Imaging strong lateral heterogeneities across the contiguous US using
body-to-surface wave scattering
Abstract
Body-to-surface wave scattering, originated from strong lateral
heterogeneity, has been observed and modeled for decades. Compared to
body waves, scattered surface waves propagate along the Earth’s surface
with less energy loss and, thus, can be observed over a wider distance
range. In this study, we utilize surface waves converted from
teleseismic SH or Sdiff wave incidence to map strong
lateral heterogeneities across the entire contiguous US. We apply
array-based phase coherence analysis to broadband waveforms recorded by
the USArray Transportable Array and other permanent/temporary networks
to detect coherent signals that are associated with body-to-surface wave
scattering. We then locate the source of the scattering by
back-propagating the beamformed energy using both straight-ray and
curved-ray approximations. Our results show that the distribution of
scatterers correlates well with known geological features across the
contiguous US. Topographic/bathymetric relief along the continental
slope off the Pacific Border is the major source of scattering in the
western US. On the other hand, sedimentary basins, especially their
margins, are the dominant scatterers in the central US. Moho offsets,
such as the one around the periphery of the Colorado Plateau, are also a
strong contributor to scattering, but isolating their effect from that
of other near-surface structures without any additional constraints can
be complicated. Finally, we demonstrate the possibility of using
scattered surface waves to constrain subsurface velocity structures, as
complementary to conventional earthquake- or ambient-noise-based surface
wave tomography.