Abstract
Sedimentary basins strongly affect earthquake ground motions of both
body and surface waves that propagate through them. Yet to characterize
seismic hazards at a specific site, it is common practice to consider
only the effects of near-surface geology on vertically propagating body
waves despite surface waves often causing strong damage. Recently,
Bowden & Tsai (2017) proposed an semi-analytical method to predict
surface-wave basin amplification and noticed that certain large regional
earthquake ground motions are under-predicted if surface waves are not
properly accounted for. Since the theory is based on a 1-D approximation
of the near-surface geologic structure and does not account for path
effects, it is of interest to know how significantly such additional
complexity affects the 1-D predictions. When considering deep basins,
several other basin parameters play a role in the amplification of
surface waves: transmission and conversion at the basin edge, basin
shape, lateral resonance and focusing effects. As surface waves
propagate back and forth in a highly dispersive medium, the
amplification also varies strongly from the edge to the center of the
basin. These effects are not always accounted for because of the cost of
geophysical surveys that would accurately constrain the structure, the
lack of earthquake data for empirical predictions, the poor
understanding of what main factors are responsible for basin
amplification, and the absence of quantitative estimates of their
contribution to the overall amplification. The current study aims to
provide quantitative estimates of the importance of these various path
effects on surface waves amplification and also extend the current 1-D
theory to more complex multi-dimensional basin structures.