Seismic Analysis by Groundwater Fluctuation and Precipitation and GNSS Data in South Korea

In this study, it was hypothesized that groundwater flow could trigger earthquakes both in the lands and seas due to its seasonal fluctuation following the wet and dry seasons. Using 1,157 earthquake data occurred in South Korea recorded from 1978 till 2017 by Korean Meteorological Agency monthly earthquake energies were analyzed to test the hypothesis. For the earthquakes occurred in the lands, following the wet Monsoon season from June to September the six-month earthquake active period (August-January) was identified with three cascades of earthquake energy releases. The other six months (February-July) was identified as the earthquake inactive period with relatively low levels of earthquake energy.

For the earthquakes occurred in the seas the six-month earthquake active period (February-July) was identified. The earthquake active period in the seas was comprised of two peaks in April and July. The other six months (August-January) was identified as the earthquake inactive period with two peaks in November and January with far low levels of energy compared with the peaks of the active period. The one month delay between the peak rainy month of August and the peak land earthquake energy month of September was supposed to be the time necessary for groundwater recharge and pressure propagation in the fault zones. This hypothesis should be studied more thoroughly as more data are available. The six month delay between the earthquake active periods in the lands and seas was supposed to be the travel time for groundwater to flow from the lands to the seas.

Also, triggering earthquakes by cyclic groundwater fluctuation was supposed to be the moderating effect of the hydrologic cycle by preventing excessive accumulation of geotectonic stress and the climatic change which could bring about abnormal behavior of groundwater recharge may cause change in earthquake patterns in South Korea.

Keywords: Earthquake, Groundwater, Climate change, Monsoon, Hydrologic cycle