Groundwater Level Changes Induced by the 2016 Meinong Earthquake

ore than 750 wells have been installed to monitor groundwater level changes in Taiwan. Co-seismic groundwater level changes may reflect the redistribution of tectonic stress and crustal strain. On February 6, 2016, 03:57 local time, an ML 6.6 earthquake occurred in Meinong at southern Taiwan. The earthquake's focal mechanism indicates E-W strike oblique thrust fault dipping to North, which is not fit to any active fault around this area. This study analysis the records of monitoring wells, the co-seismic rises of the well water level were observed in 247 monitoring wells and 53 wells observed co-seismic falls. The largest co-seismic rise was 309 cm and the largest co-seismic fall was 183 cm. The largest co-seismic change was observed in the No.1 well of the Wujia station, which is 55 km away from the epicenter of the Meinong earthquake. The magnitude of co-seismic water level change increased with decreasing hypocenter distance. Most of the large co-seismic changes were concentrated in Tainan where reached CWB-defined Intensity Level 5 or higher. Also in Sinhua District, Tainan City where had the largest Intensity Level 7, 159 cm co-seismic fall was observed in the deeper (No.2) wells of Sinhua station. Keyword : earthquake, groundwater level, co-seismic change