Résumé
Modeling studies indicate that the geosphere can dynamically respond to climate change, increasing geological and geomorphological hazards. One such hazard is climate-driven seismicity due to hydrological changes, though observational evidence supporting this phenomenon remains scarce. We present the first dataset linking climate-change-induced snow/glacier melt to increased seismic hazard. Using a template-matching-enhanced catalog (2006–2022), we analyze the ongoing Grandes Jorasses Earthquake Sequence (GJES, Mont Blanc Massif, France/Italy; ML≤3.1/MW≤2.9), which exhibits a sudden onset of strong annual periodicity in fall 2015. Our relocations identify seismicity along a major fault zone outcropping in the Mont Blanc Tunnel, where runoff and isotope data suggest that inflow is dominated by young surface meltwater. Modeling meltwater infiltration with a 1D-hydraulic diffusion constrained by the S2M meteorological snowpack model confirms that most of the GJES seismicity can be meltwater-induced. Additionally, our statistical analysis reveals a migratory seismicity component, hosting the largest events. While initially triggered by seasonal meltwater, this component expands primarily via a tectonic mechanism affected by aseismic slip. We attribute the onset of increased and periodic seismicity in 2015 to intensified climate-change-driven heat waves affecting the Mont Blanc Massif's high-altitude cryosphere. Retreating permafrost and glaciers alter meltwater-infiltration pathways, inducing pore-pressure changes that trigger seismicity in new source areas. During peak meltwater-driven seismicity, the seismic hazard levels can rise by two orders of magnitude compared to pre-2015 levels. Our findings suggest that climate change can significantly elevate the local seismic hazard in alpine regions. This phenomenon may affect other glaciated areas globally, highlighting the need for improved seismic risk assessment for impacted alpine communities