Measuring seismic attenuation in polar firn: method and application to Korff Ice Rise, West Antarctica

IF 2.8 3区地球科学 Q2 GEOGRAPHY, PHYSICAL

Journal of Glaciology Pub Date : 2023-10-26 DOI:10.1017/jog.2023.82

Ronan S. Agnew, Roger A. Clark, Adam D. Booth, Alex M. Brisbourne, Andrew M. Smith

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Abstract

Abstract We present seismic measurements of the firn column at Korff Ice Rise, West Antarctica, including measurements of compressional-wave velocity and attenuation. We describe a modified spectral-ratio method of measuring the seismic quality factor ( Q ) based on analysis of diving waves, which, combined with a stochastic method of error propagation, enables us to characterise the attenuative structure of firn in greater detail than has previously been possible. Q increases from 56 ± 23 in the uppermost 12 m to 570 ± 450 between 55 and 77 m depth. We corroborate our method with consistent measurements obtained via primary reflection, multiple, source ghost, and critically refracted waves. Using the primary reflection and its ghost, we find Q = 53 ± 20 in the uppermost 20 m of firn. From the critical refraction, we find Q = 640 ± 400 at 90 m depth. Our method aids the understanding of the seismic structure of firn and benefits characterisation of deeper glaciological targets, providing an alternative means of correcting seismic reflection amplitudes in cases where conventional methods of Q correction may be impossible.

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极地冰层地震衰减测量方法及在南极西部科尔夫冰脊的应用

摘要本文介绍了南极西部Korff冰隆起的firn柱的地震测量，包括压缩波速度和衰减的测量。我们描述了一种基于潜水波分析的改进的测量地震质量因子(Q)的频谱比方法，该方法与误差传播的随机方法相结合，使我们能够比以前更详细地表征公司的衰减结构。Q从最上层12 m的56±23增加到55 ~ 77 m深度的570±450。我们通过主反射波、多重波、源虚波和临界折射波获得一致的测量结果来证实我们的方法。利用主反射及其鬼影，我们得到在光线最上方20 m处Q = 53±20。根据临界折射，我们发现在90 m深度处Q = 640±400。我们的方法有助于了解firn的地震结构，并有利于表征更深层次的冰川目标，在传统的Q校正方法可能无法实现的情况下，提供一种校正地震反射振幅的替代方法。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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来源期刊

Journal of Glaciology 地学-地球科学综合

CiteScore

5.80

自引率

14.70%

发文量

101

审稿时长

6 months

期刊介绍： Journal of Glaciology publishes original scientific articles and letters in any aspect of glaciology- the study of ice. Studies of natural, artificial, and extraterrestrial ice and snow, as well as interactions between ice, snow and the atmospheric, oceanic and subglacial environment are all eligible. They may be based on field work, remote sensing, laboratory investigations, theoretical analysis or numerical modelling, or may report on newly developed glaciological instruments. Subjects covered recently in the Journal have included palaeoclimatology and the chemistry of the atmosphere as revealed in ice cores; theoretical and applied physics and chemistry of ice; the dynamics of glaciers and ice sheets, and changes in their extent and mass under climatic forcing; glacier energy balances at all scales; glacial landforms, and glaciers as geomorphic agents; snow science in all its aspects; ice as a host for surface and subglacial ecosystems; sea ice, icebergs and lake ice; and avalanche dynamics and other glacial hazards to human activity. Studies of permafrost and of ice in the Earth’s atmosphere are also within the domain of the Journal, as are interdisciplinary applications to engineering, biological, and social sciences, and studies in the history of glaciology.