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Abstract：
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.
摘要：
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状图案，但是到目前为止，这种现象还没有得到解释。在这里，我们检验了以下假设：在欧洲的AlpArray宽带地震网络上观察到的系统到达角偏差是由单个小规模速度异常下的表面波衍射引起的干涉图。我们使用南大西洋下两次地震的瑞利波的观测模式，并且我们将这种模式与通过简单的建模方法得出的理论到达角拟合，该方法描述了地震波场与小异常的相互作用。实现了网格搜索反演方案，这表明异常位于中非，头在喀麦隆下面。此外，反演可以表征异常：推断异常在320至420公里宽之间，在长度上与喀麦隆火山线火山爆发下的2500公里长的上地幔低速区域相匹配。我们表明，这种方法通常可用于研究全球上地幔异常。
