Abstract This study investigated the impact of a 4.9 magnitude earthquake on submarine groundwater discharge (SGD) and nutrient fluxes along the coast of Jeju Island, Korea. Significant negative correlations were found between salinity and dissolved inorganic nitrogen (DIN; r 2 = 0.94), dissolved inorganic phosphorus (DIP; r 2 = 0.53), and dissolved silicate (DSi; r 2 = 0.79), indicating substantial nutrient contribution via SGD into the coastal area. A DSi mass balance model was employed to quantify the seepage rate of SGD in a bay. Typically, low seepage rates in this bay are reported in the winter season due to low precipitation. However, the seepage rate observed 7 days post‐earthquake (14.2 cm/d) showed a tenfold increase, before stabilizing to typical levels (1.4 cm/d) 44 days post‐earthquake. The post‐earthquake data significantly deviated from typical SGD patterns, indicating the substantial influence of the earthquake. The abrupt increase in the groundwater levels observed without precipitation further supports this conclusion. Our findings highlighted the role of seismic activity in altering coastal hydrology and nutrient dynamics, with implications for coastal environments. Further research is needed to explore the long‐term impacts of earthquakes on SGD and environmental consequences, particularly in tectonically active coastal regions.