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Heterogeneity and anisotropy of seismic attenuation in the inner core

Heterogeneity and anisotropy of seismic attenuation in the inner core,10.1029/2003GL018591,Geophysical Research Letters,S. I. Oreshin,L. P. Vinnik

Heterogeneity and anisotropy of seismic attenuation in the inner core   (Citations: 9)
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We evaluate seismic attenuation in the inner core from the spectral ratio between the seismic phase PKP(DF) and either PKP(AB) or PKP(BC) at the epicentral distances from 150° to 170°. The global data set is divided into two groups according to the position of the turning point of PKP(DF) either in the eastern (from 50°E to 120°W) or the western hemisphere. In the eastern hemisphere the parameter t★ shows strong dependence on the epicentral distance and no dependence on the angle between the Earth's spin axis and PKP(DF) ray at the turning point. In the western hemisphere t★ is weakly dependent on the distance, and varies between approximately 0.7 s and 0.1 s for the angles between 0° and 90°, respectively. Our results allow us to reconcile seemingly incompatible results of many previous studies. The anisotropy of attenuation is correlated with the anisotropy of P velocity.
Journal: Geophysical Research Letters - GEOPHYS RES LETT , vol. 31, no. 2, 2004
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    • ...This hemispherical pattern has subsequently been confirmed by other authors [Creager, 1999; Garcia and Souriau, 2000; Garcia, 2002; Niu and Wen, 2001; Wen and Niu, 2002; Oreshin and Vinnik, 2004; Yu and Wen, 2006]...
    • ...Theboundaries whichhave variances within one sigma of the minimum variance are shaded in the profiles in Figure 9b. [32] The confidence interval of the variance minimization technique for the eastern boundary is 18°W to 50°E, which does not include the longitude of this boundary suggested by Garcia [2002]; and the value suggested by Oreshin and Vinnik [2004] is at the limit of this boundary...
    • ...In previous studies the location of this boundary has been suggested to be between 160°E [Creager, 1999; Garcia and Souriau, 2000] and 120°W [Oreshin and Vinnik, 2004]...
    • ...Even though none of the previous suggestions of the location of this boundary shown in Table 1 can be discounted, we find the best fitting location of this boundary using the variance minimization technique (151°W) is around 30° to the east of the values suggested by Tanaka and Hamaguchi, [1997], Garcia [2002], and Niu and Wen [2001], but 30° to the west of the longitude suggested by Oreshin and Vinnik [2004]...
    • ...The western hemisphere isanisotropic andtheeastern hemisphere is nearly isotropic; this is in agreement with the findings of Tanaka and Hamaguchi [1997], Creager [1999], Garcia [2002], Wen and Niu [2002], Oreshin and Vinnik [2004], Yu and Wen [2006], and Sun and Song [2008]...

    J. C. E. Irvinget al. Hemispherical structure in inner core velocity anisotropy

    • ...There is growing evidence of a dramatic change between a quasi-western hemisphere and a quasi-eastern hemisphere, usually defined from 40 Et o 180 E[ Niu and Wen, 2001; Wen and Niu, 2002; Cao and Romanowicz, 2004], although there has been some variation [Creager, 1999; Oreshin and Vinnik, 2004]...
    • ... been reported in the strength of anisotropy [Tanaka and Hamaguchi, 1997; Creager, 1999], the thickness of an isotropic layer at the top of the inner core [Tanaka and Hamaguchi, 1997; Song and Helmberger, 1998; Creager, 1999; Garcia and Souriau, 2000; Niu and Wen, 2002], the jump in velocity at the inner core boundary [Niu and Wen, 2001; Wen and Niu, 2002; Garcia, 2002], and in attenuation [Wen and Niu, 2002; Cao and Romanowicz, 2004; Oreshin ...
    • ...[38] Oreshin and Vinnik [2004] found hemispherical difference with the western hemisphere having elastic and anelastic anisotropy, with the fastest velocity in the same direction of the strongest attenuation (the Earth’s rotation axis); while the eastern hemisphere showed weak or null anisotropy...
    • ...The inclusion of anisotropically oriented pockets of partial melt within an isotropically oriented matrix of Fe-hcp crystals can produce anisotropy [Singh et al., 2000], as proposed by Oreshin and Vinnik [2004] for the western hemisphere...

    Felipe Leytonet al. Using PKiKP coda to determine inner core structure: 2. Determination o...

    • ...The attenuation structure of the inner core is another important constraint in understanding the mineral physics and geodynamics of the innercore.Ithasbeenreportedthattheattenuationstructure exhibits complex features [9,19–26] and that a correlation of high velocity with high attenuation exists in some parts of the inner core [9,22,25,27,28] .H owever, an overall attenuation structure and its relationship to the velocity structure are not ...
    • ...Inner core attenuation anisotropy and the velocity– attenuation relationship were studied by several previous studies [23,25,27,28]...
    • ...These studies were based on the analyses of the differentialtravel times and amplituderatios of the PKPbc–PKIKP phases [25,27,28] or inversion for the PKIKP waveforms [23]...

    Wen-Che Yuet al. Inner core attenuation anisotropy

    • ...This result is consistent with a transition between a hemispherical pattern of inner core attenuation in the top 100 km of the inner core (Niu and Wen, 2001; Garcia, 2002; Cao and Romanowicz, 2004), and homogeneous attenuation below (Oreshin and Vinnik, 2004)...
    • ...Previous studies have shown that early PKPdf arrivals along polar paths are more attenuated than along equatorial paths, suggesting an anti-correlation between inner core attenuation and inner core anisotropy (Souriau and Romanowicz, 1996; Li and Cormier, 2002; Oreshin and Vinnik, 2004)...
    • ...The decrease of both the inner core attenuation and the anticorrelation between attenuation and wave speed with depth could be explained in such a model by the decrease of the melt fraction (Oreshin and Vinnik, 2004)...

    R. Garciaet al. A new global PKP data set to study Earth's core and deep mantle

    • ... PKIKP phases also suggested complex features of the attenuation structure in the inner core, including its frequency dependence [Doornbos, 1983; Cormier et al., 1998; Li and Cormier, 2002], depth dependence [Doornbos, 1974; Cormier, 1981; Souriau and Roudil, 1995; Song and Helmberger, 1995b; Tseng et al., 2001; Li and Cormier, 2002; Cormier and Li, 2002], direction dependence [Souriau and Romanowicz, 1996, 1997; Cormier et al., 1998; Oreshin ...
    • ... dependence [Doornbos, 1983; Cormier et al., 1998; Li and Cormier, 2002], depth dependence [Doornbos, 1974; Cormier, 1981; Souriau and Roudil, 1995; Song and Helmberger, 1995b; Tseng et al., 2001; Li and Cormier, 2002; Cormier and Li, 2002], direction dependence [Souriau and Romanowicz, 1996, 1997; Cormier et al., 1998; Oreshin and Vinnik, 2004] and lateral variations [Tseng et al., 2001; Wen and Niu, 2002; Li and Cormier, 2002; Oreshin and ...

    Wen-che Yuet al. Seismic velocity and attenuation structures in the top 400 km of the E...

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