Location map

Key findings

• Major deep groundwater flow: a major fracture zone in the crystalline massif carries exceptionally large and persistent groundwater flows, from about 1,000 L/s during tunnel excavation to ~200 L/s decades later.
• High-altitude recharge: deep groundwater is ultimately supplied by infiltration of alpine surface water, with modelling indicating very slow thermal adjustment since the last glacial period.
• Temperature as a groundwater tracer: rock-temperature anomalies can be used to identify and quantify deep groundwater circulation and potentially predict major water inflows in fractured crystalline massifs.
• Groundwater–seismicity coupling: recent work shows that meltwater reaching deep faults can increase pore pressure and trigger seasonal seismicity, while a subsequent migratory seismic component involves additional tectonic/aseismic processes.

Hydrogeological model

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