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Titolo:
Seismic velocity anisotropy in mica-rich rocks: an inclusion model
Autore:
Nishizawa, O; Yoshino, T;
Indirizzi:
Geol Survey Japan, Tsukuba, Ibaraki 3058567, Japan Geol Survey Japan Tsukuba Ibaraki Japan 3058567 a, Ibaraki 3058567, Japan Toyo Univ, Dept Civil & Environm Engn, Kawagoe, Saitama 3508585, Japan Toyo Univ Kawagoe Saitama Japan 3508585 , Kawagoe, Saitama 3508585, Japan
Titolo Testata:
GEOPHYSICAL JOURNAL INTERNATIONAL
fascicolo: 1, volume: 145, anno: 2001,
pagine: 19 - 32
SICI:
0956-540X(200104)145:1<19:SVAIMR>2.0.ZU;2-O
Fonte:
ISI
Lingua:
ENG
Soggetto:
IVREA ZONE; DIFFERENTIAL SCHEME; ELASTIC PROPERTIES; WAVE-PROPAGATION; ORIENTED CRACKS; LOWER-CRUSTAL; ASPECT RATIO; MEDIA; EARTHQUAKE; AMPHIBOLITE;
Keywords:
anisotropy; composite media; mica-rich rocks; seismic wave propagation;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
55
Recensione:
Indirizzi per estratti:
Indirizzo: Nishizawa, O Geol Survey Japan, 1-1-3 Higashi, Tsukuba, Ibaraki 3058567, Japan Geol Survey Japan 1-1-3 Higashi Tsukuba Ibaraki Japan 3058567
Citazione:
O. Nishizawa e T. Yoshino, "Seismic velocity anisotropy in mica-rich rocks: an inclusion model", GEOPHYS J I, 145(1), 2001, pp. 19-32

Abstract

We calculated seismic wave velocity anisotropy caused by the preferred orientation of mica minerals by using the differential effective medium method(DEM). Spheroidal biotite crystals with their c-axes coinciding with the symmetry axis of the spheroid are embedded in an isotropic matrix up to a volume ratio of 30 per cent. All crystals are aligned with their c-axes parallel to the symmetry axis of the effective homogeneous medium, which shows transverse isotropy. The effect of crystal shape on anisotropy was studied by changing the aspect ratio (the ratio between the minor axis and the majoraxis of the spheroid) from 0.01 (flat spheroid) to 1 (sphere). The S-velocity anisotropy becomes large as the crystal shape becomes flat, whereas theP-velocity anisotropy shows only small changes with changes of the crystalshape. In particular, biotite generates large S-wave anisotropy, and the anisotropy becomes stronger as the aspect ratio of the biotite crystal becomes smaller. When the volume ratio of the mica mineral is large, the P-wave phase velocity surface shows considerable deviation from the ellipse, and the SV-wave phase velocity surface forms a large bulge and crosses the SH-wave phase velocity surface (singularity) in the plane including the symmetrya?;is. These results show an interesting contrast when compared with the effect of crack or pore shape on seismic velocity anisotropy: crack (or pore) shape affects the P velocity more than the S velocity. We also calculatedThomsen's anisotropic parameters, epsilon, gamma and delta as functions ofthe crystal aspect ratio and the mica volume ratio.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 23/09/20 alle ore 07:57:41