Abstract

Knowledge of the typically complicated near‐surface structure on volcanoes is critical for determining accurate seismic‐event locations and seismic source mechanisms associated with precursory and eruptive activity. To generate a near‐surface velocity model for the active cone of Pacaya volcano, Guatemala, we recorded seismic tremor and ambient noise with a small‐aperture array of 11 short‐period seismometers in January 2011. The diffuse wavefield was investigated using the spatial autocorrelation (SPAC) method, and we computed Rayleigh and Love dispersion curves at the array location. The phase velocities for Rayleigh waves range from 1000  m/s at 2 Hz to 230  m/s at 10 Hz; those for Love waves range from 600 to 250  m/s over the same frequency band. Such low velocities are consistent with the presence of unconsolidated tephra on the surface of the volcano interspersed with lava flows. Assuming they represent the fundamental modes of Rayleigh and Love waves, we inverted the dispersion curves to produce a shear‐wave velocity model of the upper 500 m beneath the array.

Online Material: S‐wave velocity models obtained from inversion, and Love‐ and Rayleigh‐wave dispersion curves.

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