Volcanic Tremor at Pavlof Volcano, Alaska, October 1973 - April 1986

In thirteen years (1973–1986) of seismic monitoring of Pavlof Volcano, 488 episodes of volcanic tremor have been recorded, only 26 of which have been previously described in the literature. This paper tabulates and describes all the tremor episodes and reports on the results of all analyses to date. Pavlof tremor durations range from 2 minutes to greater than 1 week; episodes accompanying magmatic eruptions have durations greater than 1 hour, and sustained amplitudes of greater than 6 mm P-P (=54 nanometers at 1.5 Hz) on station PVV, 8.5 km from the vent. Digital data provide much better amplitude resolution than helicorders do. Helicorders, however, provide continuous coverage, whereas digital data are intermittent. Correlations of tremor with visual eruption observations shows that tremor amplitudes are roughly correlated with heights of lava fountains, but the correlation of tremor amplitudes with plume heights is more problematic. Fast Fourier Transform (FFT) spectra show that Pavlof tremor is quite statinary for the entire time period, 1973–1983. All principal spectral peaks lie between 0.8 and 3.0 Hz, and may be caused by resonance of magma and gas, and resonance of the volcanic pile. Preliminary analysis of 2-and 3-component data shows that P, S, PL , and Rayleigh waves may be present in Pavlof volcanic tremor. Other waveforms can be misidentified as tremor, most commonly those caused by storms or S -waves of regional earthquakes. A strategy is proposed to distinguish tremor from noise using automatic seismic data acquisition and analysis systems. Pavlof's volcanic tremor is briefly compared with a preliminary sample of over 1100 cases of tremor from 84 volcanoes worldwide. Finally, several recommendations for monitoring and reporting volcanic tremor are discussed.