Stripe‐like patterns of surface wave arrival angle deviations have been observed by several seismological studies around the world, but this phenomenon has not been explained so far. Here we test the hypothesis that systematic arrival angle deviations observed at the AlpArray broadband seismic network in Europe are interference patterns caused by diffraction of surface waves at single small‐scaled velocity anomalies. We use the observed pattern of Rayleigh waves from two earthquakes under the Southern Atlantic Ocean, and we fit this pattern with theoretical arrival angles derived by a simple modeling approach describing the interaction of a seismic wavefield with small anomalies. A grid search inversion scheme is implemented, which indicates that the anomaly is located in Central Africa, with its head under Cameroon. Moreover, the inversion enables the characterization of the anomaly: The anomaly is inferred to be between 320 and 420 km wide, matching in length the 2,500 km long upper mantle low‐velocity region under the volcano‐capped swells of the Cameroon volcanic line. We show that this approach can be generally used for studying the upper mantle anomalies worldwide.

中文翻译：

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AlpArray 记录的表面波衍射图案：喀麦隆火山线案例研究


世界各地的一些地震学研究已经观察到表面波到达角偏差的条纹状图案，但迄今为止这种现象尚未得到解释。在这里，我们测试了这样一个假设：在欧洲 AlpArray 宽带地震台网观测到的系统到达角偏差是由单个小尺度速度异常处的表面波衍射引起的干涉模式。我们使用南大西洋下两次地震观测到的瑞利波模式，并将该模式​​与通过描述地震波场与小异常相互作用的简单建模方法得出的理论到达角进行拟合。实施网格搜索反演方案，表明异常位于中非，其头部位于喀麦隆下方。此外，反演能够对异常进行表征：推断异常宽度在 320 至 420 公里之间，长度与喀麦隆火山线火山顶隆起下 2,500 公里长的上地幔低速区域相匹配。我们证明这种方法可以普遍用于研究全世界的上地幔异常。