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 water services to half the global population. Earthquakes can disrupt this resource for years by changing subsurface permeability. Several mechanisms have been proposed for these changes, but their influence remains debated, because hydrological observations alone cannot distinguish them. We combine groundwater-derived permeability with seismic wavespeed, a measure of the rock’s mechanical state, in Taiwan before and after the 2024 magnitude 7.2 Hualien earthquake. This combination reveals two opposing earthquake effects on mountain groundwater systems. First, shaking modified fracture geometry, increasing permeability, which recovered on the same trajectory as the seismic wavespeed. Second, months later, two typhoons halved permeability without affecting the rock, whereas earlier typhoons had no effect. We attribute this previously unknown, delayed response to clogging of the seismically opened fracture network with sediment injected by overland flow. Beyond their direct, transient effect, large earthquakes can thus prime mountain groundwater systems for lasting, storm-triggered disruption.