Profile of discontinuities beneath Hawaii from S to P converted seismic waves

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Abstract
We present new seismological evidence for the depth of depression of the volcano‐crust and crust‐mantle (Moho) boundaries and the nature of the volcano‐crust interface beneath the southeast flank of Mauna Loa volcano, Hawaii, from a profile of S to P converted waves from deep local earthquakes. Three‐component seismic array observations of these converted waves indicate the presence of a low velocity layer (LVL) at a depth of about 10 km, corresponding to the base of the volcanic pile. The thickness of the LVL is estimated to be approximately 1 km. The LVL and the Moho both deepen significantly from southwest to northeast beneath Mauna Loa's southeast flank. The observed polarity reversal of the LVL conversion compared to the Moho conversion strongly supports the existence of a buried sediment layer at the volcano‐ocean crust interface, at a depth that is consistent with the depth distribution of thrust earthquakes. Our results conflict with models of lithosphere flexure at Hawaii, indicating a depression of the lithosphere greater than that predicted by flexure models. The thickness of underlying oceanic crust is observed to be relatively constant, so this discrepancy cannot be accounted for by crustal underplating alone.