Modeling the impact of melt on seismic properties during mountain building
Modeling the impact of melt on seismic properties during mountain building
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DOI：
10.1002/2016gc006705
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发表时间：
2017-03
期刊：
影响因子：
3.7
通讯作者：
Amicia L. Lee;A. Walker;G. Lloyd;T. Torvela
中科院分区：
文献类型：
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作者：
Amicia L. Lee;A. Walker;G. Lloyd;T. Torvela
中/下地壳部分熔融的开始导致P波和S波速度的降低，最近的研究表明，这些速度和熔体之间的关系并不简单。我们已经开发了一种建模方法来评估各种熔体和固相属性对地震速度和各向异性的综合影响。该建模是基于从混合岩样品测量的晶体学择优取向（CPO）数据，允许量化不同的熔体体积，形状，方向和基质各向异性的地震速度的变化。结果表明，由于所有这些物理特性的相互作用，地震特性的非线性行为又取决于岩性、应力状态、应变率、预先存在的岩石组构和压力温度条件。这种非线性行为是显而易见的，当应用到一套样品横跨混合岩剪切带在Seiland火成岩省，挪威北部。至关重要的是，即使熔体分数保持不变，固相成分和CPO以及熔体形状和相对于波传播方向的方向的变化也会导致相同地震性质的巨大变化。从构造活动区的面波解释的比较突出的问题，在目前的模型用于预测熔化的百分比或部分熔融的地区。因此，解释地震数据以推断熔融百分比或熔融程度，应始终通过对底层地质参数进行稳健建模并结合对多种地震属性的检查来支持，以减少解释的不确定性。
Initiation of partial melting in the mid/lower crust causes a decrease in P wave and S wave velocities; recent studies imply that the relationship between these velocities and melt is not simple. We have developed a modeling approach to assess the combined impact of various melt and solid phase properties on seismic velocities and anisotropy. The modeling is based on crystallographic preferred orientation (CPO) data measured from migmatite samples, allowing quantification of the variation of seismic velocities with varying melt volumes, shapes, orientations, and matrix anisotropy. The results show nonlinear behavior of seismic properties as a result of the interaction of all of these physical properties, which in turn depend on lithology, stress regime, strain rate, preexisting rock fabrics, and pressure‐temperature conditions. This nonlinear behavior is evident when applied to a suite of samples from a traverse across a migmatitic shear zone in the Seiland Igneous Province, Northern Norway. Critically, changes in solid phase composition and CPO, and melt shape and orientation with respect to the wave propagation direction can result in huge variations in the same seismic property even if the melt fraction remains the same. A comparison with surface wave interpretations from tectonically active regions highlights the issues in current models used to predict melt percentages or partially molten regions. Interpretation of seismic data to infer melt percentages or extent of melting should, therefore, always be underpinned by robust modeling of the underlying geological parameters combined with examination of multiple seismic properties in order to reduce uncertainty of the interpretation.