Determination of crystal orientation fabric from seismic wideangle data
Determination of crystal orientation fabric from seismic wideangle data
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从地震广角数据确定晶体取向结构
DOI：
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发表时间：
2012
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通讯作者：
S. Kipfstuhl
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作者：
A. Diez;O. Eisen;C. Hofstede;T. Bohlen;I. Weikusat;S. Kipfstuhl
从冰芯分析可知，冰盖的晶体取向结构（COF）是各向异性的，并且随着深度的变化而变化。更好地了解这些各向异性及其远程检测对于优化冰的流动模型非常重要。在这里，我们展示了如何使用地震广角测量来远程确定 COF。我们展示了如何通过正演模型将观测到的地震走时与 COF 特性联系起来的原理形式，然后将该形式应用于现场数据。
描述冰芯 EDML（南极洲 Dronning Maud Land）冰结构的特征值被设置为与弹性张量的关系。根据弹性张量计算预期地震速度和反射系数。此外，我们还根据汤姆森参数 epsilon 和 delta 计算 eta 值。 eta 值衡量垂直横向各向同性 (VTI) 介质的各向异性，是 NMO 校正各向异性数据的重要工具。反射层近似为双曲线在各向异性介质中不再有效。因此，时差的计算是通过以均方根速度和有效 eta 值作为变量的四阶 NMO 校正来执行的。
该方法适用于在南极洲 Dronning Maud Land 的 Halvfarryggen 进行的广角勘测拍摄的数据。根据这些数据，我们得出了均方根速度和有效 eta 值。然后将这些值重新计算为间隔速度和间隔 eta 值，以提示不同层的各向异性的测量。结果首次让我们了解哈尔法里根的各向异性。
It is known from ice core analyses that the crystal orientation fabric (COF) of ice sheets is anisotropic and changes over depth. A better understanding of these anisotropies as well as their remote detection is important to optimize flow models for ice. Here we show how seismic wideangle measurements can be used to determine the COF remotely. We demonstrate the principle formalism how observed seismic traveltimes can be related to COF properties by a forward model and then apply the formalism to field data.
The eigenvalues that describe the ice fabric of the ice core EDML (Dronning Maud Land, Antarctca) are set into a relationship with the elasticity tensor. From the elasticity tensor the expected seismic velocities and reflection coefficients are calculated. Additionally we calculate the value eta from the Thomsen-parameters epsilon and delta. The value eta gives a measure of the anisotropy of vertical transverse isotropic (VTI)-media and is an important tool for the NMO-correction of anisotropic data. The approximation of reflection horizons as hyperbolas is not valid anymore in anisotropic media. The calculation of the moveout is therefore performed by a 4th order NMO-correction with the rms-velocity and the effective eta value as variables.
This approach is applied to data from a wideangle survey shot at Halvfarryggen, Dronning Maud Land, Antarctica. From this data we derived rms-velocities and effective eta values. These values were than recalculated to interval velocities and interval eta values to give a hint on the measure of anisotropy of the different layers. The results give first insight into the anisotropies at Halvfarryggen.