Testing the Seismic Detectability of Magmatic Underplating Beneath the Hawaiian Ridge: A Synthetic Wavefield Approach

Magmatic underplating beneath the Hawaiian Ridge has been inferred from early active‐source and teleseismic studies, whereas more recent active‐source seismic imaging and reprocessed legacy data have not identified a distinct underplated layer. To evaluate whether underplating would be detectable in modern wide‐angle data, we performed two‐dimensional finite‐difference elastic wavefield simulations using a velocity structure derived from recent active‐source tomography located across Kaʻena Ridge. Synthetic records were generated for models with and without imposed underplated layers spanning the thicknesses and velocities proposed in earlier work and compared directly with observed wide‐angle seismic data. The simulations show that a laterally extensive underplated layer would produce diagnostic seismic signatures not observed in the data or in other recent wide‐angle studies along the Hawaiian‐Emperor Seamount Chain. Sensitivity tests indicate that underplated bodies thinner than ∼1 km would generate weak or indistinguishable signatures. The simulations further demonstrate that wave propagation can produce crustal multiples with travel times and moveout similar to reflections expected from a thick underplated layer, providing a plausible alternative explanation for some earlier interpretations. Taken together, these results indicate that the dominant wide‐angle seismic observations are consistent with normal oceanic crust and volcanic structure without requiring a thick, laterally extensive magmatic underplate. If underplating is present beneath Kaʻena Ridge, it likely to be thin, localized, gradational, or otherwise seismically subtle relative to the structures proposed in earlier studies.