Tracking changes in the co-eruptive seismic tremor associated with magma degassing at Piton de la Fournaise volcano

Volcanic eruptions in basaltic systems represent the most frequent expression of volcanic activity in the World, whose surface manifestations range from effusive lava flows to more explosive events. Their eruptive dynamics and style are largely controlled by the degassing of magma. In this study, we analyze seismic tremors recorded during 23 eruptions that occurred at Piton de la Fournaise volcano (La Re ' union, France) during 2014-2021 and show that their properties are strongly linked to the magma degassing. We apply the network covariance matrix method to build a catalog of tremor sources associated with all 23 eruptions, to measure their time-frequency properties, and to locate their sources. We then conduct a multi-disciplinary analysis by comparing the seismic tremor observations with images of the eruptive sites, lava flow rate measurements, impulsive earth-quakes, as well as deformation and magma composition data. The tremor depth distribution is found to be well correlated with magma gas content, indicating that the tremor generating mechanism is largely controlled by the shallow magma degassing under the eruptive site. The resulting seismic tremor signals analysis enable to track changes in degassing regimes and associated eruptive styles at the surface, thus improving monitoring and knowledge of the eruptive dynamics of the studied volcano.