气候变化领域集成服务门户(CCPortal): Deriving micro- to macro-scale seismic velocities from ice-core c axis orientations

CCPortal

DOI	10.5194/tc-12-1715-2018
	Deriving micro- to macro-scale seismic velocities from ice-core c axis orientations
	Kerch J.; Diez A.; Weikusat I.; Eisen O.
发表日期	2018
ISSN	19940416
卷号	12 期号:5
英文摘要	One of the great challenges in glaciology is the ability to estimate the bulk ice anisotropy in ice sheets and glaciers, which is needed to improve our understanding of ice-sheet dynamics. We investigate the effect of crystal anisotropy on seismic velocities in glacier ice and revisit the framework which is based on fabric eigenvalues to derive approximate seismic velocities by exploiting the assumed symmetry. In contrast to previous studies, we calculate the seismic velocities using the exact c axis angles describing the orientations of the crystal ensemble in an ice-core sample. We apply this approach to fabric data sets from an alpine and a polar ice core. Our results provide a quantitative evaluation of the earlier approximative eigenvalue framework. For near-vertical incidence our results differ by up to 135g m-1 for P-wave and 200g m-1 for S-wave velocity compared to the earlier framework (estimated 1ĝ€% difference in average P-wave velocity at the bedrock for the short alpine ice core). We quantify the influence of shear-wave splitting at the bedrock as 45g m-1 for the alpine ice core and 59g m-1 for the polar ice core. At non-vertical incidence we obtain differences of up to 185g m-1 for P-wave and 280g m-1 for S-wave velocities. Additionally, our findings highlight the variation in seismic velocity at non-vertical incidence as a function of the horizontal azimuth of the seismic plane, which can be significant for non-symmetric orientation distributions and results in a strong azimuth-dependent shear-wave splitting of max. 281g m-1 at some depths. For a given incidence angle and depth we estimated changes in phase velocity of almost 200g m-1 for P wave and more than 200g m-1 for S wave and shear-wave splitting under a rotating seismic plane. We assess for the first time the change in seismic anisotropy that can be expected on a short spatial (vertical) scale in a glacier due to strong variability in crystal-orientation fabric (±50g m-1 per 10ĝ€cm). Our investigation of seismic anisotropy based on ice-core data contributes to advancing the interpretation of seismic data, with respect to extracting bulk information about crystal anisotropy, without having to drill an ice core and with special regard to future applications employing ultrasonic sounding. © 2018 Author(s).
学科领域	alpine environment; anisotropy; azimuth; bedrock; data set; eigenvalue; glaciology; ice core; ice sheet; orientation; P-wave; S-wave; seismic data; seismic velocity
语种	英语
scopus关键词	alpine environment; anisotropy; azimuth; bedrock; data set; eigenvalue; glaciology; ice core; ice sheet; orientation; P-wave; S-wave; seismic data; seismic velocity
来源期刊	Cryosphere
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/119147
作者单位	Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, 27568, Germany; Institute of Environmental Physics, Heidelberg University, Heidelberg, 69120, Germany; Norwegian Polar Institute, Tromsø, Norway; Department of Geosciences, Eberhard-Karls-University Tübingen, Tübingen, 72074, Germany; Fachbereich Geowissenschaften, Universität Bremen, Bremen, Germany
推荐引用方式 GB/T 7714	Kerch J.,Diez A.,Weikusat I.,et al. Deriving micro- to macro-scale seismic velocities from ice-core c axis orientations[J],2018,12(5).
APA	Kerch J.,Diez A.,Weikusat I.,&Eisen O..(2018).Deriving micro- to macro-scale seismic velocities from ice-core c axis orientations.Cryosphere,12(5).
MLA	Kerch J.,et al."Deriving micro- to macro-scale seismic velocities from ice-core c axis orientations".Cryosphere 12.5(2018).