Integrating GNSS and Hydrological Data to Understand Seasonal Microseismicity at La Soufrière de Guadeloupe

La Soufrière de Guadeloupe volcano exhibits microseismic activity dominated by volcano‐tectonic repeaters, mainly occurring in swarms clustered in a sub‐vertical conduit beneath the Tarissan acid lake (TAS) at depths less than 800 m. Following the April 2018 earthquake (Mlv 4.1), which likely damaged the dome, swarms intensified and show seasonal modulation with more events in October–November. We analyze 5 years of daily seismicity, GNSS‐derived deformation, and hydrological data to investigate controls on this modulation. We enhance groundwater level resolution by modeling TAS level from daily rainfall. To isolate local seasonal deformation, we compute Global Navigation Satellite Systems (GNSS) baselines and derive regional strain time series. Using Multichannel Singular Spectrum Analysis, we identify annual and sub‐annual oscillations in seismicity, groundwater, and vertical strain, highlighting hydrological forcing. Elastic deformation from surface load cannot explain observed strain or stress at depth. In contrast, a poroelastic model calibrated with GNSS strain and lake‐level variations shows pore pressure fluctuations modulate Coulomb stresses by several kPa at microseismic depths. Stress amplitude and phase match seismicity peaks, supporting pore pressure as the main driver of seasonal modulation. Effective elastic moduli from geodetic data are an order of magnitude lower than laboratory rock values, consistent with a fractured dome. Our multi‐parameter time series analysis separates hydrologically driven background seismicity from residual signals, potentially linked to thermoelastic effects or magmatic fluid migration, offering a framework to detect departures from external forcing and improve monitoring of hydrothermal unrest and phreatic eruption precursors.