Inversion of body-wave delay times for mantle structure beneath the Hawaiian islands: results from the PELENET experiment

As an experiment to assess the nature of resolvable seismic velocity anomalies in the mantle surrounding the Hawaiian Islands, we operated a temporary network – known as PELENET – consisting of seven broadband portable seismometers on the islands of Kauai, Molokai, Maui, and Hawaii during 1995–1999. Here we report the inversion of body-wave delay times across the network, including arrivals at the Global Seismic Network station KIP on Oahu and the Ocean Seismic Network Pilot Experiment south of Oahu, to determine the three-dimensional seismic velocity structure of the upper mantle of the region. The consistent feature observed in both P- and S-wave inversions is a low-velocity anomaly beneath Maui and Molokai, which we suggest may reflect a zone of secondary melting in the asthenosphere downstream from the hotspot locus. The inversions do not resolve a cylindrical low-velocity plume in the upper mantle beneath the island of Hawaii, but resolution tests indicate that this outcome could be the result of the sparse and nearly linear distribution of stations combined with the incomplete azimuthal coverage of earthquake sources. A determination of the detailed three-dimensional structure of the upper mantle beneath the Hawaiian hotspot will require a simultaneous deployment of both ocean-bottom and land seismometers.