Effect of Impurities on Polycrystal Anelasticity
Effect of Impurities on Polycrystal Anelasticity
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杂质对多晶迟弹性的影响
DOI：
10.1029/2021jb023224
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发表时间：
2022
期刊：
影响因子：
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通讯作者：
Takei Yasuko
中科院分区：
文献类型：
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作者：
T. Hanyu;K. Shimizu;T. Ushikubo;J.-I. Kimura;Q. Chang;M. Hamada;Takei Yasuko
当且仅当衰减谱在单调背景上叠加了一个大的“高频峰”时，岩石滞弹性才会导致地震的低速和高衰减。因此，确定峰值存在的条件是至关重要的。众所周知，在近固相线温度下存在一个大而宽的高频峰，这是因为晶界滑移被称为预熔的晶界无序的显着增加而增强的。目前的研究使用有机多晶体作为地幔岩石的类似物，对杂质引起的高频峰进行了实验研究。建立了一种除杂方法，并测定了含杂质和不含杂质多晶冰片的滞弹性、粘度和颗粒长大速率。结果表明，杂质还能显著扰乱晶界，引起宽大的高频峰。当除去杂质时，这个杂质诱导的峰消失了。在此基础上，本研究得出结论：高频峰的存在与否与晶界结构密切相关。研究还表明，与现有模型的预测不同，该峰的潜在机制是扩散调节的晶界滑移，需要对模型进行进一步的修正。我进一步证实，在已公布的数据中，杂质的影响很小，这些数据证明了预熔化的机械效应。
Rock anelasticity causes seismic low velocity and high attenuation if, and only if, attenuation spectrum has a large “high‐frequency peak” superposed on the monotonic background. As a result, it is critical to define the conditions for peak existence. It is known that a large and broad high‐frequency peak exists at near solidus temperatures because grain boundary sliding is enhanced by the significant increase in grain boundary disorder called pre‐melting. The current study experimentally investigated the high‐frequency peak caused by impurities using organic polycrystals as an analog to mantle rock. A method for removing impurities was developed and anelasticity, viscosity, and grain growth rate of polycrystalline borneol with and without impurities were measured. The results showed that impurities can also significantly disorder the grain boundaries and cause a large and broad high‐frequency peak. This impurity‐induced peak disappeared, when the impurities were removed. On the basis of these results, this study draws a conclusion that the existence or non‐existence of the high‐frequency peak is strongly coupled with the grain boundary structure. This study also shows that the underlying mechanism of the peak is diffusionally accommodated grain boundary sliding, which is different from the prediction of existing models, and that further refinement of the models is needed. I further confirmed that the effects of impurities were minor in the published data which demonstrated the mechanical effects of premelting.