| Summary: | Modeling studies suggest that climate change may cause a dynamic response of the geosphere, increasing geological and geomorphological hazards. These hazards include a potential rise in earthquake activity driven by climate-change-induced changes in the hydrological subsurface conditions. So far, evidence for this phenomenon is rare and often inconclusive.Here, we investigate an ongoing earthquake swarm with thousands of shallow ML<3 events in the Mount Blanc Massif that shows an annual periodicity starting in fall 2015. Comparing its activity with runoff volumes and isotope data from the Mont Blanc tunnel indicates that the seismicity is driven by snow and glacier meltwaters. Since 2015, near-surface flow paths rearranged by permafrost and glacier retreat may have allowed these waters to reach the source region.Our QuakeMatch-analysis (Toledo et al., 2023) combines matched-filter detection sensitivity and consistent magnitude estimation with high-precision relocation and statistical analysis. It reveals that the seasonal component of the seismicity shows high b-values supporting the meltwater-driven origin, while the non-seasonal component shows a tectonic b-value around 1.0 dominated by earthquake-earthquake interaction. The seismicity increase since 2015 is associated with an increase in the short-term seismic hazard (STSH). In the high-activity phases, the STSH increased by up to two orders of magnitude compared to the STSH level before 2015.The meltwater-driven seasonality and the associated increase in STSH provide observational evidence that climate change can increase seismic hazard locally. Similar phenomena may be ongoing in glaciated regions worldwide. Our study can contribute to better quantifying the seismic risk for affected alpine communities.
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