Influence of the M9.0 Tohoku Earthquake on groundwater in Korea

The M9.0 earthquake occurred at 05:46:23 UTC on March 11, 2011 off the coast of Tohoku, Japan, causing devastating tsunami-driven disasters along coastal areas. The influence of the Tohoku earthquake was detected at 46 of 320 monitoring wells of the Korea National Groundwater Monitoring Network (NGMN) in terms of changes in water level, temperature, and electrical conductivity. Because the direction of water-level movement and its permanency was complicated, we classified water-level changes in wells into four types: Type I, wells in which the water level rose and did not recover during the observation period of three weeks (n = 7); Type II, wells in which the water level rose but then recovered (n = 4); Type III, wells in which the water level decreased without recovery (n = 23); Type IV, wells in which the water level declined but then recovered (n = 9). Type I and III wells were seen as evidence that the seismic waves from the earthquake had a significant impact and resulted in persistent changes in the groundwater system. Type II and IV wells showed changes in water levels of less than 20 cm to seismic waves transmitted through the aquifer system, indicating that these wells are earthquake-sensitive and may potentially be used for continuous earthquake monitoring. The combination of present seismic monitoring systems with groundwater monitoring at earthquake-sensitive wells could improve earthquake prediction and prevent earthquake-related disasters.