MODELING OF NEAR-SURFACE SEISMIC STRUCTURE BENEATH HAWAII REVERBERATIONS

The reverberation in near-surface layers contains valuable information about the near-surface velocity and density structure. However, previ ously the reverberation was often regarded as 'noise',to be eliminated . This paper presents an approach for modelling the shallow velocity s tructure with the reverberation in the near-surface layers. The method was applied to three-component waveform data recorded by seismic arra ys during a passive seismic experiment, Arrays for Lithosphere Observa tions in HAwaii (ALOHA). The near-surface multiple reflections were en hanced by stacking the seismograms of local upper mantle earthquakes w ith near-vertical incidence angles. By matching synthetics and observe d P and S multiple reflections, we have successfully modelled the impe dance structure for the top 2-3km of the crust beneath seven stations of ALOHA arrays in southern Hawaii. Reverberative site effects are sim ilar for stations in an array, but vary significantly from one array t o another, reflecting the lateral heterogeneity of the near-surface st ructure. Two short profiles of near-surface P-wave velocity structure were constructed across the Ainapo and South Flank areas in southern H awaii, based on interpretation of the multiple reflections recorded by two of the ALOHA arrays. The profiles reveal the detailed and variabl e shallow structure near two active volcanoes, Kilauea and Mauna Loa, and provide basic information about site effects for further investiga tions of seismic hazard assessment, earthquake source properties, and deeper structure.