Modelling of near-surface seismic structure beneath Hawaii using reverberations

Abstract

SUMMARY The reverberation in near-surface layers contains valuable information about the near-surface velocity and density structure. However, previously the reverberation was often regarded as ‘noise’,to be eliminated. This paper presents an approach for modelling the shallow velocity structure with the reverberation in the near-surface layers. The method was applied to three-component waveform data recorded by seismic arrays during a passive seismic experiment, Arrays for Lithosphere Observations in HAwaii (ALOHA). The near-surface multiple reflections were enhanced by stacking the seismograms of local upper mantle earthquakes with near-vertical incidence angles. By matching synthetics and observed P and S multiple reflections, we have successfully modelled the impedance structure for the top 2-3km of the crust beneath seven stations of ALOHA arrays in southern Hawaii. Reverberative site effects are similar for stations in an array, but vary significantly from one array to another, reflecting the lateral heterogeneity of the near-surface structure. Two short profiles of near-surface P-wave velocity structure were constructed across the Ainapo and South Flank areas in southern Hawaii, based on interpretation of the multiple reflections recorded by two of the ALOHA arrays. The profiles reveal the detailed and variable shallow structure near two active volcanoes, Kilauea and Mauna Loa, and provide basic information about site effects for further investigations of seismic hazard assessment, earthquake source properties, and deeper structure.