Upper Mantle Structure Beneath the Contiguous US Resolved With Array Observations of SKS Multipathing and Slowness Vector Perturbations
Upper Mantle Structure Beneath the Contiguous US Resolved With Array Observations of SKS Multipathing and Slowness Vector Perturbations
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DOI：
10.1029/2022jb026260
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发表时间：
2023-07
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影响因子：
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通讯作者：
J. Ward;M. Thorne;A. Nowacki;S. Rost
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作者：
J. Ward;M. Thorne;A. Nowacki;S. Rost
对地震现象的大陆尺度观测提供了地球内部的多尺度约束。在这些分析中，基于阵列的慢度矢量特性（后方位角和水平慢度）和多路径观测尚未在大陆尺度上进行。慢度矢量测量给出了地幔非均匀性的推断，如速度扰动和速度梯度强度，并量化它们对波场的影响。多路径是波与强速度梯度相互作用的结果，导致具有不同慢度矢量特性和时间的两个到达。美国邻近地区的地幔结构已经通过以前的地震研究进行了彻底的分析，并且数据丰富，使其成为用我们的方法分析地幔结构并与其他成像技术进行比较的绝佳试验场。我们将自动阵列分析技术应用于SKS数据集，以创建第一个大陆尺度的多路径和慢度矢量测量数据集。我们分析了慢度矢量偏差场的发散，以突出地震慢和快的地区。我们的研究结果解决了几个缓慢的地幔异常下黄石公园，阿巴拉契亚山脉和快速异常整个地幔。许多异常现象在0.15-0.30和0.20-0.40 Hz频段引起多路径，这表明最多存在500 km以上的速度转换。将我们的观察结果与从断层扫描模型创建的合成物进行比较，我们发现模型NA 13（Bedle等人，2021，https：//doi.org/10.1029/2021GC009674）最适合我们的数据，但差异仍然存在。因此，我们建议慢度矢量测量应作为一个额外的约束条件，在层析反演，并会导致更好地解决地幔模型。
Continent‐scale observations of seismic phenomena have provided multi‐scale constraints of the Earth's interior. Of those analyzed, array‐based observations of slowness vector properties (backazimuth and horizontal slowness) and multipathing have yet to be made on a continental scale. Slowness vector measurements give inferences on mantle heterogeneity properties such as velocity perturbation and velocity gradient strength and quantify their effect on the wavefield. Multipathing is a consequence of waves interacting with strong velocity gradients resulting in two arrivals with different slowness vector properties and times. The mantle structure beneath the contiguous Unites States has been thoroughly analyzed by previous seismic studies and is data‐rich, making it an excellent testing ground to both analyze mantle structure with our approach and compare with other imaging techniques. We apply an automated array‐analysis technique to an SKS data set to create the first continent‐scale data set of multipathing and slowness vector measurements. We analyze the divergence of the slowness vector deviation field to highlight seismically slow and fast regions. Our results resolve several slow mantle anomalies beneath Yellowstone, the Appalachian mountains and fast anomalies throughout the mantle. Many of the anomalies cause multipathing in frequency bands 0.15–0.30 and 0.20–0.40 Hz which suggests velocity transitions over at most 500 km exist. Comparing our observations to synthetics created from tomography models, we find model NA13 (Bedle et al., 2021, https://doi.org/10.1029/2021GC009674) fits our data best but differences still remain. We therefore suggest slowness vector measurements should be used as an additional constraint in tomographic inversions and will lead to better resolved models of the mantle.