5:15 PM - 6:45 PM
[U15-P60] Preliminary report : Changes in groundwater in Toyama before and after the 2024 Noto Peninsula Earthquake : Effects on groundwater as a nutrient source to the coastal area
Keywords:Toyama, Hydrochemical changes, groundwater
The Noto Peninsula earthquake that occurred on January 1, 2024, caused extensive damage in Ishikawa, Toyama, and Niigata prefectures. The Noto Peninsula earthquake caused major changes not only in infrastructure but also in the topography of the land and seafloor. Investigations of pre- and post-earthquake groundwater level fluctuations in approximately 30 observation wells in Toyama Prefecture coastal area and the central parts of the Sho-River Fan revealed that the water levels changed in many wells. The water level fluctuation tended to be small in shallow wells and large in deep wells, which is harmonic to the GPS observation data by the Geographical Survey Institute. In the central area of the Shogawa River fan, measurements of the major dissolved constituents, water stable isotope ratios (δD and δ18O), and silica concentrations showed changes in water quality before and after the earthquake, suggesting that water movement between aquifers occurred. Furthermore, approximately 20–40% of the nutrients that support primary production in Toyama Bay's shallow coastal waters are of terrestrial origin, and groundwater contributes the same proportion as river water. Earthquakes are expected to change the flow and quality of terrestrial groundwater, which may impact shallow coastal waters through submarine groundwater discharge to the Toyama Bay. In the future, we will evaluate changes in the quantity and quality of submarine groundwater discharge. In the presentation, detailed result conjunction with the analysis using the hydrologic model will be introduced.