Location of tremor sources and estimation of lava output using tremor source amplitude on the Piton de la Fournaise volcano: 2. Estimation of lava output

We propose several relations for estimating the amounts of lava emitted during eruptions of the Piton de la Fournaise volcano based on the use of tremor source amplitude. Sources for eruption tremor are located in several frequency bands with a location method based on the use of seismic amplitudes corrected for recording site effects. Sources are usually found at shallow depth and close to the eruptive vents suggesting that tremor is directly generated by the eruptive activity. Simultaneously with the location of the tremor sources, our program gives the source amplitude of the phenomenon. We assume a linear or a quadratic relation between the lava output and the tremor source amplitude. Both relations are calibrated using data for the March 1998 eruption and tested using the volumes emitted during the July and September 1999 and February 2000 eruptions. We found that the 5-10 Hz frequency band gives lava output much higher than for lower frequencies suggesting that for that band the tremor generation depends on the eruption site in addition to the lava output or that tremor at those frequencies is not directly caused by the outflow of lava but maybe rather by gas. The best estimations are obtained using the quadratic relation for frequencies below 5 Hz with an agreement better than 15% with the field observations for the July and September 1999 eruptions and 30% for the February 2000 eruption. Our results show that the cumulative amplitude of tremor recorded during eruptions of the Piton de la Fournaise is directly related to the amounts of lava erupted.