Datensatz

Zusammenfassung

Seismic precursors to the PP phase have long been attributed to scattering from mid-mantle heterogeneities, often interpreted as signatures of subducted slab remnants. However, using a global dataset of high-quality records from shallow earthquakes, we identify a signal of consistent, progressively increasing energy over time preceding PP arrivals, which strongly correlates with PP surface reflection points, particularly over continental regions. Beamforming analysis reveals two distinct slowness branches in the precursor energy that align with theoretical predictions for P waves deflected by topographic slopes. Monte Carlo simulations incorporating realistic surface topography accurately reproduce the observed arrival times and amplitudes of the precursors, whereas models based solely on mantle scattering fail to match the data. These results demonstrate that surface topography, rather than the mantle structures, dominates the generation of globally observed PP precursors. This reinterpretation calls for caution in using PP precursors to infer crust or mantle heterogeneity and highlights the critical role of surface effects in seismic waveform modelling.