Nodal Local Earthquake Tomography of La Soufrière Volcano, Guadeloupe

La Soufrière is an active andesitic stratovolcano lava dome at 1467 m elevation. It is the most recently eruptive centre of the Guadeloupe archipelago in the eastern Caribbean Sea. Previous activity has consisted of effusive, explosive magmatic, and phreatic eruptions. Many hazards are associated with La Soufrière volcano, including explosive blasts, pyroclastic flows, acid degassing and contamination of groundwater sources. Since 1992, increased seismic and fumarolic activity at La Soufrière has raised the alert level to yellow, peaking with a volcanically triggered ML 3.7 earthquake in 2018.  In the framework of the MEGaMu project, innovative geophysical subsurface imaging methods are deployed at La Soufrière to produce a high-resolution model of the volcanic edifice at up to ~1 km depth to improve our understanding of the volcano’s shallow structure. In October 2023, we deployed an array of 48 3-component 5 Hz nodal geophones around the base of the volcanic massif and the summit crater, recording continuous passive seismic data at a sampling of 250 Hz for one month. An electrical resistivity campaign was conducted at the same time, providing an outstanding opportunity to compare the derived 3D seismic velocity model with a 3D electrical resistivity model on a similar scale. In this study, we apply seismic ambient noise tomography using data from our temporary nodal network and nearby existing broadband stations to produce Rayleigh wave group velocity maps and a 3D model of shear wave velocity. This model is interpreted with the 3D resistivity model to determine the extent of the shallow hydrothermal system and known fault zones crossing the volcanic massif. Such a multi-scale and multi-physics geophysical prospection approach greatly helps in reducing subsurface uncertainty in the interpretation of geophysical datasets.We use new nodal technologies and up-to-date applications of seismic passive noise tomography to analyse Rayleigh wave shear-velocity dispersion data from a nodal seismic network of 48 3-component units, and generated 2D group velocity maps at different periods, and 3D depth insertion of shear wave velocities. We compare this to a 3D electrical resistivity, carried out simultaneously with seismic deployment, to better constrain the subsurface plumbing system based on comprehensive geophysical methodologies.