S-to-Rayleigh Wave Scattering From the Continental Margin Observed at USArray

We show examples of teleseismic S waves from western Pacific earthquakes converting to surface waves near the western U.S. coastline. Many of these events originate in the Tonga-Samoa region. We observe these surface wave conversions at USArray stations at relatively long periods (>10s). The amplitudes vary considerably from station to station and appear highly amplified in the Yellowstone region. Two-dimensional spectral element simulations successfully generate scattered Rayleigh waves from incident SV waves and models with surface topography at the coastline and crustal thickness variations across the margin, although simple models cannot explain the large Rayleigh wave amplitudes (greater than the direct S wave amplitude) observed in some regions, suggesting that the wave train is amplified by local structure or 3-D focusing effects. Plain Language Summary We show new observations of body-to-surface wave conversions at the U.S. continental margin observed with USArray. Simulation results show how simple surface topography at the coastline can successfully generate scattered Rayleigh waves from incident SV waves. These converted surface waves may be an important source of signal-generated noise in continental seismology, in particular in studies of seismic phases and parts of the wavefield between direct S and later-arriving surface waves from the source.