Typhoons reseal mountain groundwater systems after earthquake damage

Peter Makus, Nicolas Brantut, Luc Illien , Jens Martin Turowski, Wei-An Chao, Jui-Ming Chang, Wen-Yen Chang, Wen-Sheng Chen, Niels Hovius

Bedrock groundwater supplies drinking water to half the global population, and earthquakes can disrupt this resource for years by changing subsurface permeability. Previous studies proposed several mechanisms to explain coseismic permeability changes but lacked an observational tool to distinguish them; moreover, all assumed an immediate onset. Here, we analyse groundwater and seismic data from eastern Taiwan capturing the responses of the groundwater system and the rock substrate to the 2024 M7.2 Hualien earthquake. Tracking substrate and groundwater responses separately enables us to distinguish permeability changes driven by mechanisms confined to the groundwater network from those affecting the entire subsurface. Earthquakes modify permeability in two distinct ways: coseismic shaking produces immediate permeability increases that co-evolve with substrate changes. Months later, two consecutive typhoons triggered abrupt permeability decreases, unlike typhoons before the earthquake. As the substrate remains unaffected by these typhoons, we attribute this response to the combined effect of the earthquake, which increased sediment availability and enhanced infiltration capacity, and typhoon-induced overland flow, delivering the sediment into the fracture network, sealing fractures and causing potential discharge deficits of up to 24%. Our results demonstrate that large earthquakes can prime landscapes for delayed hydrological disruption, with long-lasting consequences for mountain groundwater resources.