On the measurement of S diff splitting caused by lowermost mantle anisotropy
On the measurement of S diff splitting caused by lowermost mantle anisotropy
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发表时间：
2023
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通讯作者：
Gji Seismology;Jonathan Wolf;M. Long;N. Creasy;E. Garnero;Summary
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作者：
Gji Seismology;Jonathan Wolf;M. Long;N. Creasy;E. Garnero;Summary
包括实际速度结构（如三维速度非均质性和超低速度带）、最下层地幔速度梯度特征、地幔衰减结构和地球科里奥利力的影响。其次，评价了上、下地幔地震各向异性对SH diff波的影响。特别地，我们研究了震源附近上地幔的地震各向异性是如何分裂SH diff波的，以及这种各向异性信号是如何传播到各种最下层地幔模型的接收器的。我们证明，在特定和可预测的情况下，各向异性导致S diff分裂，这可以与其他波形效应明显区分开来。这些结果使我们能够制定一套分析地幔基底各向异性引起的S diff分裂的策略，其中包括有助于避免潜在陷阱的步骤，并关注S diff的初始极化和源侧各向异性的影响。我们使用发生在西里伯斯海下的三次地震来演示我们的S diff分裂方法，这些地震是在许多可移动的阵列站在合适的震中距离上测量的。由于东北太平洋下地幔各向异性，我们求解了一致且约束良好的S diff分裂参数。
effects on S diff polarizations, including the influence of realistic velocity structure (such as 3-D velocity heterogeneity and ultra-low velocity zones), the character of the lowermost mantle velocity gradient, mantle attenuation structure, and Earth’s Coriolis force. Secondly, we evaluate effects of seismic anisotropy in both the upper and the lowermost mantle on SH diff waves. In particular, we investigate how SH diff waves are split by seismic anisotropy in the upper mantle near the source and how this anisotropic signature propagates to the receiver for a variety of lowermost mantle models. We demonstrate that, in particular and predictable cases, anisotropy leads to S diff splitting that can be clearly distinguished from other waveform effects. These results enable us to lay out a strategy for the analysis of S diff splitting due to anisotropy at the base of the mantle, which includes steps to help avoid potential pitfalls, with attention paid to the initial polarization of S diff and the influence of source-side anisotropy. We demonstrate our S diff splitting method using three earthquakes that occurred beneath the Celebes Sea, measured at many transportable array stations at a suitable epicentral distance. We resolve consistent and well-constrained S diff splitting parameters due to lowermost mantle anisotropy beneath the northeastern Pacific Ocean.