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Abstract:
We document the arrival of seismic energy in the core shadow zone up to large distances beyond 150° more than 100 s prior to the core phases. Numerical simulations of the energy transport in an established heterogeneity model show that scattering throughout the entire mantle explains these observations. Diffraction at the core-mantle boundary is unlikely in our 1–2 Hz frequency band and is not required indicating misleading terminology with reference to Pdiff for the scattered P∗P-energy. Records of the largest deep earthquakes at low-noise stations are key to the observation of the faint precursory signal which changes appearance with increasing distance from a coda-like decay over a constant amplitude level around 130° to an emergent wave train. According to our simulations, different depth layers in the mantle dominate different time-distance windows of the scattered wave train, providing the opportunity to improve the depth resolution of mantle heterogeneity models.
