Multimode phase speeds of surface waves are used to build a new radially anisotropic S wave model in the eastern Eurasian and Mongolian regions. Our dataset includes seismic waveforms of over 1655 teleseismic events (Mw≥5.8) from 2009 to 2021, recorded at permanent and temporary stations in and around Mongolia. The multimode dispersion curves of Love and Rayleigh waves were extracted using the nonlinear waveform fitting method for individual seismograms. Then, we retrieved phase speed maps for each mode and frequency, incorporating finite-frequency effects. Finally, localized multimode dispersion curves extracted from the phase speed maps were inverted for local 1-D SV and SH wave profiles, which are combined into a radially anisotropic 3-D shear wave model. Our new model exhibits significant lateral variations of S wave speeds at 70–100 km depth beneath Mongolia, i.e., slow anomalies in the tectonically active western Mongolia in contrast to fast anomalies in stable eastern Mongolia. In the radial anisotropy model, SH waves are faster than SV waves in most areas of the Mongolian lithosphere above 100 km depth, except for the northeast of the Altay Mountains. The Hangay Dome region is characterized by significantly slower velocities that may relate to its uplifting. A large-scale low velocity beneath the northeast of the Hangay Dome with a slower SV wave speed than SH may indicate the existence of partially molten layers. This study also reveals distinct lateral variations of S wave speeds across the boundary between the Amurian and Eurasian plates, characterized by the fast anomaly in eastern Mongolia, corresponding to the lithosphere in the western Amurian plate.

中文翻译：

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多模态表面波影响的蒙古地区下方的上地幔结构：对阿穆尔板块西缘的影响


利用表面波的多模态相位速度在欧亚东部和蒙古地区构建了新的径向各向异性 S 波模型。我们的数据集包括 2009 年至 2021 年在蒙古及其周边地区的永久和临时站点记录的超过 1655 次远震事件 （Mw≥5.8） 的地震波形。使用非线性波形拟合方法提取单个地震图的 Love 波和 Rayleigh 波的多模态色散曲线。然后，我们检索了每种模式和频率的相位速度图，并结合了有限频率效应。最后，从相位速度图中提取的局部多模色散曲线对局部 1-D SV 和 SH 波剖面进行了反转，并将其组合成径向各向异性的 3-D 横波模型。我们的新模型在蒙古下方 70-100 公里深度显示出 S 波速度的显着横向变化，即构造活跃的蒙古西部的缓慢异常与稳定的蒙古东部的快速异常形成鲜明对比。在径向各向异性模型中，在蒙古岩石圈 100 km 深度以上的大部分地区，除阿勒泰山脉东北部外，SH 波比 SV 波快。Hangay Dome 区域的特点是速度明显较慢，这可能与其隆起有关。Hangay Dome 东北部下方的大规模低速 SV 波速比 SH 慢，可能表明存在部分熔融层。这项研究还揭示了 S 波速度在阿穆尔板块和欧亚板块之间边界上的明显横向变化，其特征是蒙古东部的快速异常，对应于阿穆尔西部板块的岩石圈。