T phase observations in global seismogram stacks

The T phase, conversion of acoustic to seismic energy, is typically observed as a high‐frequency wave train at hydrophones or coastal seismic stations. Here we show that the T phase can be observed in broadband waveform stacks of ∼5200 earthquakes recorded by the Global Seismic Network. To enhance the phase arrivals in stacks, we apply short‐time window average over long‐time window average filtering to individual traces before stacking. Although the T phase arrival is visible in stacks from seismograms filtered at 0.5–5 Hz, it appears much stronger at higher frequencies (2–8 Hz) and is further enhanced by only stacking seismograms from oceanic paths. Stacking only subsets of the data depending on continental path lengths on the receiver side shows that the T phase can be observed at stations up to 4∘ inland from the coast, and changes in the T phase arrival time correspond to reasonable crustal velocities. Key Points T phase can be observed in global seismogram stacks T phase can be observed at stations up to 4∘ degrees inland from the coast Our results agree with the theory of acoustic to seismic coupling of the energy at continents