Shallow-velocity models at the Kilauea Volcano, Hawaii, determined from array analyses of tremor wavefields

The properties of the surface wavefield at Kilauea Volcano are analysed using data from small-aperture arrays of short-period seismometers deployed in and around the Kilauea caldera. Tremor recordings were obtained during two Japan-US cooperative experiments conducted in 1996 and 1997. The seismometers were deployed in three semi-circular arrays with apertures of 300, 300 and 400 m, and a linear array with length of 1680 m. Data are analysed using a spatio-temporal correlation technique well suited for the study of the stationary stochastic wavefields of Rayleigh and Love waves associated with volcanic activity and scattering sources distributed in and around the summit caldera. Spatial autocorrelation coefficients are obtained as a function of frequency and are inverted for the dispersion characteristics of Rayleigh and Love waves using a grid search that seeks phase velocities for which the L-2 norm between data and forward modelling operators is minimized. Within the caldera, the phase velocities of Rayleigh waves range from 1400 to 1800 m s(-1) at 1 Hz down to 300-400 m s(-1) at 10 Hz, and the phase velocities of Love waves range from 2600 to 400 m s(-1) within the same frequency band. Outside the caldera, Rayleigh wave velocities range from 1800 to 1600 m s(-1) at 1 Hz down to 260-360 m s(-1) at 10 Hz, and Love wave velocities range from 600 to 150 m s(-1) within the same frequency band. The dispersion curves are inverted for velocity structure beneath each array, assuming these dispersions represent the fundamental modes of Rayleigh and Love waves. The velocity structures observed at different array sites are consistent with results from a recent 3-D traveltime tomography of the caldera region, and point to a marked velocity discontinuity associated with the southern caldera boundary.