Seismic anisotropy and its precursory change before eruptions at Piton de la Fournaise volcano, La Réunion

Research at Piton de la Fournaise volcano, La Réunion, reveals that seismic anisotropy—measured through shear wave splitting—can serve as a precursor to eruptions. Fast directions of seismic waves align radially with the central cone and parallel to surface cracks, indicating stress-controlled crack formation. The study found that delay times in split shear waves tend to increase while surface wave velocities decrease before eruptions, correlating with GPS baseline changes. These variations suggest dynamic changes in crack density and fluid pressure. High Vp/Vs ratios under the summit compared to the flanks imply spatial differences in fluid-filled versus gas-filled cracks. The findings, derived from a combination of permanent and portable seismic networks, geodetic data, and ambient noise correlation analysis, offer a novel approach to monitoring volcanic activity with high temporal resolution.

Savage, M. K., Ferrazzini, V., Peltier, A., Rivemale, E., Mayor, J., Schmid, A., Brenguier, F., Massin, F., Got, J.-L., Battaglia, J., DiMuro, A., Staudacher, T., Rivet, D., Taisne, B., & Shelley, A. (2015). Seismic anisotropy and its precursory change before eruptions at Piton de la Fournaise volcano, La Réunion. Journal of Geophysical Research: Solid Earth, 120(5), 3430–3458. Portico. https://doi.org/10.1002/2014jb011665