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Volcano-tectonic (VT) earthquakes started to take place at shallow depths soon after the first eruption, and within 1 day shifted to the 5-10 km depth range. Power et al. (1994-this volume) explain the evolution of the seismic activity and eruptions. Chouet et al. (1994-this volume) describe the use of LP swarms as precursory indicators of tephra eruptions and build a physical model for the generation of long-period events. Stephens et al. (1994-this volume) interpret the seismic spectral data that were recorded all the time throughout the eruptive sequence. This paper information the methods applied and problems encountered in classifying and locating the seismic activity, estimates the hypocentral precision and accuracy for the different types of seismic events, interprets the spatial relationships among event types, and discusses the magnitude distribution of the seismicity, with particular emphasis on the LP swarm leading to the first eruption.