Characterizing earthquake-induced groundwater level change in Yangsan fault zone in Korea

This study analyzed groundwater level changes from 2010 to the present by total of 29 local (Gyeongju and Pohang) earthquakes and remote earthquakes at a monitoring well that is located in Korea's Yangsan fault zone. Groundwater level was changed by the earthquakes above M 5.0 at relatively close distances like Japan, but mostly by earthquakes at M 7.0 or above at a long distance like Chile. In special, raw groundwater level is changed as maximum of 0.103 m by the M 7.3 Honshu earthquake. The groundwater level data were converted by using the Hilbert-Huang transform (HHT), modified moving average (MMA), and simple subtraction (SS) methods. Firstly, earthquake-induced groundwater level changes were identified using the MMA and SS methods. Then, the HHT method was applied to the 2016-2017 groundwater level data and was compared with the MMA and SS methods. The groundwater level anomalies by the three methods were grouped by scale and distance of the earthquakes, but showed no significant correlation. However, depending on the scale, the groundwater level anomalies showed a slight positive correlation with earthquakes occurred at relatively similar regions. Besides, the groundwater level data analysed by the three methods were compared with the seismic waveforms gained from the seismometer and more sensitively reflected to S waves than P waves.

KEY WORDS: earthquakes, groundwater change, long-term monitoring, Hilbert-Huang transform, modified moving average

Acknowledgement

This work was supported by the Korea Meteorological Administration Research and Development program under grant KMIPA 2017-9050 as well as by National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (No. NRF-2017R1A2B2009033).