Constraining melt geometries beneath the Afar Depression, Ethiopia from teleseismic receiver functions: The anisotropic H‐κ stacking technique
Constraining melt geometries beneath the Afar Depression, Ethiopia from teleseismic receiver functions: The anisotropic H‐κ stacking technique
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DOI：
10.1002/2013gc005186
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发表时间：
2014-04
期刊：
影响因子：
3.7
通讯作者：
J. Hammond
中科院分区：
文献类型：
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作者：
J. Hammond
了解地壳的性质一直是地震学家在对地球成像时的目标。这在火山地区尤其如此，在那里，成像熔体储存和迁移可能对喷发的规模和性质产生重要影响。接收函数和H-κ叠加（Hκ）技术常用于约束地壳厚度（H）和P波与S波速度比（κ）。在本文中，我表明，它是必不可少的，以考虑各向异性时，执行Hκ。我表明，在一个介质与水平横向各向同性的一个强烈的变化，在κ与回方位角，这是各向异性介质的特点。在垂直横向各向同性介质中，没有观察到κ随后方位角的变化，但κ在所有后方位角上都增加。因此，κ的估计比以前认为的更难与成分联系起来。我将这些模型扩展到熔体诱导的各向异性，并表明观察到类似的模式，但κ的变化和增加更显着。基于这些观察结果，我开发了一种新的各向异性H-κ叠加技术，该技术可以反演熔体分数，长宽比和熔体包裹体取向的Hκ数据。我将此应用于阿法尔凹陷的数据，并显示，熔体存储在下地壳，这可能是最近的火山爆发和岩脉侵入相互关联的堆叠岩床。这种新技术可以应用于任何各向异性介质，它可以提供对平均地壳各向异性的约束。
Understanding the nature of the crust has long been a goal for seismologists when imaging the Earth. This is particularly true in volcanic regions where imaging melt storage and migration can have important implications for the size and nature of an eruption. Receiver functions and the H‐κ stacking (Hκ) technique are often used to constrain crustal thickness (H) and the ratio of P to S wave velocities (κ). In this paper, I show that it is essential to consider anisotropy when performing Hκ. I show that in a medium with horizontally transverse isotropy a strong variation in κ with back azimuth is present, which characterizes the anisotropic medium. In a vertically transverse isotropic medium, no variation in κ with back azimuth is observed, but κ is increased across all back azimuths. Thus, estimates of κ are more difficult to relate to composition than previously thought. I extend these models to melt‐induced anisotropy and show that similar patterns are observed, but with more significant variations and increases in κ. Based on these observations, I develop a new anisotropic H‐κ stacking technique which inverts Hκ data for melt fraction, aspect ratio, and orientation of melt inclusions. I apply this to data for the Afar Depression and show that melt is stored in interconnected stacked sills in the lower crust, which likely supply the recent volcanic eruptions and dike intrusions. This new technique can be applied to any anisotropic medium where it can provide constraints on the average crustal anisotropy.