Investigating Modifications in the Hydrological System Following the M7.2 Hualien Earthquake with Seismic Methods

In April 2024, a M7.2 earthquake struck the east coast of the Taiwanese island near the city of Hualien. Being the largest earthquake in the region for more than 25 years, the Hualien earthquake offers a unique opportunity to study the landscape and subsurface response to strong ground motion. Extraordinarily high precipitations during the following monsoon season put additional pressure on the near-surface and subsurface hydrological systems. Here, we combine multidisciplinary environmental and hydrological datasets with seismological data products recorded by a network continuously active since 2016 around the Liwu River catchment. We analyse, for example, seismic velocity change time series (dv/v) or horizontal over vertical spectral ratios (H/V) to shed light on the mechanisms causing increased river discharge and changes in water composition following strong ground motion events. In the data, we not only find a strong response to the M7.2 earthquake but also clear evidence of seasonal variation corresponding to the biannual cycles in temperature and rainfall. This study will put further constraints on the reaction of aquifers and aquitards in mountainous environments to large earthquakes. Mountain freshwater reservoirs are a primary resource for the Taiwanese population and economy. Understanding its dynamics will shed light on the chances and limitations of its exploitation and sensitivity to climate change.