse the propagation of Rayleigh waves in Scandinavia. Applying an array beamforming technique to teleseismic records from ScanArray and permanent stations in the study region, in total 159 stations with a typical station distance of about 70 km, we obtain phase velocities for three subregions, which collectively cover most of Scandinavia (excluding southern Norway). The average phase dispersion curves are similar for all three subregions. They resemble the dispersion previously observed for the South Baltic craton and are about 1 per cent slower than the North Baltic shield phase velocities for periods between 40 and 80 s. However, a remarkable sin(1θ) phase velocity variation with azimuth is observed for periods >35 s with a 5 per cent deviation between the maximum and minimum velocities, more than the overall lateral variation in average velocity. Such a variation, which is incompatible with seismic anisotropy, occurs in northern Scandinavia and southern Norway/Sweden but not in the central study area. The maximum and minimum velocities were measured for backazimuths of 120° and 300°, respectively. These directions are perpendicular to a step in the lithosphere–asthenosphere boundary (LAB) inferred by previous studies in southern Norway/Sweden, suggesting a relation to large lithospheric heterogeneity. In order to test this hypothesis, we carried out 2-D full-waveform modeling of Rayleigh wave propagation in synthetic models which incorporate a steep gradient in the LAB in combination with a pronounced reduction in the shear velocity below the LAB. This setup reproduces the observations qualitatively, and results in higher phase velocities for propagation in the direction of shallowing LAB, and lower ones for propagation in the direction of deepening LAB, probably due to the interference of forward scattered and reflected surface wave energy with the fundamental mode. Therefore, the reduction in lithospheric thickness towards southern Norway in the south, and towards the Atlantic ocean in the north provide a plausible explanation for the observed azimuthal variations.

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